Building a Cedar Strip Stand Up Paddleboard (SUP): Launch!

Our board is totally finished now and we’ve had the opportunity to take her out on a few casual trips. Isn’t she just gorgeous? My first impression is that she’s a little heavy -- at least 40 pounds! Factory manufactured boards seem to run anywhere from 28-45 pounds so she is at the upper limit but not far out of range. Be warned that if you decide to make one of these you may grow to envy those dudes who can carry their boards to the water across big parking lots under one arm without breaking a sweat!

Unlike a sea kayak, which has a cockpit and perimeter lines, a paddleboard doesn’t have a lot to grab on to, so hand carrying and cartopping a slippery, heavy board can be a serious issue. I forgot to mention that we cut a notch in the middle of the deck to use as a hand hold. This helps a lot, but what really helps is to use a carrying sling. The sling consists of a couple adjustable wide strips of nylon webbing that snap around the board with quick releases, and another adjustable padded strap that clips in between the other two that you wear over your shoulder.

I think the weight is actually real advantage on the water though because she feels very solid and stable, even in a rough chop. The extra inertia seems to help when paddling with a headwind too. We were concerned that the varnished deck might be slippery and even bought a few cakes of board wax, but it turned out not to be an issue. I felt like I had a good grip on the board with neoprene booties on, even in rough water when the deck was awash. I noticed the hard varnished surface was slippery and not very comfortable when kneeling on my bare knees though. The deck might feel slippery paddling barefoot.

The deck of a sea kayak typically does not see as nearly much wear as the hull. Unfortunately, the deck on a paddleboard is constantly exposed to the sand and pebbles stuck on the bottom of your feet and booties. I bet applying board wax might actually make the situation worse by making the sand stick to the board. I suspect our meticulously finished deck is going to look pretty scratched up before too long. Annual revarnishing is probably indicated. Wood Surf Board Supply sells a transparent traction film that protects the deck surface and provides a nonslip surface. Another idea is to use a matte rather than a gloss finish, which would hide superficial scratches. A matte finish would give it a hand-rubbed oiled look.

One small modification we definitely plan in the future is to install some simple deck rigging, probably just of a length of bungee crossed over the deck by the nose. This is primarily to hold a pfd on board when we don’t feel like actually wearing one on hot sunny days!

As I mentioned before, I haven’t been on a lot of paddleboards, but I can say that this board so far has been the best I’ve tried! Tracking is great, yet she still turns easily. Compared to Joe Greenley’s cedar strip board, she’s less responsive to changes in trim (adjusting your position fore and aft), which makes sense because she has a more volume at the ends.

Anyone who has built a wooden kayak is familiar with hearing plenty of compliments from admirers, and then getting into long conversations with people on the beach about boatbuilding as they are about to launch. Katya has been getting her first taste of that, sometimes talking so long she hardly has any time to paddle! So one final tip: give yourself some extra time when planning trips to field those questions, bask in the admiration of strangers, and share the joy of boatbuilding!

Building a Cedar Strip Stand Up Paddleboard: Finishing Touches

Fin box

Remember those blocks of balsa that we installed inside the board by the tail? Those are meant to give structural support to the fin box. To install the fin box we needed to cut a hole in the bottom with a router. We purchased the fin box from Wood Surfboard Supply. The box is plastic and the removable fin itself is glass and can be adjusted fore and aft to fine tune the trim.

If you were thinking ahead you would have carefully marked where the balsa wood blocks were after the bottom was stripped so you would know exactly where you could install the fin box. We forgot to mark where the blocks were, so our hole extended about an inch too far aft and we had to plug the bottom of our hole with more small pieces of balsa.

To get a straight cut, we marked where the fin box hole should be, then set up a simple guide using a 1/2 inch board taped and held firmly against the bottom. Because of the curvature of the board, it was difficult to clamp a guide in place.The first few passes with the router were shallow, just used to define the area. Later we cut it the hole the appropriate depth (a little over 1 inch) using multiple passes, then cleaned it up with a chisel. Be sure to make enough room in the hole for a layer of fiberglass and thickened epoxy in addition to the fin box itself.

A lip about 1/4 inch high surrounds the grove in the fin box. This lip is there to keep epoxy from getting in the fin box during installation, and is meant to be removed after installation of the box. So in order for the fin box to lie flush with the bottom, the box should be installed so that the lip will stick above the surface.

When mounting the fin box it is important to have the fin in place, so you can tell that it is perfectly perpendicular to the surface of the board. Try to avoid getting epoxy on the fin. If you do, it will sand it off easily, but you might want to cover it with tape to keep the epoxy off. Also, mask the area around the box with packing or duct tape to protect it from epoxy. We brushed the inside of the hole with epoxy, put a layer of fiberglass and wet it out, then spread a layer of thickened epoxy in the hole before inserting the fin box.

After the epoxy cured, we removed the fin from the box, cut off the excess fiberglass and epoxy, and used a block plane to carve down the plastic lip of the fin box. Be careful not to mar the board with the block plane. After we carved most of the fin box down, we removed the masking tape on the board and ground down the rest of the box lip flush with the board surface with a random orbital sander.

Leash Cup

The fin box kit from Wood Surfboard Supply also comes with a leash cup. It should be mounted on the tail of the board. It holds the leash which keeps the board from floating away from you if you fall off. The leash (sold separately) is attached to your ankle with Velcro. To mount the cup, we drilled a hole 1 inch in diameter in the center of the tail block on the deck, spread thickened epoxy in the hole and pushed the cup in. The area around the hole was masked with tape. After the epoxy cured, we ground down the cup edges flush with the board surface with sandpaper.

Placing a Vent

Simply letting the board sit in the sun for a few minutes will result in an increase in the internal air pressure, as I found out when moved our board from the garage to the yard. After just a few minutes in the sun, opening the vent released a long and dramatic rush of air. Imagine how much the internal pressure rises after letting it sit on top of a hot car for a few hours! I recommend installing a vent to equalize the external and internal pressures, and keeping it open whenever the board is not on the water. The board probably won’t burst at the seams right away if you forget to open it one day, but repeated cycles of high and low pressures will eventually lead to failure.

Ideally, you would have a hatch to drain the interior and allow air to circulate in case water gets inside. This is especially important when the inside of the board is bare wood and not sealed. If the inside gets wet the strips will start to warp and you would notice it as ridges running along the length of the board.

We placed a simple vent (also available from Wood Surfboard Supply) consisting of a screw and a neoprene washer at the tail next to the leash cup. The central spar effectively separates the left and right halves of the board into two separate air chambers so it’s important that the vent overrides the spar. The location of the vent at the tail was chosen entirely for aesthetic reasons. It is actually safer to put the vent at the nose where you can always see it, as a constant reminder to close it before you get on the water, but we felt that that would detract from the look of the nose. You may want to install two vents, at the tail and nose, to allow better air circulation.

 

Varnishing

Epoxy will discolor, turn brittle, and eventually disintegrate with prolonged exposure to UV radiation. It is important to protect it from sunlight with varnish. We coated ours with 4 layers, wet sanding in between with 300 grit paper. Before varnishing I scrub and rinse the board off to remove any dust and contaminants. I try to work in as clean and dustless area as possible. This can be difficult to create in a workshop after all the cutting and sanding that’s been going on. I vacuum the shop well, wet the floor down and let the dust settle for a couple days.

Prepare the varnish by filtering it through a paint filter into a clean container. Pour only as much as you expect to use. To improve the flow, I dilute it 10% with high quality paint thinner, the kind intended for actual thinning, not for cleaning. Once the can of varnish has been opened, it starts to go bad! To keep it fresh, you need to keep the oxygen off it. I keep a cylinder of BernzOMatic propane handy and blow it into the can as I close the lid to expel all the air out.

I like to use the roll-and-tip method for varnishing. A 1 quart can should be just enough for 4 coats on a board this size. I use thin foam rollers and a high quality brush. You definitely don’t want to use a cheap brush for this, because it will leave loose bristles behind. I pour the varnish into a pan, wet the roller, and roll a layer onto the surface, then I go back and tip it off with the dry brush. The roller gives you a thin, even layer that won’t run. The problem with rolling is that it leaves a lot of tiny bubbles. Tipping off with a dry brush pops all the bubbles. Start from one end of the board, and always work from wet to dry, to the other end of the board. Don’t go back over an area that you’ve already varnished: you will leave brush marks because it has already started to dry. When the varnish has completely dried, wet sand it down with 300 grit paper, preferably somewhere other than where you do your varnishing, and just enough to get rid of any drips and dust particles, then dry it, wipe off all the dust and repeat another layer, until the can is gone.

 

Joe Greenley’s Cedar Strip Standup Paddleboard (SUP) at the Redfish Wooden Kayak Rendezvous 2012

Katya and I caught up with Joe Greenley of Redfish Kayaks at the annual Redfish Wooden Kayak Rendezvous and talked to him about his cedar strip SUP. The Rendezvous is a casual event where local wooden kayak builders gather on the Fort Worden beach in Port Townsend with their kayaks. Instructors give presentations on range of different kayak building techniques including cedar strip building, stitch-and-glue, traditional skin-on-frame, and even folding kayaks. Although we were hoping to bring and show off our own SUP, it still needed a few finishing touches including one final coat of varnish before it was really ready to display.

Joe’s board is typical of his design skill and expert craftsmanship -- simply gorgeous! I was a little surprised when he told us it was 14 feet long. I think the tapered nose and tail make it look shorter. It looked like it was about 30 inches wide and 4 inches thick, very similar to our own board. The rails are softly curved. The transition from the deck and hull to the rail is smooth and seamless because they are stripped as part of the deck and hull.

Joe said that the method of construction is the same as his kayaks. He uses 3/16th inch thick strips, some as much as 3 inches wide. He mounts cross-sectional forms on a strongback and builds the hull first, including the fairing and glassing. Then he removes the assembly from the strongback, turns it over and builds the deck. The hull and deck are then separated from the forms. He glasses the inside as well. He then joins the hull and deck by securing fiberglass tape along the inside joint. He lays the board on its side at an angle, and, working through the tail which is still open, uses gravity and a foam brush attached to a long stick to spread epoxy over the fiberglass tape along the inside seam. A layer of fiberglass covers the seam on the outside. He then finishes the ends with nose and tail blocks. There is also an internal structure composed of three longitudinals and a few frames supporting the area in the middle of the board where the paddler stands. A small hatch by the nose gives you access to the inside for limited storage and for allowing the interior to dry in case of leaks. The fin is made of wood and permanently mounted.

Joe couldn’t tell us exactly how much his board weighs but we estimated it was about the same as ours, a little over 40 pounds. He said he could have made it a lot lighter. He used 6 oz glass inside and out, and could have used 2 or 3 oz glass for the inside. He plans to eventually sell it as a kit.

Although I haven’t been on SUPs enough to really be a discriminating judge their performance, I was impressed with Joe’s board and thought it was the most comfortable board I've tried so far. I suspect the weight gives it a lot of extra stability compared to the lighter foam boards and is a difference you will really notice in any kind of chop. The varnished deck wasn’t slippery and I think applying board wax might not be necessary. Unlike the foam boards I’ve tried in the past which couldn't go straight, Joe’s board tracked well even with a light breeze and I didn’t need to switch paddling sides at all. Although in the video I mention that the tracking is stiff, I discovered that shifting your weight more aft makes the board very maneuverable. And by standing on the very back of the board and lifting the nose up you can really swing it around quickly.

After seeing Joe’s board I would definitely strip the rails in a single layer as I stripped the hull and deck. The Orca kit that Katya and I have been building was meant to have Balsa or Pauwlonia rails 1 1/2 inches thick. Although we choose to strip it in only two layers, it still added a lot of extra weight. Stripping the rails in a single layer would require modifying the frames to have rounded corners and some fancy stripping work to get around the tight bends and compound curves of the bow, but it would definitely save quite a bit of weight.

Joe Greenley's Amazing Cedar Strip Stand Up Paddleboard (SUP) from Baby Seal Films on Vimeo.

Building a Cedar Strip Stand Up Paddleboard: Fiberglass and Epoxy

It can be a real challenge to achieve a totally clear, transparent finish with fiberglass and epoxy. I personally have never run into any serious problems, but I have heard of disasters such as mixing errors where the epoxy doesn't cure, using coated fiberglass that won't "wet out", trapped moisture causing cloudy resin, trapped bubbles, epoxy kicking off too soon, failure to wet out due to starving the glass, subsequent epoxy layers pitting or not adhering due to surface contamination or amine blush... the list goes on and on! It is important to be familiar with the epoxy system that you are using, and know that it works with the fiberglass you chose. Control of the temperature of the resin and workshop is also very important.

After our board was completely sanded, we sealed the wood with a thin layer of epoxy. The purpose of this was to saturate the wood before putting on the first layer of glass. Some builders consider this step unnecessary, but I always do it. If you leave the wood unsealed when applying the glass layer and wet it out, the wood could soak up too much of the epoxy, "starve" the glass and result in dry, blistered areas where the glass didn't wet out fully. Saturating the wood prevents this. Different wood species will soak up different amounts of resin. There is a lot of variation in color and density in western red cedar. Not surprisingly, we noticed that some strips soaked up a lot more resin than others.

When sealing the wood, keep the both the wood and epoxy warm. Heating the epoxy keeps the viscosity down. Although the higher temperature will accelerate curing, don't worry: with slow hardener you still have plenty of time to work with it before it kicks off. After applying the epoxy, allow the shop to cool. As the temperature drops, the wood will soak up the resin. You definitely do not want to start with a cool shop and warm it up after applying the resin. This could make the wood "off gas" as it heats up and create bubbles in the resin.

I use MAS Low Viscosity Resin and Slow Hardener. You will need at least one half gallon of resin and one quart of hardener for this board. (You may be able to get away with only using that if you are more careful than we were.) We placed our epoxy containers in a tub of warm water and used an electric heater to warm the shop. Back when I was building my cedar strip kayak, I used a kerosene heater to get the whole shop to at least 80 degrees F. Another effective way to heat the wood is to shine some hot lights right on the wood surface or, if you are building a kayak or canoe, put lights inside the boat.

We spread the epoxy on in a thin layer with a spreader and evened it out with a brush. You want it as thin as possible. We waited 24 hours for it to cure before doing the other side.

Working with Epoxy

The big hazard associated with working with epoxy is the development of a severe allergy. Direct skin contact with the hardener is usually the cause. It usually manifests as a contact dermatitis but can also include respiratory difficulties. It can be severe enough to keep people from ever working with epoxy again!

When using epoxy, work in a well-ventilated shop and use a respirator with an organic vapor cartridge. Wear eye protection. I wear nitrile gloves and avoid getting resin on my skin. Applying a layer of barrier cream to your hands and arms provides additional protection. If you do come in contact with the resin, use a waterless hand cleaner. You can wash it off with white vinegar, although I’ve heard that dissolving it in vinegar makes it more easily absorbed through your skin.

Another concern: you may have heard of a substance called bisphenol A, or BPA for short. BPA is a weak endocrine disruptor, which can mimic estrogen and may lead to negative health effects. High levels of BPA are associated with heart disease, diabetes, elevated liver enzymes, brain tumors, impaired immune function, and ovarian dysfunction, and erectile dysfunction. BPA is used in the plastics that coat almost all food and beverage cans, hard transparent plastic food containers, and reusable sports water bottles. Our main exposure to BPA is through food contamination, but it is easily absorbed through inhalation or the skin, for instance through handling thermal paper printed receipts, tickets, and boarding passes. In September 2010, Canada became the first country to declare BPA a toxic substance.

Epoxy resin IS BPA!

 

Wetting Out the Glass

After both sides of the board were sealed, we unrolled a layer of 4 oz uncoated plain weave fiberglass intended for clear coating. You should buy it rolled and never folded. For our 12 foot board we bought a 26 ft roll, 50 inches wide. We made a few cuts at the corners of the tail and around the nose so that the fabric would drape smoothly around the sides. Use a dry paintbrush to smooth out any wrinkles. Make sure the brush isn’t shedding any lose bristles on the glass. I would warm up the shop and epoxy as I described previously. The high temperature lowers the viscosity of the epoxy. This is especially important when trying to wet out fiberglass to get a transparent finish.

I use volumetric pumps to ensure the proper ratio of low viscosity resin to slow hardener (2:1). I discard the first squirt from the pumps if they haven’t been used recently to eliminate any air trapped in the pumps. Measuring out the volumes in separate graduated cups is going to be less accurate, especially when you take into account that you have to mix the two, and there will be either resin or hardener stuck to the side of the one of the cups. This is also the reason why I don’t measure resin or hardener by weight. The volumetric pumps make it easy to mix up even small volumes in a single container as well.

Pour the epoxy over the glass starting in the middle of the board and spread it out to the ends. Spread the epoxy in a thin even layer with a spreader, working it into the glass. Use a paintbrush to wet out the sides, again being careful not to leave any loose bristles behind. You can clean uncured epoxy with white vinegar, but you really don’t want to have to bother with that -- just use a disposable chip brush and throw it away. I cut the bristles short so they will be stiffer and work better with thick epoxy. You want the glass to be transparent from all angles. You may end up with areas with multiple small air bubbles. These may respond to the application of directed heat with a heat gun.

For an excellent example of how to wet out glass with epoxy, check out this video clip from Guillemot Kayaks. Allow the first coat to fully cure (about 24 hours, depending on the ambient temperature) then cut the excess fiberglass hanging over the edges with a razor or sharp knife. I use a scraper to feather the edge of the glass.

You will still see the texture of the glass but it should be transparent. It’s difficult to fix any areas that did not completely wet out at this point. You could carefully cut, scrape, and sand the glass off and repair the hole with a patch of new glass, but sanding into the wood will result in a discolored area.

Turn the board over and repeat the process on the bottom. The glass will overlap on the rails, so the rails will get two layers of glass total.

The strategy here is to apply just enough epoxy to wet out the glass. The weave will be filled by one or two additional coats of epoxy after the first coat is cured. You might be wondering why can’t we just lay the glass on bare wood and apply a single thick layer of epoxy on it to accomplish all three steps at once: sealing the wood, wetting out the glass, and filling the weave. Some builders claim to have gotten away with that. I’ve tried it and discovered that if you apply a thick layer of epoxy while wetting out the glass, the glass will actually float on top of the epoxy layer and create big wrinkles in the glass. I had to go back and scrape out as much of the epoxy from under the glass as possible, resulting in a lot of wasted resin. You should use as little epoxy as possible when sealing the wood, wetting out the glass and filling the weave. Extra epoxy does not add strength, only weight.

When the glass layer has cured, apply another one or two coats of epoxy, just enough to fill the weave. The subsequent layers may take longer to cure, especially in cold weather, because they are thinner. When they are completely cured, sand the whole board again with the random orbital sander using 80 grit paper to smooth and fair the surface, then again with 120 grit paper to smooth over the scratches from the 80 grit. Avoid sanding through the glass -- stop if the weave starts to show. And don't sand incompletely cured epoxy. The dust from uncured resin is much more sensitizing than cured resin. When not fully cured, sanding will take much more time and effort, and the uncured resin will clog up the paper, and clump up into small white grains. When fully cured, the dust will be very fine and the sander will cut through the epoxy much easier.

Be especially careful with the sanding dust: it contains both epoxy and glass fiber. Getting it all over your skin can make you itch. I wear a respirator, gloves and long sleeves, and immediately take a shower and wash my clothes afterwards.

Building a Cedar Strip Paddleboard: Fairing and Sanding

Now that the entire board has been stripped, it’s time to fair the deck and hull and shape the rails. “To fair” is defined as “to make the connection or junction of (surfaces) smooth and even.” Because we milled the strips ourselves, there was some unevenness in the thickness of the strips that needed to be evened out. A block plane or spokeshave works well for this but be sure to set it for a very shallow cut because they can be too aggressive and tear a chunk out of the strips. I like to use a random orbital sander with 80 grit sandpaper even out most irregularities and fair the deck and hull. If you keep the ROS moving and change the sandpaper before it gets dull the ROS will knock down only the high points. It will probably take a couple hours to sand the deck alone, so get comfortable. Take your time -- this is where you release the true beauty of your woodwork! I always say it's OK to buy cheap tools but never skimp on the sandpaper! And at the very least wear a dust mask. Even better, a respirator. Some people develop severe allergies to red cedar dust.

A word on workspaces: don’t ever think that you could complete a project like this inside your home or apartment or within any living space. The sanding, fiberglass, and epoxy work is just too toxic. Sanding should be done outside of a living space and even away from where you plan to do your final varnishing. I prefer to sand outside, in a driveway. I even close the door to my garage workshop to keep the dust from flying inside it. You might find that it’s a great way to meet your neighbors as they stop by to ask what you are building and compliment you on your beautiful woodwork.

I found that a rasp works best for shaping the corners between the rails and the hull and deck. The end grain doesn’t cut easily with a block plane -- the red cedar is brittle and tends to tear. We drew a pencil line about an inch below the top and bottom of the rail and used it as a guide for rounding the corner of the rail. After initial shaping with the rasp, we sanded the corners by hand.

After the entire board has been sanded with 80 grit paper, we sanded it again with 120 grit. Since the purpose of sanding with 120 grit is only to smooth out the scratches from the 80 grit paper and not to fair the board, it takes a lot less time. I don't think there is really any reason to go finer than 120 grit. Several coats of epoxy and varnish will smooth it out plenty.

Building a Cedar Strip Paddleboard: Nose and Tail Blocks

In my previous post, I said that the wooden structure was complete, but I forgot to mention that we still needed to install the nose and tail blocks. In a paddleboard, the bow and stern are called the “nose” and “tail”. We finished the nose by installing a nose block laminated from pieces of red cedar. We cut across the bottom at the nose to expose the central longitudinal spar and then cut off the end of the spar to expose the underside of the deck at the nose. We took six 1/2 inch pieces of red cedar and laminated them at the nose with thickened epoxy. You could use a single large solid block if you wanted to -- it just happened to be those pieces are what we had on hand. After the epoxy cured we rough cut it to shape with a handsaw then planed it to match the curve of the nose. There are no rules on how to do this. We wanted to keep it simple. You can get creative here with laminating different colors and species of wood.

The process at the tail is similar, but this time we cut across the deck to expose the inside of the bottom and glued a single block across the end.

After the blocks were shaped, we chose to extend the outer layer of the rails around the edges of the blocks. We thought it would be more aesthetically pleasing to have the pattern of vertical rails continuous around the entire board.

Building a Cedar Strip Stand Up Paddleboard: Rails

Here is a picture of the board with the finished deck and bottom. After the bottom was planked the overhanging edges were carefully trimmed with a handsaw and planed flush to the rail strips with a block plane. It still weighs almost nothing and now I’m getting really excited about taking it out on the surf!

 

The process of building the rails (sides) on this board really concerned me. The instructions recommended laminating them from several thin strips of wood (balsa or paulownia), enough to build up a rail thickness of 1 1/2 inches. With this thickness, the rails could be carved creating soft, rounded edges with the deck and hull. Since we are working in cedar, building up a rail that thick would require a lot of wood and add a ridiculous amount of weight to the finished board. Instead we decided to laminate the rails out of two layers of cedar strips, one 3/16th inch thick and the other 1/4 inch thick. This would result in more squarish sides. My guess is that it might affect performance on surf and waves but probably wouldn’t make much of a difference on flat water. By this time I have abandoned reading the instructions and am making all this up as I go along. Typical boatbuilder!

 

The inner layer was made from 3/16th inch x 12 ft stock laid lengthwise (horizonally). We choose to use thinner stock so it would bend and follow the curve of the board easily. Short pieces of 1/4 inch thick strips were glued along the edges of every other rib. The inner layer strips were then glued to them with Gorilla Glue and stapled and clamped into place. Stapling makes it possible to position and glue all of the strips into place at once. The staples are pulled out after the glue has dried. Since an outer layer of strips covers the inner layer, the staple holes are not visible.

The outer layer was made by laying short strips vertically, perpendicular to the inner layer strips. We used epoxy thickened with wood flour instead of Gorilla Glue, because we anticipated that there would be gaps between the strips, and epoxy is a better choice when you need a gap-filling glue and when joints might be exposed. The outer layer vertical strips were also secured into place with staples, but only at the ends, and stapled into parts of the inner layer that would be trimmed off afterwards. Sometimes duct tape was needed to keep strips in place. The goal is to avoid visible staple holes in the final layer as much as possible.

A word about epoxy: I like to use MAS brand epoxy, specifically the Low Viscosity Resin and Slow Hardener, because that is what I have used in the past and am familiar with. I’ve heard so many horror stories about working with epoxy so I don’t like to mess around. The last thing you want is to ruin all of your beautiful woodwork by trying to save a few cents on epoxy! The Low Viscosity Resin works well for a clear wet out of fiberglass, joints and making fillets. The Slow Hardener gives you plenty of working time. It is unlikely to kick off prematurely as you are spreading epoxy to wet out fiberglass. Because of the slow cure time, it doesn’t produce any of the dreaded “amine blush”. You also have plenty of time to add additional coats of epoxy without prior sanding. The disadvantage is that in cold weather, it may take a couple days or more for a thin layer of epoxy to completely cure. If you are in a hurry to meet a deadline this can really mess up your plans!

I save all my sanding dust from previous projects in a big can and use it as “wood flour” for making thickened epoxy for joints and fillets. It’s free! (You might be surprised to find out how much a small container of “wood flour” costs.)

After the epoxy on the second layer cured, we trimmed off the overhanging edges of the rails with a handsaw, and then carefully trimmed them flush with the deck and bottom with a block plane. Since you are planing the end grain of the outer strips, the plane needs to be really sharp. At this stage the wooden structure of the board is complete. It felt a lot heavier after putting on the rails. A lot still needed to be done to shape the edges of the rails and fair surfaces of the deck and hull, prior to sanding and glassing.

Building a Cedar Strip Stand Up Paddleboard: Planking the Hull

The process of planking the hull, or bottom, of the paddleboard is similar to planking the deck but poses a few extra challenges.

Because the deck has been installed, there is no way to use the shrink wrap plastic to hold the strips in place, so you’ll need to get a little creative in holding the strips together as the glue dries. The instructions suggest using a combination of weights to hold the strips down against the deck, and clamps to hold the strips together. When you get to close to the edges you will need some really big clamps! When we couldn’t use clamps anymore we used packing tape to hold the strips against each other. Another possibility is to make a bunch of “C” shaped pieces out of plywood and clamp them against the ribs to hold the strips both against the ribs and against each other, as shown in these images from my cedar strip baidarka build.

Since you will be working with the board lying free and not secured to the workbench, possibly on soft blankets like we did, it is easy to introduce a twist to the board if you are not careful placing the weights evenly and making sure the board is balanced side to side.

Another concern is although the hull is “flat” in the sense that is does not have any side to side curvature, it does have a lot of rocker. The strips will need to be pre-bent with a heat gun to follow this curve, especially near the nose.

The length along the curved bottom of a 12 ft board will necessarily be greater than 12 ft, so your 12 ft strips will come up a couple inches short. This extra distance will be made up for by the nose and tail blocks.

A less resource- and time-intensive way to finish the bottom is to use plywood. I would probably use 1/8th inch luan doorskin that I could get readily at a big box hardware store, and scarf it with butt joints to make a 13 ft x 32 inch panel. Painting it instead of leaving it bright-finished would hide the joints. Plywood will lack the beauty of cedar strips but there are unlimited possibilities for painting designs on it, or even gluing on a patterned Hawaiian fabric under the fiberglass. The nose end would definitely need to be pre-bent, maybe by soaking for a few days with weights at the end. The instructions suggest this as an alternative to stripping but I decided against it because I was uncertain about the practicality of pre-bending the plywood.

Fin Box Support

After the board is finished we will install a fin box about 7-8 inches from the tail. In order to mount the fin box we will need install a solid base for the box. Katya decided to use blocks of balsa from a hobby store for this. They are glued to both sides of the central spar in the three chambers between the 1st through 4th ribs, using epoxy thickened with wood flour. The blocks are planed to match the curve of the bottom of the board, and the strips glued directly to them.

Many paddle boards also feature a notch in the deck which serves as a hand hold to carry the board under your arm. We glued 1 1/2 inch thick blocks of scrap red cedar along both sides of the central spar and against the deck in the middle of the board’s length. Like the hole for the fin box, the notch will be cut into the blocks using a router after the board is glassed.

Bottom Rail Strips

Remember the rail strip we installed on the top edge of the ribs? Before we start stripping the bottom we need to install another one along the bottom edge. The rail strips are 1/4 in x 1/4 in strips that run along the bottom edge of the ribs. They define the edges of the board and provide support for the ribs while stripping. Since the distance around the edge is greater than 12 ft, the rail strips need to be scarfed from 12 ft stock, with the scarf joint in the middle where the curve is minimal. Just as before, we glued them to the ribs with superglue and taped them in place, then removed the tape after the superglue dried and reinforced it with Gorilla Glue. The instructions say that the rail strips are not “structural” supports. But knowing what I know now, that the rail strips potentially can contribute to the structure of the rails, I would have probably made them thicker, like 3/8th inch x 3/8th inch.

Planking

Just as in planking the deck, the first strip on the bottom is installed in the center. The nose end needs to be pre-bent to follow the curvature of the bow using a heat gun. Gorilla Glue is applied to the ribs and central spar after the surfaces are moistened, and the strip is positioned and clamped at the nose and the tail. Several weights (books, cans of paint, concrete blocks, etc.) are placed along the strip to hold it against the ribs and central spar.

After the first strip is installed, strips are added to the sides of the center strip, after pre-bending with a heat gun. The strips are clamped together, and weights placed to hold them against the ribs. As the stripping progresses toward the edges and the distance across them becomes to big for the clamps, you will need to use tape to temporarily hold the strips together as the glue dries. Katya said that stripping the bottom took much longer and was much more challenging than stripping the deck. It takes a lot of weight to keep the planks in place. 
In the video below she talks about installing the first central plank.

 

Watch it on YouTube.

 

 

Building a Cedar Strip Stand Up Paddleboard: Planking the Deck

Now for the fun part! You can get really creative by combining different woods, stripping in angles or curved patterns, or adding inlays. Katya choose to strip the deck in a simple pattern using full-length (12 ft) strips of western red cedar. The instructions recommend using strips no wider than 3 inches. Our strips are 3/4 inches wide and 1/4 inches thick. The thickness of the strips you use will depend on the softness and strength of the wood. Since some of that thickness will be lost during fairing and sanding the deck and hull, I don’t recommend using anything thinner than 3/16th inch.

In addition to being strong, lightweight, rot resistant, and easy to work with, western red cedar comes in different colors, ranging from pale yellow to chocolate brown. Clear cedar boards are usually available at your big box home improvement stores in 12 ft lengths. That’s probably the main reason I choose it over balsa or pauwlonia (which the instructions recommend) for planking.

By the time we were ready for planking, our strips had been pre-bending in the corner of the garage for several days. Inspect the strips that you plan to use to plank the deck, and pay close attention to any irregularities in thickness or defects that may have occurred while ripping them. Lay them out in the pattern you want and number them. Planking will start with placement of a central strip, and proceed by adding a strip on each side of the first strip, working out toward the edges of the board. The central strip should be no more than 1 inch wide.

Dry Heat Bending

The deck of this board is mostly flat, but has compound curves which follow the rocker of the board in one direction and the domes of the ribs in another. There is a relatively sharp upturn in the nose, which required us to make a tight bend in the nose end of each strip using a heat gun. To dry bend wood with a heat gun, secure a heat gun on a bench or have someone hold it. Turn the heat gun on high. I recommend wearing heavy leather gloves while handling the wood near the heat. Hold the strip with the area where you want it to bend between your hands and close to the gun, and bend it gently. If you need to apply heat close to the end of the strip, hold the end of the strip with a clamp instead of your hand. Thinner strips will bend easier. When the wood heats up you’ll feel it start to soften. After it is bent, the wood will hold its position. It may require a lot of heat, enough to scorch the wood, so always heat the surface of the wood that will be inside the board so the scorch marks aren’t visible. I would practice this a few times with scraps of wood to get a feel for it. It works well with cedar but might not work well for other species.

I am familiar with using clamps or staples to temporarily hold strips in position while planking. The instructions describe an ingenious method using plastic wrap, specifically, Pratt Retail Specialties 5 in x1000 ft “Small Stretch Wrap”, which sells at Home Depot for about $7.97 a roll. Other brands of stretch wrap are available but, in our experience, do not have the same elastic properties as this brand, which shrinks a little after being stretched into position.

Unroll and cut out at least a yard of the stretch wrap, and take a third of it and stretch it out to double its length. Leave the other 2/3rd unstreched. Tie the stretched end to the middle of the first rib, leaving the unstretched end hanging over the side so that it is out of the way of installing the center strip. Repeat this on every other rib, tying the plastic in the middle of the rib about 6 inches away from the central spar.

Apply a thin bead of Gorilla Glue to the top of the central spar. Gorilla Glue is a polyurethane glue that requires moisture to cure, so I always wipe the wood surface with a damp rag. It expands into a space-filling foam as it cures. You will get a stronger bond with good clamping pressure. It will cure in 1-2 hours but best results come from leaving it overnight. The main reason I like to use Gorilla Glue is that it has higher temperature tolerance when cured compared to regular wood glue, which is important for those times you might leave your board in baking on a sunny beach or, more likely, strapped to the top of your car for several hours.

Set the center strip in place on the spar and check to make sure it is perfectly straight and centered. Secure the center strip by stretching the stretch wrap to thin strings like you did before and wrap them several times around the strip and spar. Tie the strings to themselves. No special knots are needed because the plastic will stick to itself. The plastic will shrink slightly and get tighter after it is tied in place.

After the glue has cured, cut off all the plastic wrap and scrape off the excess glue which will have foamed up along the sides of the strip with a knife or scraper to leave clean surfaces to glue more strips to. You will need to tie more stretch wrap to every other rib, repeating the steps you followed for the center strip.

You will need to heat bend the ends of the remaining strips to match the rocker of the nose prior to installing them. Remember to moisten the surfaces of each strip if using Gorilla Glue. Spread a thin layer of Gorilla Glue onto the edge of the strip as well as the top surface of each rib and position the strip. We also secured the ends of each new strip to the end of the center strip with clamps. Stretch the plastic wrap around the strips repeatedly in a zig-zag pattern to clamp them both to the center strip and the ribs. Pull the plastic wrap tight to eliminate any gaps between the strips.

As you add strips toward the edges of the board expect to use longer lengths of plastic wrap. It will become more difficult to reach under the spar to wrap them around the board. As the board curves downward at the edges, you might need to make a running bevel along the edges of the strips with a block plane so that the strips will fit together. We have also used short lengths of plastic packing tape or duct tape to hold strips together in areas where it has been difficult to close the gap between the strips. Duct tape is stretchier but sometimes can leave an adhesive residue.

After the deck is completely planked and the glue has cured, cut all the mounting sticks with a hand saw where they join the workbench to release the board from the bench. Have another person help lift the board from the bench and set it gently aside on the floor or another surface. Cut all the protruding remnants of the mounting sticks from the bench. Place the board back on the workbench upside down, on top of folded blankets or moving quilts or blocks placed in the middle of the workbench to keep the nose and tail from touching the bench. The board is still very flexible. The blankets or blocks placed under the middle of the board will help maintain the natural rocker in the board. It is important to try to maintain a firm and level surface for planking the hull (bottom).

Remove all the mounting sticks from the ribs and spar. The sticks should sheer or twist right off but you might have to use a knife to carefully scrape the hot glue off and avoid tearing some wood off the ribs and spar.

With the board upside down, you can see how the deck strips extend beyond the rail strips. Using a handsaw, trim the edge of the deck so it is flush with the rail strips. It does not need to be perfect at this point: we will use a block plane for fine trimming after the hull is planked. You might want to turn the board over again just to admire your handiwork. It is really starting to look like a paddleboard!

 

 

Next: Planking the Hull