Surfboard Construction: Glassing the bottom

Glassing the surfboard is one of the most exciting parts of this project. It can be a little daunting if you have little experience with glassing. It helps to practice on a miniature surfboard to get used to working the resin on the cloth.

It also signifies that you are almost there. The hardest yards (shaping and designing) are now behind you. There are a couple things that you need to consider when you are glassing:

  • Materials.
  • Tools.
  • Technique.
  • Environment and ambient temperature.


In my case, the foam core consists of polystyrene. Polyester resin would react with the foam and eat it up. Therefore, we need to glass with epoxy resin which is inert and easier to deal with. I purchased some 2 to 1 UV stabilised epoxy resin from a fiberglassing supplies store.

We need to consider the strength of the glassing, and decide on a glassing scheme. For performance surfboards one might glass it really lightly, with 4 oz glass for the top and bottom. However, I wanted this board to be a little more durable, so I decided to glass it with 6 oz cloth on the bottom, and a total of 10 oz on the top (6 oz + 4 oz).

In case of any spills, etc, make sure you have a bunch of acetone and old rags for cleaning up.


You will need:

  • A plastic scraper to spread the resin across the fiberglass cloth.
  • A means of accurately mixing the correct volume of resin. I use a sensitive digital scale for complete accuracy.
  • A circular bucket that lets you mix the resin and hardener to get a homogeneous mixture.
  • A mixing stick.
  • Scissors to cut the fiberglass cloth to shape.
  • A heat gun (optional for pros only).
  • Gloves (so you don’t get epoxy all over yourself).
  • Razor blade to cut off the laps.



Glassing can get quite messy. You want to make sure that there is plenty of ventilation where you are working. And you want to prepare the space so that any drips or spills will not permanently damage your house/garage/shed. I lined my work-space with plastic sheets to prevent any epoxy getting onto the table or floor. You also want to ensure that you can walk around the surfboard relatively easily to spread the epoxy. Finally, you want to do this as the temperature is dropping (e.g. in the evening), as the foam will release gasses as it gets warmer and ruin your glassing job.


Method and Technique

First, I laid the glass cloth on the foam and used the scissors to cut around the surfboard, leaving approximately 5 inches to wrap around the rail. I kept the leftover glass since it would be useful for ding repairs in the future. At this stage it is important to decide on a free lap or a cut lap. A cut lap requires you to mask the other side and cut the cloth once it is wrapped, giving you a very clean professional line. If you do it free lap, no masking is required and you simply wrap the rails. I decided to go with the free lap for the bottom.

20160603_162706I estimated the amount of resin I would require for the job. I guessed around 150g. I poured 100g of resin into the bucket and mixed this with 50g of hardener with the bucket sitting on the digital scale. Carefully, I stirred the epoxy hardener mix trying not to introduce bubbles. Once mixed there is maximum of 15 minutes of working time before the mixture starts to gel. One way of increasing the working time is to cool the mixture by pouring it all onto the surfboard.

I poured the epoxy across the surfboard trying to spread it evenly in the middle, and left the bucket upside down on the surfboard to let all the resin out. Using the plastic scraper I spread the epoxy and let the resin saturate the cloth. You want to spread it to the rails as soon as possible to saturate the cloth at the rails so that you can wrap it around. Around this stage you will know if you have prepared enough epoxy. If required, mix more and quick add. Spread the epoxy at thinly as possible once it has saturated the cloth and then using the scraper, wrap the cloth around the rails. You should notice the epoxy start to get quite sticky (the beginnings of gelling), this is the perfect time to ensure that you have wrapped your rails. Wrapping the rails too early might result in the cloth falling off the rails due to a lack of stickiness and gravity.


20160603_173306Once I wrapped the rails, I left the board and waited until it was semi-hard. Using a razor blade, I removed any unwanted cloth. If you do not wait long enough, you can cause damage to the glassing job if you touch the wet cloth. If you wait too long, it will require much more effort to cut the cloth. I waited another 12 hours before proceeding to the next step.



Surfboard Construction: Sealing the blank

After working the blank to the desired shape, the next step was to seal the blank by filling in all the holes. I especially had a bunch of holes from filling the existing fin holes and holes I ripped into the foam from creating the concave in my board (sorry I forgot to take photos during this stage).


In my case, I went to the hardware store and bought a small bucket of spackling, but drywall and filler would probably have been fine. I made sure to avoid anything oil-based that might cause poor adhesion with epoxy for the glassing stage.

I also used a scraper tool to work and spread the spackling.

Filling the holes

First I sealed the existing fin holes by shaving some polystyrene foam into little cylinders that fit snugly inside the holes. I then used polyurethane glue to fix them in place.

Using the scraper tool, I spread the spackling onto the board and tried to fill all the tiny holes I could find. It was better to overfill the holes as some fillers shrink. After the spackling was left to dry, I followed up with some light sanding to even up the surface before glassing.


Sealing the blank gave a much smoother surface and allowed me to “fix” any mistakes and holes I introduced during shaping, such as the ones in my previous post. Another reason that you might want to seal the blank is for weight reduction. By sealing the foam with filler (lighter than epoxy), less epoxy from glassing will be absorbed into the cracks in the foam blank. Though you might start to question if the strength of the fiberglass job will be as good as if you didn’t seal the blank. Maybe someone can let me know.

Surfboard Construction: Nose, tail, and rails

Shaping the foam turned out to be a little more challenging than I had initially imagined. The lack of power tools and anything other than 60 grit sandpaper, attached to a sanding block (thank god for the sanding block), meant that I had to invest many hours of elbow grease to get any shaping done.


Ideally you would have access to tools such as an electric planer, an orbital sander, and a surfoam plane, etc. Not only would these tools give you the precision and speed to quickly shape a surfboard, they also have the appeal of making you look like a pro.

However, if the only tool in the box is sandpaper, do not fret, it is still possible to shape a surfboard. There are some perks to only using sandpaper. For example, you get to spend more time and effort shaping your board, mastering the art of sanding. And you get to create clouds of foam dust that just love exploring the micro-caverns of your lungs. As a precaution I wore both a breathing mask and eye-goggles.

Shaping rack. I made a makeshift shaping rack with some clamps, wood, and a sheet (see below).

Shaping the nose and rails

On a piece of cardboard I drew an outline of the nose I wanted to have on my surfboard. After cutting out this piece of cardboard, I traced the outline to one half of the blank and mirrored the design on the other half. I then grabbed a saw and cut off any foam that I didn’t need.


I spent much of the time flattening the top and bottom of the board to be flush with the stringer. As the stringer was orders of magnitude harder than the foam, sanding along the interface between foam and stringer resulted in small foam ditches. It was important to have a stead hand and not to sand that area too much. What helped a bunch was to use a planer to shave the stringer down. This damaged the foam a little, so I tried to reduce the damage with masking tape. However, any damage to the foam shouldn’t be an issue as I would need to fill any holes later and fiberglass the board.


After I flattened the board, I focused on introducing nice curves into the nose. Here I used the sanding technique that tatts-Markus taught me. This involved sanding at a tangent to the curve at all times such that material is not shaved off too quickly. This technique was also important for the rails.


Shaping the the tail

I spent probably the least time on the tail and most time on the rails and nose. Using an oval object, I marked the swallow tail onto the blank and cut most of it out with a saw. I then sanded the swallow tail until it looked the way I wanted it. Here I used the technique mentioned above, which allows you to sand a perfect curve.


I was not very patient and did not always ensure that everything was perfect. In fact I made a few mistakes, such as the ditch I sanded next to the stringer at the tail (The biggest mistake was probably not having any power tools!). However, this was something I was going to deal with when I sealed the blank. I still needed to fill the holes that used to host the old fin system anyway.



Surfboard Construction: Rough shaping

After making the blank it was time for the surfboard to take shape.

But first, the blank still had a bunch of polyurethane residue stuck to it, from ripping off the exterior foam. This polyurethane would get in the way of shaping, so I set out to clean it off first. For this I used a sanding block with 60 grit sandpaper to sand off any residue. After a bunch of not-too-careful sanding the blank looked a beautiful white again.

Since I was going to shape the board into a swallow tail (as designed), I cut the tail of the blank off with a saw. I started to shape the rails a bit and tried to flatten the deck to the height of the stringer.


As you can see, the clean blank is not perfectly even, but I’ll work on that when I start shaping it. There were also still holes in the tail from the old fin system but I’ll fill these with polystyrene and polyurethane glue later.

I also shaped some fins, but I’m not sure if I will end up using them.

Surfboard Construction: Making the blank

The next step of this project was to make the blank. This part of the project was not as straightforward as one would have imagined. The idea was simple: “glue the two pieces of foam together with the stringer in the middle”. However, there were a few challenges:

  1. There was a hole in the middle of the foam, where the old “stringer” used to live.
  2. I planned to introduce a flatter rocker than the original soft-top surfboard.
  3. I didn’t have any glue.
  4. I did not have any suitable clamps.

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Surfboard Construction: Making the stringer

The stringer is an important part of a surfboard. Not all surfboards need to have stringers. Obviously having no stringer means that the board will be a quite a bit lighter. But I figured that the existing foam was low density polystyrene anyway, and some extra weight from a stringer wouldn’t affect the performance too much.

I had three main reasons for having a stringer:

  1. I wanted to give my board a little more support and durability, since the original foam was already damaged.
  2. Having a stringer makes shaping the board a little easier by giving you a frame of reference.
  3. You can set the rocker. The existing foam from the soft-top surfboard had a very high rocker, and I wanted to have a flatter rocker without sacrificing too much foam. I could bend the foam and glue it to the stringer to hold it in place to reduce the rocker.

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