In this Instructable learn how to repair a surfboard. Specifically a delamination which is a significant repair but these techniques can be applied to a small repair or ding or even a snapped board.

The surfboard to be repaired was left in a hot car where the venting was not able to keep up with the off gassing of the EPS foam (Styrofoam). So a large blister formed where the glass separated from the foam.

I have posted a whole Instructable on how to build a surfboard from start finish, actually the surfboard that is being repaired. So of that interests you check that out.

https://www.instructables.com/id/How-to-Make-a-Surf...

These techniques will work for both a epoxy or polyester resin surfboard. However be extra cautious, depending on your surfboard if you use polyester resin it will eat/melt EPS foam. You can use epoxy on polyurethane foam with no issues. When in doubt do a test first.

Step 1: Overview of the Repair

Depending on the damage, how you go about the repair may differ but the techniques and steps will be similar to what is show in this Instructable.

Determine if the repair needs to be filled or if large parts of board need reinforcement, this may include needing to glue back in pieces of foam.

If the repair is a ding, typically you can just sand and fill the hole or ding with some filler first then patch.

The basic steps that will be covered are:

Cut out the bad section of the board, in this case a large blister
Gluing back the fiberglass that was cut out (in this case I was able to save the fiberglass blister as it was very structurally sound)
Sanding rough the repair area
Adding a fiberglass patch or the repair area
Sanding and blending the fiberglass patch area into the original part of the surfboard
Hotcoating (a layer of resin) the repair area
Sanding and blending the hotcoat into the original part of the surfboard
Polishing

Step 2: Video of the Whole Process

I recommend you watch the video to get an idea of how to do the repair. The written steps follow and I will do my best to explain them.

Step 3: Materials and Tools

The following are materials and tools that were used:

Materials:

Epoxy Resin
Fiberglass Cloth (4oz was used but 6oz would work too)
Disposable Gloves
Plastic Yogurt Containers
Stir Sticks
Plastic Squeegees
Sandpaper (80, 120, 180, 220, 400 grit)
Masking Tape

Tools:

Rotary Tool with cutting disc
Sander or Sanding Blocks
Razor blade or Hobby Knife
Vacuum
Digital Scale

Step 4: Cutting Out the Area to Be Repaired

Determine the area that needs to be repaired and remove the fiberglass. Using a marker the blister was marked where it separated from the foam. Then using a rotary tool with a cutting disc the marked area was cut out, a vacuum was used to keep the dust down while cutting. Don't forget to wear a dust mask to keep the fiberglass dust out of your lungs.

The fiberglass patch that was cut out was able to be salvaged as it was in excellent shape, however it was convex in shape so it needed to be flattened before being glued back to the surfboard. Using a heat gun the blister was heated gently until it flattened out, a block of wood was used to help keep it level.

Step 5: Gluing Back the Repair Area

The blister once flattened was test fitted back onto the surfboard
Using a scale the epoxy was weight to a 2 parts resin to 1 part hardener ratio. Check the spec sheet for the epoxy you are using as volume vs weight differ slightly. If you are using polyester resin, follow there instructions. Also it is important not to use polyester resin on EPS surfboard as it will melt the foam.
The epoxy was applied with a cheap disposable brush.
Be sure to not leave the epoxy container alone with a lot of epoxy as the mixture will overheat
Using a cheap brush, apply a coat of epoxy to the repair area, use a generous amount.
Set the blister back into the repair area, if you are using new fiberglass you will want to apply the fiberglass in the patch area and then apply the epoxy.
Add some weights and clamps to the repair area if you are gluing in an existing piece of the board
Let the epoxy harden
Once the epoxy is hardened sand and use a razor blade or exacto knife to scrape the edges of where the repair
area meets the surfboard, this will help keep sanding down.

Also it is important to only work with the epoxy if the temperature is above 15C (60F) or else the epoxy will take a long time to harden and the viscosity will be very thick.

Step 6: Strengthening the Repair Area

If you are repairing a ding you probably will not be gluing in an existing piece of of the surfboard like the previous step but you will need to add some fiberglass cloth to the damaged area. This repair involves a large piece of fiberglass but the steps and theory is the same for a small repair.

Sand rough using a coarse sand paper the patch area, then wipe down with denatured alcohol.
Some tape was applied to keep the epoxy off the parts of the board that were not being repaired.
A piece of 4oz fiberglass cloth was cut to the shape of the repair that overlap over the seams. Instead of patching just the area where there was an issue, I decided to fiberglass the whole front of the board so the strength would be evenly distributed.
Mix some epoxy with a scale like the previous step.
Pour the epoxy on the repair area
Using an automotive body filler squeegee, move the epoxy around the board giving it time to soak into the fiberglass. Don't rush this, let the fiberglass get saturated.
Once all parts of the fiberglass is saturated, squeegee off excess epoxy, you want the fiberglass weave to show, avoid having pools of epoxy as this will create an uneven surface
Let the epoxy harden

Step 7: Sanding the Patch

Once the epoxy has harden, remove the tape from the surfboard.

Using a sander with some medium grit sandpaper (120 grit) sand the fiberglass repair area so it blends in with the existing board. Go slowly so you don't sand too much or damage the existing part of the board. The smoother you feather the transition area the better your repair will look. I am using a vacuum to keep the dust down as sanding fiberglass with throw up lots of dust you want to keep out of your lungs and work space, wear a dust mask as well.

You can use a hand sander, palm sander or other sanding tools.

Step 8: Hotcoating the Patch

Now the repair is nice and strong, it's time to make it look smooth like the rest of the board. This is called hotcoating.

Vacuum to get rid of any dust, avoid touching the board with your hands as they have natural oils that can contaminate the surface causing adhesion issues with the epoxy.
Tape off the areas of the board where you do not want to get epoxy.
Mix up some more epoxy and using a cheap bristle brush, brush the epoxy over the repair area, making sure to cover all of the fiberglass patch. Try to blend the brush strokes into the existing parts of the surfboard, this will keep sanding down later. Use long even strokes and don't go to fast give the epoxy time to let the brush move it around.
Let the epoxy harden.

Step 9: Sanding

Once the epoxy is hardened, remove the tape. Sand using 180 grit sandpaper to blend the repair area into the existing part of the surfboard. Once the area is blended, sand the whole patch to flatten. Sand the rails by hand as the epoxy there will be thinner than other parts of the repair.

To finish the sanding, wet sanding will need to be done, any grits finer than 220 work much better if you sand them wet as the water helps remove the sanded material keeping the sand paper unclogged. Work from 220 all the way up to 1000 grit to get a nice shiny finish, try to sand all in one direction, that will keep the sanding marks down. In this repair I only took it up to 400 grit as it takes a lot of elbow grease to wet hand sand and this it's purely for aesthetics.

Step 10: Final Step: Polishing

The last step and is optional is polishing, polishing will help blend the repair area in with the rest of the surfboard. I like using an automotive clear coat polish. I use a cloth and apply a little polish and start working at the surfboard, it will take some elbow grease! You can also use a buffer if you have one and will speed things up.

The repair came out great! You can still see a small difference between the color of the repair vs the original board, if I took more time I could sand it more to make it less noticeable but since this surfboard gets a lot of use this is perfectly acceptable.

Introduction: How to Repair a Surfboard