< back to articles

Kayak Building Part 10 – Fiberglassing the Inside of the Hull

This is part ten of a multipart blog . . . Read Part One here,  Part Two herePart Three herePart Four herePart Five herePart Six herePart Seven herePart Eight here, Part Nine here.

I left off with fiberglass taping the inside of the deck and taping the deck back onto the hull so the deck would set up in the correct shape.  Now I have a few more steps on the deck, and then I move back to working on the hull.  As always, read below for details!

Day 43:  7/18/12  1.25  hours  

So what better birthday activity than to work on my kayak.  Actually, I only had to spend a short amount of time in the shop before moving on to dinner with my family!  I stopped at the lockmaster’s house after work to reinforce the rear of the cockpit and deck recess.  I cut two scrap fiberglass cloths and epoxied one over the back of the cockpit. Then I placed the second piece on top of the first and applied another layer of epoxy.   Next I rolled a saturation coat of epoxy over the entire inside deck and let it harden overnight.  When I met Mark and the kids at the restaurant, they all looked great.  I looked like I was just working on a boat in a house with no air conditioning, with epoxy on my arms as usual.  Oh well.

Reinforced rear of cockpit and deck recess with two layers of fiberglass

Epoxy the inside of the deck.


Day 44:  7/20/12  3.75  hours

I ran to Marietta after work again, but had a longer night this time.  First, I put the final layer of epoxy on the inside of the deck and then moved onto the inside of the hull.  Since the deck was sitting on the saw horses, I had to work with the hull on the floor.  This was not the most comfortable position.  It was a tight fit in between the wall and the deck, and I had to make sure I didn’t knock the deck over.  Working with three boats in progress makes moving around the lockmaster’s house exercise in itself!

First I removed the temporary frames from inside the hull.  If you recall, they were glued in place with hot glue.  To remove them, I heated up the hot glue with Dan’s soldering iron.  That didn’t get everything though.  To completely remove all traces of the glue, I had to use a cabinet scraper and sandpaper.  What a pain!  Since scraping and sanding are not my strengths, it took forever!

Melting hot glue with soldering iron to remove temporary frames

Scraping hot glue with cabinet scraper


I also had too make sure all of the holes were filled.  I actually found many holes that were not filled from the drip through from earlier work on the outside of the hull. I mixed a small batch of epoxy and filled many of the drill holes.

Inside of hull without frames and glue


I’ll keep you up to date with Gary’s and Dan’s boats too.  Gary has just fiberglassed the hull and is adding additional coats of epoxy.  Dan is wiring his hull together.

Three boats in different stages: Dan is wiring frames and Gary just fiberglassed the hull.


Day 45:  7/21/12  1.75  hours

I checked out the holes that I patched the previous night, and I still missed some.  After I filled more of the holes in the hull, I worked on strengthening the bow and stern stem seams.  I used a lot of wood flour to make a very thick batch of epoxy, the consistency of putty.  I used the wooden tongue depressor to fillet the seams.  I built up the ends to about 2 1/2″ thick, and then left the tongue depressor on top to help hold it in place.    I wanted to get a thick enough area filled so that I could drill through it for the end handles later.  Having this much epoxy at the ends produced a lot of heat.

Fillet inside seam of hull with thickened epoxy.

The tongue depressor is now a permanent part of the boat.


Day 46:  7/22/12  1.5  hours

Today I checked the epoxy fillets on the bow and stern tips.  I filed them down with a round file to make sure the deck would later fit on top.  Next I  reinforced the bow butt seam with two layers of fiberglass cloth.  The first layer was 3″ wide, and I covered that with a layer that was 4″ wide.  Once I had the fiberglass in place, I saturated the inside of the hull with a layer of epoxy and let it harden overnight.

Used a file to clean up the bow and stern tips

Reinforced bow butt seam with two layers of fiberglass

Coated hull with layer of epoxy


Day 47:  7/23/12  2.75  hours

The inside of the hull is finally ready to fiberglass!  We didn’t assemble the team this time, but I did recruit my husband Mark and daughter Arienne to help!   Dan was there, and Frank stopped in, too, and was happy to jump in and help the setup. We first layed down a strip of masking tape the entire length of the boat, 3/4″ above the upper chine. Then we layed a 9′ by 38″ fiberglass cloth from one end to the middle of the boat.  We taped one side to the tape line, smoothed out the cloth, and cut the other edge at the tape line on the other side.

Laying out first sheet of fiberglass cloth

Trimming cloth at other tape line


Next we placed the triangle piece of cloth that we just trimmed off, on the other half of the boat, and pulled it’s narrow end to the stern end of the boat.  That left a gap in the middle.  I cut a small piece of left over cloth from glassing the outside of the boat.

Laying out glass on inside hull and filling middle spot with small piece

Now it was time to mix the epoxy and roll it on the glass.  Arienne and Dan rolled, Mark followed up with the squeegee, and I mixed.

Dan, Arienne and Mark glassing the inside of the hull

The tricky parts were 1) getting the middle section with all of the overlap to smooth out, and 2) getting the glass to lay nicely at the ends, where they were earlier filled with the thickened epoxy.

Touching up the inside of the hull and working on the ends

Glassing the end of the boat

Before we could leave for the night, we had to wait until the epoxy set up and then cut the glass at the tape line.  We took a dinner break, and Mark and I stopped back two hours later.  We cut the fiberglass below the tape line and peeled up the tape.  This left an even edge to the glass.  Then we added one more coat of epoxy and left for the evening.

Next steps in Part 11 . . . Decking the Hull!  Christmas in July!


Add a comment

Comments (8)

  1. avatar
    Peter, August 12, 2012
    Could you have used a longer working time epoxy and used fewer people? I was talking to a friend that had put together a boat similar to yours and that's what he did. I was wonder if you choose the standard cure time for reasons of strength or something else. Anyway I've really been enjoy your story, can't wait to see you in the water with it! Reply
    • avatar
      nancy, August 20, 2012
      Hi Peter, The standard cure time is fine for a one person job, but having a team just makes everything easier. The folks at Pygmy Boats were surprised to hear about the team approach and mentioned to me that there was plenty of time to do it with one person. When I told them a team can pull it off in under an hour, and in fact, the last team did it in 32 minutes, they were impressed. I do know that you can purchase the epoxy with faster or slower cure times, but Dan's experience is with the standard, so that's what I used. According to Woodcraft's Product Manager, Kent, all epoxies generally take 24-48 hours for their final cure, although some are made to set faster. For more information on epoxies, you can read System Three's Epoxy Book online: http://www.systemthree.com/sys3news/?cat=6 Reply
  2. avatar
    Glenn Box, August 17, 2012
    I just finished a cedar strip kayak. While most of the fiberglass work is the same, the woodwork is different. I kept a photo journal on my Facebook page, so lett me know if you would like to check it out. I've enjoyed reading your blog! Reply
    • avatar
      nancy, August 20, 2012
      Hi Glenn, Thanks for the comment. I just checked out your facebook photos - your boat is beautiful! Well Done! Looks like you have mine beat! Several people have asked the about cedar strip kayaks and building from a plan. If you don't mind, go ahead and share your facebook link in the comment! Congrats! Reply
  3. avatar
    Charlie, August 18, 2012
    Thanks for sharing. Reply
  4. avatar
    Steve Worzman, August 30, 2012
    I used to own a high performance fiberglass catamaran. I have a lot of experience with resins and synthetic cloth. Epoxy and fiberglass were not made for each other. Epoxy does not "wet" or "soak" fiberglass the way laminating resin (polyurethane resin) does. Epoxy and fiberglass is "phobic" whereas polyurethane resin and fiberglass is "phillic". Epoxy will work with fiberglass but it will not have the strength of laminating resin with fiberglass. Epoxy is phillic with carbon fiber and kevlar. Laminating resin is not. This is the type of cloth where epoxy should be used. You should know that laminating resin with fiberglass does not sand well when cured. It gums. The workaround that boatbuilders have for this is to apply a thin layer of "finishing" resin after the laminating resin has cured. Finishing resin raises a thin film of wax to the surface when it is cured. The wax and finishing resin are sandable. Note cure times for these resins is quick depending on how much catalyst you use and the ambient temp. Since this is being used inside the hull, I would not do the next step because it adds unnecessary weight. This next step is the application of "gel coat" which is the hard white or colored shell that you see on the outside of boat hulls. This should be sprayed -- a hand aerosol sprayer like "Preval" works for this. You may need to dilute the gel coat a little (<15%) with acetone to do get a good spray. Gel coat is is also catalyzed but hardens only in the absence of air (because it is normally on the inside of hull molds). To get it to harden spray PVA (Polyvinyl Alchohol) on the gel coat. It creates a thin film which later, once the gel coat is cured, is washed away with water. Most likely you will be left with an eggshell finish. This can be sanded very fine. For filing gaps and fillets, use epoxy mixed with a West System bonding powder. Don't use wood dust, it has little structural strength. The West System "Hardware" bonding powder is the hardest. The "Fairing" powder is ultrafine for filleting but not as strong. These can be tinted to match the wood (Transtint dyes work well with epoxy). Other thoughts. Use Carbon Fiber where ultimate stiffness is desired (also very light weight). Use Kevlar where ultimate tensile strength is desired. Do not expose Kevlar to the sun, this will weaken it. Do not use Kevlar on a wear surface. It does not wear smoothly. It just gets hairy instead. Remember, pools of resin have no strength so squeegee flat. Practice on scrap first. Get multiple hands working together for large jobs or break it into smaller parts to deal with the rapid cure times. Epoxy and polyurethane resin are toxic. The more you expose your skin to it, eventually your body with react with chemical blisters. Acetone is used for clean-up but only Butyl Rubber gloves are impenetrable to acetone. The acetone molecule is too small for all other glove materials. Hope this helps. Reply
    • avatar
      Armin von Seutter, August 31, 2012
      I might add, use a carbon filter mask. Epoxy resin makes me sick. Reply
    • avatar
      Steve Worzman, September 6, 2012
      Correction: Laminating resin is polyester resin, not polyurethane. My apologies. Reply

Add a comment

(it will not be shared)