Building a KARA Hummer Layout Duck Boat #10: Fiberglassing the Hull

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Blog entry by DustyMark posted 05-28-2015 12:30 PM 3475 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 9: Applying the Plywood Deck Panels Part 10 of Building a KARA Hummer Layout Duck Boat series Part 11: Fiberglassing the Deck »


Fiberglassing the hull involves prep work, fitting the fiberglass cloth, applying several coats of epoxy, and sanding.

Prep Work

Whatever condition the hull is when you fiberglass it, is the condition it will stay, since you don’t want to sand through the fiberglass. All the corners of the boat must be rounded to a minimum of 1/4” radius because fiberglass won’t lay well across a corner that it is tighter. Outside corners can be routered or filed. Inside corners must be filleted with a mix of thickened epoxy similar to the method I used to seal the hull interior seams.

Gaps and dips must be filled with a mix of thickened epoxy.

Nail heads that stick up or are set too deep can be adjusted with thickened epoxy.

This boat will receive flat green paint, so I only sanded the hull to 80 grit.

Fitting the Fiberglass Cloth

It helps to have a second person unfold the fiberglass.

I cut the cloth for the hull so that 2” folded over onto the deck. This double protects the gunnel.

I mixed 12 ounces of epoxy for the first two batches and poured it directly to the flat portion of the hull and spread it with a flexible scraper.

Spreading the epoxy with a scraper. NOTE: Marine Douglas Fir plywood is very thirsty for epoxy on the first coat. Another technique is to prime it with a thin coat of resin ahead of time. I guess you could let it dry a bit and then lay on the cloth. That seems like too much of a bother, so I was generous with the first coat and squeegeed it in thoroughly.

Stretching out wrinkles and rolling onto the deck.

Mary cutting some darts to get the fiberglass to fold at the stern. Removing little wedge-shaped sections of fiberglass at the ends helps it to lay down better. Those areas can be sanded later.

Mary’s work.

First coat applied. I applied three coats and was careful to squeegee each coat to avoid excessive build-up and wasting expensive epoxy. Remember, the objective is to just fill the weave of the cloth. NOTE: I was careful to apply subsequent coats before 24 hours. If I had waited longer, I would have had to sand between coats.


No matter how careful you apply the epoxy, there will be imperfections that require sanding.

Deck before sanding.

Same area of deck after sanding.

Hull before sanding.

Same area of hull after sanding. NOTE: You need to be very careful around the nail heads to not sand through the fiberglass.

One last bit to sand. NOTE: Epoxy and fiberglass dust are not items you want to breathe in or get all over your bare skin. I always wear long sleeves and use a dust mask. The danger is that, with overexposure, you could become “sensitized” to them and it would become very difficult to use epoxy or fiberglass in future projects.

Hull completely sanded to 80 grit. I may sand it smoother since I may use bright paint on the bottom of the hull.

I puttied a couple of screw heads that I missed on the cockpit corners. Once those spots are cured and sanded, the deck will be ready for fiberglass.


In the next installment, I’ll discuss fiberglassing the deck.

-- Mark, Minnesota

4 comments so far

View Edwin's profile


120 posts in 2421 days

#1 posted 05-28-2015 02:10 PM

Coming along nicely Mark. Ed

-- Ed Port Republic

View SPalm's profile


5249 posts in 3305 days

#2 posted 05-28-2015 02:40 PM

Sweet. Now it really is looking like a boat.


-- -- I'm no rocket surgeon

View English's profile


512 posts in 900 days

#3 posted 05-28-2015 08:27 PM


Wetting out glass is a messy job, Looks good!!.

When I did my boat I was told that the epoxy had to go on wet on wet on wet. I had to put two layers of fiberglass on my boat. Over thirty yards per layer. I called and talked to the tech support guy at the epoxy company I was using ( Aeromarine). He said that for a structural joint wet on wet on wet is the only way to go to get the strenth of a chemical bond, but for laminating a fiberglass on a boat it was not necessary. He said that the epoxy wills stick to it’s self with a mechanical bond ten times the strength needed for laminating fiberglass no sanding between coats needed. So he told me to take may time. One coat today, one tomorrow, one next week.

-- John, Suffolk Virgina

View DustyMark's profile


342 posts in 1493 days

#4 posted 05-28-2015 09:39 PM

Thanks! The blog is caught up, so I’ll be fiberglassing the deck tonight. She’ll be ready for paint by next week.

-- Mark, Minnesota

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