Building a KARA Hummer Layout Duck Boat #7: Sealing the Hull Interior

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Blog entry by DustyMark posted 05-20-2015 01:28 AM 9030 reads 0 times favorited 4 comments Add to Favorites Watch
« Part 6: Applying the Plywood Hull Panels Part 7 of Building a KARA Hummer Layout Duck Boat series Part 8: Anchor Pole Through-Hull Hole and Collar »


This boat is going to get wet and stay wet for days at a time. I plan to seal the interior with epoxy to give it at least some protection from the elements. My main concern was with the plywood. That is sealed well with the fiberglass cloth. The keel, gunnels, and ribs will be sealed by caulking the seams where they meet the plywood with thickened epoxy and coating the rest with unthickened epoxy.


I imagine a builder could use silicone caulk to seal the joints, but I’m using epoxy since it will last just as long as the rest of the boat.

Start with epoxy that is thickened like this.

Plop the epoxy into a 1 quart bag that has the corner nipped off. I use a smooth plastic scraper to move the epoxy into the corner of the bag with the hole.

Squeeze the bag to lay a bead of epoxy on your seams. You need to squirt that epoxy in a timely manner since 3 ounces of epoxy in such a thick blob could cook off pretty quick and it’s too expensive to waste.

I cut the edge of a scraper to make a custom scraper of a small radius to spread the epoxy evenly. These beads of epoxy will help prevent water from getting under the keel and the ribs. I applied thickened epoxy to the ribs prior to applying the plywood, so the underside of the ribs are protected.

Painting on the Epoxy

The plywood is already coated with fiberglass and the seams inside are caulked. Next, the rest of the interior is coated with epoxy that is applied with a chip brush. There’s nothing special about this and it’s pretty much a drudge task. However, timing is something to consider. If you brush epoxy on your caulk seams before they are cured enough, they could run. If you paint the epoxy on at just the right time, it may smooth out any rough areas along the caulk line.

It looks like I’m obtaining satisfactory coverage with two coats of epoxy. Some would advise more, but I own a well-used kayak that I built in 1996 that is doing just fine with two coats. Hopefully I’ll be too “smart” to duck hunt 20 years from now!

I’m not neat at this paint work. I got lots of epoxy on my sleeves and some on my pants. Here they are curing before I can bring them upstairs!


In the next installment, I’ll show how to keep the anchor pole holes from leaking through the hull.

-- Mark, Minnesota

4 comments so far

View shipwright's profile


8781 posts in 4139 days

#1 posted 05-20-2015 02:38 PM

Nice job. I used to use the plastic bag method all the time. It is just so good for placing the material exactly where you need it. Around my shop we called the bag full of epoxy a “pukemouse” because it looks kind of like a mouse and it … well you get the idea. :-)

-- Paul M ..............the early bird may get the worm but it’s the second mouse that gets the cheese!

View DustyMark's profile


523 posts in 3411 days

#2 posted 05-20-2015 05:08 PM

Ha! Ha! I picked up the technique during a Chesapeake Light Craft build. It definitely beats stuffing epoxy into the top end of a syringe.

-- Mark, Minnesota

View English's profile


693 posts in 2818 days

#3 posted 05-20-2015 09:18 PM

Mark, Just found your blog, Your work looks great. I’ve gone back and read all your entries. Looking forward to your next blog entry. Finishing the outside is lots of fun, sand, sand, and then sand some more.

I’ve been working on a large power boat for 6 months now, so I have done most the tasks you have on my boat. I probably have 100 hours in sanding on my boat. I’ve been blogging it here on Lumberjocks.

-- John, Suffolk Virgina

View DustyMark's profile


523 posts in 3411 days

#4 posted 05-21-2015 12:11 PM

John, the scope and quality of your build is amazing! Launch day will be a significant event for you…

-- Mark, Minnesota

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