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Old 11-02-2009
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Deck core replacement from inside the cabin.

When I bought my Merit 25 one of the issues was a soft deck. A huge chunk of it and I knew it was going to be a chore to replace. My decks were in very good shape and since I didn't have a liner (or interior) I decided to do the core replacement from the bottom instead of removing the much thicker fiberglass shell and gel coat from the top.

If I had a liner, or cabinets, or a painted deck I probably would've thought about going at it from the topside as this would've been easier due to gravity.

Let me also say that this was my first ever attempt at using fiberglass and epoxy.

I chose to use the West systems epoxy b/c it seemed pretty easy using the pumps (buy the pumps, the mix is too sensitive to eyeball, I know b/c I tried). I used 105 resin and 205 fast hardener along with 407 and 406 filler. None of which was cheap. I believe I used 6oz cloth for the layup along with 1/2" A/B plywood (marine grade). As it turns out, I should've used 3/8".

Removing the old rotted plywood was 1/2 the hard work. It's messing, wet, and labor intensive. There was a single layer of glass on the inside of the cabin. I used an angle grinder and a circular saw to make the initial cuts. Be careful when using a saw above your head (keep track of where the cord is, don't ask...). After making some "slash cuts, it was down to using brute force with hammers, screwdrivers and chisels. Then after the big chunks were out, I used an orbital sander to smooth out the underside of the outer shell of FG.

Used the same circular saw to cut my sheet of plywood into smaller "puzzle" pieces to start 'gluing' into place using thickened epoxy (406 silica). Remember to 'dry fit' the pieces first to save on materials. Remember the fast cure 205 crap hardens pretty quickly. I used 1"x1" wood cut to various lengths to wedge under the plywood to keep it in place while the epoxy kicked. Once it had (the next day) I'd come back and fill in any gaps using thickened epoxy and then glass over the “tile work” with fabric and UN-thickened epoxy as this creates a stronger finished product. Working above your head with epoxy of varying thickness is a messy task. Your clothes, face, gloves, hair on your arms, will be trashed, just plan accordingly (a drop cloth would’ve been a fantastic idea).

I then came back another day and sanded the semi finished stuff. Cleaned the surface and used 105, 205, and 407 filler to smooth out the texture of the glass fabric. Sanded that and let it cure completely. I then put 2 coats of Brightside white on it and let it be. I also had to replace an H support at the companionway opening due to the original one rotting out. I have attached pictures of that as well as the removal of the old wet core and the replacement. I have not taken pictures of the finished faired and painted cabin roof. I’ll try to get some soon.

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Old 11-02-2009
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Nice job! When you "glass(ed) over the “tile work” with fabric and UN-thickened epoxy", how did you keep the glass from sagging? When I've tried this, that's where I've always come unglued.
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Old 11-03-2009
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Might've been the temps I was working in (March), the epoxy is a little thicker when your at the low end of the working temperature, and this helped. I would mix enough to lay a 4' long strip. Apply epoxy by brush or roller to the wood to wet that out first, then press the dry cloth onto the wet plywood. I then pressed more epoxy into the glass using a brush and plastic putty knives. This was probably the second messiest part of the job, as the unthickened stuff was dripping everywhere. Remembering not to work the epoxy too much is also helpful as you'll start to get small air bubbles in the layup and that not strong, and doesn't help it 'stick' either.

I'll be at the boat this weekend to snap some almost final pics.
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Old 11-03-2009
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Just curious, but why did you use marine plywood as the core material in your rebuild. Marine plywood is about the worst choice of core materials out there.

Many boats were built using it, but it was mostly due to cost considerations, not structural. Marine plywood is heavier than the other commonly used core materials, like end-grain balsa or foam, and it shares some of the worst characteristics of both. It rots like balsa does. It also allows water to delaminate large areas like foam does.

I'd also point out that if you had used either foam or an end-grain balsa based core material, like Baltek, you could have easily worked in larger sections than you were able to with marine plywood, as the materials are more flexible and would fit the cabintop shape better.

Nice job BTW... looking forward to seeing the photos.
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Old 11-03-2009
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Good job
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Old 11-04-2009
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Quote:
Originally Posted by sailingdog View Post
Just curious, but why did you use marine plywood as the core material in your rebuild. Marine plywood is about the worst choice of core materials out there.

Many boats were built using it, but it was mostly due to cost considerations, not structural. Marine plywood is heavier than the other commonly used core materials, like end-grain balsa or foam, and it shares some of the worst characteristics of both. It rots like balsa does. It also allows water to delaminate large areas like foam does.

I'd also point out that if you had used either foam or an end-grain balsa based core material, like Baltek, you could have easily worked in larger sections than you were able to with marine plywood, as the materials are more flexible and would fit the cabintop shape better.

Nice job BTW... looking forward to seeing the photos.
There were 2 reasons I didn't use balsa. It flexes much more. The Merit has a very thin layer of FG on the cabin roof, and I wanted the extra support of having a wood that gave some additional structural support. I understand it's heavier than the other materials, but the water logged plywood was WAY heavier the wet picture was taken a week after it rained. The other reason, as you mentioned, was cost. End grain balsa is not cheap. Foam is more expensive, and the exotic honey comb structure stuff is just stupid expensive. If I was building a boat from the ground up, sure, foam or honey comb would be my choice. I could budget for it, and justify the cost. But changing core material midship just didn't make much sense to me from a structural standpoint.

Thanks for the feedback everyone. I admit, these pics aren't the best, but I wanted to show that even a beginner can work with FG and get decent results. Certainly not like a pro, but good enough for my $1200 boat.
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Re: Deck core replacement from inside the cabin.

Preparing to cut out a section of interior on my grampian26. Both sides of cabin, where the handrails were, are totaly holding water and the balsa is mush. Cabin flexes when walking over it. Your work has inspired me to move forward. Not really looking forward to the overhead aspect but I dont want to cut through the nonskid on the deck. Thanks for the post and pics.
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Old 07-15-2014
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Re: Deck core replacement from inside the cabin.

No problem. Put down some paper, the epoxy drips everywhere no matter how cautious you are. Good luck and post some pics. BTW, I'm still racing this boat and the core is still dry.

The original post is 5 years old.
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