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post #1 of 11 Old 06-26-2012 Thread Starter
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Adhesive Question

I am trying to finish my project boat, a 1977 San Juan 26 and I ran into a problem involving adhesives. I used epoxy to glue .5 inch plywood furring strips to the coach roof (cabin ceiling) to which .25 inch thick pine strips would be fastened with screws for a nice wood ceiling. When I was about half way complete screwing the finished strips in place, some of the plywood furring strips detached. I could hear the epoxy separating from the roof. Today I removed the strips and the insulation and was able to pull all of the furring strips off with moderate force. Disappointed, but better now than on the relaunch voyage.

The problem appears to be that the epoxy did not adhere well to the roof surface. I might have skimped a little on the sanding prep, but the entire length of the epoxied strip popped off to an extent that made me think another adhesive would be a better choice. I am experienced with epoxy and it was not a bad batch. I speculated that the roof utilized polyester resin and not epoxy.

Is there a better adhesive to keep furring strips glued to the ceiling for the next twenty years? A fast curing adhesive would also help - gluing stuff to the ceiling is difficult as gravity never takes a day off. Liquid Nails, 5200, hot melt glue, epoxy, gorilla glue, cyanoacrylate, any others?.

Thanks for any suggestions. I have benefitted from reading this board over the past two years as I worked on my project. I will post some pics when she is done.
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post #2 of 11 Old 06-27-2012
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Re: Adhesive Question

In adhesion, surface preparation is critical.
Without it, you will have failure no matter what adhesive you use.
Get a good dust mask, a power sander 30 grit, and go at it.
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post #3 of 11 Old 06-27-2012
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Epoxy Failure

Adhesive joints fail when subjected to peel loadings and flexing of the deck will create this type of loading. A mechanical joint is required for your application such as screws or a routed wooden t joint.
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post #4 of 11 Old 06-27-2012
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Re: Adhesive Question

A member at our club had the same issue with his trawler, I sudgested to glass the strips in place, more labour and mess but will hold up for many years.
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post #5 of 11 Old 06-27-2012
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Re: Adhesive Question

It may not have had good contact along the entire surface. Perhaps a thickened slightly flexible epoxy (like West G-Flex) would work.
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post #6 of 11 Old 06-27-2012
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Re: Adhesive Question

Why not use screws to keep them in place. I assume the SJ26 has a cored deck. you should be able to screw into the deck above without going through.

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post #7 of 11 Old 06-27-2012
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Re: Adhesive Question

Solvent clean, coarse sand, clean again. Then use 5200, which can flex with the deck if needed but once it sets up, never lets go. Check the label, it may need 7? days to fully cure before you put loads on it.
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post #8 of 11 Old 06-27-2012
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Re: Adhesive Question

I second glassing in the furring strips. I think this is what Don Casey suggests. Might be nasty working over your head. OTOH, it doesn't need to be pretty.

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post #9 of 11 Old 06-27-2012
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Re: Adhesive Question

thickened epoxy should be fine if you prep the surface well.

sand, clean with solvent.

to ensure even better hold with epoxy, brush on clear epoxy and let it tack up before you apply the thickened epoxy.

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Re: Adhesive Question

"sand, clean with solvent."
One would think. But apparently when you sand first, you literally engrave the surface contaminants down into the grooves, making it much harder to remove them. Which is why the recommended prep is to solvent clean, with disposable rags/paper, working outward from the area. Then to sand, then to reclean, often with a less agressive solvent, again working outward with disposables so you keep removing any contamination.
That can often be overkill but "surgically clean" makes the prep job guaranteed not to cause problems, and really doesn't cost a lot more in time or materials.
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