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This is the first fiberglass boat I have owned with a balsa core in the deck and superstructure. What's the best way to repair stripped screw holes and other larger holes, like unused electronic cable holes? I was thinking of using CPES to saturate the core wood around the hole, then epoxying in a wood plug. What say the experts?
If its wet you need to get the water out and if there is any deteriorated (rotted) core that must be removed and repaired. Then rout out the core (a bent piece of piano wire in a drill makes a decent recess tool), use CPES to seal, pack with thickened epoxy, and then either insert a plug or re-drill and re-insert screw.
If it's dry inside, just put CPES inside into the core, rough up the fiberglass hole and clean it and pack it with WaterWeld (JB Weld's marine epoxy product) up to the surface. Then redrill as necessary. Waterweld is an excellent marine epoxy that's sticky when you mix it but quickly hardens to a substance like fiberglass that can be sanded, painted, drilled or tapped. They say it can be used below the waterline, but I have never done that, because I prefer 5200.
Doug
Thanks. You both mention drying out the hole. How is that done? Hair drier? Heat gun?
I used a shop vac to suck out the water soaked balsa core around my mid cabin window frames after breaking up the soft material with a cabinet screwdriver, and let it dry for a week. I filled the void with Raka epoxy thickened with colloidal silicia and wood flour. Screw holes were filled with the same mixture squirting the thickened epoxy into the holes with a large syringe. Jamestown sells 50ml syringes with 1/8" tips. You need to have a second small hole connected to the hole you are filling to allow the air to escape as you force in the epoxy. Likewise, vent holes to allow air flow when removing water soaked balsa are helpful. Since I was going to recover the interior with new veneer, additional holes could be drilled.
I've never used CPES and would question the benefit of epoxy thinned with solvents. It would seem to me that you would get shrinkage and loss of strength. Perhaps if you were sealing sound wood, CPES would be fine, but that does not appear to be what you are doing.
MAS epoxy has lower viscosity and is still solvent free.
Vincent
Two things I can't do without is west system and cpes. Anytime I get to bare wood on an old or new piece of wood it gets cpes. Had some rot on my aft deck, dried it out cpes and now harder then it was when it was new. I'd dry it out and give it hell with the cpes then epoxy of your choice. Bill
To clean the core material from a drilled hole Iuse a small allen wrench in a drill motor. If you can get to the backside of that hole I put some good masking tape on that backside and fill the hole with West System epoxy from the top.
CPES isn't a panacea but it gets into the grain structure of the wood and seals it, which is why you use it. The solvents get the epoxy in there and seal it up, killing any rot spores at the same time. The solvents are NASTY (which is the entire point); you're not trying to be KIND to that which is eating your wood!
If deterioration has started but structural integrity is still present this will stop it from progressing. If you just seal up an area that has rot in it and don't get ALL of the water out (an impossibility in a sealed, cored structure) the rot will continue to propagate. You HAVE TO kill the existing organisms and prevent any that escape your "killing fields" from being able to access more material to consume, and you HAVE TO dry it out as much as is possible.
You'd be shocked at how far that stuff penetrates into sound wood - in even mildly compromised wood it literally saturates it all the way through. If the wood is not fully sound you'll find that you can keep "feeding" CPES into it for what seems like forever - it will keep travelling through the structure until it reaches fully sound material and then keeps going for quite a ways further.
When I fixed Gigabite's bow pulpit area I removed the bottom skin from the damaged area, removed the damaged core and then ran CPES into the now-exposed core beyond the damaged area. Once that was done I then laid in new coring soaked in CPES and bedded in thickened conventional epoxy and then relaminated on new glass on the underside of the re-cored area. It was a NASTY job but when complete I'm willing to bet you could drive a truck over the repaired structure, and any vestigal rot organisms that were present beyond the removed area were definitely DEAD and of no further threat to the rest of the deck core, plus a wide radius around the removed and repaired area had been saturated with CPES and thus was no longer able to support further growth even if some of the spores survived.