Repairing rotted core

FullMonty

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Pulled out two windows to replace all the gaskets. Then noticed core was punky/wet. I plan on using coosa and just epoxying it in place. Then gonna put the old skin back on. Is this the normal method for repair?
 

leaky

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Pulled out two windows to replace all the gaskets. Then noticed core was punky/wet. I plan on using coosa and just epoxying it in place. Then gonna put the old skin back on. Is this the normal method for repair?

I don't know what's normal but don't see the point of gluing old skin back in - is still a cosmetic problem with all the seams and the epoxy seeping out may screw with gelcoat when you go to re-coat everything later.

Not to poo poo your plan more but the core you pick isn't really important either, rest of the house is balsa so not much benefit to spending coosa and epoxy $$ for the little repair. Plywood, anything really, would be sufficient. This is just kinda a patch.

For this job, the quick way, grind a ramp around the seam you cut away, prep the inside of the skin thats left there. Cut your plywood pieces, pre coat with unwaxed resin, let it cure. Coat the surface liberally with hull & deck and clamp your new core in, swipe the excess away, let it cure, sand it all flat. Pre coat any exposed plywood, let it cure, glass over it in some manner that makes fairing easy as possible. Poly fair, sand smooth, gelcoat, take it to whatever level you want cosmetically.

Before re-installing windows, do something to seal the core and prevent a recurrence.
 

Cool Boat

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I like the concept of the Coosa plus epoxy and is why we put a complete Coosa deck on our wooden Herreshoff Rozinante sailboat. I also note that the Coosa deck was significantly lighter than the wood and plywood deck that it replaced so you should save weight too. Years back I had several training sessions with Joe Lstiburek of Building Science Corporation. (excellent website for indoor air quality issues and construction details if so challenged) In the one two day training session he had the class "now repeat after me, ALL WINDOWS LEAK". If not double insulated and air gets to it you can get condensation, or other leakage. Keeping the water off of materials that can rot, or substituting rot free materials is a good thing. Vacuum bagging is a technique that can help you reattach a skin too. Some boat designers like Kelsaw (I believe is the spelling) had a system to use shop vacs, had some youtube vids. Good luck!
 

Lion's Paw

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Monty, you are on track with your rot repair. The method you are talking about will work just fine. It is a toss up on what core you put back in there and the coosa is a fine choice and my go to for this as well. It bonds very well to the old skins and is easy to work with. Reuse of the old skin is ok, but the Frankenstein seam is sometimes hard to hide completely especially if you dont get the two sides of the seam close to flat with each other. Other option of laying up new cloth works as well but is more time consuming and you still have the seam from old to new to deal with.

Just cut out and test fit the puzzle pieces together and glue away, clamping the heck out of it thru those windows openings. Take some time to clean out the entire window cutout if it is at all compromised and fill it with core or epxoy to stop more water entry into the remaining core. You may be better off ripping open a bit more then you think and just doing it all at once as you will be surprised at how far the core rot can migrate thru the balsa.

good luck and it will be better then before when you are done.
 

FullMonty

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Monty, you are on track with your rot repair. The method you are talking about will work just fine. It is a toss up on what core you put back in there and the coosa is a fine choice and my go to for this as well. It bonds very well to the old skins and is easy to work with. Reuse of the old skin is ok, but the Frankenstein seam is sometimes hard to hide completely especially if you dont get the two sides of the seam close to flat with each other. Other option of laying up new cloth works as well but is more time consuming and you still have the seam from old to new to deal with.

Just cut out and test fit the puzzle pieces together and glue away, clamping the heck out of it thru those windows openings. Take some time to clean out the entire window cutout if it is at all compromised and fill it with core or epxoy to stop more water entry into the remaining core. You may be better off ripping open a bit more then you think and just doing it all at once as you will be surprised at how far the core rot can migrate thru the balsa.

good luck and it will be better then before when you are done.
Thanks. I was thinking of opening it up a little more. But the wood is getting solid. I also purchased some total boat penetrating epoxy. I was going to drill some 1/8 holes into the core through the window opening and inject it. Then coat all the exposed core around the window opening with resin as well to seal it up.
 

FullMonty

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I don't know what's normal but don't see the point of gluing old skin back in - is still a cosmetic problem with all the seams and the epoxy seeping out may screw with gelcoat when you go to re-coat everything later.

Not to poo poo your plan more but the core you pick isn't really important either, rest of the house is balsa so not much benefit to spending coosa and epoxy $$ for the little repair. Plywood, anything really, would be sufficient. This is just kinda a patch.

For this job, the quick way, grind a ramp around the seam you cut away, prep the inside of the skin thats left there. Cut your plywood pieces, pre coat with unwaxed resin, let it cure. Coat the surface liberally with hull & deck and clamp your new core in, swipe the excess away, let it cure, sand it all flat. Pre coat any exposed plywood, let it cure, glass over it in some manner that makes fairing easy as possible. Poly fair, sand smooth, gelcoat, take it to whatever level you want cosmetically.

Before re-installing windows, do something to seal the core and prevent a recurrence.
Thanks for reply. I already purchased the coosa and it was a hundred bucks so not outrageously expensive. Thanks for pointer on the unwaxed resin.
 

FullMonty

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I like the concept of the Coosa plus epoxy and is why we put a complete Coosa deck on our wooden Herreshoff Rozinante sailboat. I also note that the Coosa deck was significantly lighter than the wood and plywood deck that it replaced so you should save weight too. Years back I had several training sessions with Joe Lstiburek of Building Science Corporation. (excellent website for indoor air quality issues and construction details if so challenged) In the one two day training session he had the class "now repeat after me, ALL WINDOWS LEAK". If not double insulated and air gets to it you can get condensation, or other leakage. Keeping the water off of materials that can rot, or substituting rot free materials is a good thing. Vacuum bagging is a technique that can help you reattach a skin too. Some boat designers like Kelsaw (I believe is the spelling) had a system to use shop vacs, had some youtube vids. Good luck!
Thanks for the info. The boat is 25 years old so not surprised there was minor leak.
 

leaky

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Thanks for reply. I already purchased the coosa and it was a hundred bucks so not outrageously expensive. Thanks for pointer on the unwaxed resin.

Nice thing about coosa is it can be reasonably decored and won't rot regardless. For different reasons, but all for adhesion, I pre coat that too.

If you are using epoxy, stuff isn't waxed/unwaxed obviously, but has a no sand bonding window - I would strive to hit that for at least the pre coating business as you only have a thin film so isn't the kinda thing you can sand.
 
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