Core rot at the chainplates thru-deck

[RichB]

Due to a failed silicone seal around my starboard chainplate that has apparently been leaking for some time, I am digging an area of plywood core out. The removal by bent coat hanger wire and gas welding rod and shop vac has been tedious. So tedious that I considered just marinating the rot with 'woodlife' and encasing it in epoxy. Woodlife being too messy, I now have evacuated an area about 18" x 10".

As best I can see with mirror and flashlight the core is not continuous and will let liquid material run by (from stem to stern) This disqualifies a standard epoxy from being poured in unless a dam is placed in the voids. The whole dam idea led me to the next point.

I think the job will be over as soon as I can inject some 8#/cf. urethane foam down the slot. Considering the volatility of the foam, I assume the original builders of foam-core boats used a long tube to inject it in the void after the deck is fitted together. If I find a mixer - gun and shoot the core solid, the foam gushes out the chainplate slot, recut the slot, water will be permanently excluded and the hardware can be reassembled and slot sealed.

So now I am happy with the method, and I have a foam located at U.S.Composites, ($20 ++ for a 2 qt. kit) I need to improvise a mixing injecting tool. The working time is stated to be a very quick 45 seconds.

QUESTIONS: 1. Is there a better material and source? 2. What can I use to inject the foam 50/50 mix ? 3. Am I exagerating the need for a high density foam where a common urethane foam such as "Great Stuff" would serve the purpose? 4. And finally, Which sealer is best to seal the slot around the chainplate?

What say you ? I'll be away from computer till monday, so I hope I provided enough info. Thanks ....Rich

 

[Steve Dion]

Rich:

I think that most of the Hunters have a plywood core in the deck areas. You best bet would be to cut out the deck area with a saw. Then you can replace the core material. The piece of fiberglass that was removed can be put back in place and the section can be resealed.

Think about sealing your chain plate with some butyl or better caulking material than silicone.

 

[Merlin Clark]

Sounds like you've done the homework on this but just thought I'd reinforce that some of those foams expand about a million times in volume!

 

[Steve Dion]

The problem with foam is that you cannot control the expansion very well. You CAN do more damage that may not be easily repairable if you are not careful.

 

[Bill1565]

I' m with Steve D. Cut off the outer skin large enuff to get to good plywood. Dig out the rot, bed new plywood in epoxy, put some on the plywood and replace the skin. Bevel the edges and use epoxy with glass fibers to fill the bevel. Make it nonskid, and you won't even see the repair.

 

[Merlin Clark]

If you can figure a way to get it in there, like a large syringe and a piece of tubing, thickened epoxy or poly resin should do the trick with out escaping down a void.
I'd do it in layers around the perimeter and work my way back towards the opening. That way there should be less chance of leaving air pockets.
For this, you could use just about anything to thicken the resin since you're not looking for structural strength. Poly resin is cheaper and you can make it kick faster by adding more of the MEK catalyst than normal.

 

[RichB]

Thanks for the comments,
Steve, Thanks for the butyl caulk affirmation. I know from experience that it is wildly messy if it gets loose. but it is very adhesive.
And to all three, I am evaluating the option of cutting out the deck and must say that it scares me more than a foam-bulge in the deck. I am not a stranger to grp work but as I weigh the options, I am now leaning back toward the injection of resin. Drilling say 1'2" holes near the outside margins will step the application of the resin down to manageable quantities. Also the trailer can be tilted to assure a full fill on the final pour.
I had not thought of poly resin but it makes sen$e for this job. The final step will be the first paint job she has ever had. Gotta get to work... I just discovered a local Sailing Assn. with Wednesday night rum runs. Thanks again.

 

[Slim pickins]

I used the foam from U.S. Composites on some soft spots in my deck. i bought some clear plastic sqeeze bottles for $2 for 2 from walmart in the craft section, was easy to make marks on the side of the bottle for measurements and just pour both parts in the bottle and shake for mixing. i drilled 1/4 holes to inject the mixture in and marinetex to fill after everything dried. really firmed up my deck. i think i used the 4lb.

 

[RichH]

Unless you physically get inside the laminate (rotted) structure and remove the fungus slimes, residual debris from cell growth .... spraying in foam will NEVER create a 'seal' with respect to future water migration into the remaining intact 'core'. The 'new' foam that you spray-in will not properly bond with the uncleaned out crud and this unbonded or poorly bonded interface will be a pathway for future water migration.

You dont want to do this job 'twice' .... open up (either from the bottom or top), thoroughly clean it out and be sure that your cutting back into solid nonwetted core, etc.
You 'can' do this job from the 'bottom side' to prevent cosmetic destruction of the deck/non-skid, etc. if you use 'thixotropic' (doesnt 'run' because of the 'fillers') resins. Blindly "pushing-in" (epoxy) resin or 'liquid foams' can result in the development of HI PRESSURE if the resin becomes highly 'exothermic'.
;-)

 

[Bill1565]

It's a -u boat. May not be worth much if the next buyer gets a good surveyor.

 

[William12213]

I would also cut out the desk top to do the job. It is really easy and you can make sure all the rot is out. Something I also do whenever I have to repair a spot it to use resin and glass in the opening. Then I redrill or slot it for the fitting. This way if the sealant fails in the future your core is safe.

 

[w4pyleii]

If you seal that area with epoxy, you're sealing in the moisture that's already in your decks, and it will remain there for a very long time. Might be less of an issue in your area, but if the boat ever moves north into a freezing climate... only takes one freeze/thaw cycle to potentially heave your deck, at the very least delaminating the core from the skin. If the moisture over time doesn't rot the wood and give you soft decks, the freeze/thaw will accelerate that process.

Sucks, but cutting the top skin off and replacing core isn't THAT bad of a job

 

[Barnacle Bill]

You are better off to fix it with solid fiberglass whether it be polyester (cheaper) or epoxy (not necessary for the deck). It will not leak again into the core material that way.

 

[RichB]

Agreed, the only way to do the job is 'right the first time'. I would say I got it all out but I can't be sure without opening her up. Boy I wish I had found it back when ME Major and I were discussing that annoying coffee colored puddle that occasionally showed up in the bilge.

So cutting out enough deck (the first time) means pretty liberal margins.
Time to also re-evaluate the under deck approach with thixotropic. Although I have always liked working from the top better.
Thanks for all the direction.