Fixing a damp balsa cored deck.

[Manateeman]

It takes a long time to try out balsa in a kiln.
Your boat is not a kiln.
Balsa is a bad joke.
Mark

[sailingchiro]

Clean out as much as you can of the wet balsa then use spray foam to fill the void. After it dries, clean out enough foam to insert about 1-2 inches of thickened epoxy. The spray foam cures using moisture thereby sucking the moisture out of the balsa. Try to keep it simple. It can get complicated very quickly.
I tore out a 5' by 3' section from the bottom to clear out "wet" balsa due to a moisture meter finding from my surveyor. Only to find out 90% was completely dry. Hanging fiberglass and foam above my head was not fun. I don't put a lot of faith in moisture readings.

[LH42]

Not sure if they travel to your area but I used a company called DryBoat to dry out a large area of wet balsa core in a power boat I owned a few years ago. Was very happy with the results.
Geoffrey

[Island Time O25]

It all comes down to
a) is your mast deck stepped or keel stepped?
b) how long (realistically) are you planning to use/own the boat? i.e. a few years or until you croak?
c) your time and $$$ constraints
d) climate of your winter storage area, if any.

A good friend of mine who happens to be a boat builder with naval architect education (and was once featured in Professional Boatbuilder magazine) tells me that fatality of rotten decks is wildly exagerrated problem. It is a problem but the severity of it is dependent on the factors above.

He says that under normal, coastal or near coastal use in warm (i.e. non freezing) areas and times on a keel stepped average or above production boat with even almost fully wet/rotten core sandwich deck will still be fine to sail years after the owner who noticed it is dead. Deck stepped boats, especially subjected to freeze/thaw cycles - not so much but even they may not need a total recore, just in the problematic areas.

According to him it's not the rottenness of the deck per se but the stresses on various portions of the deck. That's where one needs to concentrate re-coring efforts and worry less about non stressed areas.

[NevilleCat]

Originally Posted by Manateeman

It takes a long time to try out balsa in a kiln.
Your boat is not a kiln.
Balsa is a bad joke.
Mark

Helpful response

[Mauruuru]

Had an old Oday 30 with similar issues due to improperly sealed deck penetrations.
On the larger openings I scraped out the rotten wood but as you know water travels and it wasn’t possible to extract it all. So one summer week I drilled about a thousand holes from the cabin and deck top, let it dry in the hot sun then filled all the holes with thinned epoxy. It was amazing to me how far that stuff ran. A final top off of each hole finished the seal and after that there was never a spongy step or a creak. Of course I painted the non-skid to hide the holes as rebuilding would have been a wasted effort.

[OneBoatman]

Sounds like a good start. A little bit of moisture at the boundary of your repair area is no big deal. It will not interfere with curing epoxy. Repairing to prevent entry of new moisture is what you are after. If it were mine, I would first seal the entire boundary with either white JB weld or a two part epoxy to close off the possibility of future lateral water. entry Then shape a piece Okoume plywood taking up ~65-70% of the thickness of the deck or just somewhat below the original decklayer of glass. This is your new decking in place of the former balsa sandwich. Are we talking an area under 6 sq in. all told Shape the ply to interfere just enough to hold it in place for you pre-bond it using the same epoxy putty you first used to seal the deck. Let it cure and then bring everything back up to deck level or slightly proud using a two part epoxy such as Mars or West System. There are special colorants available for all epoxies that allow you to closely match the deck color. The colorants are similar, but not the same as those available for polyester resins, Otherwise I would use either white or grey resin. If desired, you can texture it or adjust the color anytime after the install. Use either a straightedge or something round that can release cleanly from cured silicone adhesive to create a temporary dam so that you ultimately can raise the immediate area around the new fill pipe. It needn' t be round it can be square. You want it about a 1/4 " larger the deckplate all around. Polystyrene works well to release from cure silicone, think smooth milk bottle plastic. Create the temporary boundary with silicone adhesive. The silicone will be peeled away once you raise this zone about an 1/8" above deck level. When finished this raised area will shed water to the deck level forever and a day stemming any future worries of water intrusion. Now you are ready to drill the hole for the new filler pipe. A little larger than needed. Then again seal the entire perimeter of the thru-hole with epoxy to integrate the exposed plywood/ epoxy laminate and it let cure. Finally install the deck plate/filler using 3M 4200 or 5200 sealant to marry the neck of the filler pipe around the edges of the thru hole plus a little extra. Put a bit of sealant in the screw holes for the deckplate before screwing it in place. Almost no sealant is exposed to UV light and your balsa core is now very far away from trouble. Done.

[Eric ROGUE]

I do not have a firm picture of your situation. If it is in a locker situation and you can cut open from below and can get to all the areas where the balsa is affected (you MUST get out ALL the affected balsa or rot will grow and spread again.

If it is a situation where you have to cut through a headliner in the interior of the boat, cut through the deck instead. The deck will be easier to repair.

I repaired a boat that was damaged in the vacinity of the mast step. Can't remember if it was under the mast step or not. In any case, the repair had to be structural. I didn't worry about weight, just strength. I cut through the deck well outside the area where I had determined the rot has spread by drilling shallow holes through the deck into the balsa. After scooping out the rotten balsa and chipping away at the structural balsa to get well back from the cut edge of the deck (minimum 8:1 scarf), I filled the void between the deck and liner with layers of fiberglass cloth and middle layer of fiberglass mat all of it wetted out with slow cure epoxy resin in the middle of summer. The original deck was the last piece set in place. Later, non-skid was glued on top covering the unsightly scar. Twenty-seven years later the boat is still sailing.

If the area needs little structural strength, you could use structural foam, but why not use fiberglass and get the strength? The weight savings of foam would be trivial. I consider strength of repair to be critical.

[Dieseldude]

Originally Posted by Cheechako

I think you can probably fill the area where you pulled out damp core and be fine if it's nearly dry.
I would probably just use "kitty hair" ....it's fiberglass strands in resin. It dries hard and solid.
-A better solution would be to temporarily replace the fitting... caulked well, leave the core open for summer, then remove the fitting later after it's good n dry and fill the space.
-Another option is to heat the boat and have a small fan on for a few weeks directed at the repair area. Air movement dries things out fast.
-And another more tedious option is to buy or rent a small air conditioner and mount it on the boat leaving it on for a week or two. AC air is very dry and will dry it out.

The AC seems like a good idea, but would a portable dehumidifier be the better piece of equipment?

[Eric ROGUE]

Originally Posted by Cheechako

I think you can probably fill the area where you pulled out damp core and be fine if it's nearly dry.
I would probably just use "kitty hair" ....it's fiberglass strands in resin. It dries hard and solid.
-A better solution would be to temporarily replace the fitting... caulked well, leave the core open for summer, then remove the fitting later after it's good n dry and fill the space.
-Another option is to heat the boat and have a small fan on for a few weeks directed at the repair area. Air movement dries things out fast.
-And another more tedious option is to buy or rent a small air conditioner and mount it on the boat leaving it on for a week or two. AC air is very dry and will dry it out.

No. "Nearly dry" is not sufficient when dealing with wood and certainly not when dealing with balsa which is perhaps the most rot prone wood of all.

Every speck of rotten wood of whatever species needs to be cut away when making repairs. That means well back into the "good wood". The rot spoors are already established past where you can see rot, and rot will spread again if this wood is not removed.

Boats live in a damp environment. Any rot will attract moisture to it and grow, rotting more wood.

"Get Rot" and similar very thin epoxy brands make claims that they will arrest rot. They will temporarily help, and it may be useful to use the product after properly preping the area as I describe above, but half way measures do not work with wood.

Note: If an epoxy repair is made epoxy must be used in the future. Other types of resin will not adhere properly to epoxy.