How to deal with long-term wet plywood

[Rusty123]

My boat has a Whale galley footpump installed inside a galley cabinet. It's the old-style pump, so instead of attaching to the back side of the cabinet, a previous owner had constructed a small plywood platform for the pump.

Unfortunately, the platform obscured the fact that the pump has been slowly leaking -- it wasn't until I removed the pump and platform that I discovered the leak (5/8 hose on a 1/2 barb!), as well as accumulated moisture under the platform.

I'm not worried about the platform (it's already in the trash), but it looks like the bottom edge of the cabinet plywood has been essentially standing in a swamp, perhaps for many years. I cleaned out all the accumulated debris and gunk, and I've got a fan running to dry everything out. I haven't found any obvious rot (bottom edge of plywood, though damp, seems pretty sound. No swelling visible). When I replace the pump, I'll use the MK3 version, which will enable me to mount it to the backside of the cabinet, so I won't need a platform. I'll probably also install a small piece of plywood as a backer to minimize flex on the cabinet face (epoxy backer to backside of cabinet, and then run the pump mounting screws all the way through both layers).

So while I'm not really worried about structural strength, I'm a bit worried that the cabinet plywood might have begun rotting underneath where I can't see it, and the rot might spread. Should that be a worry? Is there anything I should do to mitigate the risk?

(On a related topic, maybe that persistent moisture in my bilge wasn't due to condensation after all)

[flyingfin]

Put a fan and dehumidifier in the boat for a week, then drill a couple of holes 3 or 4 inches away from the worst spot and see if you pull up sawdust or wet mud. Then poke the inner wall of the hole with an ice pick to see if underlying wood is fully rotted. Just dont drill thru the bottom of the hull!

[GordMay]

Originally Posted by flyingfin

Put a fan* and dehumidifier in the boat for a week, then drill a couple of holes 3 or 4 inches away from the worst spot and see if you pull up sawdust or wet mud. Then poke the inner wall of the hole with an ice pick to see if underlying wood is fully rotted. Just dont drill thru the bottom of the hull!

Or perhaps a fanheater.

[Captsteve53]

Once confirmed dry, you may want to coat with an Epiglass/International product(Everdure) which is a very thin two pack product which penetrates well to help stabilize plywood and similar products making them basically water resistant and increasing there strength.

https://international-yachtpaint.com...imers/everdure

Cheers Steve

[Rusty123]

Luckily, the wood appears to be sound. But it seems to be taking a long time for that area to fully dry out. A small amount of moisture in the corner inside the cabinet reappears a few hours after i vacuum it out.

The "floor" inside the cabinet is the inside of the hull, a foot or so from the bilge sump. Not quite flat - slopes towards the sump. Unfortunately, that intervening area is inaccessible, since it's under the sole. I've got a fan blowing on it, so it's got to dry eventually, I guess.

Afterthought: I wonder if the constant moisture, combined with years of dirt and debris, has created a small dam of sorts up under the sole, which is preventing a quick drain to the sump. I think I'll poke around with a piece of wire and see if I can pull out more gunk.

[Blue Crab]

There's always more gunk.

[Steve Bean]

After drying the area, you might want to treat the plywood with some propylene glycol in the form of engine antifreeze, which is very hygroscopic and soaks into wood and kills fungus. Check out Dave Carnell's "Chemotherapy for rot.'

[Steve Bean]

How about treating the wood with a fungicide before coating? If rot spores are present and enough moisture is ever available, it will rot. Check out Dave Carnell's "Chemotherapy for rot.". Sorry for double post!

[UNCIVILIZED]

Whatever you use for a backer, be sure to bevel it's edges in order to avoid creating hardspots. And FRP Plate (Phenolic, G-10, etc.), or aluminum are also options. Ones which can be tapped for threads, in addition to using nuts & washers. Plus, of course, bond the backer in place.

As to drying things out, this is a wild idea which just popped into my head, so I've zero experience with it's efficacy. But if you'll be on the boat for stretches of time, you might try heating up some sand, & pouring it into the formerly damp areas. Then once it's cooled, vacuum it out, & repeat. Since dry sand does pull moisture, & heat of course drives it out.

[Steve Bean]

I use crumpled newspaper to dry boots and shoes. Stuff it in, leave it for half an hour or so, remove and repeat with fresh dry paper.

[Rusty123]

Originally Posted by Steve Bean

How about treating the wood with a fungicide before coating? If rot spores are present and enough moisture is ever available, it will rot. Check out Dave Carnell's "Chemotherapy for rot.". Sorry for double post!

Very interesting article. I had no idea that Ethelene Glycol had these useful properties (though I did know it is poisonous).

Chemotherapy for Rot

[Rusty123]

I had things pretty well dried out, when I went for a day sail a couple days ago. After returning to the dock, I noticed that the standing water was back! But it was my fault -- as described in another thread, I'm removing my pressurized water system (might replace it later - time will tell). Anyway, while the pressure system is disconnected and partially removed, I haven't yet removed the water heater and some of the hoses. With the movement of the day sail, I think a little of the residual water drained out. So my project for this weekend is to fully remove the pressure system components, and then put the fan/heater fan/dehumidifier/hot sand/crumpled papers/whatever else I can think of back to work.

Thanks for all the great suggestions!

[Rusty123]

As a follow up, here's what I ended up doing:

The area was dry when I checked today, so I tested again for punky wood (none found), and then swabbed ethylene glycol liberally on all previously wetted surfaces.

Then, I poked around with some baling wire under the sole and as predicted, pulled out a lot of garbage -- even an old plastic fork.

Then, I removed the remnants of the pressure water system.

Finally, I through bolted a new Whale galley pump (new version, which mounts to back face of cabinet) with 3/16 machine screws, fender washers, and nyloc nuts. *Much* more sturdy than the platform that the old pump was attached to.

I also replumbed the pump with 1/2 hose, instead of the 5/8 hose, which was what was causing the leak in the first place (found the same thing in the head, by the way).

On to the next project!