Stopping the rot (in plywood)

[webcraft]

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The aft anchor locker bulkhead in Avy-J has a substantial rotten area in the middle. It is OK round the edges, and I plan to repair it by fastening an almost identical sized piece of marine ply over the top.

My question is, what treatment can I use on the rotten ply to stop the rot?


- W

 

[earlybird]

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My question is, what treatment can I use on the rotten ply to stop the rot?

- W

A saw?

 

[bedouin]

You can get a substance called "Wood Hardener" Once you clear off all the loose rotten stuff you paint it on in copious quantities - let it soak in and harden. It is good at stabilising rotten wood before filling etc.

 

[Deleted member 36384]

I had a section of damaged bulkhead. The shipwrights cut the damaged section out and bonded in a new section as well as overlapped. Dont leave the rotten bit in place.

Assuming the rest of the ply is dry, then coat with a thin Epoxy Glue, see the West guides. This will prevent further moisture from penetrating. As it is in the middle I guess the moisture has not travelled in from the edge of the ply. If it has then Epoxy treatment is no use as this will not stop the problem.

More information would be needed to help. I have a moisture meter you could borrow to test of the ply outside the damaged area is dry. Email if you want to borrow it, I'll be up at the boat this weekend.

 

[webcraft]

You can get a substance called "Wood Hardener" Once you clear off all the loose rotten stuff you paint it on in copious quantities - let it soak in and harden. It is good at stabilising rotten wood before filling etc.

This stuff?

- W

 

[Tradewinds]

Penetrating epoxy for soft wood is available from East Coast Fibreglass.

See here:

https://www.ecfibreglasssupplies.co.uk/product/mas-penetrating-epoxy-sealer

Not saying this is the way to go but an option perhaps.

 

[webcraft]

I had a section of damaged bulkhead. The shipwrights cut the damaged section out and bonded in a new section as well as overlapped. Dont leave the rotten bit in place.

Assuming the rest of the ply is dry, then coat with a thin Epoxy Glue, see the West guides. This will prevent further moisture from penetrating. As it is in the middle I guess the moisture has not travelled in from the edge of the ply. If it has then Epoxy treatment is no use as this will not stop the problem.

More information would be needed to help. I have a moisture meter you could borrow to test of the ply outside the damaged area is dry. Email if you want to borrow it, I'll be up at the boat this weekend.

Thanks,. Am short of time and money, with many other problems to solve and things to fix before launch, so looking for a fix that will last a couple of seasons then maybe do something more permanent if it looks necessary.

- W

 

[Keith-i]

Dry it out, that’s the guaranteed way to stop rot. Whatever you do don’t seal in the moisture or it will just continue decaying.

 

[Poignard]

There's no point in keeping rotten wood in place. It has no strength and is useless. Cut it out until you only have sound material left. You say there is sufficient sound plywood around the edges so glue a new piece of marine ply in place to cover and overlap the hole. Find out why the original ply rotted do you can prevent it happening again. Do it properly and the repair could last indefinitely. You can coat the side facing the anchor with epoxy resin and fabric if you want. (Details on the WEST website)

 

[AndrewB]

.
The aft anchor locker bulkhead in Avy-J has a substantial rotten area in the middle. It is OK round the edges, and I plan to repair it by fastening an almost identical sized piece of marine ply over the top.

My question is, what treatment can I use on the rotten ply to stop the rot?

Surprised to hear you have plywood rotting in the middle. In my experience it almost invariably starts at the edges. Is there something behind the plywood causing it to rot? Worth investigating and if possible, fixing.

So called rot-killers, and that includes Ronseal, are useless on plywood. Sorry, there's no long-term alternative to cutting out and making good.

 

[John the kiwi]

Surprised to hear you have plywood rotting in the middle. In my experience it almost invariably starts at the edges. Is there something behind the plywood causing it to rot? Worth investigating and if possible, fixing.

So called rot-killers, and that includes Ronseal, are useless on plywood. Sorry, there's no long-term alternative to cutting out and making good.

Agreed.
The thing i have learned is that cutting out a bigger area and replacing with new is often a lot quicker and easier than trying to do "keyhole surgery" repairs.
Often the hard part is summoning the courage to cut what seems like a big hole in your boat, but if you cut back to where access is big and easy, then the replacement can be a doddle.

 

[fisherman]

Wet wood hardener bonds with the water to turn the wood into a form of plastic, which is then very good at accepting a two part filler. It does work very well on wet ply, but no structural strength. If your ply started to rot in the middle it suggests fixings have let the wet in or it came down from the top, I expect it's painted and the paint has contained the moisture. If the bulkhead is OK round the outside it still does the job, you wouldn't worry about having an acces hatch in it. I would cut out the rot , tidy and treat the edges carefully then panel over the hole. Probably last for ever.

 

[jwilson]

There is a form of water-soluble epoxy for this job, but I've never seen it for sale in the UK.

The Ronseal product is not it - it is essentially a thin cellulose lacquer that soaks into DRYISH rotten wood and sets to be a bit harder than the rotten wood, but has no actual strength. The idea is you then use a two-pack filler over the top. I've used it plus filler often enough on old house windowframes as a 'hold the fort' measure till he window eventually gets either replaced or completely rebuilt.

 

[bedouin]

This stuff?

- W

Does a pretty good job of stabilising and I would image stopping further water ingress. Good for non structural areas like rotting window cills but probably not recommended on structural components

 

[KellysEye]

If you do want to replace the ply the best quality and longest lasting is: https://www.maritimeservicesdirectory.com/kuiper-dutch-marine-panels which I have used.

 

[Deleted member 36384]

If you do want to replace the ply the best quality and longest lasting is: https://www.maritimeservicesdirectory.com/kuiper-dutch-marine-panels which I have used.

Until you find a fault in the middle of an 8' x 4' sheet that it has delaminated the ply. Such was the stockists concern that 3 years after I bought the sheet and eventually cut off enough to expose the failed laminate, that they sent a new sheet on next day delivery without even receiving the damage section. Good service but the best can fail as well.

 

[fisherman]

I built a boat in 1983 and was required to use marine ply just for the wheelhouse as it is exposed, all the rest was WBP 1088...guess which delaminated. Even when used for untreated deck the 1088 wore through but never delaminated. I was told the marine ply has the same glue but more hard wood in the laminate.

 

[lw395]

I built a boat in 1983 and was required to use marine ply just for the wheelhouse as it is exposed, all the rest was WBP 1088...guess which delaminated. Even when used for untreated deck the 1088 wore through but never delaminated. I was told the marine ply has the same glue but more hard wood in the laminate.

I've bought 1088 kitemarked plywood cheaply at B&Q and it survived loads of abuse on my tender.
I bought some more a year later and it fell apart as soon as it got wet. Variable stuff!

I think you are right though, cut out a big hole to remove all the dodgy plywood. Get it dry, epoxy the edge, board over. A fair size hole won't weaken the bulkhead much.

 

[Poignard]

Agreed.
The thing i have learned is that cutting out a bigger area and replacing with new is often a lot quicker and easier than trying to do "keyhole surgery" repairs.
Often the hard part is summoning the courage to cut what seems like a big hole in your boat, but if you cut back to where access is big and easy, then the replacement can be a doddle.

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