How to remove damp patches?

[RichM]

I have a few damp patches appear. (see attached) Does anyone know how best to treat/remove this from the plywood?

 

Cheers

[Geo]

Are they coming through the panel or are they on the surface?

 

Surface can frequently be improved or removed by an application of fresh lemon juice to the dried out area.

Edited December 4, 2016 by Geo

[Guest]

Does anyone know how best to treat/remove this from the plywood?

 

Cheers

 

Remove the source of the damp.

 

Start with tracing possible leaks from the hatch above.

[Jrtm]

Remove the source of the damp.

 

 

Welcome to my world. Find it, kill it repair it quick. Then find the next one

[Nightwatch]

I unfortunately discovered a damppatch.

 

 

I just stood in front of the fire for a few minutes.

 

 

 

 

Oh! That type of damp patch!!!

[WotEver]

Looking at the picture it appears to be oak veneer. If I'm right then the dark stains are likely to be from the tannins in the wood. If it's not oak then it could be a form of mildew. Treatment differs between the two but the good news is that if one doesn't work then you can try the other.

 

Firstly, as has been said, you must remove the source of the damp first, otherwise you're wasting your time. Once done you can proceed to treatment.

 

If it's oak then the staining is best neutralised with oxalic acid. You can buy oxalic acid neat http://m.ebay.co.uk/itm/262740953880?_mwBanner=1 or you could use something like Barkeepers Friend http://m.ebay.co.uk/itm/BAR-KEEPERS-FRIEND-250G-POWDER-STAIN-REMOVER-MULTI-SURFACE-CLEANER-/172076809855 which contains oxalic acid and has many other uses around a boat.

 

If it's not oak or if the oxalic acid doesn't appear to be working then you could try lemon juice or hydrogen peroxide (available from most chemists but you might need to order it).

 

Two big important dont's. Don't use wire wool to apply any of the above remedies as the microscopic pieces of steel left behind will stain the wood over time. Use a nylon toothbrush or similar.

 

Secondly, you might have to very gently sand the surface of the wood to get past the finish so that the above treatments can get at the wood, but whatever you do don't sand the area very hard - the veneer is paper thin and you'll go straight through it.

 

Hope that helps.

 

Tony

[WotEver]

 

Oh, and if you want to make either of the latter two fluids into a paste you can use salt.

[bizzard]

A wide beam built by a so called very bespoke builder ''laugh'' here had a bad leak in the same place. The side door weather slam angle iron that the doors close against had a gap at the bottom, in the middle, two bits of angle butted up to each other not welded or sealed in anyway. Took me a couple of mins to weld it. Open the doors and check that out.

[Sea Dog]

Another vote for oxalic acid. Have a search for it on YouTube and you'll find a lady restoring a vintage guitar by removing blackening of the top using oxalic. A delicate job indeed, but the technique is the same and her results are clear.

[Top cat]

I tried oxalic acid on our beech veneer and it didn't work, didn't do any harm either.

 

Guess it depends on the wood

 

Top Cat

[WotEver]

I tried oxalic acid on our beech veneer and it didn't work, didn't do any harm either.

 

Guess it depends on the wood

 

Top Cat

As I said above, Oxalic acid works on oak. For other woods lemon juice or hydrogen peroxide is likely to be more effective.

[Bee]

You have got other similar marks in the same positions? If so then this looks like condensation forming on the wood above the steel frames and is difficult to deal with. You can add more insulation under the wood but that means removing the panel and a whole lot of hassle. You are not the only one to have this and you could find it easier to add more insulation, polystyrene foam sheet or something over the top of the wood and then panel over that, if it is condensation then the existing wood will not rot as the damp is only forming on the surface. It is damned hard to completely eliminate condensation from a boat when its perishing cold outside and warm inside. Fingers crossed that its drips from a window or patches of uninsulated bare steel from under the gunwhale. Fix the drips and try oxalic acid, I must admit I've never used it but it is the accepted treatment.