Black spots on stripped wood ?

[olam]

I am in the process of stripping some varnish from mahogany panels inside my boat.
After I have stripped some I noticed black spots appearing.
Could I have caused them? Or were they there already but hidden in the old varnish?
I have tried a coat of varnish on a small area but spots are clearly visable.
Any ideas ?

Thanks

 

[Tranona]

Usually a clean with diluted oxalid acid will remove them. You can buy as crystals and dilute with water to strength required. Wash off afterwards and clean wood with white spirit before refinishing. Best to clean the whole area to the same overall colour and maybe stain to blend in with existing wood.

 

[AntarcticPilot]

Usually a clean with diluted oxalid acid will remove them. You can buy as crystals and dilute with water to strength required. Wash off afterwards and clean wood with white spirit before refinishing. Best to clean the whole area to the same overall colour and maybe stain to blend in with existing wood.

I've been doing this on interior woodwork on my boat, and it works very well. But I'd strongly second the suggestion to treat the entire surface; it does change the colour of the wood somewhat - lightened it in our case. Also, you have to get ALL the existing varnish off; any varnish left on the wood will protect the wood from the oxalic acid and you'll get a patchy finish. Unfortunately, with satin/matt finishes it isn't always easy to see if you've got all the old varnish off!

 

[olam]

Thanks for your advice,I don't really want to change the colour of the wood as the whole inside
is mahogany and I'd be on it forever.
I'm more concerned to know if its the stripping that causing it.

 

[john_morris_uk]

Thanks for your advice,I don't really want to change the colour of the wood as the whole inside
is mahogany and I'd be on it forever.
I'm more concerned to know if its the stripping that causing it.

Understand you don't want to change the colour but after you've stripped and bleached out the spots (and the whole of the wood) you can stain it back to match.

The easy way to check whether the colour is going to match after you've varnished is to wipe the wood with white spirit. You get a very close approximation to what the colour will be once its varnished and can make sure you match the existing woodwork.

 

[AntarcticPilot]

Thanks for your advice,I don't really want to change the colour of the wood as the whole inside
is mahogany and I'd be on it forever.
I'm more concerned to know if its the stripping that causing it.

The colour change is slight - it is no more than the natural difference between different pieces of veneer.

Black spots are almost certainly from damp or mildew in the wood.

 

[Ex-SolentBoy]

I am in the process of stripping some varnish from mahogany panels inside my boat.
After I have stripped some I noticed black spots appearing.
Could I have caused them? Or were they there already but hidden in the old varnish?
I have tried a coat of varnish on a small area but spots are clearly visable.
Any ideas ?

Thanks

Before you go mad mixing chemicals try this for less than a fiver.

http://www.lakeland.co.uk/9009/Magic-Eraser-Block

It worked on black spots on stripped oak for me.

 

[LittleShip]

I am in the process of stripping some varnish from mahogany panels inside my boat.
After I have stripped some I noticed black spots appearing.
Could I have caused them? Or were they there already but hidden in the old varnish?
I have tried a coat of varnish on a small area but spots are clearly visable.
Any ideas ?

Thanks

Without seeing the problem it's difficult...... But, normally when you get black marks on the wood it is a fungus.

The only way you can really deal with it is to bleach it (oxalic acid) this will kill the spores and then you can re varnish. Don't worry about the chage of colour it will only be slight. Don't be tempted to sand as you may find that the spores are quite deep and you will risk sanding through the veneer..... unless its solid wood

Tom