ash blocks gone black

[wstirling]

Would any one have any suggestions for the following: ash blocks untreated been left in rigging for some years and have gone black. Would like to get them back to varnish. Have heard that oxalic acid may work on oak. Would this work on ash and where does one find oxalic acid. Perhaps that doesn't work- any other suggestions would be gratefully received.
Will Stirling

 

[stephenh]

"Though surface-staining fungi do not significantly reduce the structural strength of wood, they are considered precursors to wood-decay fungi." - this from a book on my shelves.
Oxalic acid will get rid of the symptoms - you also need to get rid of the cause.

Strip the blocks and dry them out ( the fungi need 20% moisture content) soak them in 5 star cuprinol, dry them out again and then varnish / oil them to keep them dry in the future.
A long time ago we used to immerse them in linseed oil for the whole winter, I don't think people have the time anymore !!!

 

[Forbsie]

[ QUOTE ]
where does one find oxalic acid.

[/ QUOTE ]

Order it from any Boots/chemist and collect the next day. 500g - approx a fiver.

 

[Peterduck]

The blackening probably comes from a coating of linseed oil. I had the same problem with my masts and spars when I bought my boat. I had to physically remove the surface of the timber with sandpaper and scraper before bleaching with oxalic acid. I found that the acid straight on to the black surface resulted in a grey surface, which looked just as 'orrible. Using the acid to bleach the deeper furrows of the grain after most of the surface has been brought back to fresh wood is OK. You may need to use the wet-and-dry sandpaper with a sovent like paraffin to prevent the paper clogging up with oily fibres. Here in Melbourne I am able to buy oxalic acid at paint suppliers, as it is a well-known wood bleach.
Peter.

 

[Seanick]

Try this:-


To use Oxalic Acid........boil a kettle, add a teaspoon of the oxalic powder to a mug of hot water untill you have a super saturated solution. Wearing goggles and gloves (it really hurts, trust me), brush onto the blocks. Wrap them up in a bit of cling film to stop the acid drying out and keep it working. Leave for a day or so. Rinse well, allow to dry, sand up, soak in a 50/50 linseed oil/5 Star cuprinol mix for a few days, remove and rag off excess. leave for a few days then varnish as usual.

Well done on your trip to Greenland. Hats off to you and your crew!

 

[Boatmik]

I've always used a much weaker solution - probably a quarter cup in a half bucket of water - it dissolves in those sorts of quantities quite easily. It is pretty effective. But maybe it behaves a bit different here in the antipodes.

Good reminder about safety SeaNIK! It is an acid and will burn skin and holes in clothes. Take care of eyes and all skin.

 

[wstirling]

Thanks very much for the info; and now to work...
I hesitate to add that they aren't my blocks, I am trying to get a previously uncared for boat up to scratch.