Oxalic - wood - black marks - secret?

[gregcope]

Hi all,

Have a set of cheap pastimo oars (to practice on) and my laminated tiller to revarnish.

I have stripped the old varnish and sanded (80, 120, 180 so far).

Looking good bar the black marks which look like water stains between/in the grain.

I have tried my own Oxalic mix and had little impact bar mild bleaching of the wood.

What are the secretes for using it to remove black stain marks that are embedded with the grain?

1. How long do you leave it on?
2. Applied with a brush?
3. Do I need to sacrifce something?

Or am I not going to succeed?

 

[VicS]

See the instructions on AG Woodcare's website

http://www.agwoodcare.co.uk/cat/bleaches and acids.html

Some alternatives there if oxalic acid wont work

 

[gregcope]

Thanks VicS.

I am following something very similar.

On http://www.agwoodcare.co.uk/more_info_oxalic.html, when it says;

Let the solution remain on the surface for 10 -20 minutes. If staining still remains, apply more solution to the stained area only. Continue until desired colour is obtained.

I bottled out.

I applied some at 1500. Left it, at 1630 decided to leave it overnight. Next day applied some more. Left the combined lot for 30 mins and washed off.

Maybe I should start at 0900 and reapply every 30 mins?

 

[VicS]

Maybe you are trying to get oxalic acid to do something that it wont.

 

[Hoolie]

In an issue of PBO - no idea when - the wood expert said he uses household bleach for persistent black stains. In combination with oxalic acid for generally restoring the colour it sounds a promising technique.

 

[xeitosaphil]

I have come across this problem a lot in the Joinery trade, and usually the black staining is a result of acid contained in the makeup of the wood, or moisture, acting with usually ferrous metal fixings?
You don't say what type of wood it is, but oak and steel fixings used to be renowned for it?
If it’s Mahogany usually the black staining is either down to the fixings as mentioned before, or the start of decay and the only way to get rid of it is to cut it out, or remove the surface by one way or another, heavy sanding etc.
If it not practical to remove it, we used to use a really strong Bleach (peroxide)or the like , neutralize and then stain, but it was not really a final solution, because if you can't stop the source of the problem, it will come back again?
Best of luck with it anyway.

 

[fastjedi]

I have just been through the same thing with my Avon oars. Lots of sanding + 2x Oxidic acid. It looked like I had acheived a small improvement until I applied the first coat of varnish .....

 

[SAWDOC]

Black staining on oars could be quite deep rot in which case oxalic acid will not work. If it is rot, you need to consider how you will manage if one or other were to snap when under pressure some day.

 

[Sheff]

If you believe it's black mould that has penetrated the wood then Boracol 10 may be the answer........... contains a biocide/fungicide.

However, I've just paid £58 for 5 litres to treat my teak decks so the cost would outweigh the benefits unless you can find someone willing to spare you a cupfull. Also it takes time to penetrate, allegedly still working 2/3 weeks after application so not an instant miracle cure.

Hope this helps,
Paul.

 

[gregcope]

I have just been through the same thing with my Avon oars. Lots of sanding + 2x Oxidic acid. It looked like I had acheived a small improvement until I applied the first coat of varnish .....

Sounds about the same, although I have not applied varnish yet.

It could be rot, but is very small an usually a few lines only a few mm deep at most and localised to certain parts.

Am not concerned about structural strength. It is not as bad as it sounds and there is plenty of meat left.