Black staining on front door

Robin1

We built a house just over 2 years ago. We have a wooden front door which our painters were on our request treating with linseed oil rather than painting. They had no experience with the oil so it may be that they put on too little or I understand possibly too much. Anyway the door is in an awful state now for the last year and a half, covered in black stains/mould. We were told to remove the stains with oxalic acid, we used 4 tablespoons per half litre, repeated the procedure several times, even left it on overnight, but it hardly made any difference. Not sure if we were doing something wrong. We noted the oxalic acid did not dissolve well at all. Looking for suggestions how to clean up the wood? It seems to be very stubborn indeed. Any ideas welcome, we are DIY novices!

One shot on kill

What is the front door made off.

Alun

Did you use pure linseed oil or BLO (boiled linseed oil)? The pure stuff will never cure properly, and will act as a nutrient for mould and mildew unfortunately. BLO isn't actually boiled but is heat treated to oxidise it, and has solvent based additives added to it to accelerate drying and to aid penetration into the wood.

Robin1

Yes it was boiled linseed oil.

Sorry I'm not sure what wood the door is, it's quite light in colour.

Is there anything else that would work in getting rid of the black stains? Alternatively, could we now just sand the door, oil it and then paint it - we got some linseed oil based paint in a light blue so it may cover the stains, but would that mean that the wood is rotting underneath if we can't get rid of the stains, or is it at this stage purely cosmetic?

One shot on kill

I'm sure it just cosmetic now at this stage. It's more than likely teak I would say. I'd use a polyurethane exterior paint. Best stuff I e used in a long time.

Odelay

One shot on kill wrote: »

I'm sure it just cosmetic now at this stage. It's more than likely teak I would say. I'd use a polyurethane exterior paint. Best stuff I e used in a long time.

I'd agree, it's probably teak. I'm sure the quoted poster would have mentioned this but don't just paint over the linseed oil, it will obviously need to be sanded back to remove it.
Also as you're novices if sanding you want to start with 80-100 grit to start, then work up to 150-180 grit. people can correct me here, it has a while since I did any sanding but use "garnet" type. Do not use the traditional type sand paper. Use a sanding block it doing by hand. If you want to use a clear varnish rather that paint you need to be very careful about how you sand, a machine for one door in the hands of a novice would not be advisable as it is very easy to leave many deep scratches. Don't sand across the grain and think about what you're doing when sanding where two pieces of wood meet at right angles.

Robin1

Thanks Odelay, we're definitely not going near a machine! So do we sand the door now until we've sanded off all the black stains?

One shot on kill

Odelay wrote: »

I'd agree, it's probably teak. I'm sure the quoted poster would have mentioned this but don't just paint over the linseed oil, it will obviously need to be sanded back to remove it.
Also as you're novices if sanding you want to start with 80-100 grit to start, then work up to 150-180 grit. people can correct me here, it has a while since I did any sanding but use "garnet" type. Do not use the traditional type sand paper. Use a sanding block it doing by hand. If you want to use a clear varnish rather that paint you need to be very careful about how you sand, a machine for one door in the hands of a novice would not be advisable as it is very easy to leave many deep scratches. Don't sand across the grain and think about what you're doing when sanding where two pieces of wood meet at right angles.

Good advice here alright ye you have to make sure the linseed oil is weeeell gone. The cost common thing about sand paper is you use sand paper. Not glass paper. Go into a builder providers they normally have roles where you cut off what you want. Stay out of woodies and the liked for this.

dathi

oxalic acid is good at removing stains from wood but it must be mixed with boiling water and used hot to have any effect. if you used cold water i would give it another go also use one of those sponge and green scouring pads you can buy to work the acid into the timber. and finally since who ever told you about oxalic acid didn't tell you how to use it one word of caution oxalic is poisonous especially the dust that is given off when you sand the timber after treatment so wear gloves and dust mask.