Stripped floorboards - black dots appearing

[Anonymous]

I sanded my Victorian floorboards approx 3 months ago and varnished 1 month ago with a contract Ronseal varnish.

I have just noticed a large number of the boards are covered with pin heads of what black dots all over them (it looks almost like black mould) and under/in the varnish.

Can anybody suggest what has caused this, and do they know what it is. I have photos should anybody wish to view.

Thanks for your help

 

[Anonymous]

I ma not an expert but it sound like woodworm. A white poder comes out if it does, you need to get a spcail chemical which can treeat this problem, but I would not hang about as the numberof these holes wil increase.

 

[Anonymous]

Sally - I'm a bit sceptical about Peter's woodworm theory. Are these black dots actually holes? Were they apparent when you first varnished, or have they appeared since?

 

[Anonymous]

Hi,

What was on the boards before you sanded them?

If there has been an old black coating in the past and this was removed (probably many years ago even) then small amounts are often left in the grain - these are 'disolved' by the varnish leaving small black marks.

They often appear after sandblasting old exposed timbers to get the finish off then applying a solvent based/paste preservative.

Just a thought

 

[Anonymous]

The only thing I have seeen similar was on pine cladding, when it was mould - the spores were probably in the boards and got a little damp and when varnished - I think it was a water based varnish as well - they started to grow under the varnish. In that case the varnish started to flake as well which seemed to confirm the moisture theory. However, if everything is dry on your boards, the GRC theory above looks possible.

 

[Anonymous]

Really don't think it is woodworm.

There was an old Victorian 'tar' stain on the floorboards prior to sanding. However, to the naked eye nothing remained after sanding. It really does look like mould - unsure whether re-sanding and then varnishing again will not cause similar problems.

Thanks for all your views
Sally

 

[Anonymous]

Hi Sally

I have an extremely large brain. Unfortunately it's mostly filled with wood, useless most of the time...

However. The most probable answer is iron staining. (often called in the trade "iron mould") If you used wire wool anywhere in your house and some of the fine fragments (sometimes too small too see) remained on the floor then these would have reacted with the water in the Ronseal contractor finish to form a black iron oxide (form of rust) You can sometimes see black staining around the nail heads where the floor has got wet at some point. Alternatively if you used a hire shop sander you may have used some balck silicon carbide discs/sheets sometimes grain can stick into the wood leaving you with a black dot.

Regards

Toby

PS They are not signs of wood worm!

PPS Only remedy is sand off and recoat. Personally I'd leave it unless it is terrifyingly bad.