black spots on wooden floor

[llamekuf]

I have just lifted a bathroom carpet which was laid 20 years ago.
At the back left side of the toilet, on the wooden floor there are black spots composed of a hard substance.
They seem to surrounded by what looks like a 'stain' - which is dry.
Anyone got any ideas please.

[neuron]

Clearly the floor was uncarpeted at one time and some drunk idiot went for a cr@p without putting the light on.

[llamekuf]

If you cannot post a sensible answer then do not bother.

[neuron]

Well let's try some sensible suggestions then.
First of all, I'm making some assumptions because you've not told us what the floor is made of. Is it laminate, chipboard or floorboards etc? Is the wood hardwood or softwood? It really does make a difference.

You've also not said if you've lived in the house for those twenty years. Why is this important? Well, despite my apparent facetiousness in the first post, I wasn't far off the mark. One thing that's notorious for causing this problem is animal urine and yes, that includes humans. Have you had a dog or cat in the house? Urine can soak through a carpet and the result is often mildew on a wooden surface. It's not always a patch and mildew will blacken as the years pass.

Are the spots in a regular pattern? Could it be that you've got an oak floor that's reacted with the nails used to secure it? This is a common problem.

If the floor is to be recarpeted, I would try to gently sand off the spots and see what happens. What you could then try is to get a bottle of hydrogen peroxide from a chemist and apply it liberally onto a rag. Lay the rag over the spotted area for a few hours. The peroxide will bleach out the spots and kill the mildew or mould. Yes, it will lighten the floor colour, but if it's concealed it shouldn't be important.

If you're not happy with my suggestions, I suggest you provide us with further information as I said above. Certain things can then be eliminated straight away and we can stop guessing.

[llamekuf]

Thank you for your prompt and helpful reply neuron.
What I know about DIY could be written on the back of a postage stamp.
I consulted my 20 year old Readers Digest DIY Manual (in prestine condition) which suggested mould: a mixture of bleach to 5 parts water which I have done 3 times and then dried using a halogon heater.
The wood seems to be very hard and in panels, definately not the kind of wood used for floorboards.
Although there are spots against the outside wall they are not connected but are scattered for about 18" from the wall getting fewer the further from the wall.
I have been here 10 years and I have never had a pet but I could ask the previous people about that.
Any further help and suggestions would be appreciated.