Q: We just pulled up our carpet, and there are severe black spots on our wood floors.
A: It depends on how extensive the damage is. If it is only one or two confined areas, you can change the boards with new. If it is extensive, you either have to replace the floor or stain it very dark to try and hide the black. It is unlikely it will come out with a professional sander doing the work, but it is never possible to know for sure until the work is started.
How do I get out black spots?
Q imported from our old site, Face Lift Floors: I have bought a home that my grandmother had owned at one time. She told me there were hardwood floors under the carpet, so I started to tear up the carpet, but we ran into a problem. There were some black spots on the floor, how can I get them out?
A: Your situation seems to mirror my own, in that I also came into possession of my grandparents home, removed the carpet and found, in my case, one large black stain in the front hall by the front door. In my case, I just put down a runner in the front hall (to avoid water and salt being walked in during winter). This covered the spot.
You have a couple of options. You can have the floors sanded and re-finished. Only by sanding down these areas where the stains are will one know for certain if they will come out or not. If they don’t come out, you can either change the boards, which is the cheapest method, or bleach the areas with a commercial bleach (not cheap and scary stuff to work with). If the stains are in inconspicuous places such as along a wall, and you hadn’t planned on refinishing the entire floor area, you may be able to deal with just that area so that it is not as noticeable.
If you have these areas all over your floor, then you have a big problem. You could stain the floor dark to try and hide them. When I say dark, I mean something approaching ebony. Rip out and replace seems the best route to go in that case. I recently sanded a floor that was covered with carpets. I told the man ahead of time that I had no idea the state of his floors under the carpet. We removed the carpet and his floors were really old and dark. So dark that I could not tell for sure if it had such stains. When I sanded the 2 hallways, there they were! Black pet urine stains all over the place! I stained the floor twice, but they still showed through. The floor was dark, but the stains went darker still! So, in a nutshell, if you are dealing with a couple of spots, replace the boards if it is found the stains cannot be sanded out. If there is a large number, replace the floor.
Original / moved link https://faceliftfloors.com/q-and-a/blackspots.php
What would cause a large circular black “burn”?
Similar Q: My landlord is on my case about a large circular black “burn” (small baseball size) that is outside of my room door. Never noticed it before, looks like dark discoloration knot but spans into 3 pieces of wood slightly and seems to be under finish coat. Thoughts on what can cause this clean circular burn? Might it be a mistake from the sanders/finish coat floor workers?
A: Black marks can be anything from water damage to fungus to tannin in the wood reacting with the solvents in the finish.