How to fix dark marks on timber floor?

Question

The timber floor of a house my elderly mum recently moved into is starting to get marks that are dark and raised and feel a bit bubbly (but dry) and a slight separation of boards. This is at the back but a water problem at the front of the house, ie the other side, apparently had previously been fixed. Is this water tracking all the way and resurfacing (or maybe from another issue closer) and what can be done to improve it/restore it?

JacobZ · Answer

Hi @hardwarefan,

From that description, it sounds like it could be engineered timber flooring which is comprised of a very thin layer of real timber on top, usually only a couple of millimetres thick, bonded to a plywood or high-density fibreboard base underneath.

That top layer is what gives it the natural variation you’re seeing, but it also means you’ve got limited room to work with when it comes to sanding.

Light sanding may be possible, but it needs to be done very carefully. With only 1–2 mm of timber, it’s easy to sand straight through the top layer and expose the substrate underneath, which can’t really be fixed.

Before going down that path, I’d definitely want to confirm the product type though, just to avoid doing more harm than good.

Is there anywhere you can clearly see the edges of the floorboard? If so, could you snap a photo?

Assuming they are engineered timber floorboards, then I'd suggest it is best to hand sand them so you can maintain complete control over pressure and depth of your sanding. I wouldn't suggest using anything below 240 grit sandpaper. Take it nice and slow and remove as little material as you possibly can.

Let me know if you have any further questions.

Jacob

hardwarefan · Answer

Thanks Jacob! It looks the same as this for a couple of the adjacent floor boards and I think you are right, its probably water tracking from the previous problem which has now been fixed and area replaced and tile joins resealed. It is a thin piece of timber (or some sort of veneer), a mm or two thick, that is on top of some sort of wood. I think it is likely to be a timber top (even though thin) as there are variations in colours and patterns between the planks. assuming the water issue is fixed, as this isn't changing any further, would the cosmetic option be sanding the thin top wood? Could I do this myself?  (rather than replacing the whole house with the same coloured wood)? appreciate your help!

JacobZ · Answer

Hi @hardwarefan,

From what you’ve described, and based on the close-up view, it’s a bit hard to be certain. It could be moisture related, but it can also be something more benign like natural imperfections or filler in the timber that’s lifted over time.

The raised and slightly bubbly feel does point toward some sort of movement or moisture involvement, but it’s not clear whether that’s coming from an active issue or just past damage that’s now showing through.

It would really help to see a few wider photos of the area, including how it sits in the room and how widespread the issue is. That gives a better sense of whether it’s isolated or more systemic.

Also, it would be good to understand a bit more about the water issue you mentioned at the front of the house. Do you know what the original cause was and how it was fixed?

If it turns out to be cosmetic, the answer will be to sand it back, fill it if necessary and then refinish the floorboards, but the cause of the issue will determine our approach and whether this is suitable.

Once we’ve got a bit more context, it’ll be easier to narrow down whether this is something ongoing or just cosmetic that can be repaired.

Jacob