Solid Hardwood, Engineered and Laminate Flooring - Filling gaps in our hard wood pine floors

We just bought and renovated our new house. The house has hard wood pine floors but there are large gaps (approximately 1/8 inch) between many of the boards lengthwise. After refinishing the floors we noticed a-lot of dirt, dust, and debris settles in these gaps.

Does anyone know how to fill these gaps in? Could we put many heavy coats of polyurethane on top to fill in the cracks or would it be better to use some kind of wood filler? One floor guy said he could use a brown dyed high performance wood filler (like bondo) to fill in the gaps but he would then have to sand the floors again which is cost wise equivalent to redoing the floors. Any suggestions?

Thanks in advance.

It tends not to be recommended to fill gaps between hardwood flooring boards. Boards expand and contract. Fillers tend to pop out and gaps look worse than before. Gaps between floor boards tend to be a result of not properly acclimating the wood flooring to temperature and humidity of home with HVAC system up and running with temperature and humdity at occupancy levels. Installer's failure to check humidity levels and moisture content of subfloor and hardwood flooring before installation to make sure they are within recommended levels can also be cause. Too much moisture in the home and the hardwood before installation causes wood to swell. If installed with too much moisture, when it dries out it shrinks and leaves gaps.

Add humidity to the interior, and watch those gaps dissappear.

Thanks. Now I know the cause but hhhmm how do I fix it? The climate in the house is comfortable yet the gaps are still present. Plus, this floor is probably 30-40 years old hence it has been that way for a long time.
Question: If I add a really thick layer of poly would it dry properly? I know some paints that form a skin and never completely dry inside - is polyurethane also like that?

As soon as the floor shrinks and swells from seasonal humidity changes, anything you put in the gaps will be cracked or blown out. Then you have gaps again.

Now, that I reread your original post, The floors were just refinished?
Why didn't the refinisher trowel fill the floor before his second cut?

Or did you just have then sceened and recoated with poly?

Thanks again for the reply - sounds like we could have used an expert like you here in Georgia! We had the floors sanded, stained, polyed (3 coats). You think they could have fixed this during the refinishing job?

You think they could have fixed this during the refinishing job?




It is part of the sanding and finishing sequence.

Your guys cut corners and left off that important part, to have a satisfied client.

Now they want you to pay for their lack of education?

They took the job. I wouldn't pay them the balance, until they did the job right.

We have a very old oak tongue and groove flooring that had been refinished approximately 6 years ago by the previous owner and he filled in the gaps which were between 1/4-1/2" thick with wood filler, sanded, and coated. By the time we bought the house last year, all of the wood filler was either cracked or popping out. The gaps are huge, so leaving them wasn't an option (and it was drafty). We ended up screeding off the polyurethane, then we filled the gaps with wood caulk, which is flexible, and refinished with polyurethane. It has been a year and seems to be holding up ok. Anybody have any comments about this approach?

Did you have any problems with the poly not sticking to the caulk?

Over the weekend, we tried the following method. We used high performance wood filler (bondo) and concrete colorant. We added the colorant during the bondo mixing procedure and it dyed it a nice dark brown. Then we filled the gaps and put polyurethane over the top. It’s holding up great so far and looks good too.