Hello guys, newbie here.

I own an older home that looks to have original wood flooring (Douglas Fir?). There is a basement below the floor and sometimes spills on the floor will seep into the basement. In some areas of the floor you could see light coming through from the basement. Other than that, the floor looks to be in great shape and we always get positive comments about it.

Question:
I am looking at finishing the basement and would like to put up some kind of sound proofing material (Rockwool?) in between the joists on the basement ceiling, but I am concerned about spills from the floor getting into the basement ceiling. Is there something I can apply to the wood floor to keep the spills from getting through? Perhaps just a heavy application of polyurethane?

Any advice would be great. Thank you!

I t seems like you plan to keep your fir floor. If you would like to fill gaps between flooring you will need to keep the flooring from moving too much so the filler will not crack and come out. If you take the opportunity to add some blocking from below before you cover the ceiling with insulation and wall board you can stiffen the fir floor so that the filler will not crack out. Half inch plywood strips, 2 inches wide glued with sub-floor adhesive in a quarter inch bead and fastened up with short sheet rock screws until the adhesive has dried will stiffen up the flooring enough. You could use colored putty forced into the cracks and gaps, too. Once the floor is reinforced you should not have leaks that could happen in the future.Kraft faced insulation should have the paper side up when it is installed, also, but this will only keep the fiberglass from getting wet, the sheet rock could get wet if enough water was able to leak through or around any gaps.

Pete, thank you for your feedback!

Is my concern an easy fix?

Right now, I am trying to decide whether to finish and remodel my basement so we can get more house space. I didn't like the idea of spills getting through ceiling and into insulation (noise reduction) and perhaps causing mold. We would like to put a drop ceiling.

Perhaps a better idea is to replace the wood floor with something new?

Maybe fill the gaps with one of the caulks that will handle a lot of expansion/contraction to keep the liquid from making it's way through to the basement. If you can't get one that will give a good color match then maybe a thin color matched layer of filler on top of the caulking. You are right to not allow moisture to get trapped due to mold and rot.