Idailya,

I have not seen any grout or mortar that will stick to wood. when the floor was installed the boards were probably butted together but as time passed the boards probably shrank thus causing the gaps. The fix now would most likely be to install filler strips or dyed hemp rope if the gaps are not to wide.

There may be a product out there for this but I am not aware of it. Hopefully this helps and if not, hopefully I am wrong and there is a product out there for you.

try checking the floor shops in your area.

U.S.M.C. Semper Fi !!!

I have seen black sand available as a sandblasting medium.

You might mix it with Titebond II wood glue & fill the voids with it.

Black mortar colorant or black latex paint could be added to the mix.

Be careful, as the mixture will stain your pine floor. I would varnish first, & fill after.

If the cracks are less than 1/8" wide, I would use black caulk.