My home was built in 1885. It has 5-inch plank flooring (quite rustic looking). A previous homeowner put wood putty between each plank and it’s now cracking and falling out. My question: How do I prep and finish the floor in the bathroom. It has apparently been wet before and the wood is rotted in places. I’d like to keep the original wood, if possible. Is there any kind of thick, self-leveling sealant that could be used?
Filling the cracks with a non flexible wood putty almost always results in the putty cracking out. Wood moves with the change of indoor humidity and the dry hard putty filler does not. So when the wood is the narrowest in the middle of winter heating season, the putty falls out. Plank flooring is the most prone to this problem, the wider the plank the wider gap.
Next, as to wood in the bath, it really doesn’t belong there. This is a place of water spills and standing puddles (even in powder rooms), and a water proof floor like ceramic, cork or vinyl is much more suited for these areas. In fact I have seen such rotted wood around toilets, that I was afraid to sit down on this particular “throne”.
But if you must repair the floor instead of replacing it, here’s how. The gaps between the boards can be cleaned out with an awl and a vacuum cleaner. Squeeze in a latex filler, and expect to apply several coats to fill the gaps. If you are not sanding and refinishing the wood at this time you will have to keep the wood clean from filler, by wiping the wood with a wet then dry rag. Choose a filler color just a tad darker than the floors. Try the Le Pages band I use, at http://www.LePageproducts.com/products/detail.asp?catid=25x=56x=305 But expect even this stuff to pop out in just a few years, if you have big swings in your indoor humidity. At least it’s easy to replace. And you can let the last coat dry overnight and then apply a few coats of polyurethane on the gaps also. Keep the filler concave so the finish doesn’t run onto the wood.
Boat builders use all manor of more flexible seam sealers, but they cannot be coated with more finish and tend to have a strong smell. These would be available at a marine hardware store. I wouldn’t advise this though.
So now, as to fixing the rotted wood, it would be better to replace the pieces involved. It’s not such a big project, just have a read of my repair article, it’s free at https://www.woodfloordoctor.com/_how_tos/articles/repairconanddiy.shtml
But after reading this you still want to try to patch the wood without replacing it, I will continue. Make sure the rotted wood is not causing a structural problem, or causing more rot. Mold can form on rotten wet wood and cause health problems.
You can buy epoxy wood restoration kits at Lee Valley Tools, at http://www.leevalley.com/wood/page.asp?SID=x=1x=20075x=1,190,42997 With this kit you can saturate the rotten wood so that it hardens. When you use the epoxy putty though you will have to stain and “grain” the putty after to get it to look more like real wood. This kit is expensive and will only do some small areas, so don’t use it on the whole floor. I also have had good results using the carvable wood filler when I have large gouges to fill. You might try this also at http://www.leevalley.com/wood/page.asp?SID=x=1x=31064x=1,190,42997 You do have to dry out the wood before this stuff will work, and after all the “repairs” have been done, consider recoating the floor with additional coats of the same finish that is on there now. If you do not know what the floor finish is, do the tests suggested in this article (free)
Oh, and there is one more solution to this gap problem and that is to take a manila or hemp rope and stain it with a normal wood stain that matches or is slightly darker than the floor tone. Let the stained rope dry overnight. Clean out the gaps as suggested before, and force the rope into the gaps with a putty knife. Don’t glue it into place !! Keep the rope below the surface of the wood. You can untwist a strand and cut off one of the sections, to form a thinner rope when the gap gets smaller. Rope of course, comes in all different sizes. You can then apply a few coats of floor finish over the rope and the floor, this will help it stay in better. The rope has better flexibility than the solid filler does. I just saw this on an “Ask This Old House” episode. But really I’ve heard it before, it’s an old trick.