Hi Susan. There are specially formulated epoxy and polyurea fillers with higher elongation rates that can fill the joints as long as the boards are below the joint level. However, if the independent slabs expand or contract too much, the epoxy coating over the top of the joints will still crack. Joints such as yours usually are left alone when it comes to coatings since there is not a proper method available for covering them up. Of more concern is where did the water come from? Coatings do not tolerate moisture well from below. Have you moisture tested the basement? If you have moisture or moisture vapor that transmits from below the slabs, then a coating will not work as it can begin to peel up over time.

The majority of the boards are at or very slightly below the level of the slabs. I would say nowhere is any as low as 1/4″ below the slabs. The basement got wet in May and I’m still trying to come up with a viable solution for a floor covering. (It had been carpeted, which I always thought was crazy.) I’ve read about self-leveling products that I thought I might be able to use and then let the grinder smooth it all out. Thanks again for your help. Much appreciated.

Paint is more flexible, but a lot less durable than epoxy. It has more of a flat finish as well. Plus, you can’t apply a clear coat if you were planning on that. Lastly, though it is more flexible, it will still form a crack along both sides of the joint, though it may take longer to do so. One of the problems is that the boards create a large span between the slabs. Also, 2×4’s back in the day used to be closer to 2″ wide than the 1.5″ they are today. You cannot create a seamless looking joint that the epoxy will cover if that is your goal. The gap is just far to wide. Are the boards flush with the concrete height or 1/4″ or so below it?

Hi Susan. 2×4’s where fairly common to use as expansion joints up through the 60’s and into the 70’s. You can apply epoxy to the boards, it just requires sanding the surface with 80-100 grit sandpaper to remove any old residues and other contaminants so that the epoxy will adhere. Keep in mind though that epoxy does not flex. If you get any movement of the boards or expansion or contraction of the concrete, cracks in the epoxy will form between the boards and concrete. Also, EpoxyShield is a thin water-based coating. Due to the grinding, you may need two color coats. This is because the first coat will be absorbed more than usual by the concrete and can sometimes end up too thin. The result is a splotchy looking floor with pale color. If this happens, a second color will be needed.