Q: Our stairs are very old, worn down, painted pine. We are planning on leaving them painted and putting down a sisal carpet runner. Can the boards that are very worn be filled to make them flatter and less dangerous?
A: I did see a self leveling cement used on Holmes on Homes once. They were pouring it on a plywood sub floor that was quite out of level. First they applied a special sealer that had 2 functions. It prevented the plywood from soaking in the water from the cement mix. It also assisted in bonding. I am not sure if this sort of thing is what you are looking for. To me, the issue is the paint and what will stick to it without cracking or peeling off. Otherwise, you could always cover the risers with plywood. However, you have to try to make sure to keep them within code as to height of the step.