We are getting new hard wood flooring installed and I expect to be putting shoe molding around the edge of the flooring. I am expecting a half inch to one inch gap between the back of the molding and the wall underneath.

Am I supposed to fill the gap behind with caulk or spray foam or something? I am afraid if I don't, I will have a gap that will be a freeway for insects and mice. If so, what kind of caulk or foam?

  • this gap of 1/2-1 inch is between the floor edge and the wall? And the molding will be used to cover this gap? Is this correct? Thanks.
    – ojait
    Commented Dec 29, 2020 at 2:18
  • If this is a hardwood floor, why is the gap so big? If it is nail down the gaps at the ends can be rather small. The gaps at the long sides need to be bigger, but not 1" and in case the floor expands, it should not be filled. Wil the shoe mold be 1" in some direction to help cover the 1"?
    – Jack
    Commented Dec 29, 2020 at 2:18
  • I assumed the 1" would be the small amount from the shoe mold+original baseboard+drywall gap after the removal of whatever the previous flooring was
    – redlude97
    Commented Dec 29, 2020 at 4:43
  • The difference between 1/2" and 1" is substantial. There shouldn't be that much variation. Also, your flooring shouldn't be your line of defense against pest intrusion. That happens outside.
    – isherwood
    Commented Dec 29, 2020 at 14:25

2 Answers 2


The gap is no different than before assuming the original install was good. Is this going over another floor or stripped down to the subfloor? You can use a backer rod stuffed into the back of the gap but generally you do not caulk the floor to the baseboard/shoe molding to allow for expansion and contraction of the floor


Most plank floors require an expansion gap to allow for the boards expansion and contraction. Depending on the type of floor installed (solid.veneered,etc.) the expansion gap will be prescribed by the manufacturer. Usually 3/8- 1/2 inch around the floor perimeter.

The size of the gap is such that standard floor molding can span this gap so it is not seen. It's always a good idea to keep this gap open and clear. If the gap is wider than it should be and can not be closed with flooring than you may want to try to build-out the wall molding.

This involves installing 2 different (or similar) pieces of molding one attached to the other so as to decrease and cover the floor gap.

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