Joint filler is a semi-rigid epoxy or polyurea material used to fill saw cuts and control joints in a concrete slab before a coating goes down, so the finished floor is a smooth, continuous surface instead of an open gap.
Understanding Joint Filler in Coated Floors
Concrete slabs are cut with control joints to manage natural cracking as the concrete shrinks and moves. Left open, those joints collect dirt, take a beating from forklift and pallet jack traffic, and telegraph through a coating as a visible line. Filling them before coating gives installers a flat surface to work over and protects the joint edges from spalling.
Semi-Rigid vs. Flexible Joint Fillers
Semi-rigid epoxy or polyurea fillers are used under coatings that will see hard-wheel traffic, since they support the joint edges and resist compression. Flexible, elastomeric sealants are used instead where a slab is still actively moving (expansion joints, exterior slabs with significant temperature swings) because a rigid filler in those joints will crack.
Why Joint Filling Matters Before Coating
An unfilled or poorly filled joint is one of the most common places a new coating fails early. The coating can’t bridge the gap cleanly, and traffic breaks the edge down over time. Filling and grinding the joints flush before coating is a standard step in most commercial epoxy and polyaspartic installs.
Installation Tips
Joints should be clean, dry, and free of old caulk or debris before filling. Overfilling slightly and grinding flush once cured gives a cleaner result than trying to fill exactly level in one pass.
Also Called
Semi-Rigid Joint Filler, Control Joint Filler
