When to fill joints in polished concrete

Bringing a building into its normal heated or air-conditioned environment can change how quickly the slab dries and shrinks. The Concrete Polishing Council notes that activating the building’s HVAC system can accelerate slab shortening.

As concrete shortens, joints can widen. Filler installed before that change may subsequently separate from the joint walls or tear internally.

At Craftsman, we consider whether the building is enclosed, whether permanent HVAC is operating, and whether conditions represent the intended occupied environment when planning joint filling. Where practical, we coordinate filling after those conditions have been established, while also accounting for the polishing sequence and the selected filler’s instructions.

Operating HVAC does not mean shrinkage is complete or guarantee that filler will never separate. It gives us a more representative environment in which to plan the work.

We schedule filling so the remaining polishing steps can finish the material cleanly without damaging it.

Metzger/McGuire generally recommends installing its joint fillers and repair materials before or early in polishing. Subsequent grinding and honing can address overfill, potential shadowing, and slight concavity in the installed material. Filled joints can also help protect their edges from further grinding-tool impact.

However, very aggressive initial tooling can damage or pull pieces from installed filler. In that situation, filling may need to wait until later in grinding or honing.

The installation point therefore depends on both the selected material and the tools that will follow it. “Fill before polishing” is not a complete instruction.

Our joint-filler shaving and repair-grinding guide explains the separate waiting periods for shaving, removing overfill, and further processing.

Joints can be filled after polishing, but preparation and overfill removal must be planned around the finished surface. Late work can create shadowing, change reflected gloss, or remove stain protection.

At Craftsman, we select the preparation and application method with those risks in mind. Surface protection or a different placement and finishing method may be needed to avoid unnecessarily disturbing the surrounding floor.

Concrete can continue shrinking after filling. Establish how later filler separation will be evaluated and how any follow-up work will be authorized and paid for. The Concrete Polishing Council recommends addressing those arrangements in the construction documents. Our joint separation and maintenance guide explains what to assess when a gap appears.