How to Repair Cracks in Concrete Before Epoxy or Polyaspartic

Cracks and spalled (broken or flaking) concrete can cause coatings to crack, peel, or bubble. As part of concrete preparation, you need to decide which cracks to fill, which to patch, and which might be acceptable to coat over. This guide walks through how to repair cracks in concrete before applying epoxy or polyaspartic so the coating has a sound base.

Why crack repair matters

Coatings bond to the surface. If that surface is moving (active crack) or has loose material (spall), the coating can crack with the slab, peel at the crack, or bubble. Repairing cracks and spalls gives the coating a stable substrate so it can last. It's one step in the full prep process—after cleaning (including oil removal) and before profiling.

Prerequisites

• Concrete is clean and dry (no oil, grease, or old coating in the crack).
• You have the right filler or patch for the crack type (see below).
• Temperature and humidity are within the product's range.
• For large or structural cracks, consider a professional assessment.

Step 1: Clean the cracks

Remove dirt, oil, and loose material from the crack. A wire brush, vacuum, or blower can help. If there's oil in the crack, use a concrete degreaser and rinse. The filler or patch needs a clean, sound surface to bond to.

Step 2: Assess crack width and activity

• Hairline (very narrow): Often filled with a thin filler as part of the coating system, or left and coated over if the manufacturer allows. Less risk of reflected cracking.
• Wider (e.g., 1/8 in. and up): Should be filled with a crack filler or patch. Rigid fillers work for stable cracks; flexible (polyurethane, some epoxy) may be better for cracks that still move slightly.
• Active (still opening/closing): May need a flexible sealant or professional evaluation. Coating over very active cracks often leads to failure.

Your coating manufacturer may specify maximum crack width or recommend a particular filler—check the data sheet.

Step 3: Fill or patch

Crack fillers: Pour or inject the product into the crack per the label. Overfill slightly if needed, then strike off or allow to cure and grind flush. Let the product cure fully (often 24–72 hours or more) before profiling and coating.

Spalls and larger damage: Remove loose concrete, clean the area, and apply a concrete patch or repair mortar. Trowel level with the surrounding surface. Cure as recommended—usually several days—before proceeding with surface profiling and coating.

Step 4: Profile and coat

After repairs have cured, continue with the rest of prep: profile the surface (etch, grind, or shot blast), remove dust, and apply the coating when the slab is dry and within the correct temperature range. The repaired areas should be profiled along with the rest of the floor so the epoxy or polyaspartic adheres everywhere.

When to hire a pro

Very wide cracks, multiple active cracks, or structural concerns are best evaluated by a contractor. A pro can recommend the right repair product and sequence and ensure the slab is ready for epoxy or polyaspartic. Good concrete preparation often includes professional crack and spall repair.

Summary

Repair cracks and spalls before coating: clean them, choose the right filler or patch for width and activity, apply and allow full cure, then continue with profiling and coating. Skipping repair can lead to peeling, cracking, or bubbling. For more on the full prep sequence and concrete preparation, see our topic hub.