Mapei Keracaulk U Acrylic Caulk

Mapei Keracaulk U Premium Unsanded Siliconized Acrylic Caulk

Keracaulk U is a premium-grade, unsanded, siliconized acrylic caulk formulated to match all of Mapei's unsanded grout colors — an easy, seamless finish where grout lines meet movement joints. Easy to apply and easy to clean, with a smooth finish suited to unsanded grout lines and fine-jointed tile work.

Joints where flooring meets a wall, countertop meets a wall, tub meets a wall, or shower corners are all considered movement joints. Standard grout can't flex with that movement and will eventually crack — that's what caulk like Keracaulk U is for. For gaps up to 1/4", use as a flexible barrier and filler between horizontal and vertical surfaces, or where tile abuts a dissimilar surface, including around sinks, tubs, showers, countertops, and ceramic tile floors.

Includes BioBlock technology, tested to ASTM G21 standards, so it doesn't support mold, mildew, or fungal growth after install (regular cleaning and maintenance still required). Paintable after full cure. Meets or exceeds ASTM C834 for low-movement sealants. Water cleanup while fresh.

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What's the difference between Keracaulk U and Keracaulk S? Keracaulk U is unsanded, matched to Mapei's unsanded grout colors — better for fine, tight grout lines. Keracaulk S is sanded, matched to sanded grout colors and blends better with a wider, textured grout line.

Why can't I just use grout in these joints? Movement joints — where a floor meets a wall, a countertop meets a wall, or in shower corners — need to flex. Standard grout is rigid and will eventually crack there. Caulk like Keracaulk U is built to move with the joint instead.

Will the caulk match my grout exactly? It's formulated to match Mapei's unsanded grout colors, but slight variation between grout and caulk shade is normal due to differences in material and texture.

Can I paint over it? Yes — it's paintable once fully cured.