Thinsets

Thinsets, or thinset mortars, are cement-based adhesives used to bond ceramic, porcelain, glass, and natural stone tiles to substrates such as concrete, backer boards, or plywood.

Most thinsets consist of Portland cement, fine aggregate (sand), and a water-retention additive; many also include polymer modifiers to improve adhesion and flexibility. There are two broad categories: unmodified thinset and polymer-modified thinset. Unmodified thinset relies on cement, sand, and water retention to form a bond. Polymer-modified thinsets incorporate synthetic polymers (latex, acrylic, or vinyl) to improve bond strength, elasticity, and water resistance.

Use and substrates: Suitable for interior floors and walls, showers, and areas with moisture when installed correctly. Follow tile manufacturer recommendations and substrate preparation guidelines. Substrates must be clean, flat, and structurally sound; some backer boards require priming.

Installation: Mix with clean water (or with recommended additive for modified thinsets). Apply with a notched trowel; comb through the bed to create ridges; press tile into the bed to achieve 80-95% contact; use spacers; ensure at least 80% coverage around edges for floor tiles; tiles must be level.

Curing: Allow sufficient cure time; foot traffic after 24-48 hours; full cure up to 72 hours or more depending on product and conditions; temperature and humidity affect open time and curing.

Standards: In North America, thinsets are described by ANSI A118 standards (A118.1 unmodified, A118.4 polymer-modified, A118.11 epoxy-based systems), with ISO equivalents used elsewhere.