Prime Tiled Floors for Better Adhesion – Fine Homebuilding

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Written By Jim J Neal

Primer-U increases adhesion and has a low odor. It is solvent-free, 100% acrylic and water-based.

The process of setting tiles involves applying thinset mortar (an adhesive cement that holds the tiles in place), to the substrate. Next, you add a membrane (underlayment), which prevents cracking and waterproofs, before adding another layer of thinset. It can be difficult to lay tile securely, especially in remodels where the substrate isn’t suitable for tile. Thinset is not as strong with gypsum, plywood, oriented strand boards (OSB), raised accessibility panels, metal and tile that are already in place.

Primer-U is Schluter’s interior primer. It adds an extra step to the tiling process. Primer U is a translucent liquid that can be applied before applying thinset to hold the tile in its place. It is solvent-free, water-based, and has zero volatile organic compounds (VOCs).

Primer-U is pre-mixed and ready to use. It only requires a quick stir but it should be adjusted to its surroundings for at minimum 48 hours before using. Before priming thinset, the surface must be sound structurally, smooth, dry, and devoid of moisture.

Primer-U can be purchased in a 1-gallon. Primer-U is available in a 1-gal. tub.

The application is easy: Simply pour the primer onto the substrate (or onto an easel tray), then apply it to the surface with a 3/8-in. brush. You can use a medium-nap paint roll, a similar brush or a garden sprayer to apply the primer. After primer has been applied, it should be allowed to dry completely before you apply thinset mortar. The drying time will vary depending on the air temperature and humidity. Schluter says it should take less that an hour. You will need to recoat the primer within 48 hours. You can clean up the primer with soapy water and a cloth. Dry primer can be removed with mineral spirits.

Primer-U is only intended for interior use. It is available in 1-gal. Primer-U is available in 1-gallon and 5-gallon sizes. Tubs are available for purchase at prices of approximately $70 and $280 respectively.

Images courtesy of the manufacturer

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