Universal primer

Schluter®-PRIMER-U is a ready-to-use universal primer used to enhance adhesion of mortars for hard-to-bond substrates such as gypsum underlayment, existing tile, terrazzo, steel (e.g. raised access panels), flooring adhesive residue, concrete with curing compounds, latex paint, and glass tile.
  • Ideal for use with Schluter SET®, ALL-SET, and FAST-SET thin-set mortars, and Schluter underlayments such as Schluter®-DITRA and DITRA-HEAT
  • Ready-to-use, single-coat application with roller or broom
  • One-component, solvent-free, water-based acrylic formulation
  • Low odor and zero-VOC
  • Freeze/thaw stable more less

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Schluter®-PRIMER-U is a ready-to-use, one-component, solvent-free, 100% acrylic, water-based primer. It is used to ensure excellent adhesion when applying Schluter thin-set mortars to difficult-to-bond-to surfaces such as gypsum underlayment, raised access panels, and existing tile. PRIMER-U is suitable for use with Schluter SET®, Schluter ALL-SET®, and Schluter FAST-SET® in interior applications where increased adhesion is required over various porous and non-porous substrates.

PRIMER-U is a translucent orange liquid that dries to a slightly glossy film approximately 15-60 minutes after application. PRIMER-U provides a strong bond to gypsum underlayment, concrete, existing tile, glass, plywood and OSB subfloor panels, terrazzo, steel, VCT flooring, well-bonded flooring adhesive residue, and latex paint.

Shelf life and storage: 12 months from the manufacture date on the package in unopened, properly stored containers. PRIMER-U must be stored between 50°F (10°C) and 90°F (32°C). Keep containers tightly closed when not in use.

Freeze-thaw stability: 5 cycles at 0°F (-18°C). If primer has frozen, allow to thaw at room temperature. Settling of solid resin may occur as a result of freeze-thaw. Stir thoroughly before use.

For complete installation guidelines and warranty criteria, please download the appropriate Schluter® Installation Handbook and view the installation videos available below.

Surface Preparation: The surface where PRIMER-U is to be applied must be structurally sound, clean, smooth, dry, and free of moisture. Any contaminants (i.e., paint, grease, oil, sealers, curing compounds, etc.) and/or flooring adhesive that is not well adhered or may prevent proper bond must be removed. Thoroughly clean surface to remove dirt and debris.

Mixing: Solid resin may settle during shipping and storage. Stir thoroughly before use. Do not dilute.

Application: The application area shall be fully enclosed, weather tight, with an operating HVAC system. PRIMER-U must be acclimated to ambient conditions and applied when the ambient temperatures are between 65°- 85°F (18 - 29°C). Ensure the primer and application area are acclimated for 48 hours prior to use. The relative humidity of the application area shall be maintained between 35-55%. Carefully read all instructions before application. Do not dilute primer. Pour an adequate amount of primer from container directly onto the substrate or pour primer from container into a paint tray.

1. Apply a thin, even coat using a 3/8" (10 mm) medium-nap paint roller, or a similar brush, broom, sponge, or garden-type sprayer. Do not leave any bare spots or excessive amounts of primer. Keep roller wet throughout the application process.

Notes: Replace rollers regularly and between applications to avoid drying on roller. Very absorbent surfaces, such as gypsum underlayment, may require more than one coat of primer.

2. Once applied, the primer must be allowed to dry to the touch and not transfer to finger. Allow the coat to dry fully before applying thin-set mortar. Note: If PRIMER-U remains uncovered for more than 48 hours, apply a second coat.

Clean Up: Clean roller or brush with water while PRIMER-U is still wet. Remove wet primer from tools and equipment with soapy water and a clean cloth. Use mineral spirits to remove dried primer. Use caution when handling flammable solvents.

Drying Time: The drying time of PRIMER-U depends on the porosity of the substrate, the air temperature and relative humidity. Under average drying conditions of 70°F (21°C) and 55% RH, PRIMER-U will dry in 15-60 minutes. Protect from exposure to moisture for at least 4 hours.

Data sheets

PRIMER-U Data Sheet
522.57 KB

Safety Data Sheets

Safety Data Sheet PRIMER-U
1.17 MB

Product Table

16.27 KB
95.89 KB

Does PRIMER-U require any mixing or dilution prior to application?


PRIMER-U is a ready-to-use product that does not require mixing or dilution.

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How long can I leave a primed floor before applying a membrane?


The membrane can be installed as soon as the thin-set can be applied to the primed substrate...

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What applications is PRIMER-U best suited for?


Concrete, OSB, plywood, gypsum, steel, existing tile, vinyl, subfloors with adhesive residue.

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May PRIMER-U be used in wet environments?


PRIMER-U is to be used only in dry, interior environments.

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Do I have to be in a well-ventilated room when applying PRIMER-U?


No, PRIMER-U is very low odor and has no VOC’s so there are no special ventilation requirements.

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Watch & Learn
About the product

Schluter®-PRIMER-U: Universal Primer for Hard to Bond Surfaces

Schluter®-PRIMER-U: Universal Primer for Hard to Bond Surfaces


Find some existing tutorials and project documentation videos to learn how-to get the best out of our products - for more fun in your life, start now!

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