When do I need to prime and how many coats should I apply?
Installers often ask, “When do I need to prime?” or “How many coats should I apply?” Although priming can seem complicated, following a few core principles makes the process straightforward and reliable.
Why does priming matter when tiling?
Before tiling, many wall and floor backgrounds require priming to ensure a durable and successful installation. Priming is essential for:
- Controlling porosity – reducing excessive absorption that can cause air bubbles or premature drying.
- Preventing chemical reactions – avoiding incompatibility issues between cement-based products and sensitive substrates such as gypsum (plaster, anhydrite).
- Consolidating weak surfaces – strengthening friable or dusty backgrounds.
- Supporting waterproofing and levelling – creating an ideal base for subsequent preparation stages.
- Ensuring product performance – allows cement-based tile adhesives and levelling compounds to fully hydrate, aiding open and working times.
Choosing the right primer is just as important as choosing your adhesive or grout.
What are the right primers to use for tiling?
Acrylic and synthetic polymer-based primers—such as BAL Prime APD, ARDEX P 51, or BAL Bond SBR—are recommended for most tiling applications.
While PVA is inexpensive and easily available, it introduces significant risk and is not recommended for tiling or flooring projects. Many PVA products re-soften or emulsify when exposed to moisture. When cement-based adhesives or levellers hydrate during curing, they exert stress on the softened PVA film. This can severely reduce bond strength—especially on vertical surfaces, where downward load from the tiles increases the likelihood of failure.
For this reason, BAL strongly advises using manufacturer-approved acrylic or polymer primers instead of PVA.
Key Substrates and Recommended Primers
Always follow manufacturer dilution guidance. Typical recommendations include:
- Gypsum plaster (with cement-based adhesives):
- BAL Prime APD – two coats neat
- Gypsum plaster (with ready-mixed products):
- BAL Prime APD – 1:1 dilution, one coat
- Anhydrite/calcium sulphate screeds:
Crucial to prime before applying cement-based products to avoid ettringite formation.- BAL Prime APD – 1:1 first coat, second coat neat
- Concrete, cement:sand screeds, render, tile backer boards:
- BAL Prime APD – one coat to reduce suction and support hydration
- Tongue and groove floorboards:
- BAL Prime APD – two coats neat
Best Practice Application
When applying two coats, apply the second coat at 90° to the first ensuring full coverage. Allow each coat to dry completely.
The Benefits of Good Priming
Using the correct primer helps:
- stabilise the background,
- prevent chemical incompatibility,
- manage porosity, and
- support proper hydration of adhesives and levelling compounds.
The result is improved adhesive performance, extended open time, and easier installation—particularly over larger areas.
Need Help?
If there is any uncertainty about whether or how to prime a surface, the BAL Technical Advisory Service is always available to provide guidance.
