The right primer for Earthaus plasters is any interior-grade PVA or latex primer, ideally with zero or low VOCs. Earthaus does not manufacture a primer — but a compatible primer layer is essential for proper adhesion and consistent absorption before applying Earthaus plasters.
Which Substrates Need Primer?
Whether you need to prime depends on the substrate, not on which Earthaus finish you are applying. The rule is the same across the range: porous mineral surfaces do not need primer, sealed or non-absorbent surfaces do.
Primer IS required over:
Drywall (Level-4 finish)
Existing painted walls, including previously painted textured drywall
Painted or sealed interior masonry (brick, concrete block, or stone)
Any surface that is sealed, glossy, or does not absorb water
Primer is NOT required over:
Brick, stone, or concrete block (unsealed and unpainted)
Lime or cement stucco
Lime, clay, or gypsum plaster
Earthen substrates such as adobe, cob, or compressed earth block (CEB)
These porous mineral substrates allow moisture exchange and form a direct mineral-to-mineral bond, which maintains the breathability of the system. On any of them, lightly dampen the surface before applying to prevent flash drying. This holds for exterior work as well: primer is never used over lime, clay, or gypsum on exteriors — the same mineral-to-mineral bond applies outdoors.
Always make sure the substrate is clean, dry, sound, and free of dust or loose material before you prime or apply the first coat. If you are unsure whether your surface counts as porous, test it: flick a little water onto it. If the water soaks in, it is porous. If it beads or sits on the surface, prime it.
Wet areas are a separate matter. A Tadelakt shower requires a code-approved waterproof membrane and a thinset key coat regardless of substrate — see "Tadelakt: Shower Substrate Preparation."
Recommended Primer Characteristics
For health and environmental integrity, Earthaus recommends selecting a primer with zero or low VOCs (volatile organic compounds). These products maintain indoor air quality and align with the sustainability values of the Earthaus system.
Compatible primer types:
Any interior-grade PVA or latex primer is suitable for use beneath Earthaus plasters.
Choose a primer designed to promote adhesion while equalizing surface porosity.
Primers should be fully dry before applying Earthaus Primer Grit or plaster.
Earthaus does not endorse or certify particular primer brands. Any product meeting the description above is suitable, and the choice of brand is yours.
Why priming matters: Primers create a stable, uniform surface for plaster application. Without proper priming, absorbent or inconsistent substrates can cause uneven drying, leading to irregular texture or adhesion issues.
Always Add Primer Grit
Earthaus always recommends the addition of Primer Grit to your primer of choice. Primer Grit establishes the mechanical bond necessary for mineral-based finishes.
For detailed application guidance and system compatibility information, see the Earthaus Primer Grit Product Guide (PDF).
What to Avoid
Avoid high-VOC, solvent-based, or glossy primers that may interfere with mechanical adhesion. When choosing a primer, always pick a flat/matte, zero- to low-VOC product — never a glossy one. (Existing glossy paint already on your wall is a different matter — see "Can I Apply Earthaus Plaster Over Drywall (Sheetrock)?")
Always verify primer compatibility with the substrate and follow manufacturer drying times.
Remember: primer choice does not replace proper substrate preparation.