When tiling over gypsum plaster, pre-cast gypsum panels, or anhydrite screeds, Primer G prevents the chemical reaction between substrate sulphates and cementitious adhesives. By isolating these incompatible materials, it stops the formation of ettringite crystals, which otherwise cause the tile adhesive or smoothing compound to de-bond and separate from the floor or wall.
Primer G is a water-dispersion synthetic resin primer that dries to form a flexible, compact, shiny coating that consolidates the substrate surface. It regulates water absorption across uneven porous substrates, including cementitious renders, chipboard, cement fibre boards, and foamed concrete.
When used under self-levelling compounds, this absorption control reduces the formation of pinholes and air bubbles while preventing the levelling pour from drying out too fast. When applying sprayable gypsum plasters, it slows water loss into the backing wall to prolong the workability window and help prevent shrinkage cracks.
Primer G is suitable for preparing internal walls and floors prior to subsequent installations:
The substrate must be clean, dry, and free from oils, grease, residual paint, and loose material. Repair cracks in concrete beforehand with Eporip or Epojet. Sandpaper anhydrite screeds before application. Dilute and apply as follows:
Primer G prevents a chemical reaction between sulphates in gypsum and cement aluminates, which can form "ettringite" and cause delamination. It forms a barrier, ensuring a stable bond.
No, Primer G is not recommended for external use or where rising damp is present. It is designed for internal applications and will not prevent water ingress or perform reliably in damp conditions.
The drying time before applying levelling compounds or adhesives is 30 minutes on concrete substrates. For gypsum substrates, allow 30-60 minutes, assuming 23°C and 50% relative humidity.
It reduces the formation of air bubbles in the compound and prevents over-rapid drying of the leveller. This extends workability and simplifies the self-levelling process for a smoother finish.
| Application | Key benefit | Primary trades |
|---|---|---|
| Preparing gypsum for ceramic tiling | Prevents ettringite formation and delamination between gypsum and cementitious tile adhesives. | Tilers, Floor & Wall Preparers |
| Priming before self-levelling or smoothing compounds | Reduces air bubbles and prevents premature drying, improving workability and finish quality. | Floor Preparers, Tilers |
| Anchoring coat for gypsum-based sprayable plasters | Regulates substrate absorption, prolongs workability, and helps prevent shrinkage cracks. | Plasterers |
| Fixative for wallpaper or paint on gypsum walls | Uniformly reduces substrate absorption, reducing glue consumption and easing future wallpaper removal. | Painters, Wall Paperers |
| Between layers of smoothing compounds | Ensures consistent absorption and adhesion for subsequent layers, maintaining system integrity. | Floor Preparers |
Ensure the surface is structurally sound, dry, and free of oils, grease, paint, or dust. Sand anhydrite surfaces, vacuum thoroughly, and repair cracks if required.
Stir well before use. Dilute Primer G as follows: 1:1 with water for cementitious substrates, 1:2 for anchoring gypsum plasters, 1:3 for wallpaper primer. Apply neat on gypsum-based substrates.
Apply evenly using a flat brush, roller, or spray pump. Avoid puddling and ensure uniform coverage over the entire surface.
Mapei Primer G is not classified as dangerous according to Australia WHS 2 (2021).
Eye protection is not required for normal use. Operate according to good working practices. Suitable materials for safety gloves include Nitrile rubber (thickness >=0.35mm, breakthrough time >=480min) or Butyl rubber (thickness >=0.5mm, breakthrough time >=480min).
Primer G is non-flammable and can be used in closed, unventilated environments without special precautions.
Store in original unopened packaging for up to 12 months. Protect from frost. Keep away from food, drink, and animal feed in adequately ventilated premises. Dispose of product and contaminated packaging according to local regulations; do not dispose into drains or waterways.
Proper substrate preparation is critical for adhesion and system performance. This guide details specific prep and priming instructions for common surfaces.
Surface prep: Substrate must be clean, dry, and free from oils, grease, residual paint, and loose material. Follow manufacturer's recommendations for moisture content and surface finish. Abrade particularly smooth or glossy gypsum plaster surfaces.
Primer: Required. Apply neat (undiluted) for smoothing compounds or use undiluted for ceramic tiles. Dilute 1:2 with water for anchoring gypsum plasters. Dilute 1:3 with water for wallpaper adhesives.
Surface prep: Must be clean, dry, and free from contaminants. Repair cracks with a suitable product like Eporip or Epojet. Ensure surfaces are sound and free of loose material.
Primer: Required. Dilute 1:1 with water before applying smoothing or thixotropic compounds. Use undiluted if applying gypsum-based products over cementitious renders.
Surface prep: Sandpaper the surface thoroughly before application to ensure proper adhesion.
Primer: Required. Use Primer G undiluted before applying cement-based products or when installing ceramic tiles with cementitious adhesives.
Surface prep: Ensure surfaces are clean, dry, and structurally sound, free from dust, oils, and loose particles.
Primer: Required. Apply Primer G as a fixative prior to papering or painting, typically diluted according to absorption.
| Property | Value |
|---|---|
| Consistency | liquid |
| Colour | light blue |
| Density | 1.01 g/cm³ |
| pH | 8 |
| Dry Solids Content | 18 % |
| GEV EMICODE | EC1 Plus - very low emission |
| Maximum VOC (2004/42/EC) | 0 g/l |
| Application Temperature Range | 5°C to 35°C |
| Drying Time Before Levelling Compounds or Adhesive (Concrete) | 30 min |
| Drying Time Before Levelling Compounds or Adhesive (Gypsum) | 30-60 min |
| Consumption | 0.08 - 0.15 kg/m² |
Here are some common examples on where Mapei Primer G used by our customers.
