Plastering, Painting, Drylining or Tiling our Concrete Blocks

Airtec, Ultralite, Insulite and Dense Concrete blocks provide an excellent background for accepting plasters. Cement, lime, sand plasters provide a tough surface against impact damage and enhanced sound insulation. To obtain a smooth finish, the final coat should be gypsum plaster because a cement, lime, sand mix does not generally provide a smooth enough finish coat.

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Before applying the plaster, the block surfaces must be cleaned and free of dust and debris. Adhesion can also be improved by raking back mortar joints to provide an additional mechanical key. For closer-textured blocks, a proprietary bonding agent can be used if desired.

Standard plasterboard and thermal laminate drylining boards can be applied directly to blockwork using dabs or other proprietary adhesive. The adhesive manufacturer’s instructions and recommendations should always be followed to ensure correct adhesion.

Paint-Grade close-textured blocks can be painted directly with any masonry paint whose breathability and durability properties are better suited to blockwork than standard water-based internal emulsions. Standard texture blocks are not intended for direct painting due to their open texture but will accept paint if desired. Similarly, Airtec blocks have smooth surfaces which will accept direct painting but are not intended for a paint-grade finish as the block surface may contain a number of larger air pockets; a natural and harmless result of the manufacturing process.

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Newly built walls will be slightly damp and should be left to dry out before applying paint. Some general good practice points for painting are:

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• Surfaces should be clean and free of dust and debris.
• Solvent-based masonry paints e.g. Pliolite, are highly recommended. Standard water-based internal emulsions are suitable but can introduce excessive amounts of moisture into the blockwork, particularly where watered-down mist coats are used, and lengthen the timescale for the drying out of the walls.
• The first coat can be slightly thinner (no more than 10% thinned down) and left to dry.
• The final coat should be normal thickness.

A 1 : 5 cement : sand render mix applied in 2 coats with a final scratched surface provides a suitable and strong background to adhere tiles to. No special preparation of the standard-texture block surfaces is required before applying the render although for close-textured surfaces, pre-treatment of walls may be necessary. (Go to Mortar Mixes for further information) The cement : sand render should be left to dry out for around 2 weeks before applying the tiles.