VPI Base Coats for Medium Density Blockwork

Medium-density blockwork can provide a suitable background for VPI render, but its suction, texture and condition should still be assessed before application. Depending on the selected finish and substrate, a separate base coat may be optional rather than essential.

Using a base coat can nevertheless help regulate the background, create a more uniform working surface and allow the finishing render to be applied in thinner, more controlled layers.

Products in This Range

• VPI Accrolor 2 – A suction-control and bonding agent used to regulate substrates with high or low absorbency. It is suitable for internal and external use.
• VPI MonoCal Gris GF – A weather-resistant, one-coat render that can be used internally or externally as either a base coat or finishing coat. It can also form a base for VPI MonoCal GM and GF finishes.
• VPI Reinforcing Mesh – An alkali-resistant mesh for compatible cement, lime and polymer-modified render systems, helping improve resistance to cracking over masonry.

When Is a Base Coat Required?

A separate base coat is not always required before applying a compatible VPI scraped-texture render to suitable medium-density blocks. Direct application may be possible where the masonry is sound, consistent and prepared in accordance with the render specification.

However, a base coat or suction-control treatment may be beneficial where:

• Block suction is inconsistent
• Mortar joints create an uneven background
• The wall contains repairs or mixed materials
• Additional reinforcement is specified
• The surface requires levelling
• Thinner finishing layers are preferred

Preparing Medium-Density Blockwork

The blockwork must be stable, sufficiently cured and free from dust, loose mortar, efflorescence, oil and other contaminants. Open joints, damaged blocks and significant surface variations should be repaired before rendering begins.

The substrate’s suction should be checked across several areas. Where absorbency is unusually high, low or inconsistent, VPI Accrolor 2 may be used where specified to create a more uniform background.

Using Reinforcement

Reinforcing mesh may be required around openings, across changes in substrate or in areas with an increased risk of cracking. It should be fully embedded within a compatible wet base coat, with suitable overlaps between adjoining sections.

The correct build-up depends on the blocks, exposure conditions and selected finish. Always consult the relevant VPI technical data sheets for direct-application suitability, preparation, reinforcement, application thicknesses and curing requirements.