VPI Base Coats for Lightweight Blockwork / High Suction Backgrounds

Lightweight blockwork is often highly absorbent, meaning it can draw water from freshly applied render too quickly. Without suitable preparation, this rapid moisture loss can reduce working time, affect adhesion and contribute to an inconsistent or weakened finish.

VPI products for lightweight blocks include suction-control treatments, render base coats and reinforcement for areas requiring additional crack resistance. The precise specification should reflect the strength, condition and absorbency of the blockwork.

Products in This Range

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

Typical Applications

These products may be used to:

• Regulate suction before rendering
• Prepare absorbent lightweight blocks
• Create a base for compatible VPI finishes
• Reinforce areas vulnerable to cracking
• Support internal and external render systems
• Improve consistency across variable masonry

Controlling Suction

The blockwork’s absorbency should be checked before rendering begins. If the background draws moisture too quickly, a suitable suction-control treatment such as VPI Accrolor 2 may be required.

Preparation must be even across the wall. Localised differences in suction, including changes around mortar joints or repairs, can lead to variations in drying and appearance.

Substrate and Reinforcement Considerations

Lightweight blocks should be sound, dry and free from dust, loose material, efflorescence and other contamination. Their strength and thermal properties must also be considered when selecting a render because an excessively strong or unsuitable coating can place unnecessary stress on the background.

Where reinforcement is specified, VPI mesh should be fully embedded within the compatible wet base coat. Suitable overlaps and additional reinforcement should be provided around openings, corners and areas where different materials meet.

Always refer to the relevant VPI technical data sheets for substrate suitability, suction-control requirements, application thicknesses, curing conditions and compatible finishing products.