Fixing Render Not Sticking to Blockwork: Ultimate Guide

Simple Solutions 4 U brings over a decade of expertise in diagnosing and repairing issues where render not sticking to blockwork undermines the appearance and integrity of your property. Our specialists combine premium materials, advanced primers, and meticulous workmanship to deliver results that stand the test of time. Discover the difference in our approach by learning more about our team and processes here.

Why Is Your Render Not Sticking to Blockwork?

Proper adhesion depends on a well-prepared substrate, controlled moisture levels, and compatible render systems. When any of these elements are neglected, the bond between render and blockwork can fail.

Common Causes

• Poor Substrate Preparation: Surface dust and loose debris prevent mechanical key and suction control; always clean thoroughly with a block brush or power wash.
• Excessive Moisture in Blockwork: High suction or trapped condensation can lead to rapid drying or retention of moisture; address by installing damp-proof membranes and resolving condensation pathways.
• Incompatible Render Mix Ratios: Through-coloured renders require precise powder-to-water ratios; follow manufacturer instructions for products like Ceresit ZU render.
• Insufficient Primer or Bonding Agent: Skipping a specialist primer layer compromises adhesion; always apply a quality bonding primer such as Ceresit CT16 Primer.

7 Proven Fixes for Render Adhesion Issues

1. Thorough Surface Preparation: Begin by removing all dust and laitance with a stiff block brush; follow with a low-pressure wash and allow the surface to partially dry to achieve ideal suction.
2. Porosity and Moisture Control: Lightly mist high-porosity blocks to prevent rapid water loss in the render; install a damp-proof membrane and repair any condensation leaks before rendering.
3. Primer Application: Use a deep-penetrating primer on porous substrates and a universal primer on smooth blocks to create a reliable mechanical key.
4. Proper Render Mix: Accurately measure and mix through-coloured or silicone renders like Ceresit ZU according to supplier guidelines; aim for a creamy consistency that holds its shape on the trowel.
5. Correct Layer Build-Up: Apply a parge coat where needed to level irregularities, then embed mesh within the basecoat; build thickness in even coats up to 10–20 mm total.
6. Mesh Reinforcement: Embed corrosion-resistant fibreglass mesh within the basecoat at stress points and around openings to distribute loads and reduce crack propagation.
7. Regular Maintenance: Conduct biannual inspections for hairline cracks or delamination; seal and repair promptly to preserve adhesion and prevent moisture ingress.