What Is a Waterproofing Primer?
The purpose of waterproofing primer is to ensure the surface is fully sealed and prepared to apply waterproofing membrane. It also provides bonding strength between the substrate with waterproofing membrane. Waterproofing primers usually used on porous surfaces, and additionally strengthen the surface.
Failure to prime the areas before preparing for the application of waterproofing membrane is the second most repeated problem in waterproofing failure. This is due to the waterproofing membrane unable to bond to the substrates.
Each manufacturer for waterproofing membrane would suggest priming on surfaces before applying. There are various primers available for different kind of substrate and surfaces.
How to apply waterproofing Primer?
Recommend to always use primers that are specified by manufacturers especially for surface priming for CFC, mortar, concrete, mortar screeds and plywood substrates. Priming the surfaces will decrease porosity, air-entrapment (pin hole), dusting and high residual moisture in surfaces where it could potentially cause blistering on the waterproofing membrane after curing.
However, not all primers are the same. For example, one-part solvent or water based primer such as Primer-W are usually used to cover the substrate and increase adhesion of the waterproofing membrane. Two-part water based epoxies work in similar method but can also use to seal off high residual moisture in the surface.
Types of Waterproofing Primer
- Bituminous primer — most common with torch-on and bituminous membrane systems; seals porous concrete and improves bond strength
- Acrylic/water-based primer — used with liquid-applied membranes; faster drying, lower odour, easier cleanup
- Solvent-based primer — deeper penetration into porous or damp substrates, often used where faster cure and stronger bond are priorities
Why Skipping Primer Causes Membrane Failure
- Poor adhesion leads to bubbling and delamination, especially in humid climates like Malaysia’s
- Porous or dusty concrete surfaces absorb moisture that later pushes the membrane away from the substrate
- Most early membrane failures traced back by contractors come down to skipped or poorly applied primer, not a faulty membrane product
How to Apply Waterproofing Primer Correctly
- Clean and dry the surface thoroughly — remove dust, oil, and loose debris
- Repair any cracks or uneven areas before priming
- Apply primer evenly with a roller or brush, following manufacturer coverage rates
- Allow full drying/curing time before applying the membrane (check product-specific timing — this varies by primer type)
- Avoid applying membrane over primer that’s still tacky or hasn’t fully cured
How to Choose the Right Primer for Your Membrane System
- Torch-on or bituminous sheet membrane → bituminous primer
- Liquid-applied membrane → primer recommended by the specific liquid membrane manufacturer (often acrylic or polyurethane-compatible)
- Damp or porous substrates → solvent-based primer for deeper penetration
Need more information and waterproofing advise of Primer for your projects?
If you would like any further information about primers, please contact us or send us an email to info@chemind.com.my . Our friendly team of waterproofing specialists pride themselves on providing great service and will be delighted to help.
Frequently Asked Questions
Yes — primer improves adhesion between the substrate and the membrane, and skipping it is one of the most common causes of early membrane failure.
Drying time varies by product, typically ranging from 30 minutes to a few hours, but always check the specific manufacturer's guidance before applying the membrane.
No — primer should match the membrane system. Bituminous membranes generally need bituminous primer, while liquid-applied systems usually require a primer specified by that product's manufacturer.
The membrane may not bond properly, leading to bubbling, peeling, or early failure — always follow the primer's stated cure time before proceeding.
Primer W
- Single-pack, water-based sealer — applied directly from the pail, no mixing
- Brush, roller, or broom application — accessible without specialised equipment
- Protects against concrete carbonation
- Compatible with CHEMFLEX R-100, DECORFLEX, DECKTOP 3000S, and TARFCOTE