Bituminous Primer

The correct name for this material is bituminous primer or undercoat. It is a critical element in any roofing system using self-adhesive waterproofing membranes.

Bituminous primer serves several key purposes:

• Improves adhesion between self-adhesive waterproofing materials and the roof substrate.
• Seals and saturates concrete surfaces.
• Removes dust and debris from the surface to be treated.

Overview of the Primer

Bituminous primer is made by dissolving bitumen in gasoline at a 1:3 ratio (by weight). Due to this, the material is highly flammable and must be handled with care during storage and application. The primer is supplied in metal pails of 15–20 kg, typically packed on euro-pallets for delivery.

Working temperature for application is approximately 80°C. Drying temperature is -15°C. Application methods include brush or roller. The primer must be stored in tightly sealed containers, as the gasoline component is highly volatile and evaporates quickly. Do not allow the product to freeze during storage.

Surface Preparation and Primer Application

Before applying bituminous primer, clean the surface thoroughly: remove debris, visible dirt, and dust. Better preparation reduces the amount of primer needed. The material has good coverage on its own, but performance improves significantly on clean substrates.

Next, heat the primer to around 80°C and mix thoroughly. If the primer is newly produced, heating may be omitted, as bitumen remains workable for a time after production. In such cases, simple stirring in the pail is sufficient.

Application Methods

• Brush: Low efficiency, used only in hard-to-reach, small areas.
• Roller: Higher efficiency than brush, but not suitable for large-scale roofing or façade applications.
• Paint sprayer: Highest efficiency, ideal for repair and restoration work.
• Flow application: The primer is poured directly from the pail and spread using a rubber squeegee. This method is suitable only for flat or low-slope surfaces and results in high material consumption.

Application is possible only when ambient air and surface temperatures are between +5°C and +30°C.

Due to its high flammability and volatile components, open flames must be strictly avoided during application. The applicator must wear protective gear: gloves, respirator, and safety goggles. Avoid contact with skin, mucous membranes, eyes, or mouth. If used indoors, ensure proper ventilation to prevent accumulation of gasoline vapors.

If adjustment of consistency is needed, dilute with petroleum solvent (naphtha) or white spirit. Always stir continuously during dilution.

Subsequent treatment should not begin until several hours after application, allowing the primer layer to harden. Important: When applying bituminous waterproofing membrane with a propane torch, the flame must strike the membrane directly, not the primed surface. Otherwise, the primer layer may degrade.