Baumit Base Coats For Painted Substrates

Rendering over a painted surface requires careful assessment because the strength of the new system ultimately depends on how securely the existing paint is bonded. Loose, flaking or unsuitable coatings must be removed, while stable paintwork may be retained when it passes the required adhesion checks and is prepared using the specified Baumit system.

This range combines a fibre-reinforced bonding mortar with alkali-resistant reinforcing mesh to create a stable base for compatible Baumit finishes.

Products in This Range

• Baumit MultiContact MC55 W – A natural-white, fibre-reinforced, multipurpose bonding mortar suitable as a renovation render over stable mineral and synthetic-resin renders, plasters and paintwork.
• Baumit StarTex Fine – A fine, non-slip and alkali-resistant glass-fibre mesh designed for embedding within compatible adhesive and levelling compounds.

Typical Applications

These products may be used to:

• Renovate stable painted façades
• Create a bonding layer over suitable paintwork
• Reinforce existing rendered surfaces
• Bridge inactive cracks and vulnerable areas
• Prepare substrates for compatible Baumit finishes
• Refurbish weathered external elevations

Assessing Existing Paintwork

Existing mineral or organic coatings must be sound and securely bonded. A pull-off or cross-cut adhesion test should be completed before determining whether the paint can remain.

Peeling paint, limewash, loose coatings and film-forming layers must be removed. The background should also be clean, dry and free from dust, grease, efflorescence, algae and mould. Cracks and underlying defects should be investigated and repaired rather than simply covered.

Low-suction, highly absorbent or friable surfaces may require additional treatment with a compatible Baumit primer.

Creating a Reinforced Renovation Layer

Baumit MultiContact MC55 W can be applied as a reinforced renovation layer, with Baumit StarTex mesh embedded while the mortar is wet. Adjacent mesh sections should overlap, and the reinforcement must remain completely covered by the base coat.

When MC55 W is applied over a sound painted substrate or existing render, Baumit recommends installing a suitable scrim-and-pin system.

Before Applying the Finish

Rendering over paint is only appropriate when the existing coating and underlying substrate can support the additional load. If there is uncertainty about adhesion, moisture or the condition of the original render, further investigation or removal may be required.

Always follow the current Baumit technical data sheets for adhesion testing, mechanical reinforcement, application thicknesses, drying periods and compatible primers and finishes.