If you're looking for how to prepare the wall step by step, read Painting a damp wall: step-by-step preparation.
Peeling is a symptom, not a diagnosis
When a paint film lifts, the bond may be failing between finish and surface, between several coats of paint or within the substrate itself. Water is a common cause, but dust, poor cohesion of the render, incompatible products, curing time or incorrect application also play a part.
What happens with water and the paint film
Vapour transport through a wall depends on vapour pressure and the permeance of the layers. Under certain conditions, a build-up of moisture can contribute to blistering and detachment. If there are also soluble salts, crystallisation in the pores can push the coating off from within. Where the damage is and what it looks like give clues, but don't replace an inspection.
Sellador Total L44
Sealing primer: it evens out the absorption of the substrate and seals the wall before painting.750 ml, 4 L and 15 L · 9–10 m²/L per coat
How adhesion is assessed technically
There are standard methods, such as ASTM D3359, that qualitatively assess the adhesion of coatings using tape and cuts under defined conditions. This test doesn't diagnose the cause of damp and can't simply be applied to any job: the standard itself warns about its limitations and about the differences between adhesion failures between coats.
Preparation you shouldn't skip
Before painting, find and fix any water getting in, remove loose film and weak material, clean off salts and check that the surface is dry and cohesive. A suitable primer can help regulate absorption and improve adhesion, but it doesn't replace making the substrate sound. Waiting times between coats and environmental conditions must also be respected.
Solutions by surface
Sellador Total L44 is a clear, water-based polysiloxane sealer designed for use before painting new, absorbent or weak surfaces; its documentation states that it regulates absorption and improves adhesion of the finish. As a primer it's diluted 1:1 with water; as a sealer it's applied neat. It isn't an anti-mould or biocidal treatment: if there's already mould, it has to be removed first and the cause of the damp corrected. Nor is it designed to fix active damp.
Conclusion
A new coat will only be as reliable as the surface beneath it. The aim is to remove the cause of the deterioration first and restore proper conditions for adhesion and drying.
Technical and scientific sources
- ASTM D3359-23, Standard Test Methods for Rating Adhesion by Tape Test
- Whole Building Design Guide, Moisture Management
- Historic England, Masonry Buildings (2025)
Guía escrita y revisada por el Equipo Humix Paint con los datos de las fichas técnicas de cada producto. La pintura actúa en la superficie: si el agua sube del suelo o entra de fuera, primero se trata la causa.
