Paint defects – Identification, cause and solution – Exteriors

Rust staining

Cause: Rust from imbedded iron works, nails etc.

Solution: Clean the substrate thoroughly and let it dry. If feasible, remove or grind back the source of rust. Use a suitable primer to block the staining from coming back through and reapply top coat.

Moisture ingress

Possible Causes: Either, issues with roof line, absence or breach of damp proof course (DPC), cracks in surface or broken pipes

Solution: Identify entrance point for the moisture and repair accordingly


Cause: High moisture content forcing the coating away from the wall. Typically as a result of excessively high moisture levels within the substrate, often combined with poor adhesion of the coating to the surface. High moisture levels may be a result of water ingress through building defects or application to a damp surface.

Solution: Identify the source of the high moisture content and remedy. Then remove the affected area of coating and allow substrate to dry. Rectify any causes of poor adhesion, such as weak, old paints, friable render etc and reapply coating.


Cause: Efflorescence is the result of salts contained in the structure being carried to the surface by moisture. This is typically caused persistent penetrating damp or water from construction.

Solution: Decorating should be left until any building defects have been repaired and salts have stopped coming through the wall. A water based coating with high vapour permeability is best. A clear silicone based treatment could be used on bare brickwork or stone if the original appearance needs to be preserved.

Chalking and fading

Cause: UV light breaking down paint resin prematurely.

Solution: Clean down the substrate and reapply with necessary primer and top coat. All Andura exterior coatings use high quality resins and light-fast pigments to ensure they do not chalk or fade over time.

Peeling and flaking

Cause: Coating failed to gain initial adhesion due to issues with the surface.

Solution: Prepare surface properly by ensuring the following: Substrate is clean, dry, free of dust, has no failing paint already on it and any recently repaired surfaces are sound. Apply an appropriate primer if necessary.

Mould and algae growth

Cause: Organic growth is typically caused by poor preparation of the substrate prior to coating or use of a cheap paint that is not adequately protected with biocides. Persistent dampness resulting from building defects may exacerbate the problem.

Solution: Prior to coating the substrate should be thoroughly cleaned and shall have a biocide wash applied. Repairs to any building defects causing dampness should also be made. E.G faulty rainwater goods or failed DPC’s.


Cause: Usually found when spray applying paint to pebble dash or roughcast with deep depressions. The Paint film traps air pockets in the depressions and when it dries and shrinks back the pinholes appear and let out the air.

Solution: Thin down the coat of paint you are using. Note, you may need to use a brush in some areas so that you can force the paint into the deeper crevices.

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