OTHER SUBSTRATES TROUBLESHOOTING PAINT PROBLEMS RELATED OTHER SUBSTRATES JUNE 2010
1. CRACKING (PART 1)
Description Cracking caused by stress throughout and between the film and substrate. The underlying window putty in this example has shrunk, causing stress cracking in the enamel topcoat by compression.
Possible diagnosis A less flexible topcoat such as enamel has been applied over a more flexible substrate such as bitumen or linseed window putty that is still in the process of drying.
Water-based paints applied directly to linseed oil putty may fail to adhere.
Thick coatings subject to extreme temperature changes which result in expansion and contraction.
Remedy Remove cracking top coat and recoat with a compatible system.
Allow linseed window putty to harden over several weeks. Consult manufacturers instructions.
Recoat with solvent based alkyd enamel NEO Dur High Gloss (SABS Grade 2).
2. CRACKING (PART 2)
Description Cracking caused by stress throughout and between the film and substrate. The underlying black bituminous coating and alkyd enamel topcoat in this example have expanded differently, causing the stress cracking in the enamel topcoat.
Possible diagnosis A less flexible topcoat such as enamel not compatible with a more flexible substrate like bitumen.
Remedy Remove cracking top coat and recoat with a compatible system such as NEO Gloss Acrylic.
3. PAINT FLAKING FROM FIBRECEMENT BUILDING PRODUCTS
Description Flaking top coat with friable, powdery fibre cement underneath.
The top coat consists of enamel paint.
Possible diagnosis Omission to remove dust and dirt from new or well weathered fibrecement boards.
Omission to remove mould, moss or lichen from weathered boards.
Omission to use an alkali-resistant water-based primer such as NEO Acrylic Wall Primer.
Over coating a water-based primer with an alkyd enamel.
Remedy Remove all loose and flaking paint.
The surface may be damp but not wet.
Apply a solvent-based alkali-resistant primer.
Note: Pure acrylic emulsion paints such as NEO Dur (SABS Grade1), NEO Multi Dur (SABS Grade 2) or NEO Roof Paint are best for fibre cement building materials.