The soaps use in the concrete process tend to 'leach' through coatings and hence the reason for a good quality product which also has high alkaline resistance. Prior to the start of painting the GRC, we strongly recommend that a test area be set up to trial the sealing of Alkaline staining and the integrity of the primer for adhesion to the substrate.
The use of Dulux Trade Alkali Resisting Primer (thinned up to 1 part White spirit to 20 parts of product as appropriate) is critical as the quality of the Oleoresin Binder used gives it a unique advantage over other Linseed Oil based products. The thinning of the product is minimal but it does aid adhesion and enables the film to be finer than normal.