The white dust is probably efflorescence – moisture in the stonework will draw out any salts and, provided this isn’t excessive, is perfectly normal.

One coat should normally be sufficient but very porous surfaces may require additional coats. Drying time will vary depending on the ambient temperature, but normally 4 – 8 hours should be allowed for each coat to fully dry. For the best results allow surfaces to cure for a minimum of 24 hours before applying the Weatherflex Smooth Masonry Paint. DO NOT apply when air or surface temperatures are below 8 °C.

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Tools and equipment should be cleaned with warm soap and water immediately after use. Pump sprayers especially should be thoroughly flushed through with warm soapy water and then flushed with clean water until free of all residues. DO NOT allow to dry before cleaning.

Using a stabiliser where not absolutely necessary can impede the performance of any subsequent coats because it isn’t ‘breathable’ and may keep any natural moisture trapped beneath the wall’s surface. Normally, masonry walls can be primed with a thinned solution of water-based masonry paint. But, sometimes, the surface can be loose and/or powdery and this can cause problems. Would you ever used a watered down first coat on areas of render that are dry and chalky so have been treated with stabilising solution? Below is a sample of questions received on the subject of stabilising primers… White dust on stonework?

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I would not normally advise painting since this is going to present yet another barrier to any trapped moisture evaporating away naturally without causing further damage. Remove as much as the dust as you can with a dry brush and scraper and see how it looks. If the surface is fairly solid try priming it with a thinned coat of masonry paint. If that goes OK proceed with over-painting. If it’s still loose you may have to seal the areas affected with a stabilising solution – but only as a last resort. If this be the case then scrape off any loos paint, allow to dry out over a period of a few weeks and paint again. You may well find this is an ongoing process or it may be isolated to one or two problem areas.

Furthermore, the stabilising solution and PVA will both act to keep any moisture within the concrete, hence why you experiencing problems. The moisture will force its way out eventually. I am planning to go over the loose areas with a wire brush and paint scraper. Would you say that it would be best to go over the areas that have the white dust build up with a stabilising solution, as the old paint is very flaky in these areas?Kingfisher “Weatherflex Stabilising Solution” is available in 5 litre plastic containers. It should be stored in a cool, dry area, AVOID frost and direct sunlight. Shelf life of the product in, unopened sealed containers is 12 months. This moisture may force itself out eventually and cause the paintwork to bubble and/or subsequently flake-off.