P = A T P A − ( A T P B ) ( R + B T P B ) − 1 ( B T P A ) + Q . {\displaystyle P=A

Dry and chalky areas can sometimes be primed with a watered down coat. But if the area has already been treated with a stabilising solution I would paint over this with unthinned masonry paint. With newly rendered surfaces, it is normal to have a certain level of dust and/or powder on the surface as a result of the drying-out process. 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.Just bear in mind that the stabilising solution will impair the breathability of the finishing coats so only apply to areas where it’s really necessary.

This usually ensures that the walls have had sufficient time to dry-out in depth and that any loose material is washed away naturally when it rains. You may find that this process removes a lot of the loose particles on the surface, presenting you with a solid surface which can easily be primed with a thineed solution of masonry paint. This moisture may force itself out eventually and cause the paintwork to bubble and/or subsequently flake-off.Regular masonry paint is formulated to allow small levels of moisture to escape through evaporation. It’s important, therefore, to avoid the use of sealers or primers unless absolutely necessary. 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. A subject that crops up a lot on the topic of exterior wall paint is ‘Stabilising Solution’ or ‘Primer’. 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. Below is a sample of questions received on the subject of stabilising primers… White dust on stonework?

I am about to re-paint some stonework outside my house. It has previously been painted, but in areas it is a little flaky and kind of like white dust build up, think it’s salt or something like that. 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.

ORIGINAL RESEARCH article

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. 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? Eventually I repainted with a water based masonry paint. Every year since then the paint has bubbled and I have had to scrape and repaint.