Another subject that crops up a lot on the subject of exterior wall paint is ‘Stabilising Solution’ or ‘Primer’.
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.
In severe cases, it may be necessary to use a stabilising solution in order to bind the surface together and present a stable paintable surface.
However, in most cases, any loose material can be simply brushed off before painting.
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.
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.
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.
In such cases, I always recommend that the wall is left exposed to weather for at least 12 months prior to painting.
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.
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.
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?
I plan to use Macpherson powerkote, hopefully three coats to give it a strong finish. Do you think the powerkote will be suitable to use?
The white dust is probably efflorescence – moisture in the stonework will draw out any salts and, provided this isn’t excessive, is perfectly normal.
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.
Powerkote is OK and 3 coats should do the job perfectly well.
Cement render with a dusting of grit
I am painting an external sand cement rendered finished solid brick wall to my house. The render when you rub it creates a minor dusting of grit.
However, once it’s rubbed the surface below is relatively solid. I am worried that if I paint the surface with sandtex it could bubble if I don’t stabilise.
Would you recommend the use of sandtex stabilising solution as a primer to prevent the paint failure??
If the surface is loose, as you describe, it will possibly need stabilising?
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.
However, if the surface is fairly new it can be advantageous to leave it for 12 months in order to ‘weather’.
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.
Recurring problems with paint bubbling?
Three years ago a blocked gutter soaked the concrete bay of my Victorian semi. I scraped most of the paint off and left it to dry out.
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.
I have tried stabilising solution and PVA but the problem keeps recurring. Any suggestions to prevent this happening would be helpful.
It’s possible the affected areas had not fully dried out before you repainted?
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.
Scrape off as much as you can and let it dry-out naturally, which could take a long time, before attempting to redecorate.
Painting over previously stabilised areas?
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?
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.
Flaking paint on brickwork?
I have brickwork that has previously been painted with masonry paint, but it’s flaked off in several areas and I’m just wondering whether
I need to use a stabilising solution before applying any further masonry paint?
You’ll need to remove any loose paintwork completely and prime any bare brick-work with a thinned coat of masonry paint in order to provide a key.
It’s likely that when the brickwork was first painted they used a paint direct from the tin and it hasn’t adhered properly. It could also be high levels of trapped moisture?
Stabilising solution should only be used in area where the surface to be painted is loose and powdery.