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.
Ann – Hi I have just had an internal brick wall built as a feature wall and would really like some advice on what to treat it with now , do I use stabiliser and a sealer on it , any help would be appreciated. READ MORE…
Assuming you want to keep the finish as authentic as possible I would recommend a clear sealer such as Zinsser Gardz via amazon.co.uk which dries clear and binds any loose material to the surface.
This is a water-based product so dries quickly and is easy to use. Some alternatives are solvent based and apart from being less pleasant to apply can trap moisture below the surface of the wall which can cause problems later on.
A very cheap alternative to the above is a solution of PVA adhesive (available from any DIY store) and water.
Mary – I have a newly rendered garden wall that we were advised to use stabilising primer before painting with masonry paint. We were told we could do this within a few days of the rendering being completed, but I understand from your site this is not advisable. Everyone seems to offer different advice and I have put a lot of work into the wall so don’t want to spoil it all by following the wrong advice. The render is over thermablocks, incase that affects things. READ MORE…
You say you ‘understand from your site that it’s not advisable’ so what else do you want to know?
RD – I have a small passageway at the side of the house that was built about 30 years ago of wood but in the last 10 years slowly deteriorated until it collapsed in 2018. Last year I had a local builder replace it with a brick structure but the outer wall is non cavity and through the winter we noticed some mould on the interior render. The builder has since sealed the outside but has advised using stabiliser on the render on the inside before painting to prevent anything coming through. I’ve read a lot of bad things about stabiliser so good idea or not? READ MORE…
Very bad idea. Your builder is advising on matters he doesn’t understand, this usually causes problems that only become apparent long after he has been paid and disappeared off into the sunset.
David – I want to paint some of the exposed brickwork outside the house. Some of the bricks are weathered and flaky. Others have a white chalk/salt like colour to them. Should I use a stabiliser first? I also live but the coast and it’s exposed to bad weather. READ MORE…
Both problems are indicative of moisture penetration.
The weathered and flaky appearance is a result of spalling caused by trapped moisture freezing, expanding and forcing away the surface of the brick. The white, salty residue is where minerals within the brickwork have become diluted and worked there way to the surface.
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. However, if the surface of the brickwork has become damaged than this in itself will result in abnormal moisture penetration and painting with a breathable coating may mitigate this?
There is, of course, the matter of simple aesthetics and painting is often the easiest solution.
Any white powdery residue should be removed with a dry brush as far as possible. Avoid using water since this will simply dilute the residue and result in it being absorbed back below the surface.
When you have removed as much loose material as possible, treat the worst affected areas with a stabilising solution which will bind any reaming loose martial, presenting you with a solid surface on which to paint. Only do this on the very worst affected areas though.
Overall, you can prime the brickwork with a diluted solution of water based masonry paint, thin enough to soak below the surface but not so thin that it just becomes coloured water.
You should then be able to paint the wall as normal with 2 regular coats of masonry paint but keep an eye out for any signs of bubbling in the weeks after. This would indicate a high density of moisture content that is trying to force its way out.
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.
If the bubbling is persistent then it may be indicative of a problem elsewhere, such as a defective damp course, in which case you will need to investigate further. In most case though, it is just old brickwork which has become gradually more porous over the years.
PJ – Hi there I am going to paint the exterior of my house but was wondering should I use a sealer/stabiliser before I paint ?the house is around 7 years old and has never been painted. I have sprayed all walls with all in one green algae remover & left it for about 3 days & then power washed it all off so the render is good. What do you think? READ MORE…
It sounds like you have the ideal surface on which to paint. I would use a regular masonry paint – the best quality you can afford. You don’t suggest there are any problems so no need for anything specialised.
Thin the fist coat so that it soaks into the surface but not so thin that is spatters everywhere. It depends on the quality of the paint how much water you should add but start with a small area first so you judge it.
Finish with one or two full coats although you may need to still thin these a little for ease of use but don’t over do it.