You buy good quality trade masonry paint to spruce up that garden wall. You sheet up, sand off, blow the cobwebs off your brushes and away you go. Only to notice big brown horrible looking stains coming through the paint!! This is not a good look for your garden!! Shock horror, but what did you do wrong? In this blog, I’m going to talk about how you stop stains on a painted garden wall.
Why do we See Stains and How do we Stop Them?
Let’s have a look at what is causing the issue. A garden wall rarely has a damp membrane, meaning it contains a certain amount of water. That is a problem when painting for a couple of reasons; firstly, as you’ve experienced, you get nasty stains coming through your new paint. The other issue is eventually that water is going to build up behind the paint and cause it to lift. In fact, if you phone Dulux Tech Support, they’ll tell you not to paint a garden wall at all! For me, get it painted to your taste, but expect to have to re-do it every couple of years.
Let’s deal with those stains to stop them coming through! The issue happens because you’re using water-based masonry paint. The water stain can simply bleed through. To stop water, you need oil!!
There are a couple of different techniques you can use. Presumably at this point you have already applied a coat of paint to your wall. You could simply block out the stains using oil-based undercoat, touch up with your water-based masonry paint, then apply a full coat of masonry to the whole wall. You can use other products such as Zinsser Cover Stain.
Or, and a better option, why not use oil-based masonry paint? It’ll block the stains and will look fresh for a good couple of years. Get a good trade paint (sometimes called pliolite based masonry), and dilute it slightly with white spirit. The advantage of using an oil-based coating over the whole wall is that the water stains will not manifest somewhere else. The paint will still fail over time, there’s no stopping it.
Eventually the moisture underneath will build up and the paint will flake. You’ll probably get a couple of winters out of it before you need to paint your wall again.
Just try not to get too much pliolite on your skin because it can be hard work to remove.
It’s worth mentioning, if this is the first time you’re painting said garden wall, lime or mineral paint is the way to go. It won’t stain and allows water to pass through, so your finished wall will remain looking new for yonks. However, lime or mineral based masonry paint will not help if your wall is previously painted.
There is plenty of other information available on the Decorators Forum UK
Best Paint to Use on a Garden Wall
I just wanted to end by giving you my recommendation on the best paint to use. As mentioned earlier in the blog, oil-based or pliolite-based masonry paint is the way forward. There is a brand of pliolite-based masonry paint that blocks stains but remains breathable, which will help with longevity of finish. My paint of choice is the Wethertex PP77. You can buy it online at Rawlins Paints.
Summary
Stains on a garden wall are a real pain, and there’s no ideal answer. Breathable paint like Emperor Masonry will last for years on a garden wall, but it won’t block stains. Oil-based masonry paint will block stains but won’t last more than a couple of years.
I suppose the best thing to do in theory is have a damp membrane added to the wall, but this is a lot of work and can be costly. That’s why I think painting every couple of years with an oil-based product is the way forward.
Cleaning Algae on a Garden Wall
I thought I’d include a section on cleaning algae on a garden wall, just because algae can cause stains too.
Algae isn’t always green, sometimes it’s a reddish brown (it looks a bit like rust). A lot of people make the mistake of pressure washing the wall. This does clean it, but the algae soon comes back.
The best way to clean algae is to use a fungicidal wash. All you need to do is apply it to the wall and then leave it for 24 hours. It’s like magic! The algae just disappears overnight.
Some of the fungicide stays on the wall for a period too. So, not only is the existing algae eradicated, but your garden wall will stay clean for longer.
Make sure you go for a trade brand. There are loads of cheap fungicidal products on the market, but they don’t work very well. My favourite is Dulux Trade Weathershield.
FAQs
What are the brown stains on my exterior walls?
There are a handful of reasons that you may be getting brown stains on a garden wall. The most common cause is water bleeding through the paint. It may also be algae or even a rusty nail in the wall.
How to clean painted garden walls?
You can clean painted garden walls with a fungicidal wash. All you do is dilute it with water, apply it to the wall, then leave it for at least 24 hours. Pressure washing does work on garden walls, but if you’re having trouble with algae, then fungicidal wash is a much better solution.
What is the best filler for garden walls?
You need a filler that is hard and doesn’t hold onto water. I recommend Toupret Rock Solid Repair Filler. You’ll find it easy to use and because it’s cement-based, it’ll last, which is the most important thing.
What paint blocks stains on a garden wall?
Any oil-based paint will block stains coming through a garden wall. Some people use oil-based undercoat on stains and then apply water-based masonry paint over the top. However, it’s much easier to use a pliolite masonry paint.
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