Exterior Paint for Surfaces
When is deciding what exterior paint to use, you need to determine the existing surface. Here in the UK most of our buildings are built with solid brick and then rendered.
In the US most houses are built from timber with timber cladding.
Like all decorating, preparation is everything.
But first I will go through the types of paint available for render.
Exterior paint for render
- Standard masonry paint
- Silicate paints
Masonry paint is the most common type of exterior paint you’ll find on rendered surfaces.
This is the most common type of exterior paint for render you will find in the UK.
If your surface has already been painted then this would be the best option for you.
Masonry paints contain a high level of vinyl to protect the rendered surface from water. This sounds ideal, but can cause problems with flaking.
These paints are ideal for newly rendered surfaces.
They allow the render to breathe and therefore prevents flaking of the surface and retains the colour for much longer.
Limewash paints are used primarily for specialist lime rendered surfaces for buildings of a certain age. They act very much like the silicate paints and allow the render to breathe.
The surface must be dampened first before applying the limewash. Limewash is applied very thinly with multiple coats and applied with a brush
Exterior paint for timber
- Oil based undercoat and gloss
- Water Based undercoat and gloss
- Self priming finishes
Oil based undercoat and gloss
Oil based undercoat and gloss has been the traditional method of painting exterior timber for many years.
This process has stood the test of time and it’s still the process I use when painting timber sashes externally.
It will withstand the weather very well and paints like Dulux Weathershield are very good.
Water-based undercoat and gloss
These type of paints are becoming much more popular to use on the exterior of your property.
They dry quickly and work well against the elements.
It is still hard to see how they beat oil based undercoat and gloss but I have used them on the exterior and they are good.
Due to health and safety reasons water-based paints are being used more and more.
Self priming paints
Self priming paints are exactly that, they self prime.
Paints like Zinsser Allcoat are a typical self-priming paint. Basically you do not need a primer on bare timber.
Simply paint on two or three coats and you’re done whether it is gloss or eggshell finish it doesn’t matter.
I use these paints on timber cladding, soffits and fascias mostly. They are quick drying, fast to use and a separate primer is not required.
Surface preparation for exterior painting (rendered)
If your surface is rendered you’re a few things to look out for.
If it has been previously painted then it could well flake. This is caused by moisture getting beneath the paint and exiting through the paint film.
Efflorescence is another thing to watch out for on newly rendered walls. Cement based render is very alkaline.
Efflorescence is a type of alkaline salt which appears in render when it is either cold or damp. This has to be removed first.
The best way to remove efflorescence is to simply brush it off. Do not use water as this will help the salt be absorbed back into the render.
You can treat efflorescence by using Alkali Resisting Primer if particularly bad. Sometimes efflorescence will appear on broken down paint surfaces as well.
Make sure all flaking paint is removed. If the flaking paint is particularly bad this may have to be burnt off by using an electric heat gun.
Make sure all cracks are also opened up further. Use some form of a scraping tool or knife to widen the crack.
Widening the crack is important to allow the filler to take hold and provide a stable surface for exterior paint.
Priming with exterior paint for render
If you have new render, or exposed render on previously painted surfaces, these need to be primed with a watered down version of your masonry paint.
This watered down masonry paint will allow the render to absorb the paint.
You need to make sure this is done prior to applying any filler in order to seal it
Do you need stabiliser?
Do not use stabilizer for new render. Using stabiliser for new render is a common mistake people regularly make
Stabiliser should only be used if the surface Is dry and powdery, basically unstable, hence the name.
Stabilizer is commonly used when the paint surface has broken down and the render is dry and powdery. That’s the only time to use it.
People who work in the building trade, a bloke down the pub, it doesn’t matter they will tell you that all new render should be stabilised. That’s nonsense, only if the surface is unstable should it be used.
I prefer to use a cement based filler like Toupret Touprelith cement based filler. This can cause some issues with trying to cover it, as it does dry to a dark grey colour.
There are some external fillers which dry to a white finish. I had a tendency to stay away from ready mixed fillers as they can be expensive and dry far too hard.
Use the filler to repair holes and cracks and sometimes to ‘feather off’ large areas of flaking paint.
‘Feathering off’ is a process of losing hard edges of existing painted surfaces with the filler, in order to take your eyes away from the uneven surface.
You use the filler in a wide application to lessen the uneven surface.
Use a large 6 inch filling knife or plasterers trowel to achieve a wide surface and even out the uneven surface.
Timber preparation for exterior paint
When using undercoat and gloss all bare areas of timber should be primed first.
Make sure all flaking paint is removed and sanded down to a firm edge.
If you have any rot you must write this out and remove it and treat with wood hardener. Wood hardener firms up the area around where the rot has been and makes it solid.
If rot has removed part of the sash or large holes in the actual cill you can use epoxy resin, such as Timbabuild or Repair Care to make these areas good. This process is expensive to purchase but is the best solution to replacing rotten timber.
For small areas of repair you can use 2-pack wood filler. Do not use this for large holes as it can have a tendancy to split and come out as a timber expands and contracts.
Use epoxy resin instead.
If any putty around the window glass has become loose, simply use linseed oil putty to replace them will do the trick.
For areas of timber where they meet the render, you will see that these areas of timber have come away from the render.
Internally these areas would be treated with caulk and a caulking gun.
Do not use caulk externally. Instead use external paintable frame sealant and a caulking gun to apply.
Make sure you apply the correct preparation process for each of these systems. That way your exterior paint surfaces will last for many years.