As a professional decorator, most of what I do could be described as “cosmetic.” Yes, there are some functional or practical benefits, but mostly it’s about making things look better (and if you decide you don’t like the paint or wallpaper, it’s easy enough to change it). However, this isn’t true for exterior painting in general.
In this blog, I’m going to explain everything there is to know about how to seal and waterproof an exterior wall. I’ll take you through the benefits, the tools you need, my recommended product, and the steps you should take to carry out the process.
There’s a video towards the end, just in case you prefer to be shown rather than read the guidance.
I’m going to add a warning here. The word “sealing” might be a bit misleading. The last thing you want to do is trap moisture in your walls, as it may lead to big problems further down the line. The name of the game is to protect your walls while allowing them to breathe. I’ll go into more details as we go on.
Why You Should Waterproof External Walls
There are several benefits to waterproofing exterior walls. You may be looking into it because you’re having issues inside your home, or it might purely be a preventative measure. Either way, I’ve listed the reasons below.
- It can help prevent or stop damp – you’re essentially keeping your exterior walls drier, which means there’s less chance of moisture penetrating to the inside.
- Improves the energy efficiency of your home – believe it or not, waterproofing your exterior walls with the right product will help them retain heat, so your energy bills will come down.
- Improves aesthetics – I know most exterior sealers are invisible, but they still help prevent your walls from holding onto dirt. They also help reduce algae and lichen growth.
- Prevents frost damage – with less moisture in your walls, there’s less chance of frost damage.
- Slows erosion – your walls will last longer.
Tools and Materials You Will Need to Waterproof an Exterior Wall
- Possibly a small amount of mortar and pointing trowel
- Dust sheets, masking tape and clear plastic film to cover doors, windows, etc
- Scissors
- Pressure washer or stiff brush
- Fungicidal wash
- PPE (gloves, eye protection)
- Emperor Masonry Creme
- Masonry brush, roller and pole
- Roller tray or skuttle, paint kettle
- Ladder or other safe access equipment
How to Waterproof an External Wall
Assess
Check over your wall to assess its condition. This will help you determine which of the following steps (2–4) are actually needed in your situation.
Clean the wall thoroughly
(Either with a jet wash or a stiff brush) – dirt, grime, and pollution will not help the absorption of the product into the substrate. If using a jet wash, keep it on low pressure to avoid damaging the wall.
Treat any biological growth such as lichen, moss, or algae
Emperor’s Masonry Cleaner is great for this – simply apply the product to affected areas using a brush or pump sprayer, allow it to dry for 2–3 hours, and then rinse off.
Repair any gaps in the mortar
Missing pointing will allow water to get into your wall, regardless of what you treat the rest of the surface with, so “plug those gaps” before you begin.
Wait
Allow the wall to dry out, and if you have repaired any mortar, allow it to fully cure before continuing to the next step.
Protect areas that you don’t want to get the product on to
Put dust sheets on the ground, and use masking tape and plastic film (“tape and drape”) to cover any doors and windows.
Prepare your product
I’ll go into “why” further on in the blog, but you should be using Emperor Masonry Creme for this type of work. Stir the masonry creme well to ensure an even consistency, then pour some into a paint kettle (you’ll find it much easier going up and down steps with a brush and small kettle rather than a big 10L tub of masonry cream!).
Cut in
Brush the creme around the edges of the wall, working it into the surface with your brush (a stiff brush will make this easier).
Roll
Pour some masonry creme into a roller tray or scuttle and apply it to the rest of the wall using a long-pile roller. Work both up and down and side to side, as this helps to work the product into every nook and cranny. A long-pile (“nap”) roller sleeve will also help with this – I’ll go into my product choice later.
Check for any small areas you may have missed
While the product is still wet, it’s creamy in colour, so easier to see; once it’s dry, it’ll be impossible to tell if you’ve missed a patch. You only need to apply one coat, as long as it’s a generous one and you make sure the surface is thoroughly coated.
Allow it to cure
It should be touch-dry and pretty much invisible after 2–3 hours, depending on the temperature. Then sit back and know that your walls are protected for years to come — it really is that simple!
Recommended Products
Emperor Masonry Creme
This is the key to success. Some sealers sit on top of the wall and create a barrier between the surface and the outside. Others claim to be “breathable” but don’t publish an SD value, so you don’t actually know how breathable they are. You should avoid both of these types of products.
Trapping moisture in your walls can cause major issues inside. Emperor Masonry Creme soaks into the wall, chemically bonds with it, and is super-hydrophobic (which means it repels water) — but it doesn’t trap moisture.
Water droplets are repelled, so the walls stay dry, but water vapour can still pass through. This means any moisture within the wall will dry out naturally through evaporation.
The SD Value of Emperor Masonry Crème is 0.01 (anything below 0.1 is classed as “breathable”).
Purdy Colossus Roller
Any long-pile roller will do, really. I’m mentioning the Purdy Colossus because masonry creme is quite thick, and the Colossus just handles it better than most. You’ll find it slightly easier to work the product.
Go for the 9-inch roller — you’ll find it easier to work the masonry cream into all the nooks and crannies.
Axus Static 31
This is the film I use to protect doors and windows. Again, any tape-and-drape type product will do, but Static 31 is just a bit easier. Static electricity holds it in place long enough to tack it down with masking tape. This is a godsend when you’re working outside in even the slightest breeze or when working at height.
A Video Demo
Protecting a brick wall against the weather
Decorator Mike Cupit shows how to seal an exterior wall to make it waterproof.
FAQs
How do I stop water from coming through my external walls?
There are a few reasons water might be penetrating an exterior wall. It could be that the cavity wall has been bridged, or the pointing needs to be replaced. Applying a hydrophobic waterproofer like Emperor Masonry Crème is a big help, but you need to diagnose the problem first.
How do I waterproof an exterior painted wall?
If your exterior wall is already painted, then the best thing to do is paint it again with a hydrophobic paint like Emperor Masonry Paint. This will repel water and keep your wall much drier.
Do external walls need waterproofing?
Exterior walls don’t necessarily need waterproofing unless you’re experiencing issues caused by moisture. However, there are several other benefits to waterproofing exterior walls.
What is the cheapest way to waterproof a wall?
My advice would be to apply a coat of Emperor Masonry Crème. There are much cheaper products on the market, but if you trap water then you will cause issues.
What is the difference between a water sealer and a waterproofer?
A water sealer acts as a barrier coat between a surface and the outside world. A waterproofer bonds to a surface and repels water.
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