Wall Coatings And Heat Loss: What They Really Do For A Warmer Home

The Honest Answer First

The old title of this article talked about wall coatings and thermal insulation in the same breath. We would rather be plain about it. An exterior wall coating is a thin protective finish. It is not a layer of insulation, and it will not do the job that loft insulation, cavity wall insulation or an insulated render system does.

So why do people who have their walls coated so often say the house feels warmer? Because of water. Scottish walls spend a lot of the year wet, and wet walls are cold walls. Keep the rain out and the wall can do its job properly again.

That is a real benefit, and an honest one. The rest of this guide explains how it works, and where the limits are.

Why A Wet Wall Loses More Heat

Think about a woolly jumper. Dry, it keeps you warm, because it is full of tiny pockets of still air, and still air is a poor carrier of heat. Get that jumper soaked and it is useless. The water fills the air pockets, and water carries heat away far more quickly than air does.

Brick, stone, render and roughcast behave in the same way. They are full of tiny pores. When driving rain soaks into them, the pores fill with water and heat from your rooms passes through the wall more easily. On top of that, as the wall dries in the wind, the evaporating water cools it further, in the same way you feel cold stepping out of a shower.

In the west of Scotland in particular, a weather-facing gable can stay damp for months over winter. That wall is working against your heating the whole time.

How A Wall Coating Keeps Walls Dry

The wall coatings we apply, such as ProPerla, are hydrophobic, which simply means they repel water. Rain forms beads on the surface and runs off, where on bare render or ordinary masonry paint it would soak in.

Just as important, the coating is breathable. Every house produces moisture inside, from cooking, showers and breathing, and some of it passes out through the walls as vapour. A breathable coating lets that vapour escape while stopping liquid rain getting in. Compare that with a cheap masonry paint, which can form a sealed skin, trap moisture behind it and then blister and flake.

So the wall gets a chance to dry out and then stay dry. It is worth knowing that a wall which has been wet for years does not dry overnight. It can take months for the moisture already in the masonry to work its way out.

What You May Notice Afterwards

Every house is different, so we will not put a number on it. These are the kinds of changes a dry wall can bring:

• Rooms on the weather side of the house feel less chilly, and the inside face of the outer wall is less cold to the touch.
• Less condensation and fewer patches of black mould in the corners of outside walls, because a warmer wall surface attracts less condensation.
• That cold, damp smell in a rarely used front room fades.
• Less frost damage. Water that soaks into render freezes, expands and breaks the surface apart. A dry wall does not suffer this.
• The outside stays cleaner, because dirt, algae and green growth struggle to grip a water-repellent surface.

Those last two are about protecting the building as much as warmth. For many customers, they are the main reason for having the work done.

What A Wall Coating Will Not Do

This is the section that matters most if you are trying to cut your heating bills.

• It will not insulate an uninsulated wall. If your cavity walls are empty, or your solid stone walls have no insulation, a coating does not change that.
• It will not fix rising damp, a leaking gutter, a cracked downpipe or a failed seal round a window. Those need repairing at the source first.
• It will not stop condensation caused by poor ventilation. If the moisture is being made inside and cannot get out, you need better extraction and airflow.
• It is not a substitute for loft insulation or decent windows. Heat leaves a house by many routes, and walls are only one of them.

Be wary of any company that promises you a set percentage off your heating bill from a coating alone. Nobody can promise that without knowing your house, and we do not.

Signs Your Walls Are Soaking Up Rain

Take a walk round the house a day or two after heavy rain and look for these.

• Dark, patchy areas of render or roughcast that stay dark long after the rest has dried.
• Green algae or moss on the walls, most often on north-facing and shaded sides.
• Hairline cracks, or render that sounds hollow when tapped. Hollow render has come away from the wall behind it, and water collects in the gap.
• Flaking or bubbling paint.
• Worn or missing pointing (the mortar between bricks or stones).
• Inside, damp patches or peeling wallpaper on outside walls, worst after wind-driven rain.

If rendering has failed badly, coating over it is not the answer. It may need roughcast or render repairs first, and we will tell you so at the survey.

Why Preparation Decides The Result

A coating can only keep water out if the wall underneath is sound. So most of the work happens before any coating goes on. We power-wash the walls, treat any growth, repair cracks, replace loose or hollow render and re-point where needed. Windows, doors and paths are masked, and then the primer and coating are applied.

It suits most wall types: pebbledash, roughcast, smooth and textured render, brick and stone. You can pick any colour from the RAL range (the standard colour chart used across the building trade), so the house gets a fresh look at the same time.

Most homes take 2 to 5 working days, depending on size and weather. The work is carried out by trusted installers and all workmanship is guaranteed.

Getting The Most Warmth: Coating Plus Real Insulation

If a warmer home is the goal, think of a wall coating as one part of the plan. The usual order of value is:

1. Top up the loft insulation. It is normally the cheapest way to save heat.
2. Deal with draughts and tired glazing. Modern windows and doors make a clear difference to comfort.
3. Check whether your walls can be insulated, and if they already have cavity insulation, make sure it stays dry. Insulation that gets wet stops working, which is one more reason to keep rain out of the outer wall.
4. Look at the heating system itself.

For impartial advice on insulating your home, Home Energy Scotland is a free advice service funded by the Scottish Government, and a good place to start.

A wall coating fits alongside all of this. It protects the walls, keeps them dry so they hold heat as well as they are able to, and makes the house look cared for.

Cost And Next Steps

Most full-house coatings we carry out land between £3,500 and £8,500, including scaffolding, power-washing, repairs, primer and coating. Large detached homes cost more. The size of the house, the height, how much repair the walls need and the access for scaffolding are what move the price.

A wall coating is available from £22 a week, subject to status. See our finance page for how that works.

We coat homes across Scotland, including Glasgow, Edinburgh and Kilmarnock. The survey is free, and you will get a straight answer on whether a coating is right for your walls.

Quick Answers

Is a wall coating the same as insulation?

No. It is a protective, water-repellent finish. It helps by keeping walls dry, and a dry wall loses less heat than a wet one, but it does not replace insulation.

Will a wall coating lower my heating bills?

It can help if your walls are currently soaking up rain, but how much depends on the house. We do not quote a saving, and you should be wary of anyone who does.

Does a wall coating stop damp?

It stops rain soaking in through the walls, known as penetrating damp. It will not cure rising damp, leaks or condensation from poor ventilation.

Can walls still breathe with a coating on?

Yes. The coatings we use are breathable, so moisture vapour from inside the house can pass out while rain is kept from getting in.

How long does it take to coat a house?

Most homes take 2 to 5 working days, depending on size, repairs needed and the weather.

What types of wall can be coated?

Pebbledash, roughcast, smooth and textured render, brick and stone, as long as the surface is sound or is repaired first.