Old houses have lots of quirky charm. Lime plaster walls, traditional finishes, and thick stonework combine to create a home that modern construction would never achieve. Maintaining the integrity and health of old houses means you need to understand the need to use breathable building materials, including interior and exterior paint.
In this guide, we’ll help you Understand why breathable paint for old houses is a vital requirement when you renovate or decorate a period home.
Pictured: This old house has been finished in Graphenstone Ambient Pro Exterior Paint. This is a lime based breathable emulsion suitable for interior and exterior use, this colour is Clotted Cream. See the Graphenstone Colour Chart for more shades.
What Does ‘Breathable’ Paint Actually Mean?
Paint breathability refers to the ability of the coating to allow water vapour to pass through its film.
Whilst plastic based paints will seal moisture into walls, breathable paints will let it evaporate naturally. This helps regulate humidity and prevent damp forming in your home.
How is Paint Breathability Measured & What Do You Need?
Breathability in paints is measured using an SD value (equivalent air layer thickness), which indicates how easily water vapour can pass through a surface.
The lower the SD value, the more breathable the paint, allowing moisture to escape and helping prevent mould and damp. Clay paints are naturally breathable and a popular choice for this reason.
So what level of breathability do you need to apply to your period property? Anything below 0.5 should be sufficient for most homes, with SD Class 1 (under 0.14m) offering the highest level of breathability.
What Does 0.5 SD Mean?
0.5 SD value means the paint has “has the same vapour resistance of 0.5 metres of still air”. That means water vapour can pass through it without much resistance.
SD Classes of Breathability
SD Class 1 - Highly Breathable - 0 to 0.14m
SD Class 2 - Moderately Breathable - 0.14 to 0.5m
SD Class 3 - Limited Breathablity - 0.5 to 1.5m
SD Class 4 - Low Breathability - 1.5m+
Why Breathability Is Vital in Old Houses
Old houses need breathable building materials and paints to be used during renovation because they’re typically built with solid walls rather than cavity construction. Many don’t have damp proof courses, relying on natural moisture balance to stay dry.
Breathable plasters and paints were used during the original construction of these homes, which allowed moisture to evaporate. This is why many old houses which have been renovated using gypsum based plasters can suffer from dampness.
Using modern, non breathable paints like vinyl emulsion or masonry paints on these buildings can cause all sorts of issues, including damp, mould and sometimes even damage
Once moisture gets trapped behind impermeable layers, it can’t escape, and that’s when problems start.
The Role of Natural Paints in Breathability
Modern natural paints are made from plant or mineral based ingredients which are breathable. This includes clay paint, lime based paint, or casein.
The materials used in these paints are the traditional ingredients which were available when older houses were constructed, meaning they’re incredible well suited to the needs of older properties. Using natural breathable paints will help protect walls, remove moisture, and maintain healthy indoor air quality in your home.
- Compared to synthetic paints, natural paints:
- Are free from harmful VOCs
- Don’t trap moisture
- Are often biodegradable and environmentally friendly
- Work in harmony with traditional materials
Choosing the Right Breathable Paint or Finish
You’ll need to understand what the right paint is for the construction of your home. Different surfaces and materials need different breathable paints.
Here’s a quick overview of the best breathable paint types for old houses:-
Limewash
Limewash is a breathable paint and is perfect for application on lime plaster, stone, and brick.
Suitable for internal or external use, it can be applied to lime plaster, gypsum plaster, stone, and brick. It soaks into the surface, bonding with porous materials rather than sitting on top like traditional paints. Its high alkalinity naturally inhibits mould growth.
Further Reading: Limewash pros & cons when renovating old houses.
Lime Paint
Lime paint is suitable for use on older houses that have lime plasters. It’s made mainly from natural lime, and is a water based paint. A highly effective and breathable alternative to modern paint. Provides an attractively textured surface finish, ideal for period authenticity. Lime paint is naturally higher in ph than standard paint, meaning it helps inhibit mould and mildew growth.
Clay Paint
Clay paint is a natural paint which uses clay as it’s main pigment and binder. A popular choice for internal walls and ceilings on older homes, it creates a beautiful texture on walls. A common choice for lime plastered surface, and easy to use apply.
Further Reading: Clay Paint - a Natural Choice for Old Houses
Casein Paint
Made from milk protein (casein) and white lime - casein paints have been used for centuries. Supplied in powder form, they are highly breathable paints which help regulate humidity. Provides a soft matt finish, and can be tinted with pigments for a coloured finish. This is peak ancient paint technology!
Breathable Exterior Paint for Old Houses
Exterior walls of old houses face the full force of the weather. So it’s vital to use a breathable exterior masonry paint that allows trapped moisture to escape.
Plastic based modern masonry paints can can trap moisture leading to damage to the plaster, render, or the paint itself. Instead, opt for mineral based breathable paints like limewash, silicate paint, or natural lime paints.
Breathable masonry paints are especially well suited for use as paint for heritage buildings, helping preserve the fabric of the building while maintaining a natural, matt appearance.
Painting on Lime Plaster: What You Need to Know
If your home has lime plaster, you must carefully consider what paint will be used. You’ll create a time consuming problem if you use modern paints, they’re too impermeable and will fail quickly.
It’s vital to use the right paint for lime plaster. If you don’t, it can be expensive and time consuming to put right.
The Importance of Lime Plaster in Breathable Systems
Lime plaster is a key part of a breathable wall system in a period property. It’s soft, flexible, and naturally breathable.
If you’re renovating or repairing old walls in your home, choosing a breathable lime plaster and finishing with a natural paint will preserve the fabric of your home. You’ll also avoid issues with damp, mould, and damage in the long term.
What If Your Walls Have Been Painted with Modern Paint?
A very large number of old houses have been coated in layers of modern, non breathable paints.
However, this doesn't mean you can't use breathable paint if you are overcoating old paint. As long as your paint surface is sound, i.e. not peeling or flaking, you can use natural breathable paint on top of modern paints.
Breathable Paint for Old Houses - Naturally The Best
Choosing a breathable paint for your old house is a simple and effective way to protect the structure of your property.
Use natural paints like limewash, clay paint, and casein to regulate moisture.They’ll also create an attractive and authentic finish which will enhance the period charm of your home. Our range of heritage paint colours may be of interest.
You may need to use heritage colours on your property exterior if you live in a listed building or conservation area.
Do please consider ordering one of our free paint charts, or very reasonably priced paint colour swatches which you can stick to the wall, and reuse as many times as you like. You can also browse our range of paint colours by shade.
