Is plaster breathable? Yes, it can be. But it depends on the type of plaster you are using, and how you want it to perform.
Traditional lime plaster is highly breathable and helps moisture pass through walls and ceilings rather than getting trapped. Gypsum plaster is breathable to an extent, but is not as permeable as lime. The difference can be important when choosing building materials for both older properties with solid walls and modern eco builds.
This guide takes a look at how breathable gypsum vs lime plaster is, and helps define breathability, also known as vapour permeability.
What Does Breathable Plaster Actually Mean?
Breathable plaster is a vapour permeable plaster which allows moisture in the form of water vapour to pass through it, rather than creating a vapour proof barrier. Breathable plasters, particularly lime plaster, absorb moisture into their pore structure and release it again as surrounding conditions change.
This allows walls to go through natural cycles of wetting and drying instead of holding excessive moisture within the structure.
Breathable plaster can be described in a variety of ways, here’s a few commonly used terms:-
- Vapour permeable plaster
- Vapour open plaster
- Porous plaster
- Moisture permeable plaster
These terms are used slightly differently, but all refer to the ability of a wall finish to manage moisture rather than creating a highly resistant layer over the wall.
Is Gypsum Plaster Breathable?
Not really. Gypsum plaster allows some moisture to pass through it, but it’s a lot less breathable than lime based plasters and not generally suitable for older buildings with solid walls that need moisture permeability. Many older buildings are high moisture environments, and Gypsum does not perform well in those conditions.
By comparison, Lime Plaster has a connected pore structure which makes it highly suitable to absorb and release moisture. In stone and brick walls, this helps keep them dry naturally and is a main reason for lime plaster being recommended for period and heritage properties.
Renovating an old house? Read our guide on why lime plaster is important in old houses if you’re considering replacing lime plaster with gypsum. Spoiler: don’t!
Lime Plaster vs Gypsum Plaster
The biggest difference between lime plaster and gypsum plaster is not just that one 'breathes' and the other doesn't. The materials behave very differently when exposed to moisture.
| Lime Plaster | Gypsum Plaster | |
|---|---|---|
| Water vapour permeability | High | Some permeability |
| Moisture buffering | High | More limited |
| Porous structure | Highly porous | Porous, but behaves differently from lime |
| Traditional solid walls | Highly compatible | Suitability depends on the wall construction |
| Modern cavity wall construction | Can be used | Commonly used |
| Flexibility | Relatively flexible | More rigid |
| Setting and application | Generally slower | Generally faster |
| Typical use | Heritage buildings, solid walls and breathable construction | Modern internal walls and finishing |
The important question is which plaster is appropriate for the building and the wall construction.
When Should You Use Lime Plaster?
Lime plaster is the right building material to use when maintaining a breathable, vapour open wall is important. If your building was originally constructed with lime plaster, replacing or reinstating lime plaster should be a serious consideration, particularly if you’ve identified damp issues.
Using modern plaster finishes over traditional walls can create damp issues. Make sure you consider the construction of your home when deciding which material to use.
You can find a fuller explanation in our guide to what lime plaster is.
When is Gypsum Plaster the Best Choice?
Gypsum plaster is highly suitable for modern construction where rapid setting, ease of application, and a smooth finish is a priority.
Gypsum is widely used in modern homes and extensions, but it should not automatically be treated as a direct replacement for lime plaster in period properties.
Is Breathable Plaster Better for Damp Walls?
Yes. Gypsum plaster traps moisture and can cause damp and black mould, breathable plaster helps keep walls dry by allowing moisture to move through the surface.
If you have an older solid wall building with lime mortar and render, a breathable plaster is an important part of your home’s “vapour open system” - helping the building to breathe and stay dry.
If your home is suffering from moisture ingress, it’s important to address the underlying causes before you apply new plaster. Make sure leaking gutters, roof issues, defective pointing, condensation, and drainage issues are all addressed before applying fresh plaster.
Once the source of excess moisture has been dealt with, lime plaster can help the wall dry naturally rather than trapping moisture behind less permeable finishes.
If existing lime plaster is largely sound, it may also be possible to repair damaged areas rather than replastering the entire wall. See our lime plaster patch repair guide for advice on repairing cracks and small areas of damage with compatible breathable materials.
Has mould gained a foothold? Our guide on removing mould naturally will help!
Finishing Walls with Breathable Paint
If you decide to reinstate or replace lime plaster walls, make sure you apply a suitable breathable paint.
If you coat your beautiful breathable walls in plastic based paint, you’ll trap moisture inside them. Traditional limewash is one option, or a modern lime based paint for easier application and enhanced durability.
For a detailed comparison of suitable finishes, see our guide to choosing the best breathable paint for lime plaster.
By treating the plaster, repairs and decorative coating as parts of the same wall system, you can maintain the moisture permeability of the surface and make sure your building can breathe the way it was designed to.
Fill and repair with materials that breathe like the wall does. Ordinary plastic fillers can seal in the very moisture a lime wall is meant to release, so we use natural, breathable Auro fillers instead.
A breathable wall needs a breathable finish, otherwise a standard plastic emulsion seals the moisture straight back in. These natural mineral paints let the wall keep working, from an everyday emulsion to an air-purifying top-end option.
