Lime plaster or gypsum plaster — which should I use?

Lime and gypsum are not interchangeable. The choice is mostly about how the wall handles moisture.

How the two materials behave

Gypsum plaster sets through a chemical reaction in hours, builds up quickly and dries to a hard, smooth, easily decorated surface. It is relatively cheap, widely available and the plaster nearly every modern UK home is finished in. Its weakness is that it is not breathable and does not tolerate ongoing moisture well: in a persistently damp environment it can soften, blow and shed salts.

Lime plaster is made from lime, sand and water and is vapour-open — it lets moisture move through it and evaporate. Older solid-wall buildings were designed to manage water this way, absorbing it and releasing it again rather than keeping it out entirely. Lime also stays slightly flexible, accommodating the small seasonal movements of old buildings without cracking the way rigid gypsum can. The trade-off is that lime is slower to cure, needs more skill to apply, and usually costs more.

Why breathability matters in old homes

Pre-1919 houses typically have solid masonry walls with no cavity. They keep dry not by being waterproof but by being breathable: moisture that gets into the wall evaporates back out through breathable plaster, lime mortar and limewash or breathable paint. Seal that wall with a non-breathable gypsum plaster and modern impermeable paint, and the moisture has nowhere to go — it builds up behind the plaster, dissolves salts, and shows as damp patches, blown plaster and spoiled decoration.

Indicative guidance for UK homes. Listed buildings and conservation areas may require lime by condition or for authenticity.

Durability, finish and working differences

On a dry, modern wall, gypsum is hard-wearing and gives a crisp, smooth finish that takes paint beautifully — there is no reason to use lime there. On an old solid wall, gypsum's hardness becomes a liability: it is more rigid than the soft historic masonry around it, so movement and moisture make it crack and blow, while its impermeability traps damp. Lime, by contrast, flexes with the building and lets the wall breathe, which is why it lasts on old fabric where gypsum fails.

Lime is more demanding to work with. It cures slowly through carbonation (reacting with air over weeks rather than setting in hours), often needs several thin coats with curing time between them, must be protected from drying too fast or freezing, and requires a plasterer experienced in lime work. Gypsum is quicker and more forgiving, which is part of why it dominates ordinary jobs. The extra time, cost and skill of lime are justified specifically by the breathable, flexible performance an old building needs.

Choosing for your property

The decision is largely made by the building. A modern house with cavity walls or plasterboard should be plastered in gypsum: it is faster, lower-cost, hard and entirely appropriate for a wall that does not rely on breathing. A pre-1919 solid-wall, cob, stone or timber-framed property — and any listed building — should generally be plastered in lime, so the wall can manage moisture as it was designed to.

If you have a damp problem in an old house that was previously 'fixed' with gypsum plaster and impermeable paint, the cure is often to remove the gypsum, let the wall dry, and replaster in lime with breathable finishes — working with the wall rather than against it. The reverse is rarely needed: there is little benefit to lime on a sound modern cavity wall. Match the plaster to the wall's construction and how it handles water, and both the wall and the finish last far longer.

If you do go the lime route on an old building, the rest of the build-up needs to be breathable too, or the benefit is lost. There is little point applying breathable lime plaster and then sealing it with a modern impermeable emulsion or a plastic-based paint — the wall still cannot let moisture out through the finish. Traditional choices such as limewash, clay paints or other vapour-open finishes keep the whole system breathing. The same logic applies outside: hard cement render or impermeable external paint on a wall you have carefully plastered in lime inside will still trap moisture in the masonry. Breathability is a property of the whole wall build-up, inside and out, not of one layer, so on a period property the plaster choice should sit within a consistently breathable specification rather than being a single isolated decision.

It also helps to know the practical demands of working with lime, because they shape both cost and programme. Lime plaster is usually applied in several thin coats with curing time between each, and it cures slowly by carbonation — reacting with carbon dioxide in the air over weeks — rather than setting chemically in hours like gypsum. During that time it must be protected from drying too fast (which causes shrinkage and cracking), from frost, and from heavy knocks, often by keeping it damp and covered. This is why a lime job cannot be rushed and why it needs a plasterer genuinely experienced in lime rather than a general skimmer. Gypsum, by contrast, is quick, forgiving and ideal where speed and a hard smooth finish are what the wall needs. Neither is 'better' in the abstract — they are simply suited to different buildings, and the slower, more demanding lime process is the price of the breathability and flexibility an old wall depends on.

Frequently asked questions

Sources & further reading

• Historic England — traditional building materials and lime
• The Property Care Association — damp in older buildings

Figures on this page are typical UK ranges drawn from published sources and depend on your specific room. They are guidance, not a quotation.