It's a common and understandable mistake: a wall gets correctly re-plastered in lime, addressing a damp or cracking problem properly, and then gets decorated with whatever paint the decorator normally uses, standard vinyl or acrylic emulsion. That single decision can undo much of the benefit of the plaster work underneath it.
Standard modern emulsion forms a semi sealed film across the surface it's applied to. On a lime plastered or lime rendered wall, that film blocks the evaporation the lime is specifically there to allow. The result is often blistering or flaking paint within a relatively short time, as moisture trying to pass through the wall gets trapped just behind the paint film instead.
Limewash is the most traditional option, a thin, breathable finish applied in several coats, that weathers gradually and is generally expected to be refreshed every few years externally, which is normal for the finish rather than a fault. Silicate, or mineral, paint is a more durable, lower maintenance breathable option that chemically bonds with a lime or mineral substrate. Breathable emulsions, formulated specifically for lime and other traditional substrates, offer a smoother, more contemporary appearance while still allowing the wall to breathe.
Limewash suits a genuinely traditional appearance and lower budget, but needs periodic refreshing and shows the character of the wall underneath rather than giving a perfectly flat, uniform finish. Silicate paint suits owners who want a breathable finish with less ongoing maintenance and a more even appearance. Breathable emulsion suits interiors especially, where a smoother, more modern look is wanted without sacrificing the wall's ability to manage moisture.
Confirm the substrate is actually lime before assuming breathable paint is necessary, a later extension built in modern block, for instance, may be entirely appropriately finished in standard paint. And if there's existing modern paint already on a lime wall that's now failing, it usually needs to be properly removed before a breathable system is applied, rather than painted over.
Breathable paint systems generally cost more per litre than standard emulsion. On a lime finished wall, that additional cost is almost always cheaper in the long run than the alternative: standard paint failing within a few years and needing to be stripped, sometimes taking some of the lime finish with it, before being redone properly.
Breathable paint systems, particularly limewash, aren't applied the same way as standard emulsion. Limewash typically needs several thin coats rather than one or two thick ones, and the wall needs to be properly prepared and, in some cases, dampened before application. A decorator used to standard modern paint, applying it the way they're used to, is one of the more common ways a breathable paint job underperforms even when the right product was chosen.
If standard emulsion has already been applied to a lime wall and is now blistering or flaking, the usual fix is removing the failed paint back to a sound surface (which can sometimes take some of the lime finish with it if the bond has failed badly) and repainting in a breathable system. It's a more involved job than simply repainting over the top, which is why getting the right paint specified at the outset, alongside any lime plastering or rendering work, is worth the extra conversation before decoration starts.
