Plastering & Rendering in London

Where existing plaster is sound but tired, a skim coat over the top gives a flat surface at modest cost. Where it has blown — hollow when tapped, because it has lost its key to the background — skimming over it only buries the problem, and the new surface fails with the old one.

Tapping a wall tells you which you have. It is a five-minute check that decides a large part of the cost, and it is worth doing before a specification is written rather than after.

Solid-wall Victorian and Georgian property was usually plastered in lime, which is softer and allows moisture to move through the wall and evaporate. Covering it with modern gypsum or cement traps that moisture, which then finds another way out — typically as damp or as blown plaster somewhere else on the wall.

That does not make gypsum wrong everywhere; it makes it wrong on a wall that needs to breathe. Getting this decision right matters far more on a period property than the smoothness of the finish.

Render fails for two reasons: it was applied to an unsound or unsuitable background, or water got behind it and could not get out. Cracked render that is holding water against the wall does more harm than no render at all, which is why patching over a crack without establishing where the water is coming from usually buys a year rather than a fix.

Weather governs the work. Render needs suitable temperatures and dry conditions to cure; applied in the wrong conditions it fails regardless of the mix.