The Crack That Wasn't There Last Spring: A Plasterer's Autumn Check
By Roger Amada, PRA Plastering · 4 min read
Hairline crack in your render, or a damp patch that keeps coming back? What's safe to leave, and what's worth checking before winter.
A hairline crack in render, and a slightly darker patch on a bedroom wall, are two of the most common things a homeowner notices in autumn and does nothing about. Most of the time that's fine. Sometimes it isn't, and the difference comes down to a few specific signs, not guesswork.
External render cracks
You notice it on a dry day, running a hand along the wall out of habit more than concern. A thin line, barely wider than a pencil mark. It's probably been there a while, it just hadn't caught your eye before.
Most hairline cracks in render are nothing to lose sleep over. They form as the render moves slightly while it dries and settles, and they're common enough that most houses have one somewhere. What matters is not whether a crack exists, but whether water can get into it.
A hairline crack left through one dry summer stays cosmetic. The same crack left through a wet winter lets water in, and when that water freezes, it expands. A crack you could once ignore becomes render that's come loose from the wall behind it.
If you can fit a coin edge-on into it, or if it's grown since you last looked, get it checked before the weather turns. If it's genuinely hairline and hasn't changed in months, keep an eye on it and mention it next time someone's round for other work.
Internal plaster and damp
Inside, the signs are different, but the timing works the same way. A patch on a bedroom wall that's slightly darker than the rest. A corner that feels cold even with the heating on.
Most of this is condensation: moist air from cooking, showering and drying clothes meeting a cold surface and turning back into water. It's the most common cause of damp in UK homes, and it's rarely a sign the building itself is faulty. Usually the air simply has nowhere to go.
Ventilating properly when you cook or shower helps, as does keeping a low background heat through the coldest months rather than letting rooms go properly cold. Where plaster has actually blown — gone soft, sounding hollow when you tap it, or crumbling at the edges — that's a repair job rather than something ventilation will fix.
A cold patch that stays dry is usually fine. A cold patch that's also damp to the touch, or that's started showing black speckling, is condensation turning into mould, and it's worth sorting before it spreads.
Repair now or repair in spring
The honest answer to "can this wait until spring" depends on what "this" is, but waiting rarely makes the job smaller. A crack that's a twenty-minute patch in October can be a full re-render by March after a hard winter has had its way with it. That's not a sales pitch, it's simply how freeze-thaw damage works. Water gets in, freezes, expands, and takes a little more render with it each time.
If the crack has grown, if you can see daylight or feel a draught through it, or if a patch of plaster sounds hollow when you knock on it, it's worth booking before the queue gets long, which is really a question of timing more than urgency.
This is one of ten checks in our free autumn & winter home guide — what's fine to leave, what's worth a professional look, and why the timing matters. If any of this sounds familiar, Roger and the team cover Rickmansworth, Watford, St Albans, Harrow and Hemel Hempstead, and a five-minute look now is cheaper than a re-skim in spring. Get a quote or send us a photo on WhatsApp.
Frequently Asked Questions
Is my crack something to worry about?
If you can fit a coin edge-on into it, or if it has grown since you last looked, get it checked before the weather turns. If it's genuinely hairline and hasn't changed in months, keep an eye on it and mention it next time someone's round for other work.
Do I need to worry about a cold patch on the wall, or is that normal?
A cold patch that stays dry is usually fine — some walls are simply less insulated than others. A cold patch that's also damp to the touch, or that's started showing black speckling, is condensation turning into mould, and it's worth sorting before it spreads.
When should I call a professional?
If the crack has grown, if you can see daylight or feel a draught through it, or if a patch of plaster sounds hollow when you knock on it. None of these need an emergency callout, but they do need booking before the queue gets long.
About the Author
Roger Amada is the founder of PRA Plastering, based in Hertfordshire, specialising in interior and exterior plastering, render repair, and damp diagnosis. Roger's approach prioritises identifying the root cause of a problem before recommending any fix.