Put the Trowel Down Until Spring: Why I Would Not Repoint a Listed House in November

"We can start Monday." It is a kind offer, and in November I would turn it down. Fresh lime mortar needs weeks without a hard frost after it goes on, and a hard night inside that window can ruin joints that look perfect on the day. My advice is to repoint in the spring and to use the winter to get ready.

What frost does to a new joint

Mortar is wet when it goes in. If that water freezes before the mortar has set, it expands and pushes the material apart from the inside. The Mortar Producers Association (the trade body for factory-made mortar) puts it in two sentences on its winter warning of 1 December 2023: "If the temperature of newly laid mortar falls below 0°C there is the probability of some form of frost attack." And: "The water in the mortar may freeze and expand therefore forcing the material apart and breaking the bonds."

Lime mortar is kind to old masonry, but while it sets it is exposed. Lancaster City Council's conservation guide for Morecambe, written for a heritage grant scheme that began in 2012, gives the plainest advice I opened:

"It is essential that lime products are not used when the temperature could drop below 5˚C."

The same guide adds that frost "can be very damaging whilst the lime goes off, and it is worth remembering that this is the case for several weeks after the lime has been applied". The guide's general rule of thumb is that lime "should not be used externally in the late autumn or before late spring". That is one council's view, in a guide that is now several years old, so ask your own council and your own mason what they work to. I agree with the direction of it.

The calendar I would keep

These are my own habits, not a rule. The only dates that come from a source are the late autumn and late spring in the Lancaster guide.

Nothing in that table is wasted time. A repoint that starts in April with a sample panel agreed and consent in hand goes better than one rushed in a cold week because a scaffold was already up.

What the winter is for

The walls are at their most honest in winter. Rain finds every failing joint, and the damp patches show you where the water is lodging, which is often not where the pointing has failed. My piece on where roof water goes is a good first read, because a joint rotted by a dripping valley will rot again if the valley is left alone. The same goes for any gutter that spills onto the wall.

Here is how I would spend the months:

• Photograph each wall in raking light, joint by joint, with a tape or a ruler in the frame. Date the pictures.
• Mark where water meets the wall: a blocked downpipe, a splash zone, a path banked up against the brick. Mend the cause before the mortar.
• Look for cement. Kirklees Council warns that cement "will trap moisture in brick or stone which can then cause frost damage and the deterioration of the bonded material". If your walls have cement pointing, do not start removing it in the cold. Taking it out is a job to plan carefully for the spring.
• Ask for a sample. A good mason will show you a trial panel before touching the whole wall.

Does repointing need consent?

The law turns on the effect of the work. Under section 7 of the 1990 Act, works that would affect a listed building's character as a building of special architectural or historic interest need authorisation first (section 7 of the 1990 Act).

Lancaster's guide says bluntly that "the re-pointing of listed buildings requires the benefit of listed building consent". Other councils draw the line differently, and a small like-for-like patch may not need consent in some areas. I set out how I weigh that in the related guide above. GOV.UK's planning practice guidance (GOV.UK) encourages owners to talk to the local planning authority early, and in winter you have the time to do so.

When a professional earns their place

If the joints are failing and you do not know why, if the wall is damp, or if you suspect the old pointing is original and worth keeping, a survey in winter is worth more than a quick repair in the cold. I would also bring someone in if a builder promises a "waterproof" finish. That is the sort of promise I explored in the damp article, and it rarely suits old walls.

A patient kind of repair

There is a quiet pleasure in letting a building keep its schedule. Lime has waited a few hundred years for its next coat, and it can wait until the blackthorn is out. A wall repointed in good weather, in the right mortar, may well outlast the owner who commissioned it.

Speak to Giles about a wall that worries you: book a conversation, get in touch, call +44 (0)7737 745211, or send a WhatsApp voice note.

Giles Paul Shorter — ARB registered · RIBA Chartered Member · on the RIBA Conservation Register · 17+ years specialising in listed and historic buildings.