Repointing old brick and stone walls with lime

What pointing is for

Pointing is the mortar in the face of the joints between bricks or stones. Repointing means taking it out and putting new mortar in. Done well, it keeps the weather out and slows decay ¹.

In old walls the mortar is meant to be the weak point. SPAB explains that lime mortar is more permeable than the brick or stone around it, so moisture leaves the wall through the joints ². Salts and frost then do their damage in the mortar, not the masonry ¹². That makes the pointing sacrificial, and it is cheaper to repoint now and then than to replace bricks or stone ².

Does it need doing?

Often not yet, and usually not all of it. SPAB says repairs are usually localised ¹. Its test is simple: repointing is premature until the mortar has worn back to a depth about equal to the joint’s width, or is very loose ¹. Soft mortar alone is not a reason to repoint ¹. SPAB also warns that unnecessary repointing, however careful, risks chipping the edges of bricks and stones and losing clues to how the building was made ¹.

If water is getting into a wall, fix the cause first. SPAB says addressing the cause of dampness is always preferable, where possible, to dealing merely with the symptoms ⁴.

Why cement pointing harms old walls

Hard cement pointing turns the logic round. Water can no longer leave through the joints, so it leaves through the face of the bricks or stones instead ². They then take the frost and salt damage, and decay faster ¹².

Should existing cement pointing come out? SPAB’s advice is to remove it only if a trial shows it can be done without more damage. Otherwise, leave it until it has worked loose ¹.

What good lime pointing looks like

These points come from SPAB’s guidance ¹:

• Match what’s there. Old pointing is usually best seen in sheltered spots such as under the eaves. Usually, match it in material, colour, texture and strength.
• Softer than the masonry. New mortar should be weaker than the bricks or stones and suit how exposed the wall is.
• Usually lime. Lime is the usual binder, occasionally clay. SPAB discourages adding cement to lime mortars now that a wider range of limes is available.
• Sand. A well-graded sharp sand is advised. The largest grains should be no more than a third of the joint’s width.
• Rake out deep enough. Old mortar should be raked out to about twice the joint’s width, deeper for wide joints.
• Flush, not recessed. A flush or nearly flush finish is often appropriate. SPAB describes deeply recessed pointing, especially on stonework, as a late 20th-century fashion.
• Try it first. SPAB advises making mortar samples and trial panels.

On the choice of lime, SPAB’s general rule is to use materials that match the originals. For a moderately exposed outside wall it gives a weak hydraulic lime as one example that may suit pointing ³. The right mix depends on the wall, so ask someone experienced with old masonry.

Weather and timing

SPAB says many pointing failures come from ignoring the weather ¹. Avoid repointing in winter where you can. At any time of year, new work needs protecting from frost, from drying too fast in sun or wind, and from rain ¹.

Listed buildings

Repointing a listed building can need consent. SPAB says listed building consent may be required for work that exceeds like-for-like repair, and that carrying out work that needs consent without getting it beforehand is a criminal offence ⁴. If in doubt, consult the conservation officer before you start ⁴.

Further reading

SPAB’s repointing page covers the main questions on timing, mortar and finish ¹.