Strange holes in lime mortar

[Ushy M]

Hello all, we are in the process of having our chimney taken down and rebuilt (it was dangerously cracked, wobbly and starting to leak smoke through the thatch so well beyond patching up).

Quite a few of the old bricks we've taken down have holes in the original lime mortar, round and about the size of a biro in diameter. Some of the holes have the remains of what look like chrysalises (chrysali??) in them, which look like a biggish rice krispie.

Our builder, who is very experienced, has never come across anything like this before. Any ideas what they are and whether we should worry? (whatever they are, they appear to be long dead)

 

[David Q]

Only thing I can think of is the mason bee. These little items are quite capable of excavating mortar or even soft stone. However they come under the heading of 'mostly harmless'.

 

[Gervase]

You've got (or had) mortar or masonry bees - osmia rufa. Many old buildings are affected and often they don't do any harm. They can, however, dig out so much mortar that the brickwork is weakened.
The infestation may be past, but it's worth repointing and, if possible keeping an eye on the ground below the attack to see if any more moratr is being dug out - look out for little piles of sand.
You can spray the wall with an insecticide (ideally a safe on like pyrethrin) and the best time for this is around now.

 

[hive-mind]

Please don't spray insecticide! British bees are in decline as it is without period property owners waging war on the poor blighters!

Think of the flowers!

 

[Ushy M]

Thanks to all for this. The lime mortar affected was under several layers of repointing, so I think this is an old infestation and won't need spraying.

 

[Sue Wilkinson]

I'm worried that you say your builder is very experienced but hadn't come across the little bee holes and chambers before. He may be experienced, but not in old property.

You should start talking to him now about how he proposes to rebuild the chimney and what materials he's going to use. My guess is he won't be using anything particularly traditional and therefore what he does use could be less good for the property.

Masonry bees are (or have been) very evident in old mortar. I find them all the time. I am happy for them to come back after repointing as it takes years for real problems to occur from them. I can always repatch again in years to come if necessary. As someone else said, lets help nature, not repress it.

Sue

 

[Penners]

For fuller information on masonry bees and their habits, see:-

http://www.spab.org.uk/publications_Q&A_masonry_bees.html

 

[biffvernon]

This one is particularly sweet. And you can brush up on your French.

 

[Ushy M]

Sorry, don't know how to do the quote thing, but just in reply to Sue's earlier post - our builder is indeed experienced in working with old properties and I'm happy with the approach we've taken - using lime and reclaimed, sympathetically matched and locally-sourced materials.

Turns out 'Never seen that before' meant he'd never seen so many holes in one place and with the bee larvae still inside, where presumably where the poor things had been 'walled in' by one of the earlier (botched) repointing efforts.