Lime Mortar pointing peeling off

wdorninger · 12 Nov 2021

Hi All,

i have a question on repointing. I had the exposed brickwork around my house (1910) repointed with Lime Mortar (supposed to be the best thing for that kind of house). All good but on the west wall and a corner the pointing is peeling off. All the other walls seem to be good

Initially I thought maybe this is damp. The wall there is a 40cm-50cm solid brick wall and there is also a chimney breast (however the chimney is closed at the top) and the peeling not only happens near the chimney but also 2-3m away from there and also on the corner. On the corner its not even at the bottom of the wall but around 1.5m above ground. No pipes, downpipes etc in this area either. Sometimes I even have some good lines of pointing and then again some lines that are peeling.

The repointing was done in May this year. Now 6 months later this happend.

Any idea what could cause this issue?
- Is it damp? - Why is are some pointing lines ok then?
- Or just a mix thats too soft? - Why are the other pointing's ok then?
- Maybe the walls were not properly dried out before? (there was cement mortar before which was removed and replaced with lime mortar)
...

Thanks
Walter

jeds · 12 Nov 2021

There are so many variables; the mortar, the substrate, technique, weather conditions, it could be almost anything? I'd guess the mix is too weak, but it is only a guess.

Deleted member 292770 · 12 Nov 2021

just can’t get my head around the lime obsession.

stuart45 · 12 Nov 2021

What lime and mix was used?
Was it kept damp and covered with hessium?
When a metal tool is used to finish it brings laitance to the surface which is what's coming away.
A flush finish and whacked with the churn brush is a more popular finish with lime.

wdorninger · 13 Nov 2021

I think my builder used nhl 3.5 and a weatherstruck pointing.
saint astier nhl 3.5, 3 soft builder sand + 1 lime

No was not kept damp I think as he said its in the shade anyways. I terestingly the pasts that were in the sun are all good and the pointing is hard

Yes he used a metal tool for pointing.

stuart45 · 13 Nov 2021

Have you told the builder about it?
Soft sand isn't the best to use with lime.
Also NHL needs a longer mix time than cement.
Was the brickwork well damped down?

wdorninger · 13 Nov 2021

Yes discussed it with the builder as well. He suggested to just do the wall again but eventually we agreed that I consult a damp specialist first as we believe - if we just repeat the exercise - why would the outcome be different?
After all the other walls all look OK so far. Only at some corners i can see a slight different color of the pointing.

Re the sand I checked as well and seems people tend to mix in sharp sand to prevent cracking... (not being an expert at all here)

Also I thought maybe I put some flashing on the top layer of bricks (which stands out a bit) to prevent them from water flowing down the pebbledash wall. Would this a sensible thing to do?

I'm currently creating a checklist of items that I could do before redoing the pointing to reduce the risk of happening it again. After all I guess it will be a bit of try and error. I also thought maybe I do only a small part and see if it works (eg wait 6 months and then assess the situation - if working proceed with replacing the pointing) - can't repoint every 6 months

tell80 · 13 Nov 2021

I'd suspect the projecting brick ledge is pooling water an allowing it to penetrate at tht top area.
The render should be finished with a Bellcast tht will throw water beyond the lower ledge and brick face.

Pointing depends on prep. Youshould rake out 20mm to 25mm no matter whatstyle pointing you use.
Blow the chase clean and brush or spray a drop of water into the beds and perps - try not to wet the brick faces.
My suggestion is a flush joint thats pressed in and brushed as stuart45 suggests above. Flush btw means just that.

You mention a chimney. has it been swept and is it ventilated from bottom to top in each flue?
What about inside the house, any signs of water damage penetrating your solid wall?

The grey sand and cement plinth needs removing - theres historic attempt to inject a DPC, see the drilled holes.

The bottom beds of pointing are great pointing.

wdorninger · 13 Nov 2021

Thanks for all that suggestions and feedback.

I was wondering about the cement plinth as well. I asked the builder to just renew it as it was already there (not sure when it was added there). So you would just remove the plinth and leave the bricks just as they are?

And Yes i saw that DPC as well (forgot to mention it) I think it has no function as the wall is quite thick 40-50cm. The chimney is currently not ventilated afaik - I had it cleaned/lined and a woodburner installed approx a year ago. is it possible to put an airbrick at the bottom of the outside wall where the chimney ends? guess it will be difficult to find the flutes throught the 40-50 cm thick wall.

Inside everything looks ok to me also all dry. The only thing I noticed is that a few bricks of the fireplace (raw brick) I exposed inside are getting a bit white (presume thats salt drawn out of the bricks) - But they seem to be dry (when touching them they dont' feel wet). Also the plaster around the bricks seems dry. Attaching a picture (of the inside

tell80 · 13 Nov 2021

Remove the plinth, ID the DPC bed, clean the briks and hack out and repoint as above.
No new pics as yet.
Dont go installing any airbricks.

wdorninger · 13 Nov 2021

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Lime Mortar pointing peeling off

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