Disappointed with my lime mortar.

[RaceDiagnostics]

I used NHL 3.5 for this mortar but am not to happy with it. It's cracked up the side of the stonework. I'm thinking about going back to a cement mortar for the remainder of the windows. Any thoughts?

 

[JOEPRO]

Stay with lime mortar. The small crack there looks normal to me and nothing to be concerned about.

You don't mention the period of the property but obviously its natural stone wall and likely solid wall construction so stay with lime mortars. Cement mortars will stop the wall from breathing properly and stick to hard to the stone, damaging the stone and also being very hard to remove for future maintenance.

 

[sako243]

How did you control it drying out? I've found lime is pretty forgiving in all other aspects apart from how quickly it dries out.

 

[arther dailey]

did you wet down the stone thoroughly before applying ?

 

[Blue Chips]

When we were restoring the old house that we sold in '23, I used a lot of lime plaster and mortar. I don't know anything about the specific mixture that you used, but generally speaking, I had good luck if it was allowed to dry slowly. When pointing old soft-fired bricks, I pre-wetted the bricks to allow them to soak up some water to keep the mortar moist longer, and for repairing/replastering walls with lime putty plaster, I sprayed the wooden lath with water before plastering, spritzed each layer of plaster periodically to keep it moist, and after the final layer was applied, I taped poly sheet over it to extend the drying time. That said, I found that if I added too much water when mixing the plaster or mortar, it would be more likely to crack than a stiffer mixture.

 

[RaceDiagnostics]

It was done on a hot day with full sun on it, I did wet down the stone first but was concerned about the hot sun. So maybe it just dried to quickly.

Ok I'll give it another go but wet down more and avoid a sunny day.

 

[ajlelectronics]

It was done on a hot day with full sun on it, I did wet down the stone first but was concerned about the hot sun. So maybe it just dried to quickly.

Ok I'll give it another go but wet down more and avoid a sunny day.

Yes, my first thought was excessively fast drying.

 

[Rudi McAnichal]

In this disctrict, lime mortar repair work on old stone walls, bridge parapets, etc is usually covered with wet hessian sacking for at least a week or two.

 

[OJCar]

Did you cover the mortar while it was drying?

I understand that for pointing like that you should add 4% by vol Linseed Oil to the mortar to improve water proofing.

 

[Mikey D]

I've seen Hessian used to cover pointing , and kept moist

 

[sako243]

It was done on a hot day with full sun on it, I did wet down the stone first but was concerned about the hot sun. So maybe it just dried to quickly.

Ok I'll give it another go but wet down more and avoid a sunny day.

Based off my experience limewashing 600m² of wall last summer that's 100% the issue. Hessian sacks as @Mikey D says are a good shout on something that small.

 

[Craigrob]

When I did mine I used Burt Sand Mastic from Masons Mortar in Leith. horrible stuff to use but its been up for 5 years now (covid project) and still looks brand new. I was led to believe it was what was originally used between sash & case windows & the stone. sand & linseed oil, basically. Masons Mortar only do 'heritage' mortar products and so I imagine would be able to advise you. Plus, reasonably local to you, I think

 

[RaceDiagnostics]

When I did mine I used Burt Sand Mastic from Masons Mortar in Leith. horrible stuff to use but its been up for 5 years now (covid project) and still looks brand new. I was led to believe it was what was originally used between sash & case windows & the stone. sand & linseed oil, basically. Masons Mortar only do 'heritage' mortar products and so I imagine would be able to advise you. Plus, reasonably local to you, I think

I've just finished the second window at the rear which has worked out a lot better, I made up the mortar a lot wetter, soaked the stone work and kept the pointing damp for a couple of days. It's now drying out without any cracks. However the mastic sounds like it will be an easier solution. I'll look into that to see if I can get a good colour match for the front of the house.