A little while ago, I was advised on this forum to use NHL3 hydraulic lime to repoint a south facing corner of my house which is located about 750 yards from the sea. This corner of the house gets full sun during the summer and salt ridden winds off the sea during autumn /winter. Consequently hydrated lime putty mortars tend to fail and crumble away. Whilst speaking to a plasterer recently who is familiar with lime, he suggested that if he did the job, he would put a quantity of Lime putty into the NHL3 mix in order to give it some “fat”. Dose anybody agree with this recommendation and if so what proportions of Hydraulic, hydrated and sand would you recommend?
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Should I add lime putty into an NHL3 mortar mix?
- Thread starter michael
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christianb
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- Helford River, Cornwall
Hi Michael,
There's no harm at all in adding some putty to the hydraulic. If anything, it makes it so very much more workable.
In fact, bear in mind that most rendering and external pointing was almost always done with lime putty. What ratio you use is up to you, but 1 hydrated to every 2 hydraulic probably wouldn't hurt in areas of high weathering. Anyway, mortars are supposed to be 'sacrificial' to the stonework.
C.
There's no harm at all in adding some putty to the hydraulic. If anything, it makes it so very much more workable.
In fact, bear in mind that most rendering and external pointing was almost always done with lime putty. What ratio you use is up to you, but 1 hydrated to every 2 hydraulic probably wouldn't hurt in areas of high weathering. Anyway, mortars are supposed to be 'sacrificial' to the stonework.
C.
biffvernon
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The mixture might be called NHL2 or another small number depending on how much hydrated lime you added.
hoppy
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For outside high weather exposure you are better to use NHL5
skier-hughes
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YOu#d normally use somewhere between 3:1 sand to lime, so I putty: 2 NHL : 6/9 sandmichael said:Thanks Christian. So just to make sure I understand your recommended mix for high weathering areas correctly, would that be 1 lime putty, 2 hydraulic (NHL3) , 1 sand
christianb
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Hi Michael,
However you do it you want to end up with a 3:1 sand:lime mix, as Skier-Hughes has pointed out.
I know a guy who works for SPAB who would probably recommend lime putty alone. Personally, there's no harm in using NHL3, but give it a year or two and it'll be as hard as cement. Using the hyudrated lime putty in the mix does tend to fatten it up a bit and help retains moisture during the drying process - I find this helps to reduce shrinkage cracks, particularly during warm weather.
Either way, as I said earlier, the mortar should be sacrificial to the stonework anyway.
C.
However you do it you want to end up with a 3:1 sand:lime mix, as Skier-Hughes has pointed out.
I know a guy who works for SPAB who would probably recommend lime putty alone. Personally, there's no harm in using NHL3, but give it a year or two and it'll be as hard as cement. Using the hyudrated lime putty in the mix does tend to fatten it up a bit and help retains moisture during the drying process - I find this helps to reduce shrinkage cracks, particularly during warm weather.
Either way, as I said earlier, the mortar should be sacrificial to the stonework anyway.
C.
biffvernon
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I've never really understood what 'fatten it up a bit' means in the context of bricks and mortar, rather than pig rearing.