Lime Mortar

[fidom]

I have been doing pointing work on weak Eastern European bricks using a 6:1:1 mix of sand, OPC and hydrated lime. I would like if possible to go to a proper lime mortar and avoid using the OPC. I have watched various YouTube videos on lime mortar but am just getting more confused! In one video they are making "practice mortar", presumably for teaching bricklaying. This is made with sand and hydrated lime and apparently gives a mix which will never set. In another video someone is making lime putty using hydrated lime and water. This is later used with sand to make a lime mortar. Presumably that mortar does set? What is the difference between using the lime powder in the mix rather than the putty? There is also hydraulic lime, does that also need to be made into a putty?

 

[stuart45]

There is also hydraulic lime, does that also need to be made into a putty?

No need to make it into a putty, just make sure it's well mixed up with the correct sand.
Pure lime putty sets only by absorbing CO2, whereas NHL sets partly by that and partly by hydration so tends to be more popular with external work.
In chemical terms the bags of hydrated lime you get to use in cement mortar are the same as the lime in the putty, although plasterers much prefer to use a well matured lime putty.

 

[StephenStephen]

I'm not an expert but have learnt a few things about lime in the last couple of years of diy:

-Hydrated lime - avoid if you're lime plastering unless you know the ins and outs of it all

-Hydraulic lime also known as Naturally Hydraulic Lime or NHL -comes in a dry powder, mix with sand, use similarly to sand and cement. DO NOT be tempted to add any cement to it. Limited shelf life. The higher the NHL number, the more it is like concrete and the less it is like lime

-Lime Putty (my favourite). Comes in a bucket, mix with sand, slow to set, you need to control the amount of moisture before and after (basically make sure surfaces have been soaked some time prior to use, and don't let it dry out too quickly. Putty in a bucket keep indefinitely, and gets better with age. If you're using lime putty I'd recommend you read 'Lime in Building' by Jane Schofield, available here: http://www.theblackdogpress.bigcartel.com/
Very good source of information are the videos from Mike Wye (on youtube)

 

[fidom]

Thanks for the replies. It looks like the cheapest option is to make my own lime putty using the hydrated powder. The NHL 3.5 and the ready made lime putty seem quite expensive. Another option seems to be to re-use the stuff you rake out. I saw that on the BBC TV series "Victorian Farm". What puzzled me there was they added more sand but the old mortar / plaster would already have contained sand. On the subject of sand, one video stated you must wash the sand if making mixes for internal plastering. I do get salt deposits forming on the surface of the brickwork and have wondered if it is leaching out of the sand.

 

[stuart45]

Another option seems to be to re-use the stuff you rake out. I saw that on the BBC TV series "Victorian Farm". What puzzled me there was they added more sand but the old mortar / plaster would already have contained sand.

Didn't see it, but they must have ground the old mortar down properly and used it as the aggregate and added new lime.