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Hi. We have recently bought, quite an old house, and can see a considerable amount of pointing that requires attention. I'm wondering/trying to learn, how and what is the correct way to mix 3.5 hydraulic lime-mortar, which I presume should be mixed with sand (but type is the most appropriate). I have read that portland cement should not be added to the mix.
Although, just finding lime-mortar suppliers is not easy, I've now tracked 3.5 down at a local merchants, which I presume is easier to use than lime-putty mixtures?
Is it best to mix differently for repointing and or brick-laying. Many thanks to anyone who can help.
Lime mortar basically falls into two main catagories; 'Pure' lime is that which has been produced with no impurities and is reliant on good drying conditions for a 'set' to be acheived (often sold as lime putty)and hydraulic lime is basically the same, but with impurities within the fiished lime in the now, powder form.
This is known as hydraulic lime. As the name suggests, it sets with the additon of water. The higher the 'NHL' number (natural hydraulic lime) the more eminent the set.
When mixing (one part lime to two and half sand-medium to sharp) put some water into the mixer first, then adding sand, lime and finally sand. It is important not to allow the mix to become too dry at this stage, as the lime/sand will ball up. Equally, too much water will not allow the mix to mix thoroughly; you need to acheive a state whereby the mortar is stiff enough to 'lump' round in the mixer, to entrain as much air as possible (without the use of plasticisers). Allow this 'lumping' round for at least 20 minutes. Now add further water to reach the desired consistency. You will probably find that mortar mixed in advance, patted down and covered with wet hessian/tarpaulin will make better quality and more workable mortar when used several days later. This is definately normal practice for mortar made with lime putty for instance, but the same practice cane be used for hydraulic lime mortar providing it is not left too long!
It should be noted that lime putty is the same chemical compound of Hyrdrated lime- NOT hydraulic and can be used as a more economical alternative, although it has to be said that lime putty is richer.
If using NHL 3.5 at this time of the year, then yes use it for repointing. Try and not smudge the arris of the brickwork and consider what is the best finish to compliment any areas that may not need repointing.
Hope to have been of help.
jholley 23rd May, 2011
The best type of sand to mix with hyraulic lime is soft yellow builders sand.
If its just pointing, I would suggest getting some ready mixed lime putty, its a lot easier to use if you havent done this before.
Google Trad-Lime they have got several outlets and will deliver, If there is one anywhere near you, you can get a rep out, he will advise and work out your quantities and colour.
B J D BUILDING/ROOFING 23rd May, 2011
i am a bricky by trade with 30 yrs expierence,i wouldnt take onthis job ,get somebody in who knows what there doing ,lime work is for a specialist.ive seen houses ruined by amateurs trying to save money..
rmb contractors 23rd May, 2011
Hi for plenty of information on lime you could speak to Martin at Anglia Lime they are very helpful and they would also supply the materials you need ready mixed.
Maltby Plastering 31st Jan, 2013
Using Lime mortar is not as simple as it may initially seem. It needs to be correctly colour-matched and there are various strengths of mortar available, which one you use depends on the type of material ( eg soft or hard stone,or brickwork ).
Ready mixed Hydraulic lime-mortar does not need to have sand added, the mix simply needs the addition of water.
For further information go to http://www.lime-mortars.co.uk/lime-mortar/hydraulic
Steve Kennedy 23rd May, 2011