Does any one know how to mix lime mortar???

I have to repoint some of the brickwork in my old house and I was told not to use cement based mortar if the original was lime mortar. Something about the difference in hardness and rate that it will absorb dampness, it all makes sense.

I asked how do I mix up lime mortar and I have not got the same answer from any 2 people.

So do any of you guys know how they used to mix up lime mortar like they used to in the 20's or 30's and is there any advice you guys can give me to make the job easier or more sucessful?

Thanks in advance, hope you can help.

Lime is still used in mortar mixes by many brickies and the mixes are always specified as the proportion of cement to lime to sand, and always in that order.

My Dad's mortar mix was made from portland cement and was one part cement to one part lime and 6 parts of sand (abbreviated to C1: L1:S6 or more simply 1:1:6). Note hydrated lime is used for this purpose. Always use masks and gloves too - lime is very corrosive.

In the pre-war period it was not uncommon to use 1 cement, 1.5 lime and 6 sand which gave a lighter coloured mortar that was a little softer when set and easier to work and a little slower to cure than a 'stronger' mix (one with more cement). That also meant that cleaning the bricks for re-use some years later was easier too.

Nowadays you can get touch up mortar pre-mixes that are coloured - it can take a bit of trial and error to get the dried colour to match, but if you have a small area to do they might be a good choice - I think Bunnings might stock them. You can mix and test little batches of your own on a spot that is not too visible to get a better match. Of course if you are scraping the joints and re-pointing the lot then matching is not an issue.

G'day MIW,
I once did a hobby course (a whole 20 hours) in block laying and our instructor told us you only needed to add lime to the mortar mix if the sand was too coarse. He also said that getting the mortar right was 80% of brick laying.

I assume the mix you are taking about contains no cement and is merely sand and lime and was the original before cement came along.

Any older tradesman brickie should be able to help with this one.

Barry Hicks

How old is this place? if it was built in the 20"s or anytime after 1900's then it is likely that the mortar is a cement based type probably with lime added for working properties.

If it was built before 1880 then the mortar is probably lime based with very different properties to cement based mortar ( which is totally incompatible with lime base mortar).

If you are not sure what type of mortar you have - break a little piece out and drop some 10% acid on it - if it fizzes and dissolves it is slaked lime mortar - if it doesnt fizz but seems to dissolve then you have a hard lime compo mortar probably with some proportion of cement in it.

Recipes vary for the true old style lime mortar and some off the processes are very dangerous.

True lime mortar is made by mixing slaked or hydrated lime (calcium Hydroxide) with water slowly until a rubbery putty like blob is formed. You may notice that the blob will start to sweat - exude moisture. At this point add 2 to 3 parts parts of pure washed course sand. If the blob doesnt sweat add less sand. You should be able to roll a sausage shape out of it and pick one end up without it breaking. It takes about 2 weeks to harden and needs protecting against rain until set.

If you add too much water discard the batch - or use it diluted a little more for limewash paint. Do not add more slaked lime to that batch in an attempt to thicken it - sorry it doesnt work like cement!

Do not breathe in the slaked lime dust or let it remain on your skin.
Do not let any lime mortar or slaked lime powder set on glass. Do not let mortar stay on your skin. Wash thourghly after handling it.

Slaked lime is the asbestos of traditional building practise. If you get a lungfull you face a chance of asphyxiating as the slaked lime gives off massive amounts of CO2 as it reacts with water/moisture in your lungs.

Once the lime mortar is mixed up there it should be applied within 10 minutes.

Also dont let its dust near your eyes, it'll mix with your tears and make a corrosive solution that will(not may)render you blind!
Lime is pretty nasty stuff.

I was just talking to a friend of mine who lives in Melbourne and he said that you can buy 15 litre drums of lime putty mortar from heritage renovation shops.

Ask a bricklayer here

Thank you to all for the great info, meantime I have also been doing some homework. I was advised by a guy from Blue Circle Southern Cement that I should make a blend of 80 to 90% hydrated lime and 10 to 20% ordinary portland cement, in my case off white. Then mix this blend 1:3 with washed sand (dry). Add water to make a mortar consistancy and it should set or cure with very similar properties to old style lime mortar without the issues.
I also found a pdf file from the NSW heritage council that gives a lot of good and relevant info.

I have copied the info and pasted it below because I can't seem to attach the file.

OOPS post is too long I will post again.

BTW the house is a weatherboard Californian Bungalow built late 20's to early 30's and the mortar problems are mostly in the foundations and a bit in the chimneys.
Thanks again for the info, especially safe handling procedures.

Alan M

Repointing Mortar Joints — Some Important Points

1. Match previous mortars:
• binder — if the original was lime, then use lime;
• sand — seek to match colour, grain size, grain shape and grading;
• match finished appearance of original joint — flush, struck, tuck pointed, etc;
• match mix proportions — traditional mixes were commonly 1:3, lime:sand.

2. But you may need to modify the mortar mix:
• because of the nature of the limes or sands available; or
• to make it weaker (sacrificial) to control salts; and
• more porous to promote evaporation (breathing); or
• to make it slightly stronger by adding pozzolanic materials.
• sacrificial mortars might be 1:3.5, or 1:4, (lime:sand); or possibly 1:3:16, or 1:3:20 (cement:lime:sand) for more exposed locations;
• adjust mix by adding lime putty (not water) to make sharp sand more workable, or to account for fine grained sands; e.g. 1:3 » 1:2.5 » 1:2 as sands get finer or sharper.

3. Some mortars should not be matched:

• hard cement repointing of original lime mortar may need to be replaced in

lime;

• where good breathing is needed, ‘mason’s putty’ (lime, whiting, linseed oil ± fine sand) may be too impermeable.

4. Lime mortars are best made with slaked lime putty:


• slaked lime putty is more workable (buttery or creamy) than dry hydrated lime;


• prolonged maturing of putty before use leads to finer particle size and better working properties, these are even more important for plaster and limewash;


• lime putty mortars are stronger than those made with dry hydrated lime, and more elastic than those made with dry hydrated lime;


• the workability of dry hydrated lime can be improved by running it to a putty in water;


• the longer it can be kept (sealed) before use, the more workable it will become.

5. Sands should be washed clean, be sharp and well graded:

• washed clean to remove all clay and organic material;

• sharp (more angular in shape) to ensure good bond to adjacent masonry;

• well graded so that there is a range of coarse, medium and fine particle sizes;


• sands of a uniform grainsize (whether coarse or fine) lead to higher void ratios and require more lime to fill the voids;


• finer grained sands have greater surface areas requiring proportionally more lime;

• dry sand makes for a better bond between lime putty and sand;

• damp sand may produce too wet a mix for good repointing work.

Repointing Mortar Joints — Some Important Points

6. Mixing mortars:

• lime mortars are best made by pounding and chopping the lime putty into the

sand with a mason’s hoe (larry), or with a roller pan mixer;

• conventional cement mixers can be used, but require wider blades; and

• adding heavy balls, such as used in milling, to force the lime and sand together;


• do not add water to the mix — there is enough in the lime putty;


• lime putty should be drained of any free water, and o nly putty-like material used;


• lime mortars can be mixed well ahead of use, kept sealed and then ‘knocked up’;


• knock up with a mason’s hoe, by beating with the end of a mattock handle, by beating and chopping with a spade, or using a roller pan mixer, but do not add water.

7. Raking out old mortar:

• failure of most repointing is due to inadequate raking out of joints;

• thin feathered out pointing does not adhere well, fails rapidly, traps water;

• rake out to at least 25 mm — the depth should be twice the width of the joint;

• rear of joint should be square, with clean sides;


• never widen original joint, no matter how narrow;


• use correct tools — hacksaw blades, skates, quirks or plugging chisels;


• chisels must be sharp — tungsten tipped if possible;


• clean out joint with compressed air, or low pressure water spray.

8. Pre-wetting:

• pre-wet masonry thoroughly, to control suction and prevent premature drying

of mortar;

• for many old (porous) walls it will be necessary to wet the wall the day before, and then several times on the day, the last shortly before placing the new mortar;

• walls should be thoroughly damp, but not glistening with water.


9. Pointing up joints:

• a relatively stiff, dry mortar mix is much better than one that is too wet;

• packing a joint requires compression of the mortar, not just placing with a trowel;


• use considerable force to compact mortar tightly into the joint;


• don’t overwork by dragging the tool as this brings too much lime to the surface;


• always fill any deep voids, pointing only the outer part of a joint will trap water;


• use correct tools — jointing irons (keys) that fit into the narrow joints, or plasterer’s small tools for wide joints in rubble walls;


• narrow joints — use a stiff dry mix carefully, or tape either side with masking tape.

10. Finishing the joint:

• match known previous joint finish (struck, lined, etc), otherwise use plain flush

finish;

• lightly scrape off excess mortar with a trowel or small tool;

• tamp joint with a stiff bristle brush to prevent shrinkage, expose sand, remove laitance, increase surface area — do this when just still possible to push a fingernail into mortar


• spray with fine water spray as soon as tamping is complete.


11. Curing:

• good curing is an essential part of making durable lime mortars;

• water must be present for the curing process to occur which is why mortars should be kept damp during curing;


• protect mortars from adverse weather conditions, eg too hot, too windy, or too wet;


• stage work around a building to avoid hot sun on new work;


• ideally work only below 25ºC;


• spray with water several times a day and cover with damp hessian for at least a week, preferably ten days;


• improved results can be achieved by then allowing a week’s drying (protected from rain), then wetting again thoroughly.


Prepared by David Young OAM and Elisha Long For the Technical Advisory Group of the Heritage Council of NSW

November 2006

Hi MIW, Thats handy info - Thanx