# Forum Home Renovation Brickwork  lime based mortar

## zongatron

hi guys 
building a rock retaining wall. 
Have been advised previously to use clean coarse sand and NOT brickies sand to build with rock.
ALso been advised to use a lime mortar not cement.
Has to do with lime mortar being more fatty and able to hold up the heavier rocks better than cement mortar.
Also has to do with the evaporation rates of water out of the mortar and rock once complete... 
However, advice was given in regards to a house rock wall, not a retaining wall. 
Should i use cement mortar and load up on the lime to keep strength as one side of the wall will be buried in clay? 
What you guys think?

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## GeoffW1

> hi guys 
> building a rock retaining wall. 
> Have been advised previously to use clean coarse sand and NOT brickies sand to build with rock.
> ALso been advised to use a lime mortar not cement.
> Has to do with lime mortar being more fatty and able to hold up the heavier rocks better than cement mortar.
> Also has to do with the evaporation rates of water out of the mortar and rock once complete... 
> However, advice was given in regards to a house rock wall, not a retaining wall. 
> Should i use cement mortar and load up on the lime to keep strength as one side of the wall will be buried in clay? 
> What you guys think?

  Hi, 
I've built several such walls on a cliff out the back, but they are not really retaining walls, just with garden beds behind. I thought my aim should be to match the expansion and contraction of the sandstone lumps I was using, and also the colours as much as I could. 
Did a lot of reading up and used 1:2:9 cement:lime:sand. It has been successful over 10 yrs. It is true that the lime retains moisture and permits slow curing of the mortar, which is then stronger. I don't understand that bit about it holding up the heavier stones, that sounds like a bunyip story to me. 
Another mix which is fairly close is 1:3 lime mortar with 10% cement added. I believe lime-only mortar would be too weak although it is very flexible. 
Now for a real retaining wall you might vary the mix from 1:2:9 to 1:1:6 (stronger)depending on the height of the wall. To keep the stronger mix from being grey you can use white cement. Clean sharp river sand is recommended as brickies sand has a lot of clay in it. 
Your local Council will also have requirements. A typical provision is that you have to submit plans for any retaining wall over 1 metre above natural ground level. You should also have good drainage on the inside of the wall but you probably do know that. 
One point worth mentioning is that a critical requirement for a long lasting retaining wall is the footing. You need a good strong footing or the wall will not last, and in soil this should be about 300mm deep and wider as the wall goes higher, say 400-450mm wide for a 1 metre wall, made of concrete. If the wall rests on rock, good. 
Another good thing is to slope the wall back (batter) about 1 in 10. 
Sorry if that is too much info, I could not stop  :Biggrin:  
Cheers

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## Bloss

Lime weakens the mortar, it does not strengthen it. High lime mortars are more resilient to use and also softer and more flexible when dry - so allow more movement and flexibility in the joints (where you want it - if the joints are too strong then movement will create cracks in the bricks or blocks etc - not an issue with stone mostly, although sandstone can be a problem). 
Stone-masons I have worked with used straight sand & cement mortar 4:1 or 4.5:1 usually with washed sand not brickies sand and no lime, although some use a 2:2:1 brickies sand:washed sand:cement. Generally in small batches as they are not usually able to get a 'run' on. 
As Geoff said - the prep is really important - so footings/ foundation needs to be suited to the sorts of loads the wall will carry. Also important to include weep hoes and make suer that once you start back-filling you use something to stop them getting blocked. 
Goeff's comments on approval eyc are valid too - most local governments have rules that apply after certain heights etc, but the main things is to remain aware of how much force can be involved in any retaining wall - from the weight of the soil itself, the slope (gravity is powerful!)  with any captured water adding to the issue.

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## autogenous

_ 			 			Lime weakens the mortar, it does not strengthen it. _ This is incorrect. It actually strengthens mortar. It does not weaken the mortar.
Its all about ratios and what the product is going to be used for. 
If it weakened mortar it wouldn't be used as a standard engineering specification of 6:1:1 for brickwork. If it was true that it weakened the mix then straight cement sand mixes would be used. 
Lime in mortar mixes provides adhesion and reduces the brittleness of mortar. :Smilie:  
The principle of mortar is that it should be slightly weaker than the product being used.
There's different ratios used according to the product. :Smilie:  
Once the mortar is stronger than the stone extra strength becomes pointless as failure results in cracks through the stone. :Smilie:  
At that point you need to be looking at foundation and footing.  
There are still buildings standing today built with lime mortar which have stood the test of time way beyond some modern construction. Even though their slaking process poor. 
Mortar mixes are very complex especially with stone as it depends very much on the stones composition as to how the ratio will be proportioned. 
Really in this day and age you need an engineers certificate as when it falls down that's what will be asked for when the insurance company is looking for someone to sue.

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## intertd6

just thought I would comment on this one
"There are still buildings standing today built with lime mortar which have stood the test of time way beyond some modern construction. Even though their slaking process poor."
The only way these buildings are standing is with constant maintenance programes.
I have done quite a few renos in sydney & hobart on terraces & other buildings built around the turn of the century & older, all had lime mortar masonry, where the masonry was fully exposed to the elements & you looked out from inside the roof areas they were like swiss cheese & it was possible to just pull bricks out of the walls with your bare hands, if they were not like that they had been repointed several times in the past, still terribly weak & a small earthquake they would be a deathtrap
regards inter

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## Bloss

> _ 			 			Lime weakens the mortar, it does not strengthen it. _ This is incorrect. It actually strengthens mortar. It does not weaken the mortar. 
> Lime in mortar mixes provides adhesion and reduces the brittleness of mortar. 
> The principle of mortar is that it should be slightly weaker than the product being used.

  So you are actually agreeing that lime is sued to weaken mortar - as I said?  :Confused:  
Yes - it makes the mortar more suited to the task of holding masonry together precisely because it is not as strong as straight sand and cement mixes so is more resilient and not as brittle as you say! Lime mortars have been around for along time and if under covered will last very well, but as Interd6 says if there is direct weather exposure and poor maintenance the lime mortars break down quickly. His description of being able to pull masonry work apart by hand is something I have experienced many times. 
I have also seen the problems of cracks propagating through bricks rather than through mortar joint lines because a too strong mortar has been used with no lime or insufficient. Of course the cracking is caused by foundation movement for whatever reason - not the mortar type. But repairs are made more difficult if the masonry itself has failed rather than imply the joints. 
Not really a need for an engineers to certify a retaining wall - unless of a scale that needs council approval -  especially not due to some misplaced concern about a future liability claim.

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## autogenous

> intertd6: The only way these buildings are standing is with constant maintenance programes.
> I have done quite a few renos in sydney & hobart on terraces & other buildings built around the turn of the century & older, all had lime mortar masonry, where the masonry was fully exposed to the elements & you looked out from inside the roof areas they were like swiss cheese & it was possible to just pull bricks out of the walls with your bare hands, if they were not like that they had been repointed several times in the past, still terribly weak & a small earthquake they would be a deathtrap

  Slaking in earlier periods had limited quality control. Quality of stone was an issue, soil type was an issue.
Many projects were done with the soil from the project ground and the stone used sometimes from the same site. Calcium proportion wasn't monitored or measured.
Some soils had a higher clay content than others not to mention impurities.
Transport costs for products were expensive so they were kept to a minimum by sourcing as local as possible. 
The buildings are usually quite old before the maintenance begins. There is houses that are built of cement/lime mortar around the country that have the same issues not even 15 years old. 
Its all relative to ratio. You think old houses are susceptible to earthquake you wait till you see the new ones when a decent earthquake arrives. *
Sorry Bloss, I sounded a little abrupt*. Taking lime out wont make it stronger.
Its a confusing statement. 
I actually like 9 sand 2 lime 1 cement for laying bricks. 
However older houses were built to work totally with compression in mind. 
Modern designs have tensile forces that require the mortar be much stronger in a range of ways.
It was quote of what you said Bloss. Lime in mortar actually increases the strength of mortar used for bricks and stone. 
A true mix of 6 sand, 1 cement, 1 lime is extremely strong. At one stage lime was replaced with aeration agents with disastrous effects. 
Here's a test for you, make a mix of 6:1:1  lay the brick pick it up off the mud put it back on the same mud and pick it up again. 
Do the same with a cement only mix or one with aeration. 
If you are laying hard non-porous stone you will have a higher ratio of cement and drier mix as its needed to accelerate curing to build the hard stone wall. 
You have to achieve a matrix aggregate ratio for certain applications. The more cement you put in the faster the mortar will cure. Cement mortar also has a life once it is mixed. 
Mixing a pure cement sand mix goes off fast and cant be woken up with water without losing some strength.  
However putting lime in concrete is a big no no because of the wanted desired properties. 
Ive seen walls built with 4:sand :1cement. I have had the opportunity for a brilliant tradesman build a corner for me by hand as an apprentice with a level. He showed me when it had been immediately been built demonstrating it to be dead plumb then 5 hours later. The mortar was so strong it contracted pulling the 1200 high corner out of plumb 4mm in the curing process. 
The reason for the 4:1 was to have the mortar dark and not using oxides to have black mortar on white clay bricks.

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## autogenous

> Have been advised previously to use clean coarse sand and NOT brickies sand to build with rock.

  This is because they are trying to achieve a hungry mix as the heavy dense hard stone tends to slip with very fatty mortar that has soil with high clay content. 
Soils vary greatly around Australia. 
I don't know what brickies sand is like in you neck of the woods Zongatron. 
Mixng the mortar drier is needed so the stones don't sink or slip.
Picking and laying the stones correctly is as crucial in the slippage and sinking of the non-porous stones.  
If the mix is really hungry the finish will look quite sandy. It can even become quite brittle. It really does depend what the two soil types you discuss are like. 
Very high loam soils with high fines are prone to shrinkage. So is very high cement ratio mortar.

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