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QuestionWhat type of mortar mix should I use for a rubble stone wall?
I've got a bunch of rough stone that I dug up in my garden, and I'd like to build a wall as a landscaping feature. I've heard different views on whether to use a cement mortar mix or a lime one. Wondering what people out there think, and why.
I disagree with Nick. External walls are prone to drastic temperature changes and extreme amounts of moisture. So the cement binding the stone should be more flexible. I recommend a 1:1:3 mix - cement, lime, sand
Lime has benefits because of its flexibility and its porosity; it helps moisture that has penetrated a wall to evaporate. Lime is also less prone to crack than cement. Lime helps to repair fine cracks by allowing carbon dioxide to penetrate which then reacts with free lime to harden and close the cracks.
HMC Locksmiths 17th Feb, 2011
Hi there i was always told the mortar should never be harder than the product being layed to alow it to move the same as the product so if it was sandstone i would say 5 parts sand and 1 part cement still will be strong enough. many thanks sean
Ransom Building Services 17th Feb, 2011
I would use a 4/5 soft yellow building sand to 1 part cement.
Reason is you state it is a wall/garden feature, if you have soil behind it or below it wont last long with lime in the mix.
Soft yellow sand wont be much stronger than the stone.
We use lime in stone work above dpc
Walcrete was phased out because it contained lime and people were using it below ground,and not cement.
These are my preferences, but different parts of the country have different types of sand, stone, as mentioned there is nothing wrong with adding coarse sand or plastering sand, but I wouldnt add lime to be used below or against ground.
B J D BUILDING/ROOFING 19th Feb, 2011
In my opinion the best mortar to use for this is NHL 5, 2 soft sand and 1 sharp. NHL lime is different to hydrated lime in that it sets to a strength over a period of around a month. Putting hydrated in any cement mortar offers no additional movement or breathability because it is countered by the cement. Cement soaks up water and holds it and will over time cause the stone to erode. 90% of our work is of a traditional nature so can vouch for this mortar, the only thing regarding this mortar in order for it to remain solid when finished it needs to be compacted i recommend you build the wall leaving all joints flush and then beat the mortar with a churn brush when nearly dry.
D M Allanson 28th Feb, 2011
has with all stones they are different mixtures.everyone uses lime in mixes ,but depends where the wall is being built.if in a garden then use lime in your mix.i would,t use a lime mix if it was on a main drag roadway,because it would,t take long to start corroding pretty quick,so look where it is going to be built then you can judge what mix is ok,thanks nick
kentish builder 17th Feb, 2011
4 to 1 mix is far too strong. a 6 or 8 to 1 with an added 1 part lime is perfect for stone. in your case i would go for 6 sand, 1 cement, 1 lime. make your mix stiffer than brickwork mortar and keep your joints as small as possible, fill all joints as you go. at the end of the day scratch off the joints flush and brush with a soft brush.
jd kent 17th Feb, 2011
I personally would use hydrated lime with sharp sand for a grey colour stone so that you don't need to use cement as the lime will harden over time but will still be able to breathe. If the stone is over a lighter or yellow colour then try using a washed sand to match the stone colour. Try 4 and 1 as the gauge you will still be able to point this up the next day or brush it off to get an old authentic look to the stone.
L J Fletcher Builders Ltd 18th Feb, 2011
If you are not putting in a footing go for a lime based mortar ,it will take longer to set but will allow movement ,I would use a 4 sand (as sharpe as you like for texture) 1 lime if you like add 1/2 of cement to aid setting, dont make it any stronger or you are defeating the point of lime but you will need to protect from frost till it sets. if using a footing (on concrete) 5 sand 1 cement if you dont mind cracks over time but dont make a wet mix it only needs to be damp enough to hold together when squeezed in your hand
createascape 18th Feb, 2011
This seems like a very contentious issue from the comments! It depends how weak and crumbly the stone is, if its crumbling in your hands dont even bother using it! If its pretty solid I would go for a 5 sand, 1 cement, 1 lime mix. Ransom building services is correct in that the cement should never be stronger than the brick/stone/block being laid and the lime provides flexibilty as Handy man col suggests. I am building a sandstone wall at the moment and am using a 4 building sand, 1 sharp sand, 1 lime and 1 cement mix. I am only adding the sharp sand to add texture to the mortar. Each to their own though.
R.Hughes Building and Conservation Ltd 17th Feb, 2011
sharp sand and cement 4:1 and add waterproofer with built in hardener. it will last forever and you will be able to jetwash it as well.
northview property mainenance 17th Feb, 2011
In my opinion do not use a cement based mix, as previously mentioned this is due to the fact that cement does not have any type of breathability. This usually causes any moisture trapped in the wall to be vented through the stone, this then causes the stone to erode through moisture transportation and the process known as freeze thaw. Lime also survives and weathers a lot longer than cement, I have worked on a 1500 year old clapper bridge where the mortar was still bedding the stones satisfactorily.
If the stone is of a very hard and dense nature you can use a NHL 5 lime. However usually I find a NHL 3.5 is preferable mixed with a 2.5 sand to 1 lime ratio. Usually the sand is 2 parts coarse (ish) building sand and half part fine sand. Different colours can be achieved by using different sand colours
Lyons Stonemason 15th Oct, 2015
Allanson knows his stuff, I agree. Good luck.
Louis Kingwill 2nd May, 2011