Aggregates for Mortar (London)

Preparing the mix - Mortar 

• Mix the lime and aggregate by volume (check the specification for exact mix ratio for the job or refer to the table below), measuring of material must always be with a gauging box or bucket. The sand/aggregate should be sharp, well-graded and washed.
• A conventional cement mixer can be used although for larger projects a roll pan or paddle mixer is preferable. Lime mortars mixed in drum mixers can be prone to balling but use of particular mixing techniques can reduce this. Switch the mixer on and dampen down the inside of the drum as this will help to reduce the amount of dust and prevent the lime from sticking too much. Switch the mixer off before adding two thirds of the water and half of the sand followed by all of the lime. Switch the mixer on, allow the water to thoroughly disperse throughout the mix (15-20 minutes) before adding the rest of the sand and more water if required. You will have to experiment for the first mix as the quantity of water will vary with sand moisture content – but be CAUTIOUS, for a 3:1 mix, initially add 6 litres of water, 30 litres of sand and then 20 litres of lime, mix, then add the remaining sand and adjust the water.
• Use the mix within 2 hours.
• Keep the mortar stiff - mortar for pointing should be kept stiff and dry in order to compress it into the joint without smearing. Take care not to get mortar onto the face of the brick/stonework. Mortar for laying bedding work needs to be a little wetter but should still be kept as stiff as possible to avoid excessive shrinkage. The mortar needs to be just wet enough to be workable.

Preparing the Mix - Plaster / Render

• Mix the lime and aggregate by volume (check the specification for exact mix ratio for the job or refer to the table below), measuring of material must always be with a gauging box or bucket. The sand/aggregate should be sharp, well-graded and washed.
• A conventional cement mixer can be used although for larger projects a roll pan or paddle mixer is preferable. Lime mortars mixed in drum mixers can be prone to balling but use of particular mixing techniques can reduce this. Switch the mixer on and dampen down the inside of the drum as this will help to reduce the amount of dust and prevent the lime from sticking too much. Switch the mixer off before adding two thirds of the water and half of the sand followed by all of the lime. Switch the mixer on, allow the water to thoroughly disperse throughout the mix (15-20 minutes) before adding the rest of the sand and more water if required. You will have to experiment for the first mix as the quantity of water will vary with sand moisture content – but be CAUTIOUS, for a 3:1 mix, initially add 6 litres of water, 30 litres of sand and then 20 litres of lime, mix, then add the remaining 30 litres of sand and adjust the water.
• Add hair or synthetic fibre (approx 1.5kg per tonne) to improve the strength and durability of the render, tease it in towards the end of the mixing.
• Use the mix within 2 hours.