How to Mix Hydraulic Lime Mortar

Equipment

The mortar can be mixed using a variety of equipment including a standard drum cement mixer, forced action mixer or a paddle, whisk and builder’s trug (75 litre). It can also be mixed by hand on a board using a shovel if you prefer.

Breathable

It is breathable (vapour permeable), absorbing and evaporating moisture from surrounding masonry. This also helps to protect the masonry, there is less risk of salt and frost damage.

Potable water

A good quality mortar requires clean, drinkable/potable water.

Method

1. Place the aggregate into the mixing vessel first.
2. Next place the lime powder in the vessel.
3. Dry mix the aggregate and lime together for 2 to 5 minutes.
4. Add a small amount of water and mix together for a further 5 minutes until a stiff consistency is reached.
5. Leave to stand for 10 minutes.
6. Slowly add more water and continue to mix until the desired consistency is acquired.

In total, mix for a minimum of 15 minutes. This gives the aggregate enough time to absorb the lime and to help plasticity, any water raised to the surface being absorbed back into the mixture as it is remixed.

Consistency

The mortar’s consistency is varied by adding more or less water.

The ideal consistency is something a tradesman learns instinctively from experience over time. It may vary on personal preference but typically depends on the work at hand.

Pointing

The ideal pointing mortar is similar in consistency to a snowball. This can be handled easily, compacted well into the joint and tends to cause less staining on the surface of the masonry. Using Conserv® Hydraulic Lime Mortar, a pointing mortar typically requires the addition of 8% to 10% water:

Bedding

A bedding mortar should be spreadable and contains more water than a pointing mortar. You can make allowance for the density of the masonry, for example, a bedding mortar for porous bricks should contain more moisture than a mortar to bed large granite blocks.

Using Conserv® Hydraulic Lime Mortar, a bedding mortar typically requires between 12% and 14% water:

Bedding

Adding too much water will cause separation of the lime from the aggregate, it can also affect the colour of the mortar. The idea is to add just enough water to make the mortar workable, the masonry itself can be dampened to reduce the absorption of the moisture if you’re working with porous masonry.