Mortar Mixing

Mixing your Mortar

A conventional cement mixer can be used, although for larger projects a roller-pan or paddle-mixer is preferable. Lime mortars mixed in drum mixers are prone to balling. However, the following mixing procedure can reduce this problem. It is vital to ensure that when measuring materials this is done by volume. A gauging box or bucket will be necessary for this task. Measuring by shovel is not acceptable since quantities will be inconsistent:

1. Start with an empty mixer.
2. Add 1 part sand
3. Followed by 1 part lime
4. Followed by 2 parts sand
5. Mix dry for at least 5 minutes
6. After 5 minutes slowly add water until the desired consistency is reached
7. it is very important not to drown the mix by adding too much water.
8. Once the desired consistency is reached mix for a further 20 minutes
9. (The above example is based on a mix ratio of 1:3).

The mix, to begin with, will appear dry but as mixing time increases the mortar will become much ‘fattier’. If too much water is added the risk of shrinkage will increase and the final strength reduced. Do not use any plasticisers.

Water Content

The addition of water should be considered carefully, as it will directly affect the ultimate strength and durability of a mortar. The more water introduced into the mortar mix, the weaker will be the final result. However, too little water will prevent the chemical processes taking place and weaken the material. Generally, water should be added sparingly, until a useable consistency is achieved.

The masonry background may also affect mortar strength. Dry backgrounds can quickly ‘suck’ moisture from newly applied mortar. This should be controlled by dampening down the background prior to mortar application.

Storage of Lime & Aggregate

Roundtower Natural Hydraulic Limes are supplied in water-resistant paper bags. If the bags are allowed to get wet they may be irreversibly damaged. Also, once opened the exposure to air will start to weaken the hydraulic set. As a result any opened part

bags left at the end of the day should be carefully folded over at the top and put into a dry store. In this state the lime will remain useable for a further 2 or 3 days. Thereafter it should be discarded. For larger orders Roundtower Natural Hydraulic Limes are supplied in 1400kg (56 x 25kg bags) plastic wrapped pallets.

Aggregate should also be covered since if left exposed fines can be washed out and the material as a whole can gradually separate.