Mixing Mortar by Machine
1. Set the mixer up according to the manufacturer’s instructions. It is always a good idea to use polythene to sheet down under and around the mixer to minimize mess.
2. Ensure you have sufficient materials and small tools.
3. Start the mixer.
4. Add three-quarters of the water using a bucket.
5. Add three-quarters of the sand and three-quarters of the lime.
6. Gradually add the cement and allow to mix in.
7. Add the remainder of the sand, lime and water.
8. Allow the materials to mix for enough time to ensure a uniform colour and full integration.
9. Add more water as necessary to achieve the required workability.
10. Allow the materials to mix for a further 3-5 minutes – any longer, and too much air may be entrained into the mix, which will weaken the mortar. Timing should be taken from when all of the materials are in the barrel of the mixer and all batches should be mixed for the same length of time. Insufficient mixing time results in a non-uniform mix and poor workability.
11. Turn out the mix into the wheelbarrow, after making the inside wet.
There is some difference of opinion as to the order in which materials should be added to the mixer. With regard to the order listed above, some take the view that unless the cement is added extremely carefully it is likely to ‘ball’ together and not be evenly distributed throughout the mix. This will lead to a weaker mix and long-term problems of staining.
An alternative method is to load the mixer with three-quarters of the water then gradually and slowly add all of the cement, to achieve a thin paste with no lumps in it. The remaining dry materials and water are then added.
There is one point on which everyone agrees, however: if all the dry materials are added first, before adding any water, much of the cement will cling to the inside of the drum, resulting in a lean, weaker mortar mix.