22 Jan How to Mix Mortar for rendering
STORING SAND AND CEMENT
Storing the materials should not normally be necessary because it is best that they be bought as required and used up by the end of the job. However if you are held up for a time after taking delivery you should store the powder or pre-mixed materials on plastic sheets in a dry place. Sand should be stored in a neat heap on a board or plastic sheet and protect it from windblown dirt and rain with plastic sheeting. NB. Dirty sand can affect the set of the cement. Keep it covered.
ADDITIVES
Proprietary additives which modify the properties of mortars are added to the mix in precise proportions according to the manufacturer’s instructions. Their functions vary. Water proofers which make mortars impervious to by sealing its pores may be used when rendering exposed walls. Plasticizers, additives which make the mortar easier to work with can be used instead of lime.
MORTAR MIXING FOR RENDERING
Mix only as much mortar as you can use in an hour, and if the weather is very hot and dry shorten this to half an hour. Keep all your mixing tools and equipment thoroughly washed so that no mortar sets on them.
Measure the required level bucketsful of sand onto the mortar board or for larger quantities – onto a smooth, level base such as a concrete drive. Using a second dry bucket and shovel, kept exclusively for cement powder, measure out the cement, tapping the bucket to settle the loose powder and topping it up as needed. Tip the cement over the heaped-up sand and mix sand and cement together by shoveling them from one heap to another and back again and continue to turn this dry mix – the sand will actually be damp until it takes on a uniform grey colour. Form a well in the center of the heap and pour in some water but not too much at this stage. Shovel the dry mix from the sides of the heap into the water until the water is absorbed.
DRY MATERIAL
If you are left with dry material add more water as you go until you achieve the right firm, plastic consistency in the mortar, turning it repeatedly to mix it thoroughly to an “even colour. It is quite likely that you will misjudge the amount of water at first so if after turning the mix it is still relatively dry sprinkle it with water. But remember that too much water will weaken the mix. Draw the back of your shovel across the mortar with a sawing action to test its consistency. The ribs formed in the mixture by this action should not slump back or crumble, which would indicate respectively that it is either too wet or too dry. The back of the shovel should leave a smooth texture on the surface of the mortar.
Make a note of the amount of water used in proportion to the dry materials so that further mixes will be consistent. For cement-lime-sand mixes the lime powder can be added with the cement and dry-mixed as described above. Otherwise lime putty can be mixed with the sand before the cement is added, or the cement can be added to prepared coarse stuff. When you have finished, hose down and sweep clean the work area particularly if it is a driveway as any remaining cement slurry will stain the surface.
If you have any further questions please call our office to Pre Purchase Building Inspection in Perth.
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