Mixing plaster

Mixing Plaster;

The first thing that needs to be understood is "How to mix plaster correctly".

Mixing plaster is one of those black arts that people often find themselves struggling over, consistency is gauged by using a bucket trowel, let's mix a bucket of plaster.

Firstly we need to understand how much water it takes to mix a full bag of finish plaster, on average a full bag of plaster mixed to the correct consistency (or thereabouts) will take around 15 litres of water, so half a bag will take around 7.5 litres and so on. Cold clean water *MUST* be used, do NOT go mixing finish plaster (or any plaster come to think of it) in dirty water, why? Because it will set very rapidly indeed and may not even allow you to take it from the bucket onto the hawk before its set, you have been warned!

So I pour 7.5 litres of cold clean water into a plasterers mixing bucket, then I add the finish plaster using a scoop the best one I recommend is the ones used to scoop dry dog food out into their bowls, available at major supermarkets. One scoop at a time until I see a small island forming on the top of the water, from here I then mix the plaster/water using a stick (2 inch (50mm) by 1/2 inch (13mm) by 2 feet (600mm) long) mix it rigorously culminating in a pink water, add another couple of scoops and mix that, how's the consistency looking? At this point it should now resemble that of whipped cream, if not add more powder and mix, once it is at a consistency where it is just sticking to the mixing stick you are in the ballpark! Now pop the whisk into the bucket and give it a good blast, 20-30 secs no more, using our bucket trowel pick some out of the bucket and look at it, does it stand on the trowels blade or does it slump and fall off the sides, if it does its too watery, add a little more powder and whisk it. Does it seem a little thick? When you pick some out of the bucket does it feel as though it like soft toffee? If it does then add a little water to it, usually a cup of water or a scoop of plaster will bring the consitency right if either of those conditions appear.

The plaster is now mixed and resembles whipped cream, not too wet and not too stiff.

Mixing a backing plaster is identically the same, you are looking for a "workable" mix, if its too wet i.e. falling off the trowel, then its going to be no good on the other hand if it is too thick you have got your work cut out for you, not only will it be hard work but will set quicker too!