Finish Plaster

There are many finish plasters available and they all have different characteristics. One of the easiest finish plasters for a beginner to use is – 'Thistle Multi Finish'. Being used my most professionals it is widely available and can be used on any surface. The plaster should be mixed in a bucket with a whisk attached to a drill. Always put the water (clean, cold tap water) in the bucket first. If you want a full bucket full of plaster then the bucket will need to be half filled with water. By the time the plaster is added it will almost have doubled in volume.

'Multi Finish will set within 1½ hours - but remains workable for application for around ¾ hour. You should aim to have applied the plaster during this time. It is always advisable to clean the bucket as soon as it has been emptied. Clean water must be used for mixing - especially not water that may have old plaster in it from cleaning tools previously. If during the skimming process another batch of plaster needs to be mixed then it should be kept separate from a previous mix – as they will be setting at different times.

If you are skimming on to plasterboard then all joints should first be taped up with plasterer’s jointing tape (sometimes referred to as 'scrim'). This will stop the joints cracking. The tape is self adhesive. If you have any big gaps then sometimes two layers of tape may be beneficial.

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High or Low Suction?

High suction backgrounds (porous) will suck the moisture from the plaster you apply very quickly. Plaster applied to a high suction wall will stick very well but may dry too fast - before you have a chance to flatten it. This suction can be controlled simply by the application of water. Water should either be sprayed or painted over the entire surface. As a general guide you know when you have controlled the suction as you will see the water running down the wall as no more can be absorbed. In some instances a hosepipe (where practical) can be very effective on walls with very high suction.

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Low Suction backgrounds (slightly porous) will not suck the moisture out of the plaster. The plaster will only firm up due to it setting or by evaporation if working in hot temperatures. A background that provides no suction at all (painted surfaces etc.) must be properly prepared or the plaster will not stick. The use of a bonding agent such as PVA will need to be painted to the wall to ensure adhesion.