Stop the Plaster Drying too quick

Is the Plaster drying too quickly – before you have a chance to properly work it?

The following check list will help ensure you have the maximum period of time possible to work the plaster.

Workability Time

The plaster should stay workable and possible to apply to the wall for 30 - 40 minutes. However, once the plaster is on the wall it should be workable for around an hour - and still continue to be just workable enough to complete the very final stages for an hour and a half or more with the addition of water if needed. Thistle Multi-finish setting time

If the plaster is drying and workability is less than this it has to be due to excessive evaporation or suction. On a small wall this can be helpful and allow the wall to be completed in a very short space of time rather than having to wait for an hour or two - but on a larger area this extra time afforded as a result of proper preparation will be invaluable.

Plaster drying will be affected by the following factors

1. Thickness of Plaster being applied

The thickness of the plaster will have an effect on the plaster drying time - but the thickness should be dictated by the flatness and finish you are wanting to achieve. If you start to put it on too thick in an effort to control drying time then other issues will result. It is better to control the suction.

2. Suction

Some walls whether they be a backing coat or a re-skim, over old plastered walls, can be very porous and suck the moisture out of the plaster causing the plaster to become firm.

High suction on a backing coat is best controlled by paining/flicking water on until the wall has absorbed as much water as it can and it starts to run down the wall. In extreme cases a hosepipe is needed - which will give you some idea of just how much you may need to do this.

High suction on an old wall that you intend to re-plaster can be controlled with PVA. The first coat of PVA should not be too thick, but diluted to a milky consistency to ensure it properly soaks into all the small pores present in the old surface. If it is too thick it can just lay on the surface and not be absorbed - ready to peel off at any time in the future, so the first coat has to be weak and watery to ensure proper adhesion - but this does not tackle the suction issue. Another coat of PVA will invariably be needed to do this. Subsequent coats can be made slightly thicker to ensure the surface is sealed more effectively. It is not unusual on very porous surfaces for 3 coats of PVA (the dilution increasingly thickened) to be applied. The PVA should stay wet for at least 20 minutes, if it becomes tacky with 10 minutes then another coat may be needed to prevent the plaster drying too fast.

3. Plaster Consistency

The peak test will ensure that the plaster is not too thick. When the whisk is pulled out of the plaster - it should leave a peak of about an inch - any higher and the plaster is too thick. Further details are at: Mixing Plaster

4. Water for the mix

Always use clean & cold tap water.

5. Environment

Ensure the room is not too hot - or a breeze is not drying out the plaster.

Plaster drying too fast

If the plaster is firming up too quickly - after all the above points have been addressed - just check that the plaster is in date and that it has not been stored in a damp environment. If the plaster is to be left for any period of time in a damp environment it is possible for the humidity to effect how quickly the plaster will set in the future - so ensure any unused partial bags of plaster are kept in a polythene bag.