Hi I am new to plastering and have found issues with it going off too quick although I have used PVA. Is this because I am applying it too thinly and therefore is drying out too quick? I am also finding that before I finish a small wall with first coat its starting to go off to the point that it seems unworkable due to it drying and therefore smoothing down ready for second coat is problematic. I am also finding that the amount of pressure I am having to apply to do anything with it for stage 3 becomes quite painful over time. Could my mix be too thick maybe?
Thank you in advance,
Kind regards
Answer
Hi
The thickness of the plaster will have an effect on the 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.
A quick check list is below:
1. 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.
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. 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.
2. 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.
3 Environment. Ensure the room is not too hot - or a breeze is not drying out the plaster.
Workability time. The plaster should stay workable and possible to apply to the wall for 30 - 40 minutes.
Hopefully this will help you!
Paul