This section really just elaborates on the terminology and gives you more of an idea of what each process involves, its pros and cons and suitability to different applications.
Having a wall 'floated' and subsequently 'set' will leave you with a very durable and solid finish unlike plasterboard. If you are thinking of fixing anything of any significant weight to your walls then floating is the better option. The quality of work on this process can vary depending on requirements. A higher quality job will be needed for kitchens and bathrooms for example as extra time and care will be taken to get the float coat true and flat in order to accommodate the fitting of units and baths etc. which will benefit greatly from a flat surface.Using plasterboard instead of floating and setting also has implications with regards to architrave, skirtings and door frames to name a few so each job needs looking at based on its individual merits.
The setting or skimming process is the finish coat of plasterwork that will be decorated, it is applied to a thickness of between 3-5mm.It is important to understand that a skim coat will make a wall smooth but will only ever follow the contours of the existing background - if the background has large undulations, so will the finish of the new skim coat (it will however be smooth and as long as the undulations are unnoticeable then skimming will be fine). If you want a true and flat wall then you will need a float coat applying before it can be skimmed.
PVA is used widely to prepare walls and ceilings prior to plastering. It is diluted and applied in two or three coats, the first of which must be applied the day before any plastering can commence. The purpose of this is to control or kill the suction in the background material - if plaster is applied to material with too much suction it will dry before the plasterer can get it flat and in worst cases will crack and lose its adhesion with the background, so the first stage of killing suction is very important. If suction is extremely high a second coat of PVA may be needed to seal it.The final coat of PVA is a 'tack' coat. This is applied immediately prior to plastering and is plastered onto while still tacky, this coat of PVA gives extra adhesion for the plaster.
Drying times for plaster will vary depending on thickness and conditions in the room. If the wall has been floated as well as skimmed it will take considerably longer than just a skim coat of 3-5mm, a guideline for which is 3-5 days for drying. Finish plaster when drying will first go dark brown and then light pink. Once the whole area has turned thislight pink colour it can be decorated but not before as decoration will keep moisture in the plaster and could cause paint to flake, wallpaper to peel or the plaster to lose its adhesion to the background.It is important to note that heaters should not be used to speed up this process as this could also cause cracking and weakness, it is also recommended to turn radiators down or preferably off to avoid this, however you can use a de-humidifier to help extract the water content from the plaster.Prior to decorating, the plaster should be painted with a 'mist coat' which is cheap MATT white trade-type emulsion watered down a little, (around 25% water). This will help seal the plaster, stop it taking too much of the more expensive paint you will be using and taking the moisture from the paint too quickly causing peeling, two coats of which will normally then suffice once it has been sealed with the mist coat.Quite often people believe that the best way to seal new plasterwork is to use a diluted PVA solution - this is NOT TRUE and should be avoided, as this could lead to horrible problems when decorating.
As nice as a shiny, glass-like surface may be to look at on new plasterwork it is far from advisable: plaster burnished to this level will cause you trouble when decorating, especially when painting, ever tried painting glass? What you really want is a matt, flat finish.
This is just a tiny amount of information compared to how much we could put on this page and it's by no means meant to be a complete source of information, so if you feel you'd like more information than is listed here, either email us or use one of the two forums below.