Types Of Plaster - A Guide For The Non Plasterer
PVA Bonding and Glue
PVA bonding is white in color and is usually supplied in large plastic containers; this is the same glue that we used as kids in school. PVA is often used when skimming over existing walls and it's particularly useful when skimming over artex as it forms a water tight barrier and helps the plaster stick to the wall. Another benefit of PVA to plasterers is that it helps to prevent plaster from drying out too quickly. The problem with skimming over existing finishing plaster is that it soaks up water like a sponge and this makes the new plaster dry out straight away and start cracking. To overcome this problem PVA glue can be spread over the work surface first to slow the rate of water absorption and give the plaster much more time to work with the plaster once it's on the wall.
Backing Plasters / Bonding Plasters
Backing plasters such as those called 'browning' or 'bonding compound' is usually used during building and renovation projects. Almost all newly built houses are dry lined with plasterboard rather than wet plastered using browning or bonding compound. This is because plasterboard possesses many different advantages over traditional backing plaster. Bonding plaster and particularly browning are what is know in the trade as 'wet' materials. If these finishes are used on walls it can take several months for them to dry out fully. Plastering a full wall with backing plaster is also a very skilled job and requires a skilled tradesman to carry it out properly. In comparison dry lining rooms with plasterboard can be done quickly and to acceptable standards by a competent DIY enthusiast. Browning plaster is a backing coat plaster; it is invariably a pink or grey colour. Browning is used on surfaces such as house bricks and breeze blocks, or building surfaces which are absorbent. Browing should be put on in quite thick layers of about 10mm. Browning usually takes around 2 hours to set. Bonding Compound is arguably better than browning. Bonding is usually best applied to non absorbent material such as hard faced bricks or treated surfaces that have been glued with PVA. Usually bonding is put on around 8mm in thickness. Bonding Compound usually takes around 2 hours to set.
Skimming / Finishing Plaster
Skimming plaster is some times put directly over either browning or bonding compound. But in todays building industry it is more commonly applied directly to plasterboard. There are multi finish versions of skimming plaster which are very popular as it is suitable for use on most internal surfaces. You can also get hold of plasterboard finish, as its name suggest, it is used for skimming over plasterboard and it not intended for use over bonding compound or browning. Skimming plaster is normally put on much more thinly and as a final coat. It is usually applied around 2mm thick.
One Coat Plaster
There are lots of different companies manufacturing one coat plaster. Such companies claim that this plaster will serve as a backing coat and finish coat all at the same time. Although allegedly these plasters are highly versatile, in our experience such plasters are best left alone. We believe that you are better off adopting the traditional backing coat / finishing coat approach.
Remember, as a general rule for all plasters - the drying time will depend on the ambient temperature of the room, finishing plaster needs to be polished with a trowel as soon as it has started to firm up to the touch. If you delay too long before trowelling it up the plaster will harden and then your only option is to sand down the walls!
