Types of Plaster Used in Construction
Plaster is one of many building products that has been around for centuries and has been refined over the years to arrive at the variety of plasters we have today. In its primitive form it was used as a mud plaster and its basic purpose was to hold a simple structure together. Most plasters today are only suitable for use internally and their main purpose is to provide a smooth finish ready for decorating. They also help to add strength to a wall or ceiling and help to seal together building materials.
There are several types of plaster available today which cover every aspect of coating a wall to provide a finish. The most commonly available is called Multi Finish. It’s a plaster that is used as a final finish on all internal walls that have been undercoated in either sand & cement or one of the under mentioned 1st coat plasters. It’s also used as the final finish on plaster boarded walls and ceilings.
This white liquid is used as glue and has been popular in school classrooms for years. It is also marketed in different forms for use in the construction and DIY industries. It can also be used as a sealing & bonding agent and it is often diluted and brushed on to walls to allow the plaster to stick more easily and to prevent it from drying out too quickly. Be warned always use wet on wet. Do not allow the PVA to dry or it will form a sheet of plastic on the wall and the plaster will not stick.
Browning plaster (not so commonly used now has been replaced by Bonding & Hardwall)
This product is used as a 1st or backing coat to the finishing plaster and is grey or pink in colour. It is suitable for use on more uneven surfaces, such as brick or blocks, and can also be used to cover surfaces that are more absorbent. The plaster can be applied in several layers of about 10mm thickness if required.
Bonding plaster is very similar to browning plaster. Its very sticky will adhere to most surfaces it can also be applied to non-absorbent materials such as engineering bricks and can also be applied in several thick coats. It has the ability to be built up in depth to enable really poor walls that are out of true to be aligned However its very Hydroscopic and should not be used water borne areas.
This plaster used as a 1st coat or backing plaster it dries to a hard finish and is ideal for areas where impact resistance is required. It’s quick drying and can be applied either by hand or by mechanical means.
Used for areas containing x-ray equipment in medical and dental installations.
Tough Coat plaster
This undercoat plaster offers better impact resistance. Suitable by machine or hand application
One coat plaster
This product is marketed as having the ability to do the job of providing a base coat as well as the finishing top coat. It has not been so well received amongst the building fraternity and is usually passed by in favour of the other products.
Multi-finish or finishing plaster is applied over any of the surfaces mentioned above as well as directly to plasterboard. A board finish plaster would only be suitable for coating plasterboard. In either case the plaster is applied in a coat about 2mm thick. There is an art to achieving a fine finish which involves experience and patience. The plaster is applied over a wall and is allowed to set to a certain level before smoothing and then finally polishing.
Metal Lathing plaster
A plaster designed specifically to be used on expanded metal Lathing.
Metal lathing is a galvanised or stainless steel mesh used in the construction industry it can be fixed over poor backings including timber in preparation for a plaster finish.
The plaster is used as a 1st coat or backing plaster and can also be used on timber laths on heritage type projects.
Has been used since 7200bc
This product is becoming increasingly popular with eco-friendly building work as it is an extremely environmentally friendly plastering substrate. It is mixed using hydrated lime, sand & water. Horse hair was traditionally added as reinforcement. The down side to the professional builder is that it can be more expensive and time consuming to use.
Because plastering is classed as a ‘wet trade’, it can take several months for the walls and ceiling to dry out properly and so new properties are often ‘dry lined’ to avoid using any plaster or other coating.
This technique involves fixing or bonding sheets of plasterboard that have a tapered edge to the walls and ceilings. The sheets are then taped along the edges and then the joints are filled with joint filler which, when it has dried, is rubbed down to a fine finish. Because of the amount of rubbing down required it is not necessarily quicker to apply but the advantages are that the new walls are dry in 24hours & the property is ready to decorate and to move into straight away.
Plaster coving is not so popular in contemporary properties today but still has a large following. Using a coving avoids unsightly cracks that commonly occur where the walls meet the ceiling. A standard plaster coving is basically made in the same way as a sheet of plasterboard. The gypsum plaster is moulded and a paper sheet is wrapped around it to ensure it keeps its shape.
Traditional Victorian Cornice, Coving & ceiling roses
Many companies specialise in manufacturing period plaster cornices, mouldings, & ceiling roses. These are sometimes very elaborate and are made of casting plaster mixed with fibres which act to reinforce the cornice. This can be important as they can be very heavy and will be suspended above people. The lengths of cornice are formed in moulds which can take several days to ‘cure’. Once the plaster is cured the finished product is released from the mould.
In the first instance they are usually fixed into place using screws then the joints and gaps are all filled with plaster. This is then scraped into shape using various tools.
In heritage building moulds can be taken from the existing plasterwork so an identical match can be made.
Image credit: LOVE STITCHING RED