Plaster
When building a home or remodeling, people usually think about the granite countertops, the extensive square footage or the number of windows in the new space. Much of the time, little thought is given to one of the most integral parts of the home, the interior walls. Most people don't think about the walls in their homes unless there's a problem or they move into a studio apartment. Yet, interior walls provide privacy and separation. They can also act as sound barriers, insulators and even offer additional fire resistance.
Whether you're remodeling a kitchen or just hanging a mirror, understanding wall coverings is essential. The most common interior wall surfaces are gypsum wallboard, also called drywall, and plaster.
What is plastering?
Plastering is a process used to produce an acceptable final wall or ceiling finish to a building prior to decoration. Plaster is a mixture of lime or gypsum with sand and water; hardens into a smooth solid; used to cover walls and ceilings. A substrate is the surface to which the plastering system is to be applied. The Plasterer is a skilled craftsman who can spread plastering materials over a substrate producing a finish as required by the client.
Plasterboards
This is a flat sheet of gypsum between 9mm and 12.5mm thick, sandwiched between sheets of durable paper. Boards are also available with various backings of differing thickness to improve insulation, restrict the passage of water vapour and to protect against fire. It has become common practice to bond or fix plasterboards to substrates to serve as the backing plaster coat. This method is known as dot and dab or drywall.
Finishing Coats
Finishing coats are usually between 3mm and 5mm and bring the backing coats to a smooth skim finish. Finishing plasters used to produce these setting coats are available as premixed gypsum plasters. Finishing coats can also be lime putty and fine sand or a mixture of lime, sand and gypsum known as gauged setting stuff.
Solid Plastering
Solid plastering denotes backing coats of a paste or mortar-type consistency comprised of an aggregate and a binding matrix. Binders include lime, gypsum and cement. Aggregates include sand, vermiculite and perlite.
Choosing a Plastering Material
Lime plasters are compatible with old buildings containing slight dampness. They are said to breathe, which means they allow moisture to evaporate from the wall before it shows as damp patches.
Gypsum plasters set much quicker than lime plasters, so speed up waiting times between coats. In cold conditions gypsum backing plasters can take a long time to dry. Gypsum backing plasters cannot be used on damp walls. Gypsum plasters are compatible with dry brickwork or block work, preferably to internal surfaces of cavity wall construction.
Cement-based plasters or renders can be gauged with lime and used externally, and can be useful for waterproofing and tanking. Strong mixes can pull away from weak backgrounds and are brittle cracking if slight movement of the building occurs, they can also be cold and attract condensation.
Ornamental Plastering
Decorative plasterwork has a long history. Mouldings were originally run in-situ with ornaments cast in carved boxwood, pear-wood or hard plaster and gelatine moulds using composition materials and gauged setting stuff.
Here are a few more pointers to help you along.
' Plaster won't stick to just any surface and you don't want it to start falling away, so ensure your surface is ready to be plastered. Make sure it is clean; remove bits of existing plaster, dust or wallpaper.
' Check the suction of your wall. High suction porous backgrounds can suck the moisture from the plaster meaning it dries too quick so you may need to wet the wall before you start.
' Low suction backgrounds, such as painted surfaces will also need to be properly prepared.
' While plasterboard or backing coat can be skimmed over without preparation, existing plaster or previously painted surfaces will need treating with a bonding agent, such as a mix of PVA glue and water to ensure the plaster sticks to the wall.
' You could also try adding a handful of sand to the PVA mixture to give it a rougher texture and better adhesion.
' It's vital to have clean buckets, tools and equipment to ensure your plaster doesn't go off and you get a better finish that lasts.
' Also, dry plaster is a nightmare to remove from your tools and can cause drags in the plaster finish on your next job.
' Always use clean water, again to avoid contaminating your plaster and make it go off or set too quickly.
' Always mix plaster by adding plaster to the water and not the other way around.
' Add just enough plaster first to make a heap on the top of the water and mix it so that it's lump free, then slowly add the plaster to get the correct consistency either with a wooden stick or mixer drill.
' Plaster must be applied when a surface feels tacky, but not too wet, to help it bond to the surface well.
' When plastering a room, try not to do two walls that are touching each other as you risk damaging one wall while plastering the other.
' Keep it cool in the room you are plastering, radiators should be turned off or the plaster will dry out too quickly, making it difficult to apply and crack.
' Beginners should start on a small area first to ensure they're getting the technique right. Start with an area which only takes 30 minutes or less for the first coat.
' A good plaster finish can be achieved with a combination of confident firm pressure and the correct angle of your trowel.
' Don't try and get your surface perfect in the first coat, it takes too much time and the plaster may dry too soon. Imperfections can be ironed out in later stages.
' When you first apply your trowel to the ceiling or wall, start with one edge of the trowel angled away from it. As the plaster on your trowel gets less and less with your movement, the angle between your trowel and the surface gets smaller.
' If you're doing a ceiling, don't stand directly under your trowel, just in case you get plaster in your eye.
' Artex ceilings can be plastered by just using a thicker coat of plaster.
' Ensure the thickness of the plaster is even on the first and second coat. Use firm pressure to ensure it is flat with no bulges.
' Make sure the first thin coat is wet and pliable when you apply the second coat.
' Don't worry about filling every little hole at this stage; it's better to avoid your plaster firming up too quick.
' After the first two coats, the 'trowelling up' process begins. This is time to fill all those holes, remove your trowel marks and get it smooth.
' As the plaster sets it will darken in colour, which means it's time for the final trowel.
' Don't over polish the plaster on the final dry trowel stage ' it should be even and slightly polished, but feel like eggshell ' any smoother, it makes paint and wallpaper a nightmare to stick to.
' Choose the right tools for your DIY Project
' Make sure you know you can comfortably get to hard to reach areas with stilts or scaffolding.
' Love your trowel, it's a vital piece of plastering kit. Make sure it's clean, rust free and the correct type. Just any trowel will make the job harder. For beginners, a good size to start with is 11 inches. While a larger trowels covers areas faster, it's harder to control.
' Plastering tools must be of good quality.