How to get started with Plastering What to do and what not to do
Plastering a wall or ceiling is often considered a job for a Pro, with some kind of dark magic involved in order to get a smooth, even finish but there is no reason that a competent DIY’er cannot achieve good results and without the need to sacrifice any chickens!
Breaking down the process of applying plaster to a surface there are just two basic criteria:
the plaster should stick well to the background surface
it should be smooth and flat when finished.
Easy right… well yes and no sorry, let’s look at some of the techniques and the tools you will need to get any plastering job done.
To plaster a wall first prepare the base surface it should be clean, dry free from loose material, Mix plaster with clean, fresh water, trowel the base coat on to the wall build up the thickness, level with a straight float, allow to stiffen, apply a thin skim coat, polish and smooth the surface as it stiffens.
Seems easy right? It is a simple process that can be done by anyone with a good arm, however practice is the key element, the more you try the process the better you will become, the trick is to have a go, and not to let the thought of plastering being difficult stop you,
With a bit of practice, some careful preparation and a small selection of good quality tools you should be able to achieve good adhesion and the ability to produce a smooth, flat surface
Take a look at the rest of the post as I go over the process in more detail and break down each step, offering some great tips along the way helping you to learn a new skill.
Basic plastering tools
Picking up the plaster and learning how to handle it
Knowing how to handle the plaster and being comfortable using it goes a long way to getting good results, it also helps to have the right tools.
Using a plasterer’s Hawk and trowel are the first things to work on, the Hawk is a small, square, flat tray that is held in one hand with a small amount of Plaster on the top. Hold the hawk in your left hand if you intend to plaster with your right hand, or your right hand if you are left handed.
Offer the edge of your Hawk up to the edge of your mortar board, it should be just below the surface of the mortar board to allow you to transfer plaster from the mortarboard to the Hawk
Using your trowel to drag a workable amount of fresh plaster on to the top of the hawk. I recommend that you take no more than one full trowel to begin with.
Now start to play with the plaster and get used to the way it behaves and handles, it will feel heavy on the hawk and getting up to speed with transferring the material from the Hawk to your trowel will mean your arms won’t be loaded for too long.
In one, continuous movement tilt the Hawk towards you and with your trowel held in the other hand, take approximately half the plaster off the hawk, pushing the trowel up and away from you.
Transferring plaster like this from the hawk to the trowel will take a little practice, I suggest that you mix up a spare amount of plaster and have a go.
Use our Guide to Mixing Plaster to get the best from each batch you mix.
Stand on some thick drop sheets and to worry about dropping any just get used to handling the hawk, trowel, and plaster.
How to Plaster
Applying the plaster to the wall
Now that you have mastered or at least know how to hold the plaster on the trowel, it’s time to apply it to the surface you want plastered.
Hold your trowel horizontal and inline with the surface of the wall, it should be loaded with plaster and the face tilted at a slight angle away from the wall.
Feed the plaster from the trowel on to the wall in an upwards movement, pressing the trowel firmly against the surface to help bond the plaster to the wall, as your arm move upwards and the plaster flows onto the surface, reduce the angle of the trowel, this maintains the flow of plaster evenly onto the wall.
Don’t worry about how thick or level the plaster is just yet, just ensure you don’t lay the trowel fully flat against the surface of the wall as this will ten to pull the fresh plaster off the wall.
Repeat the process applying the plaster over the area in strong even strokes, it doesn’t matter at this stage how flat or level things are, just get the plaster onto the wall.
Leveling the plaster up
Getting the surface built up to somewhere near the right level is the next step in producing a well-plastered wall.
Use your trowel to apply more plaster and build extra thickness, applying it as evenly as possible, then use a long, straight edge or plasterers Darby to level up the surface, work from the bottom upwards, moving the straight edge from side to side in a ‘sawing’ motion, pulling excess plaster and filling hollows.
As general guide I suggest working on smaller plastering repairs before taking on a complete wall, as this allows you to practice the techniques and become familiar with working and skimming plaster.
If your plastering project requires a large area to be skimmed, a great tip is to break the surface down into smaller, manageable sections, you can do this by using battens as screeds fixed to the wall at regular spacings.
The screeds need to be the same thickness as the required finished plastered surface, and fixed so that any screws are below the surface, this allows for a plasterer’s Derby to be held against the battens and run easily over the surface to the level required.
As you pull the Darby up, apply pressure so that both ends stay in contact with the guide screeds , gently move the tool from side to side in a sawing motion, this will cut the plaster surface and pull any excess material up with the Darby.
At the top of your reach or the repair patch, lift the Darby carefully away from the wall taking any excess plaster with the tool, this can be dumped onto the mortar board if it is not too stiff.
Any hollow areas can be filled using the plastering trowel and then re-run the Darby over the surface again to level it out.
If you are using a one coat plaster allow it to stiffen before you polish the surface for a final finish with your trowel.
You may need to scrape back the surface if you are using a base coat and a top coat type plaster, this is to allow for the top, skim coat to sit level with the surrounding surface or the screeds.
Finishing the Plaster surface
Its is best to apply the finish or skim coat over gypsum plaster base cost as soon as it has set, check our post on how long plaster takes to dry off more details
Cement based Sanded plaster should be left to dry completely and the surface then dampened with a water spray to control the level of suction prior to applying the top coat.
Drywall plasterboard can be skimmed straight away without the need to make is wet.
Use your hawk and plastering trowel to apply the finishing plaster over the basecoat. Use the same smooth upward stroke technique to smooth the plaster heavenly over the surface
Generally a skim coat should be 1/16” (2mm) thick any more than ⅛” (3mm) is too much, remember to hold the trowel at an angle to the wall and as you move the trowel upwards feed the plaster onto the wall.
Once the surface start to stiffen use a water spray or brush to apply a light mist of water to the surface, then trowel over the surface applying pressure with the trowel held at a shallower angle
This final polishing process helps to solidify and bind the plaster and will produce a smooth matt finish, if there is any excess water use a sponge to lift it from the surface,
My tips for getting the skim coat to a fine finish are to take your time, don’t use too much water and be gentle with the trowel. Applying too much pressure will lead to marks and the trowel catching on the surface.
It’s far better to repeat the process a few times and not to panic, a smooth steady hand is better than rushing and making a mistake.
Find out more on how to finish Plasterboard in our in-depth guide
How to Reinforcing a plastered corner
As you would expect the external corner of plaster walls can take a beating especially when they are in high traffic areas like corridors.
Plaster corners will need to be strengthened and reinforced using a beading, which gives the change in angle a protective layer and helps to hold the corner together and keep it looking sharp.
Using a corner beading
Damage to corners often is localized to a small area however if left long enough this can crack and extend along the edges of the corner profile, a metal or plastic reinforcing beading should be use to add strength and protection from further damage,
Most Hardware stores, builders merchants and DIY stores stock various profiles for plastering corners.
I prefer to use the expanded metal type, as this very robust and can be easily cut with snips or a hack saw, it will also hold a shape it it needs to be formed around or over an obstruction or change in level
Metal beading is usually coated or galvanized to prevent it from rusting and when cut the exposed edges should be treated or sealed with metal primer to stop any corrosion.
Preparing the corner and surface
Use a bolster and lump hammer to cut back any damaged plaster, taking away any loose areas, cutting back to a good, solid surface.
Brush any debris and lose plaster away then use a spray gun or sponge to wet the underlying surface or brickwork.
Mix up a small batch of plaster and using a trowel put down some evenly spaced patches of undercoat plaster on each side of the corner, this will hold the beading in place whilst you plaster over the wings.
Cut the beading to the correct length and prime the edges then press the wings of the beading into the plaster patches.
Using a straight or a long builders level align the outer face of the with the original plaster surface of both walls forming the corner and check it is level and plumb.
Leave the beading and plaster fixings to set before applying any more plaster. Then build up a base coat over the wings of the beading and spread this out of the area you cut back, filling up to the original plaster.
Give the base cost time to set a little and then check the level, if needed scrape back the top surface so that there is enough room, so that when you apply a 1/16”(2mm) skim coat it will be level and flush with the old plaster.
Allow the base coat to set and then trowel on the finish coat. The beading should now be used as a guide for the final surface.
Be sure not to nick or damage the beading as this may break the galvanized surface allowing rust to leach through the plaster later, this is a pain as it is difficult to stop and will ruin wall coverings, so its best to treat any damaged areas now with a little metal primer.
Things to avoid when plastering
Weakening the plasters strength
Gypsum and cement plasters have a chemical reaction when mixed with water which causes them to set hard.
If they are too dry because not enough water has been used in the mix, they will dry out before the chemical reaction has had enough time to full set and hardened the mixture, the plaster will be weak, crumbly and will need to be removed from the surface and replaced with a better mix
If too much water is added the plaster will be thin and can take too long to dry before it can be trowelled, this makes the mixture weak.
Adding more water to a batch of plaster has begun to set will also lead to very weak mixture, it is always best to discard old plaster mix and replace with fresh batch.
Check out our full post about how long plaster takes to dry for more details
Sanding uneven, rough surfaces
I recommend having a go at plastering following the steps and tips in this post, rather than be afraid or put off by having to achieve a perfect finish. They will help to avoid a rough finish which many would be tempted to sand flat and level.
Often beginners will have this as a back up to getting the surface flat and smooth but it’s better to go carefully and practice these techniques, as rubbing down a plastered surface is a nightmare.
Sanding just makes dust and mess, the dust will get into everything, it permeates in to area of your home and furniture and you will be cleaning it forever
Sanding will also provide a poor surface finish as the breaks the surface making it a permeable, and rough, it is much better to try for a good surface applying the plaster with bladed trowel
Any ridges left behind should be carefully shaved with filling knife before the plaster sets hard
A great tip to check for uneven edges and ridges over a wide surface like a wall is to place a lamp low down and close to the surface, this will project light across the surface and any high spots, ridges or dips will show shadows across the wall.
Avoiding Cracking and Crazing
Sand and cement based plasters need to be fully dry when used as undercoat layers, fine cracks that form in the skim coat are often due to the base coat shrinking as it dries out.
If the surface of the plaster is cracked but not ‘blown’ the surface is usually still sound and one way to recover it is to use a wall covering or wallpaper, rather than strip the plaster off back to the base surface.
Skim coats can also become cracked if they dry out too quickly, working in warmer temperatures can speed up the drying process and using heaters should be avoided, always plan ahead and allow at least a week for the plaster to fully dry out and longer if a large area has been re-coated.
For more great DIY tips and ideas check out our blog post and Podcast with information to help everyone improve their home, follow the links below:
This article was written by: Richard Quinton – The DIY Help Desk Owner, Engineer & technical specialist.
Richard is one of the key partners in The DIY Help Desk team. He is a qualified Engineer, writer, and publisher, educated to Master’s level. He is a keen advocate of DIY and home improvements.
Richard enjoys helping others to learn new skills and reach their goals and believes that passing his knowledge and experience on through his writing is an effective way to positively impact the lifestyles and well-being of others on a larger scale.