Plastering Guide Basics
Author Stuart Kentish
Hopefully with this quick guide I will help prepare you, Preparation is key when working with any product that has a time limit, you should know your tools and how to use them, the area that needs plastering should be prepared 100% ready for final wet plaster, these steps will save you time and money.
“Practise Makes Perfect” and who needs perfect plastering if you can say it was done by yourself, you will still be very proud of yourself if you take the plunge there's worse things in life than bad plastering, I can not think of any personally but i’m sure your lives do not revolve around plastering like mine after 20 years i can spot bad plastering everywhere i look, ive become a perfectionist, I’ve Learnt that the painting is more important and cutting in your different colours as sharp as possible. Plus new dry plaster sands down very easy with a coarse sandpaper and work your way down to a fine grade, even white wash before sanding process and you will smooth out lots of texture imperfections.
What You Need To Know First
What kind of Project are you diving into? The short simple answers are as follows
Only a Depth of a few millimetres of plaster has fallen off and behind I can either see plasterboard or more plaster, I just need finish plaster coat, PVA or unibond area and then it is ready for finish plaster
I can see Brick I will need to clean area with water or weak PVA and fill any holes deeper than 3 mm with Background Plaster (Browning/Bonding coat/Hardwall)
I can see a hole or the inside of hollow wall, you can use this guide to show you how to make new supports or find old one to install new plasterboard/sheetrock
Brand New Just Installed PlasterBoard by professionals is best scenario, Lovely and flat and the joints are tight and almost invisible, if you have done the boarding you may want to do a little more preparation work before you plaster, i.e. fill big gaps
A Ceiling! Difficult for beginners but not impossible obviously, wear goggles! Chance of plaster in your eye is high and can cause serious harm to your eye
I have new walls built out of wood framework, learn how to plasterboard new walls in this guide
I have new walls built out of brick or block, learn how to plasterboard brick walls and learn how to wet plaster onto brick or block using this guide
I have loose sounding plaster but not sure how big the job will be, in this guide i will show you the best and worst case scenarios with tricks to avoid worst case scenarios
I have removed all the old loose plaster and revealed brick and studwork (wood frames) in this guide you will learn how to patch using plasterboard and wet plaster application
The term Over Skim just means to use finish plaster only, because the old background is still flat enough even if there are different levels of a couple of millimetres.
First even tho you think you have removed all of the loose plaster you should check again and use a stiff brush to sweep the as much loose dust and bit of grit as possible.
Then we need to be sure the plaster will stick to the old wall properly here we use PVA or UNIBOND. PVA is a sealant and adhesive.
Plaster when mixed is full of water and you do not want that water to disappear too quickly so to ensure the plaster does not dry to fast on our old surface we can paint on sealant, any sealant would do this job but some may not be suitable for plaster to stick to.
PVA will fill little holes you can not see and these tiny holes if not filled will suck the water out of your plaster very quickly like a sponge.
Bricks, blocks and old plaster surfaces have different sponge like characters or different porous surfaces, we use different strengths of PVA for these different circumstances.
Strengths of PVA just means mixing it with water to thin it down, it usually comes in 5 litre bottles we normally mix it with water to a ratio of 4-1 4 parts water to 1 part PVA, you can use this mix on every surface but some surfaces will need more coats than others, the PVA mix you apply should stay tacky or wet for 5 minutes, if the area is drying immediately it will need 2 maybe 3 coats.
Applying the PVA mix you have made is very easy but also easy to do badly, because you can barely see the PVA mix once watered down and spread out plus it dries clear.
When applying PVA with a brush do 3 or 4 strokes with your brush over the same area to force PVA mix into every tiny hole if applying with a paint roller i suggest the same thing, also you should see areas stay shiny and some areas after 1 minute will be dry so just apply a little more to those areas, if you take these steps you should only have to do one coat.
Maybe you do not want to tackle whole walls, how big are the patches of plaster that have fallen off, maybe you can just fill out the patches like here.
If you are thinking about plastering over whole areas so you have 100% brand new walls you can and should for best finish put scrim on the cracks that are easy to see and new angle beads on your external corners not internal like here
If you decide to patch and not do the whole area keep your edges or blends wet during applying and smoothing down, even after PVA your edges will dry quicker and your blends will dry quicker because depth of plaster goes from 3mm to 0mm keep cleaning excess plaster of the surrounding area too, otherwise you could pick up these bits later on when they are dry, these dry bits will scratch your plaster if you accidentally drag them into your patch during the smoothing process.
Preparing your walls for Finish PlasterCovering Brick or Block or Concrete
If you have brick work on show after removing your old loose plaster you will need to apply backing plaster, brick and block are base coated with ½ - ¾ inch deep layer of the base coat plaster, otherwise known as Hard wall, Browning, Bonding coat, 25kg Bags, i like to use Bonding coat all the time because it sticks to everything and it is stronger.
After you have cleared loose plaster and dust you can either drench the area with water just before laying the base coat so the base coat plaster does not dry too quickly or use a 4 part water to one part PVA mix on the area.
The base coat plaster should be mixed and laid quickly so preparation is key, have your area completely ready for application have your working area in the room protected from plaster, i.e. sheets or plastic floor protectors and polythene over shelves and decor electronics e.t.c. polythene is great for keeping dust off things but done work on them, too thin and will tear, plaster can sometimes stain in certain circumstances carpets, wood or tiled floors should be covered up to a mtr further from your work area, splashes can happen.
Your tools must be clean and wet, your trowel should have no debris or old material on the face also no rust, around the edges, rust will drag the surface of the plaster whereas a shiny polished metal edge glides over the plaster. If you use a rough trowel you will move and drag the plaster around too much, if your trowel is just a little rusty the plaster itself will polish the metal on your trowel just like sand paper.
for this task and most plastering tasks
4 inch paint brush
1 inch paint brush
Snips for cutting Angle Bead
1 mixing bucket for you plaster mix
1 cleaning bucket, half filled
1 bucket for very clean cold water
A means of mixing the plaster, whisk, paddle, drill, bucket trowel (once mixed it has to be smooth with no lumps!)
If patches are wider than trowel length we use a straight edge or feather to level the base layer like this
Here are the materials needed for base coat plastering
Clean cold water supply
PVA or UNIBOND
Base coat - Base coat plaster names- Browning, HardWall, BondingCoat
hole in hollow walls (stud wall)
Normally we would make the hole bigger first, removing enough to reveal the stud (wood) underneath the plasterboard then we can fix new plasterboard to that wood, if for some reason you can not do this there is another way, simply add your own wood and stud, long but thin pieces of wood can be slotted in and then screw through the area around the patch to fix the wood in place, ideally the wood spans across the hole and is attached with 2 screws either end and the screws should not be closer than 1 inch to the hole because the edges of the hole will be weaker plasterboard, be careful not to put too much pressure on the plasterboard best to hand screw and not use a drill.
New PlasterBoard installed
If you are lucky enough to have professionals plasterboard your project then plastering should be easy, things to look out for are flush edges sharp corners with small or no gaps between plasterboards pieces any gap over 3mm wide can cause a bump in the plaster later because the plaster will sink out the gap during the set, however in time you will start filling them gaps first and then lay the coat properly, that way the plaster has time to firm up in the gap before first coat goes over the area.
The preparation you must do before plastering if the professionals did not do it for you is scrim or joint tape all the joints between plasterboards and snip your angle beads for all your external corners in the room or area to be plastered scrim is a fibreglass mesh it strengthens the plaster over cracks or places of different material i.e. PlasterBoard and HardWall
Goggles for practise please, plaster is so easily dropped in your eye when laying your coats plaster on the ceiling, rinse your eye out quickly do not rub your eye at all and try not to blink and keep your eye closed until you are under a running tap and keep your eye closed to flush it out, if your eye feels like it is on fire go to emergency to have it flush out also if you are plasterboarding it goggles are a good idea because the bits that fall from plasterboard edges and screw holes are like grit in your eye not nice and do not rub your eye! Blink it out or use tiny piece of dry tissue paper to stick to the grit
Laying a Ceiling is much like laying a wall you should think of it just like a wall but be more careful with your eyes
Your reach is very important, you do not want your head to be touching the ceiling and you do not want your arm stretched out to touch it, my favourite height to plaster a ceiling will give me 4 inches my head and ceiling, any closer and you will start crouching and that is terrible for your back, also do not be so far that you can not touch the ceiling with your fingers or trowel for 3ft of the ceiling, you can do 6ft strokes if you can put one leg far forward to start the stroke and with the same foot during the stroke step backwards, Be sure you know you are stepping onto a sturdy platform, we use hop ups, step ups, milk crates, step ladders, step ladders are not great for plastering but sometimes needed for a hi little bit, saves building a tower to stand on
If your ceiling is PlasterBoarded or has holes even as small as 4mm in diameter these must be filled because plaster is almost a liquid when you spread it so gravity will be against you and big gaps in plasterboard and holes in your old ceiling can sag or even fall out, your scrim joint mesh tape should be over the gap but the scrim can also be pulled down and a lot more plaster with that, on a ceiling any gaps over 3mm should be filled with a little mix while scrim taping.
PlasterBoarding stud work/ timber framing
Have you ever done a jigsaw puzzle? Just like that but even easier than a jigsaw because you choose the shape of the pieces, the important thing about plasterboard is that it does not move once fixed in place, you should not be able to move the plasterboard when you push on it because you will be putting pressure on it when flattening your plaster with your trowel and you do not want movement during any of the plastering process.
PlasterBoard actually cuts up very easily, once the paper layer is cut the rock part can snap and the paper layer the other side folds and then you cut the folded paper layer, remember paper cuts and folds but does not snap evenly, this is why we scour through the paper on one side with a sharp knife then it will snap along that line like this
Cutting PlasterBoard could not be easier, score snap cut basically
We Score one side of the PlasterBoard, This is just a collection of sheets of paper so even a blunt box knife cuts through it or at least scores it, then on the otherside gently put pressure directly on your scored line, it should snap with a firm tap, do not put stress on any other part of the PlasterBoard except for your score line on the other side.
After snapping you can cut the paper free hand because you can follow the,fold if it snapped in the correct place
You need a tape measure for measuring your cuts, any joins between cuts should share the same stud or support your fixing to, no flapping edges! Use drywall screws, depends on the PlasterBoard thickness what screws you need but as short as 32mm is good for most
When you start planning your jigsaw pieces start against one edge of the area and cut your pieces as big as possible you want your cut edges to land on half of the stud joist / timber beam and your plasterboard should be strong enough to go from joist to joist without bending much went lent on, there may be a slight! Bounce with a firm push of your finger in the very centre of the wall studs/joists.
your measurements should be as accurate as possible and then take off 2mm off both measurements for an easy fit, when i say both measurements i mean most pieces you will cut, which are height and width but there are many awkward cuts, different angles or pipes and boxes to work around, you can practise those cuts on a piece of paper, divide all you measurements by 10 and draw it on paper to check you are going in the right direction.
Draw your lines on the plasterboard with pencil before cutting with a knife you can then see the shape again in full size and it will be easier to tell if it will fit in correctly and you have it the right way round, you must plaster the unstamped white side or blue/pink/ Pink Plasterboard is extra fire retardant, Blue Plasterboard is extra sound insulation
New Brick or Block or Concrete
PlasterBoard Or Wet Plaster/Basecoat Plaster it is up to you
Wet Plaster Vs Plasterboard
Place plasterboard in the patch and use a Straight edge i.e a Level or straight wood to check it sits 10mm lower than the finish level there is not much room for plasterboard adhesive so we fill the hole with basecoat plaster. I try to use plasterboard as much as possible but lots of holes or awkward angles can take longer to plasterboard than to basecoat plaster.
There are benefits to basecoat plaster walls Hard wall is appropriately named but Browning and Bonding Coat do the same thing, it will be a solid wall great for……..sometimes fixing into plasterboard can easily damage the plasterboard because of the gaps between the old wall and where no adhesive was put.
To stick your PlasterBoard to your Brick walls or Block walls, first wash the area from dust and this will also dampen the masonry which will help the adhesive stick, put your adhesive in lumps each lump the size of a big handful or a full Bucket Trowel also use the Bucket Trowel to apply the lumps.
How to apply the adhesive onto the PlasterBoard using the Bucket Trowel, scoop your adhesive mix which should cut like soft butter, you can have your Bucket Trowel fully loaded and be able to slowly move around with it without dropping any, then swing your arm towards your spot on the wall or PlasterBoard and suddenly stop as close as you can to your spot and the lump should fly off your Bucket Trowel and stick to the wall or PlasterBoard without sliding down, I mentioned wetting the wall earlier, the wall must be clean and damp can be good but not wet! Your adhesive will slide down the wall, generally we put it on the PlasterBoard but then it is harder to maneuver the PlasterBoard because of the extra weight and the risk of adhesive falling off.
Spacing the adhesive lumps on your wall or PlasterBoard, stud walls have a 16 inch gap between the stud work, adhesive will give the same strength if each lump is around 12 inch from each other and edges of your PlasterBoard should have adhesive along it with 12 inch gaps again it should look like a domino face or dice faces in between your edge lumps you actually have more hollow area than solid area but the wall will be strong
HardWall is harder than plasterboarding, the plasterboards almost flatten and level themselves whereas HardWall is half an inch thick on average, and the flatness of the wall will be down to you entirely, you will need a level or a nice sharp edge preferably metal, we use Fathers and Straight Edges and levels and the side of anything straight i can find really, longer the better, apply your base coat just like plaster but much thicker, the mix should be like butter, it should be laid half an inch thick, it’s good to be generous when you are spreading your Hardwall because we use our straight edges to drag off excess and when we put too much on it’s easier because we will only have to drag the straight edge across the patch once and all that will be left is a nice flat patch, when i say drag it, hopefully your straight edge spans both sides of a patch so the straight edge touches the original wall level, so then you can drag it hard against it.
Hollow Plaster or Blown
If you can feel the plaster move and tap as you push on it then you should take it off or wait for it to fall off, behind Blown Plaster you will see a gap you should chisel Plaster off until you can not see a gap between the old Plaster layers and the masonry, or if it’s already cracked and falling out but you're not sure whether to start or where to stop then do not panic, even if the plaster is soft it does not mean it will fall off, old plaster can go soft and sandy underneath but it could last another 10 years still, so if you do want to just patch and keep the job as small as possible then use a chisel and hammer or even paint scraper if Plaster is soft enough and do not aim chisel or scraper away from hole, aim your chisel towards the whole or patch and that will stop plaster falling off that does not need to come off, Light but quick hits if using a hammer, really small holes dig out with screwdriver till you hit brick or hollow area then wet the hole for filler or plaster to fill and stick nicely, PVA is good here too but optional.
PlasterBoard And BaseCoat
Here is a classic case of PlasterBoard and Bonding Coat (BaseCoat)
The old layer of Plaster on the Brick work is not thick enough to fit in adhesive and PlasterBoard but he FirePlace hole is was too thick for Base Coat and the stairs boxing is wood plus the ceiling has stud work for screwing PlasterBoard to, if your PlasterBoard edges meet Base Coat they must be scrimmed together (joint Tape fibreglass mesh) but there is no harm in doing some of the patch with PlasterBoard and BaseCoat if you top coat at the exact time the Base coat is going to hard to dent with your finger but still full out moisture or when it is dry you can PVA the Base Coat to stop the Plaster Drying too fast
Plastering Instructions During A 2 Hour Set
we are mixing plasterboard finish plaster 2 coats about 2mm thick each final thickness between 3mm & 4mm
for small mixes you can mix this by hand you are looking for a smooth and creamy consistency without lumps
make sure to clean your tools regularly especially your mixing tools lumps in a mix cause massive problems later
it hard to explain how to use a hawk and trowel properly, practise is really needed before use a little bit of your powder to make a tiny mix to practise with or sand and water can do.
any left over mix we can put back in the bucket and use for 2nd coat because it is still soft add some water and mix a little
keep your tools clean and the top of the mixing bucket
this is first press or pressing down
pressing down is flattening the plaster smoothing out lines and filling dips and holes
stroke the wall with the trowel in fluid motions overlap your strokes the top of the trowle blends
so apply a little more pressure towards the back of the trowel so each stroke leaves a line at the back next stroke should flatten and blend that line
we use a wet! 1 inch soft paint brush for lining in our corners and edges but try and keep them sharp with your trowel during the set
mixing up 2nd coat now check your 1st coat plaster it should be firm but moist to touch not dry!
if your left overs have gone to hard to mix discard and make new mix 2nd coat should be thinner consistency than 1st coat and almost half the amount
used for first coat
just like thick custard or yogurt
if your hawk is very wet spread the plaster around your hawk before you lay remember to keep your tools clean and don't forget about your bucket!
Now time to press down the plaster again 2nd press as we say
the back of the trowel is nearest your elbow when it is against the wall you can see the lines disappearing with the front of your trowel adding a little more pressure to the back of the trowel is good too
its another good time to line in after you have pressed down your area get all corners and finished edges you don't have to line in the plasterboard
check your plaster a few minutes later if still wet check a few minutes after that and so on until the plaster is almost dry to touch but you can still leave
a fingerprint in the moist surface without denting it
we apply water to the plaster surface with a 4 1/2 inch paint brush do not apply too much water and gently stroke the brush you should see really fine lines not scratches!
after troweling up we will leave it for 5-10 mins then go over the plaster just once more with just the trowel you can now go in any direction the plaster should be tough enough that the trowel leaves no lines
you are making flatter even if you can not tell your pressing down air bubbles that try to escape when drying or lines you left from troweling
now the final line in for a super sharp corner
this is beading
the metal corners for plastering 3mm thin coat bead measure your gap and cut to fit
measure each gap after fitting the last bead because the gap distance may change
i'm using a stanley staple gun but other products are available
also good old nails do.