How to Skim Coat Plaster onto Plasterboard

Before this blog post, the only thing I'd skimmed was icing on a cake. Now? Well, I've just painted four walls I'd previously skimmed and they look perfect, even the wife says so ūüôā


Don't think you're in the right place? This is Step 5 in a 6 part course covering re-plastering.

Start at Step 1 - How to Remove Plaster From Brick Walls

Watch the video for the main points, read below to get more...

INTRODUCTION

What is skim coating and what's it for?

It's plaster, just really thin, about 2mm is what you want to aim for. You mix a powder with water and get a gooey slop, then chuck it on the wall (not literally), spread it about with some decent tools and hey presto, you have a perfectly straight wall.....

Hm, I think I missed a few bits out there, lets get more detailed

Is it difficult to skim coat plasterboard?

Yeah, it's pretty tricky, I won't lie to you, I suggest you give it a go on a practice board first, or a few goes, whatever works. If you haven't got the space to put up a temporary board, no worries, just grab your wife's latest cake baking achievement, mix up some plaster, slap it on and have a go at spreading it with a knife. If you do, send me a picture, it will look great on the website.

Anyway, there are a few tips I'd like to give now, just to make things a little less daunting for you, here we go...

Tip 1 - Get the right tools first. Speaking of which, I've made a list of these, see below. Be warned - there are good floats and bad floats, don't go cheap on floats!

Tip 2 - Try the cake, if it's good, practice on a bit of scrap plasterboard instead.

Tip 3 - With the first coat, speed is crucial. Slap on the first coat quick sharp, then tidy it up after.

Tip 4 - The more walls you plaster, the better you'll get, so don't give up!

Why would I want to do it myself?

Good question! Well, the materials are cheap for one. I just spent about £100 on plastering materials to plaster the whole of my dining room, brilliant! And, I learned how to plaster in the process, giving me the confidence to tackle a few more rooms in my house.

That's the satisfying part.

On the numbers, I reckon it would've taken a plasterer one full day to skim coat my dining room. With the prices as they currently are, this would have costed me anything between £400-£600, plus the materials.

One last thing - a number of people who have visited my home since being plastered, have asked who did the plastering. When I told them it was me, they we're pleasantly surprised. There seems to be this myth that plastering is too difficult for the DIYer, I beg to differ.

TOOLS FOR THE JOB

What tools will I need?

No expensive tools or materials required, just a few bits and bobs. Although a good trowel is a little pricey.

Tools:

  • Finishing Trowel¬†(aka a Float, it's a rectangular sheet of metal with a handle on it, mine's a Tyzack)
  • Bucket (for water)
  • Trug (for mixing the plaster)
  • Small Step Ladder or Stool
  • Soft Paint Brush (about 1" wide will be fine)
  • Hawk (No, not the type with wings, it's a flat thing with a handle, I'll cover this later)
  • Scraper (you always need a scraper!)
  • Large Drill and a Paddle Mixer, to stir things up a bit!
  • Spray Bottle of Water, for smoothing off the final skim

Optional:

  • Bucket Trowel (for scooping the plaster out the bucket). If you haven't got one, a gardeners trowel will do.

Materials:

  • Water (for mixing with the plaster and wetting it)
  • Disposable sheets & maybe a bit of masking tape
  • Thistle Multi Finish Plaster (here's their website)
  • Cup of tea

Helpful Tip

Before you continue, I just wanted to check with you that you've already applied the scrim tape and corner anglebead (these open in a new tab by the way). Yes? Great! you're good to go.

PREPARATION (GET YOUR DUCKS LINED UP)

Just to make sure you get off to a good start, we'll need to talk a little bit about preperation.

You will need the following:

First Things First, Materials

You will need the following:

Plaster - I used Thistle Multi-finish, which comes as a dry powder in 25kg bags.

If skim coating your plasterboard to 2mm, the coverage comes in at around 10m¬≤ per bag. That's about 3¬Ĺ plasterboards. Or, if your rooms a standard height (2.4m), one bag will spread about 4m along a wall.

You'll need water, about two full buckets per bag of plaster. That's not to say you'll need two buckets in one go, because you'll probably mix half a bag at a time. You can get water from a tap... that tips for free by the way, and you're welcome!

Next Up, Tools

I'm going to go into a little detail on the tools, because there's good reasons for getting them and I think it's important we get this right.

The Finishing Trowel, aka a float. These come in two sizes, 11 inches and 13+ inches. If you're new to this, go for the 11 inch, it'll be easier for you.

One other consideration is the grip. Half way into that first wall and you'll be cursing the day you got a cheap trowel. I use a Tyzack, I would recommend them but it will fetch you back around £25-£30, well worth the money though.

Here's a picture of mine:

picture of trowel tool, has a rectangular flat plate with a handle attached


Large Drill and Paddle Mixer. Essential bit of kit to mix the plaster up. Be warned though, the dust created from mixing the plaster doesn't agree too well with the twirly whirly things inside drills. So try to mix in a well ventilated area, preferably outside. Professional plasterers have a mechanical paddle mixer, with its motor encased so the dust can't harm it.

I used my Bosch Professional SDS drill for this and it worked a treat. You'll need a powerful drill to do this. If you only have a battery drill, I reckon anything less than 18v will struggle.


The trusty Trug. Like a bucket but made from bendy rubber like material. Due to their flexibility, the make it easier to scoop out the plaster mix. They tend to last a lot longer than buckets too. Make sure your bucket or trug is squeaky clean, nothing worse than a few dried lumps to get in the way when skimming!


The Hawk. Basically a 1ft x 1ft board with a perpendicular handle pointing out the back. You hold it in your hand, so the board is flat, and use it to carry dollops of plaster around the room. Make sure you keep this clean, because you want the plaster to slide off easily.

Workstation / Table

Save your back from utter annihilation, well, not quite that bad but a few sore bits at least. Get a table set up, put a smooth surface on it to protect the table, one that you don't mind getting mucky and scratched. I used a plastic sheet, about 5mm thick and non-porous, meaning the lumps of plaster I put on it didn't dry out. You should be able to get an acrylic sheet from your local window glazing company for a cheap enough price.

Cut the sheet to a good size (mine was 0.9m x 1.1m), using a standard hand saw. This will be your spot board, and you can use it to store your tools so you don't trip over them! Here's a picture of my workstation:

picture showing a table with a plastic sheet over the top. tools and plaster are on the sheet

Helpful Tip

Whilst plastering, keep your tools as clean as possible. It's a really messy job but if you keep reminding yourself to keep your stuff clean, you'll save a lot of hassle later on, and it will make the plastering that little bit easier.

Protect the Floor

Believe me, dried plaster doesn't wash off wooden flooring easily, it sticks well! The same can obviously be said for carpets.

Take the time to get some heavy duty plastic (none porous) sheets down. Use masking tape to hold them in position. You want to cover the entire floor area, the plaster gets everywhere and if you're a beginner to this like me, you'll be messy.

Check the Plasterboard First

There may be the odd lump of rogue adhesive stuck to the plasterboards. Give the boards a quick once over to remove any obstacles, tie back cables etc.

Where Shall I Start?

For the DIYer, I suggest taking a look at the wall and having a good think about your game plan.

Firstly, you need to pick the right wall for your first attempt.

Helpful Tip

Aim to complete one full wall  in one operation. It'll be too difficult to join skim coats together seamlessly.

Choose the smallest wall first, to give you the best chance of skimming it's entire face in one operation.

I found that starting from the top was best. I kept dropping blobs of wet plaster off my trowel, onto the lower parts of the wall. If I had plastered the lower part first, I would've had to go back and re-skim it.

Also, have a look to see if there are any awkward areas, like that narrow gap between a light switch and a door frame. Check to see if your trowel will fit in that gap. If it doesn't, grab a thinner spatula, maybe raid the kitchen drawers.

SKIM COATING YOUR WALL

When it comes to actually skim coating plasterboard, it's mostly about timings and less about technique. It's true, plastering is an art and I admire good plasterers who seem to make it look so easy, but that's because they've done it for years and as such, instinctively know when is the right amount of time to leave the first coat before applying the second coat. Or, they'll know how long to wait for the 2nd coat to go off, before going over it once again.

What I'm saying is, for the newbie plasterer, keep a good eye on your timings and the rest will be fine.

With that in mind, let's get detailed.

Making the First Mix

The plaster, even though it's only 2 millimeters thick, needs to be applied in two coats. The mix for the first coat is slightly different to the 2nd mix, the 2nd mix has more water in it.

Just to check - you should've already put up your corner anglebead and scrim tape. If not, check out how to below (opens in a new tab):

Remember up the page, where I mentioned about the coverage? It was where one 25kg bag of plaster would provide a 10m2 area at 2mm thick. Well, the first coat wants to be 1mm thick, so half a bag would cover 10m2. My 3.6m long wall took up a bit under half a bag for each coat, it was 8.6m2.

This is good news if your wall is the same or similar in size, because I found that working with¬†¬Ĺ bag gave me just enough time to apply the plaster before going off.

Helpful Tip

Mix the plaster in a trug, it's far easier to clean than a bucket.

Tip half a bucket of water into the bucket, followed by half a bag of plaster. If you can, set your drill to low speed (high torque), and attach the paddle whisk.

Make sure you keep the paddle well in the plaster during mixing, try not to introduce air from the surface too much, otherwise it'll set quicker.

picture showing plaster being whisked up in a trug

 

Gradually add water whilst paddling until you end up with a smooth consistency. It really is best to watch my video at this point, at the top of the page, which shows and describes the plaster. The paddling would take about 3-5 minutes.

A way to test if it's the right consistency is to take your trowel and dip the end about an inch into the plaster. Pull it through the plaster to make a 1 inch deep void. You should have felt little resistance from the plaster, yet the trough you just made retains its shape really well. It'll also look wet and brown in colour.

picture of a large blob of plaster with a groove running through it

I'll cover the consistency of the 2nd mix later on, for now I'm going to talk about applying that 1st mix to the wall.

The First Skim Coat

This wants to be about 1 millimeter thick and you want to chuck it on quick, don't worry too much about little bits sticking out here and there.

Start off by scraping a dollop of plaster onto your Hawk, not too much for your first attempt, you want to get the feel of it for now and the amount you put on will increase as your confidence grows.

Go over to your wall and tip the Hawk slightly, whilst meeting it with the flat face of your trowel, hook the trowel under the dollop whilst symultaneously tipping your hawk, so it kind of tips onto your trowel. Ok great, we now have a dollop on the flat face of your trowel, which you should be holding upwards.

Keeping the trowel held upwards (flat face facing up), meet the trowel edge with the plasterboard and start to turn the trowel into the plasterboard, so that it begins to squeeze the plaster between the trowel and the plasterboard. Then, whist applying a bit of pressure, sweep the trowel in the direction you want to plaster. This should spread the plaster along the plasterboard, albeit fairly unevenly at his point. Then use your trowel to even it out a bit.

Once done, repeat for the whole wall, really get a move on though. Don't worry about getting it perfectly flat, you'll be able to sort that out after the entire wall is coated.

Once the entire wall is coated, this should take no more than 20 minutes for a first timer, check for any big bits sticking out and, using your trowel, squash them into the plaster using the same sweeping motion as before.

Then go back and sort the smaller bits that are sticking out. Remember, there will be another 1 millimeter thick coat of plaster going on this, so don't spend too much time getting the first cost perfect.

By the way, the second skim coat wants to be applied before the first coat dries, so don't call it a night at this point, there's still some more DIYing to do! You can have a cup of tea though, that's OK.

Making the Second Mix

Whilst the first coat is drying, you want to get on with mixing up the second batch of plaster. This is much the same as the the first lot but with one key difference - it's got more water in it.

Mix it in the same way as the first batch. Add the water to the bucket first, then the plaster etc. When it comes to checking it by pulling a flat edge through the mix, the sides want to slump in slightly, or collapse if that makes more sense. If they don't do this, whisk in some more water a little at a time until you have it.

The Second Skim Coat

Wait for the first coat to become tacky, usually 20-30 minutes after applying the first coat, depending on how warm your room is. An easy test for this is touching the plaster lightly with your finger, it should be firm but still soft. When you pull your finger away you'll feel a little bit of suction but the plaster remains in place, you shouldn't have any sticking to your finger.

Once tacky, you're good to slap on that second coat, again 1 millimeter thick. If it ends up 2 or 3 mm thick, don't worry about it, the worst this'll do is cost you slightly more in plaster.

Using the exact same method as the first coat, get a blob on your trowel. Go for a smaller amount this time, because it's more wet than the first coat so has a tendency to slide off the trowel easier. That's a good sign, it means you've got a nice clean trowel!

As before, spread it over the first coat. You can take a little longer with this coat but I found that anything over 30 minutes and I was struggling with the plaster going off.

Be quick at first, but not too rushed, they'll be plenty of time to even out the lumps and bumps after you've covered the entire wall.

Once the wall is covered, go back to the start and crack on with smoothing it out with the trowel. You may find that it's still too wet to do this, it wants to be in between that wet and tacky stage. If it is too wet, that's good because you have 5 minutes to make yourself a cuppa.

After you've had a brew, possibly a biscuit, go back to the part of wall where you started off, and gently glide your trowel over the skim so that it evens out the bumps. If you find that the plaster sticks to the trowel, do two things:

  • Check the flat part of the trowel to see if it's clean and free from any sticky bits of half set plaster, it's wants to be as smooth and shiny.
  • Grab your water spray bottle, if you haven't got one of these, your sons water pistol will do. Not those Super Soaker kind, that'll just obliterate your plaster! Spray a couple of times on the flat part of your trowel, and on the plaster you're about to skim, then glide the trowel over it and you'll find it doesn't stick, and starts to shine a little as it becomes smooth.

Continue to smooth the wall out in the order that you first applied that second skim. Even now, don't spend too much time on getting it perfect, about 10 minutes will do.

Then repeat another time to get the final finish. Don't aim to get it as shiny as possible, that's not the goal here, you just want a smooth, flat surface. If you do over shine it, they'll be less traction for that first coat of paint, it will be like painting a mirror and risks the paint flaking off further on down the line. If it is shiny, don't worry, just make a mental note to water down the first coat of paint a little bit more than you normally would, it's totally fixable.

Do a final check for any protruding bits, sort them out and take a step back, admire your work and well done for getting this far.

You're not quite out the woods yet, there's still the corners to sort out.

Plastering an Inner Corner

Corners are easy to get right, it's simply a case of using the right tools, actually just one in this case. You'll need a brush, not one with stiff bristles but a painters one will work well, about an inch wide will be spot on.

When plastering that first coat, make sure you squeeze the plaster right into the join of the plasterboards, so that it squeezes through the scrim tape.

After skimming the 2nd coat and smoothing it out, dip the brush into some water and shake off the excess, it doesn't want to be saturated here.

Lightly press the brush into the corner and run it downwards. You'll find that the lumps get merged with the walls and form a nice right angle. Repeat until the corners are done, easy!

Plastering an Outer Corner

This is even easier than and inner corner. You should've already put up your corner anglebead. If not, check this post out and make sure you put up the beads before commencing skimming (opens in a new window).

 

Whilst skimming the first coat, use your trowel to press in the plaster through the holes of the Anglebead, this helps it to stay put. To do this, keep one end of the trowel against the beading and the other end against the wall whilst gliding the trowel along the length of the bead, until the plaster runs out. The trowel needs to be at 90 degrees to the anglebead and you want to keep one edge of your trowel on the metal corner bead the whole time.

By using this technique, you're ensuring the angle bead is merged well with the wall, and doesn't poke out.

Helpful Tip

They'll be many buckets of water in the plaster and the water has to go somewhere. So leave your windows on vent for a few nights to avoid damp.

And finally, clean your tools down and you're done, good job!

This is Step 5 of my 6 part course on re plastering a wall, the next step covers preparing the skim coat prior to painting, and goes into detail on ways to remove the lumps and bumps. The previous post was all about using Anglebead on corners.

So, if you find that your plaster isn't quite as smooth as you'd like, don't worry, I've got it covered in the next How-to.

Thanks for taking the time to read through this page, I appreciate it. If you have a comment or would like to get in touch, fill out the email form below and hit subscribe, I look forward to hearing from you.

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