How to Plaster a Skim Coat - 5 Simple Steps
Updated: Feb 1, 2022
A DIY tutorial by @edshomereno
This 5 step full proof guide will help you to efficiently navigate the world of plastering and give you the skills to skim a wall in minutes. Its easy to have a conversation with a friend in the trade and think you're ready to give something a go, although these types of conversations are priceless always make sure to back them up with proper research.
Lots of people will tell you that plastering should be left to the professionals and it isn't worth doing it yourself, these people are wrong. Forgive me when I say this, I don't mean to take anything away from tradesman, you will get a great finish using professional's and they can get the job done quickly, however it comes at a premium cost. If you are prepared to take your time and give DIY plastering a go you will not only learn a new admirable skill but you will save copious amounts of money. Just to give you an example, professional plastering averagely costs £400 a room (size dependant), I have plastered 3 entire rooms of my recent house, this means I have made a saving of £1200 just from these rooms, minus material costs.
This DIY guide with 5 easy steps will help you to quickly master plastering a 3mm skim coat on an existing or new wall, the wall can be either masonry or plasterboard the same rules apply to both with some minor tweaks. Remember take things slow at first, do thorough research, and enjoy the learning process.
Plastering Tools You Need
Before starting any DIY and renovation project you need to make sure you have all of the necessary tools and materials to finish the job. There is nothing worse than starting a job and not being able to finish it because you were under prepared.
Before attempting this skim coat plastering tutorial please make sure you have the following tools and materials.
- PVA Glue
Preparation is key! Like with any home improvement or DIY project the preparation is always a big part of the overall job, if you forget to prepare the surface correctly you will be destined to fail, a house is only as strong as its foundations so make sure you don't skip this section.
Including: Brick, Block, & Plasterboard dot and dab walls.
For this these type of walls you will need to make sure that the surface you're skimming over is dry and reasonably flat, usually there will be a layer of backing plaster which is what goes over the existing brick or blockwork, if there are any obvious holes in it make sure to fill these in, a good product for this is Wall Filler this can be picked up at most trade and DIY stores.
If there are any areas that you are worried the skim coat won't bond very well to you can use a product called Plaster bonding agent. This product is essentially a mix of glue and sand and helps the skim coat adhere to the existing wall in problematic areas.
Including: Plasterboard & Plywood.
For these type of walls the preparation process is very similar, you need to make sure any areas that are not filled in are filled to ensure you have a true and sound surface to skim onto. Where there are holes for screws and where the plasterboard sections meet etc fill these in, you can once again use Wall Filler for this process.
Wherever there might be movement (for instance between the ceiling and wall) it is good practise to introduce some Scrim tape. The tape allows for movement below the skim coat and reduces the risk of cracking in the drying process of the plaster. on existing walls use this at every junction between different sections, on new plasterboard walls introduce the tape over every joint between the boards also.
Top tip You can lay the tape over areas that have visibly cracked in the past this should stop the cracking persisting in the future.
To achieve a professional finish with clean straight lines on all corners, you are going to need some Angle Beads. These create perfect edges and provide a thickness guide to plaster up to. Fix these to masonry walls using screws and raw plugs or on plasterboard walls with nails or staples.
PVA Glue Base Coat
This step is essential so please do not forget this part, the first time I attempted plastering I forgot to prep the walls with PVA Glue and I had to remove the entire plaster layer, don't let this happen to you its painful! PVA glue forms a barrier between the existing wall and skim coat, if you forget the PVA glue, the skim coat will dry out to quickly and it wont form a proper bond to the wall. The PVA Glue should be mixed at a ratio of 70:30 glue to water. Allow the glue to dry until it is tacky to the touch at this point you are ready to start skim coating!
Skim Coat Plastering
Now that you have carefully followed all of the necessary base wall prep, we can move onto the plastering stage. Plastering is a skill and there's a reason plasterers are paid so highly, like learning any new skill you will need to take it slow and be prepared to make some mistakes along the way.
Step One - Mixing
Mix the multi finish plaster in a big bucket, use the Shank Mixer for this. Put fresh clean water in the bucket first and begin adding multi finish until it is the consistency of a thick yogurt. Always mix plaster to water and never the other way around.
Make sure there are no lumps and the plaster is completely smooth, this stage is critical if the plaster isn't 100% smooth it will cause you some big issues when applying it to the walls.
Top Tip, make sure all of the tools you use for this stage are cleaned thoroughly, the last thing you want is a piece of old dried out plaster getting into the mix, this will drag through the skim and ruin the finish when applied to the wall.
Step Two - Plastering The First Coat
Take this stage slowly at first and don’t rush yourself, it becomes evident that the plaster is drying from the moment you have mixed it but don’t let this panic you. If you are right-handed, then start plastering from the top left of your wall across and vice versa if you’re left handed.
Depending on the size and height of the wall or ceiling you can either do it in one go or break it down into sections. If this is your first time plastering, I would advise choosing a small wall that you can quickly apply an entire coat to.
First things first fill two buckets with water and rinse all of your tools in clean water removing any dust and debris. I always have a small bucket and brush of fresh water, and another larger bucket again with fresh water but this will be used to wash your tools throughout. Get a little amount of plaster on your Hawk and smear it around with your Trowel, this will help the plaster stick to the hawk. Next, get a healthy lump of plaster on your trowel and put it onto the middle of your hawk.
Now apply the plaster with your trowel at around 15° – 20° facing the wall. Steadily glide your trowel and plaster across the surface narrowing the angle as you go until it’s almost flat, apply even pressure throughout, this first coat should be around 2mm thick. Don’t worry to much if you aren’t achieving a completely smooth finish at this stage, we are going to apply a second coat next.
Continue this process until you have completely finished the top half of the wall.
For the bottom section, guide your trowel as before starting just short of the floor, if you are plastering with an existing skirting board make sure to start as tight up to it as possible. Using the same technique and angles as before apply the plaster to the bottom half of the wall. Always apply even pressure and this will help you keep it flat. If you hear scraping noises you are pressing too hard, and If you end up with a big lump on the wall then there isn't enough pressure.
Complete this process across the entire room. Make sure to clean the tools between coats with clean water.
It is perfectly normal to see some lines and dots on the walls after this first coat so don’t panic. As it starts to dry, approximately 15 minutes after the first coat, you can start to get rid of the lumps and lines by trowelling over the entire area, Get it as flat as possible.
You will need to pay attention to the corners at this point, top and bottom of the wall, using the edge of your trowel to cut away any excess plaster also use a small brush which is very useful.
Step Three - Plastering The Second Coat
You should start applying the second coat once the first coat has become tacky. You can push into it and leave a print, but you won’t pull the plaster off the wall, if some does come away leave it a little longer.
Now mix your second coat exactly as you did the first, however, you should not need as much plaster as the first coat. The second coat should be slightly runnier, this allows you to apply it easier, it should fill in any final imperfections. The second coat should be around 1mm thick giving an overall thickness of 3mm.
Apply the plaster to the wall in exactly the same way you did before starting and finishing in the same places with big long strokes filling in all areas.
Here's an idea, one of the most annoying parts of plastering is getting the plaster in your hair, not only is it quite irritating but its a nightmare to try and get out, something I found very useful was wearing a cap, and nothing is better suited to the job than a Reno Gear cap...
Step Four - Wet Brush Smoothing Out
Leave the second coat to dry until it is tacky just like the first now using a bucket of clean water prepared earlier, we can begin to completely smooth our plaster with water and a trowel. Wet the brush and apply along the wall by splashing it evenly across the plaster, then trowel across with a good even pressure. If the water runs down, trowel it out.
If there is creamy plaster left on the edges of your trowel, this is called “Fat”. This is what gives the wall it's smooth finish, keep it on the trowel using it to fill any final small imperfections.
Step Five - Final Trowel
Here it is the final step, once the skim is almost dry give the wall another finishing trowel.
Make sure to clean the trowel thoroughly, there is nothing worse than dragging a bit of muck through your perfectly flat wall right at the end. This is where you give the plaster its shine, don’t go to crazy as we want the paint to adhere to it once it is finished.
The plaster will generally take 2-3 days to dry depending on the weather conditions and how thick it has been applied, allow a maximum of 5 days until painting.
Well done you have plastered a wall, what an achievement!
Painting Tips - Mist coat
When you come to paint onto the skim coat if you see any final blemishes or imperfections use some sand paper to smooth them out.
You will need to apply a base layer of mist coat before painting on any new plaster, this is a mixture of paint to water 70:30. It is best to use a cheap emulsion paint for this a good one that i use is Crown Brilliant White.
The mist coat allows the paint to seep into the dry plaster much more deeply and affectively than standard paint, it will stop the paint flaking away later down the line.
I hope this DIY plastering tutorial has been useful, a home improvement/renovation blog will be released every month moving forward with helpful DIY tips and tricks, send us an email at firstname.lastname@example.org to let us know which area you would like us to discuss next.