Learning how to plaster is an advanced D.I.Y. project. The techniques and methods involved in plastering are not easy to master. However, if you have the time and the patience, it can be a rewarding project to take on yourself.
If you’re new to plastering, this guide will take you through everything you need to know. Whether you want to know how to plaster damaged walls, how to mix plaster to the right consistency, or how to plaster external walls, we will explain every step of the process. So read on to discover how you can become a plastering pro!
Tools and equipment you will need
- Trowl – to apply the plaster to the surface
- Hawk – to hold the plaster as you apply it to the surface
- Wire scratching brush
- Mixing stick
- Jointing knife – allows you to plaster in tight corners and to create straight lines at the edges
- Clean tap water
Preparation before plastering
Plastering is usually a very messy process. Make sure that you use protective plastic and drop cloths to cover large furniture and your flooring. You will also need to cover any electrical sockets and fittings. Cut the power to the room.
It’s very important to make sure that your tools and surface are clean before you begin mixing the plaster. Any dirt or grit that is left behind could leave you with an uneven finish. Wash the surface gently with warm water but don’t soak it.
Do you have a high suction or low suction wall?
Properly preparing the surface that you want to plaster is essential if you want to achieve a great finish. Many D.I.Y. plasterers are unaware that the suction of their wall has an enormous impact on the finish of their work. But why is suction so important? Suction is vital because it bonds your plaster to the wall. So, before you start plastering, you’ll need to determine if your wall has a high or low level of suction.
A high suction wall will soak up moisture very quickly. This will cause your plaster to dry too rapidly, and you won’t be able to smooth it out. However, if your wall is low suction, you’ll find that your plaster struggles to bond to the surface. The plaster will be fragile and it may start to crumble.
The best way to check the suction of your wall is to do a patch test. Take a small section of your wall, around 50mm x 50mm, and apply freshly mixed plaster to it. Leave the area for a few minutes. Use your finger to lightly trace a line through the plaster.
Dealing with high and low suction walls
During the patch test, if the plaster feels considerably drier than before, you have a high suction wall. If it still feels just as wet as when you applied it, then you don’t need to do anything. However, if the patch has not dried at all after a long period of time, you have a very low suction wall.This problem can be fixed using a primer. Applying PVA ensures that the plaster bonds to the surface. For a low suction wall, one coat of PVA diluted with water should be sufficient. Usually, a ratio of
This problem can be fixed using a primer. Applying PVA ensures that the plaster bonds to the surface. For a low suction wall, one coat of PVA diluted with water should be sufficient. Usually, a ratio of 3 parts PVA to 1 part water will work well. Always read the instructions on the tin before you begin.
High suction walls can also be treated with PVA. Apply a thin layer of diluted PVA to the surface. If it has dried within 15 minutes, you will need to apply another coat. Every wall is different, so some surfaces may need multiple coats. You will be able to tell if enough PVA has been applied if it is still damp after the 15 minute wait.
Make sure that the layers you apply are not too thick, otherwise, the PVA will struggle to properly bond to the wall. Once you apply the PVA coat, don’t wait for it to totally dry before you start to apply the plaster. It needs to be tacky but not wet.
Mixing plaster isn’t too difficult. However, there are several tips and tricks that can help. You will need to mix equal parts water and plaster in a clean bucket. Make sure that you add the plaster to the water and not the other way round. This allows you to control the consistency and the amount of plaster you make.
You can test the thickness and consistency of your plaster using a mixing stick. It should be able to stand up on its own without you holding it. Make sure that you stir the plaster thoroughly to remove any lumps. It’s also really important to use fresh water when you are mixing plaster. Stagnant or polluted water can affect the finish of your plaster, and it can even cause it to go off. If you are working on a large project, your plaster will keep for a few days. Just make sure that you wrap it tightly with plastic to prevent air from entering.
How to plaster a wall
Wielding a trowel and a hawk requires confidence and a certain technique. Practice moving the plaster from the hawk to the trowel before you actually apply the plaster to the wall. Stand close to the wall to avoid mess and spillage. Lean the hawk into your trowel as you transfer the plaster. Hold the trowel horizontally, but keep it angled towards the wall. However, you should never totally flatten the trowel against your wall, as this can pull the plaster away from the wall. Throughout the plastering process, you need to keep the trowel and the hawk damp.
Go slowly, and don’t try to cover a large area in one go. Once you have applied the plaster you will need to smooth it. Go back other the same patch, again holding your trowel at a slight angle. Be aware that after 45 minutes to an hour, your plaster will begin to set. During this stage, you should go over the surface with a damp trowel. This will help you to fully smooth the surface. Once you have done this, wait again for another half an hour, and repeat the process.
After you apply the first layer, you need to lightly scratch the new plaster using a wire scratching brush before you can apply a second coat. This will prevent the second layer from coming away from the first layer. Applying two layers of plaster should leave you with a nice finish. Just be careful not to trowel the same area too many times. This may cause the paint to peel off the wall later on.
The time that it takes for the wall to dry will depend on the temperature and dampness of the room. During the summer you can expect it to take two days. In the winter, it can be up to five. However, every case is different. Make sure that the wall is completely dry before you attempt to decorate it.
Repairing a damaged wall
You don’t always need to completely replaster a wall. It’s also useful to know how to plaster holes and other imperfections that might arise. Before you can start, you need to determine the size of the holes. Small holes can be repaired using a filler. However larger holes will often require re-plastering, otherwise, you won’t get a smooth finish.
Start by clearing any dust and dirt around and inside the hole. This process is very important as it allows your plaster to properly adhere to the wall. So, take your time, and make sure that it is fully cleared before you continue. For patching up holes, you might want to try a one coat plaster. It has two main advantages; it allows to avoid waiting around for it to dry, and it dries white. However, for larger jobs, one coat plaster is not recommended.
When you’re ready to start, you’ll need to add water to the whole. Once again, this is to make sure that the wall doesn’t soak up the moisture from the plaster too quickly. The number of coats that you will need to apply depends on how deep the hole is. Any hole under half an inch should only require one coat. Deeper holes will need two coats. Just like when you’re plastering an entire wall, make sure you scratch the first layer of plaster before you apply another coat on top.
How to plaster a plasterboard wall
Many modern and new build homes have plasterboard instead of traditional plaster. With plasterboard, one of the key advantages is that you don’t need to fully plaster it. Plasterboard is designed to be skimmed. That means you only need to apply a thin layer of plaster but you can still achieve great results. This can significantly speed up the process compared to normal plastering.
Prepare your plastering for skimming by using scrim tape. Tape over any joints. Just make sure that you do not overlap two pieces of tape at any point. The process of applying a skim coat is very similar to that of plastering a normal wall.
Remember to keep your tools damp, spread the plaster evenly, and scratch the plaster between coats. The trick with skimming is to make sure that the plaster is not too thick. 2-3mm is the ideal thickness for a plasterboard wall.
How to plaster an external wall
When it comes to external walls, plastering is more commonly referred to as rendering. The methods and techniques used in rendering tend to be very similar to plastering. Rendering also requires a lot of patience and practice. Mastering the process is not easy. However, it can be achieved if you take your time. If you’re unsure, or if your building is old and fragile, you might be better off hiring a plasterer to avoid expensive mistakes.
It’s important to remember that the weather will play a critical role in this project. Avoid rendering during the winter, as freezing temperatures can lead to cracking. As always, make sure that the area that you want to render is totally clean. Any loose particles and debris will need to be swept away.
The key difference between plastering internal and external walls is the type of plaster you’ll need to apply. Internal plaster should never be used on external surfaces. Instead, you need to use a mix of cement and plastering sand. As with internal walls, external walls will benefit from a few coats of diluted PVA. Apply the render with a trowel like usual. For the first coat, the layer should be around 5mm thick. This is the optimum thickness so that the render can sink into the wall.
As always, make sure that you scratch the render before you apply the second coat. A wire scratching brush is likely to be too small for a large external wall. You may want to invest in a larger combing tool to save time. The second coat should be 10mm thick.
Once you have finished plastering your walls, you’ll need to decorate them. Learn more about wallpapering and painting and how much it costs with our guides below.