When applying new wallpapers, smooth plaster is the ideal surface. Unfortunately, not all homes provide such perfect conditions. Quite often, the keen DIY enthusiast or professional is faced with rough plaster in all its incarnations and graining degrees, which, alas, is completely unsuitable as a surface for wallpaper. The reasons are obvious, but we will explain them in more detail in this blog.
Whether wallpapering on rough plaster is at all possible depends on the structure and also the type of wallpaper. But fear not: there are solutions which will enable you to hang wallpaper even on rough plaster walls. This might require a bit of extra work and some additional cost for materials, but it will make your dream of a beautiful patterned or designer wallpaper come true!
Smooth v rough plaster/render
The term plaster or render stands for both the building material and the wall treatment, and depending on the type of plaster and the technique used, it can be smooth or grainy. Smooth rendering, usually consisting of gypsum, cement or synthetic resin, is the basis for many types of wall décor, e.g. paint, wallpaper or panelling. In addition, there are a number of decorative plaster types made from a variety of materials with differing levels of graininess. These are usually left completely untreated or just painted. They are generally referred to as stucco plaster or finishing coat/skim, whilst the smooth plaster is known as rendering. Textured or structured plaster are types of rough plaster which come in a large variety of sub-types and appearances.
Render mortar can be bought ready to mix or pre-mixed and comes as mineral plaster (gypsum, lime, cement, clay) and synthetic resin plaster in various grain types. The main difference between mineral plasters and synthetic resin plasters is water permeability. Unlike mineral plasters, synthetic resin plaster is not permeable, but very robust and highly elastic. Depending on individual composition as well as application technique, all render mortars can create a smooth or a rough surface.
Why rough plaster is not suitable for wallpapers
As we now know, a smooth, clean, stable and adhesive surface is required to apply wallpapers correctly and achieve damage-free and aesthetically pleasing results. Rough or structured plaster do not or only partially provide this precondition. As a consequence, wallpapers might be difficult to hang or could be damaged during the wallpapering process. Your beautiful, high quality wallpaper could be destroyed before the paste has dried!
Even if you succeed in applying the wallpaper without damaging it, the structure or grain of the plaster will become visible, severely impairing the overall look, plus it will make the wallpaper much more likely to develop holes or rips. Generally speaking: Wallpapering on rough plaster does not make sense - the surface needs to be smoothed out first.
But there is one exception to this rule: When dealing with a very fine structured plaster, thick PVC or vinyl wallpapers could potentially be used and might provide an acceptable solution. Of course, we are unable to give any guarantees, as every wall is different. Apart from the slightly rough surface and graininess, the base also needs to be intact, undamaged, suitable and clean - which means it might require pre-treatment. The solution: Use a specific surface preparation product which will smooth over small holes and make for a perfect adhesive base for vinyl wallpapers. Ensure you use the correct product for vinyl wallpapers.
How to wallpaper on walls with rough plaster
Let's proceed to the practical aspects: What do you do when you are dealing with a very rough plaster surface but have fallen in love with the perfect designer wallpaper and cannot wait to get it on your walls? There are two practical solutions:
- Adding a layer of smooth plaster
- Applying plasterboard cladding (either by glueing it on or by screwing onto slats)
You can probably envisage that both solutions require a certain amount of preparation in order to ensure a pleasing result. As with every other surface, the first step is to go through a check-list in order to decide on the next necessary steps. When it comes to rough plaster, these are the questions you should ask:
- a) What is the basic material? Lime plaster, lime-cement plaster, clay plaster, synthetic resin plaster, or other materials?
- b) Is the rough plaster still intact or is it crumbly or mouldy in places? Is it very sandy or dusty?
- c) Has the structured plaster been painted, and if so, what type of paint was used (open-pored or sealed)? Latex paints, for instance, are classed as sealing paints. Is the paint flaking or rubbing off?
Regarding a): As a layman, you won't be able to tell the basic plaster material. (Unless of course you plastered the walls yourself, in which case you are bound to know the type of plaster that was used. ;-) If you are unsure, it is best to ask an expert, e.g. a brickie, a plasterer or a painter/decorator. And don't shy away from the potential cost for their advisory service - after all, you are hoping for the perfect end result! At the same time, it will give you the opportunity to find out which smooth plaster can be applied wet with a trowel. Furthermore, you will be able to ask whether the old plaster will need to be pretreated (depending on its absorbency and other issues) in order to make sure the new plaster will actually adhere and stay in place. Similar rules apply for glueing plasterboard to the rough plaster. If, however, you plan to attach the plasterboard to slats, you don't have to worry about the state of the existing plaster.
Regarding b): Conduct a knocking/pressing test to find out whether the old rough plaster is still stable. Tap the plaster with your hand and press various areas with a fingernail or a pointed object. If bits of plaster come off or you can see an imprint, there is not sufficient stability to put a layer of smooth plaster on top. The old, damaged plaster will have to be removed first.
Always check damp areas and mould stains thoroughly. The reason for these issues must be investigated before re-plastering or putting up plasterboard. Make sure that the area is completely dry (and disinfected, if necessary) before re-plastering or putting up plasterboard.
If you move your hand over the wall and there is a lot of "sand" or dust dropping off, you will have to pre-treat the surface so that new wet plaster can stick to the wall. When mounting plasterboard that doesn't need to be glued on, you can skip this step.
Regarding c): Older layers of paint can be problematic when adding new smooth plaster. The old paint could also come through the new plaster (and consequently show on the new wallpaper, as soon as the newly plastered wall becomes damp again by applying wallpaper paste). Test the paint layer by rubbing it with a damp cloth to see if it comes off. To check for stability, apply a few strips of strong sticky tape and yank them off quickly. If you find remnants of paint on the sticky tape, the surface is not viable and needs to be removed or pre-treated.
Applying smooth plaster - best ask the experts!
Unless you are a passionate do-it-yourselfer who is au fait with plastering - either as a result of years of experience or a related professional background - you should always ask an expert to apply the new smooth plaster. Otherwise, check the surface as described above and find out which pre-treatments and smooth plaster materials are suitable. The new layer of smooth plaster should be strong enough to cover the rough structure underneath. Once it has dried completely, it needs to be finely sanded/polished before you can start your wallpapering project. As always, make sure the surface is adhesive; for very absorbent surfaces, you might have to apply deep primer first.
Attaching plasterboard to walls
You can buy ready-to-use plasterboard in any DIY shop, and they will also be happy to cut it for you (unless you are keen to do this yourself). There are two options for applying plasterboard: Gluing the plasterboard directly to the pre-treated wall, or screwing it onto a slats construction which is fixed to the rough plaster wall. Both variations can be handled by a seasoned DIYer, but please remember that the plasterboard grouting will have to be filled. Once this is done, the filler will have to be smoothed out to make sure there are no gaps between the grouting and the plasterboard and the surface is even. If you feel unsure about doing this yourself or are lacking experience, you should always consult your trusted drywall builder. Plasterboard walls require pre-treatment with deep primer as they are very absorbent.
Info: Lime plaster/render and clay plaster/render
Both these plaster types can produce a rough or a smooth finish. But they have special characteristics which can be negatively affected or rendered void by cladding or covering of any type. Both variations regulate pollutants and humidity in a room as they are highly breathable.
Lime render is one of the more sophisticated plaster materials, and using it requires a certain amount of experience and know-how. It is characterised by its exceptional climate-regulating qualities, it is breathable, mould-resistant and moisture-dispersing. Lime-cement render has the same features, but is easier to apply. Rough lime render walls cannot simply be covered in any smooth plaster, and might require pre-treatment for strongly absorbent surfaces.
According to the experts, clay plaster is not suitable for wallpapering. This breathable natural render has a humidity-regulating function and is permeable. This feature is affected or can even be rendered void if the clay plaster is covered with wallpaper or wall cladding of any sort. Technically, it isn't impossible to smooth out a structured clay render, but it is difficult and should only be attempted after consulting (or commissioning) an expert.
Important Information for tenants
At the end of this guide about rough versus smooth plaster, we would like to point out that tenants need to discuss any changes in the appearance of the walls (e.g. smoothing the rough plaster by various means as mentioned above, for instance applying new smooth render or attaching plasterboard to the walls) with the landlord or landlady first. Generally speaking, the landlord or landlady can refuse these changes if they might affect the basic structure of the building or lead to a potential decrease in rental income from future tenants. All changes that can easily be reversed before moving out are usually unproblematic and the landlord will give his approval.
When it comes to changing, removing, cladding or covering rough plaster, it should be contemplated if the original state of the wall can easily be recreated - or whether it might entail a costly and complicated procedure. In addition, we recommend to draw up a written agreement with the landlord which includes the conditions for the tenant in order to be on the safe side, should it come to a dispute.