- 1 Should you use a ready mix or mix the cement to the sand ratio for plaster yourself?
- 2 How to cement plaster a wall
- 3 Conclusion
Cement plaster is most often used for rendering walls, even when there are multiple alternatives these days for facades. It’s for decorative purposes as old brick, and concrete walls can be quite uneven, and some could be described as plain ugly.
With cement plastering, you can level the walls a couple of inches with no problem; you need a few layers for that to work out.
Before you begin, you need to decide on the product. Traditionally a sand and cement mix can be used or ready-made mixes from the hardware stores. I think ready-made is easier to use, but you can compare prices and estimate how much time it takes to make your mix.
Should you use a ready mix or mix the cement to the sand ratio for plaster yourself?
Cement plaster can be made by mixing the cement to the sand ratio for plaster with a shovel or by buying a ready-mixed bag where you add the right amount of water.
For plaster, the cement-to-sand ratio could be something like 1:5. For rendering purposes, the scratch coat is harder, so it can be 1:3, then 1:4 for filling and 1:5 for the rendering layer. The idea is that the surface layer is the softest.
So it will be harder if there is a lot of cement compared to sand. For plastering or rendering, you don’t want it to be too hard.
I’ve done outdoor rendering with a shovel, sand, cement, and a concrete mixer, and I’ve done it with ready mixes. I much prefer the ready-made ones, to be honest.
If you work alone, it saves you some time.
Whether you make the plaster mix yourself or use ready-made cement plastering bag mix like polymer and fiber modified, this article is for you. Before I moved up in my career, I used to do these a bit, so I decided to put up a short guide.
You can also cement interior plaster walls like you would be rendering outside. It’s not often preferred as sand is hard, and most want to work with more straightforward-to-handle products inside.
But if you know your game, you can make durable decorative walls.
If you’re considering alternatives to plastering a wall, there are also drywalls and other boards for exteriors, like cement boards. If you’re looking for how to smooth a wall without plastering or an alternative to plastering a ceiling, these can work out too.
Now, to move on to cement plastering, or rendering, in other words.
How to cement plaster a wall
Cement plastering a wall is a simple process, so it’s pretty easy to break into steps.
- We prepare the wall
- Mix the plastering cement
- Work out the number of layers
- Finish the surface
How to prepare a wall for plastering
So how do we prepare a wall for cement plaster? Well, with no jokes in mind, it depends on the wall and what kind of surface it has.
Plastering old walls is a form of art. If it’s indoors, the walls will be only as hard as the surface they adhere to.
It’s more than likely your surface is bricks or concrete, so if there is no paint, a brick surface is most often ready to go. With concrete, the cement glue on the surface of the concrete might need to be removed if it’s not done already.
Suppose your wall has old rendering/plastering. In that case, I’d most likely remove it and clean the surface with a power washer if you’re working outside or an industrial vacuum cleaner if working inside.
That will remove the dust from the surface pores, making the cement a suitable ground to adhere to. We must remember that cement is the glue that holds everything together; if it can’t adhere to the surface, you’re wasting time and money, and we don’t like that.
Here is a guide for removing plaster from those surfaces.
Plaster cement and how it is made
This part is as essential as doing the groundwork for the plastering.
Cement plaster mix is made out of sand, cement, and water to simplify it. That’s why it’s usable both inside and outside, and it’s durable against the weather. Once it cures, it makes a tough surface.
Like when mixing concrete, it’s essential to use clean water, sand, and cement. If the ingredients are not pure, it will produce a weaker mix.
Also, you can’t mix more water when the mix starts to cure. Cement to water ratio will weaken, and you will have significantly weaker parts in your wall.
I like to think of the wall as almost like a living being. If there are parts that are greatly different, it’s more than likely the first part to crack. After that, water gets in, and erosion begins.
The cement-plaster mix ratio can be different from one surface to another. If you do it yourself, 1:4-5 cement to sand will do it for bricks as it’s close to mortar mix, and 1:4 would be for outdoor work. The less cement you have, the softer it will be.
For me, it has been infrequent to mix it myself. Only building facades that are done traditionally have been done like that.
Most of the time, the render mix has been delivered on ready-mixed bags. That’s also the easiest to get for households.
Cement plaster is a surface I’d not be sanding, which is out of the picture in this guide. So let us move on to how to plaster a wall with sand and cement then.
How to apply the cement plastering
Cement plastering work is different from plastering in a way that the wall will have to be good when you do the final layer. I mean, you have to get the surface level and smooth.
So it involves spreading the cement plaster and using the float to make it smoother.
For thin plastering/rendering, you can do only 2 layers. For a wall that needs a thicker layer, 3 layers might be needed.
Cement plaster for the scratch coat
This is the coat made with the hardest mix. 1:3 or something close to that.
It has more cement, so it’s harder but, on the other hand, adheres better on the surface. We leave it rough surface because we want the second layer to adhere well to it. It should not be “higher” than the intended surface of the finished product.
So high points we flat out with our chosen tool like a trowel. There are tools like a stucco sprayer that can make this part easier.
Professional tools are quite expensive, so think about renting as an option. Old school workers used to throw this layer into the wall, but most people lacked that skill.
Cement plaster for the second coat
This is the coat that makes the wall level. It’s also more difficult to achieve, so the steps are below.
- With big walls, we choose a high and low point from the side of the wall.
- Then we use a plumb bob or another tool to check how straight the wall is. You can even use spirit level if the wall is small enough.
- For the high and low points, we make a small patch of plaster to the level we want the second coat to be.
- Repeat this process with the width of the tool you use to screed.
- Let the patches be until the next day.
- Fill the space between the high and low patch points with plaster.
- Level it vertically in between patches
- Let it be until the next day.
- Use those vertical plaster benches to fill the in-betweens and screed them with your chosen tool.
- Use a big wooden or plastic float and float the surface with a circling motion.
- Water the surface for three days for the cement to cure as hard as possible.
Cement plaster for the finish
The floated cement plaster wall finish can be done in multiple ways. If you want texture, go wild and do it with different methods, like spraying with a hopper gun or making marks with a notched trowel. The world is yours.
If you want it smooth, you need to float it. You can’t float the cement plaster straight when you spread it; it needs to start to cure a bit.
When you can touch it without leaving deep finger marks, or it starts to turn grey, it’s time to take a hard wooden float and start circles with it on the wall.
If the cement plaster starts to roll with the float, it’s too soon. You should be able to press it gently while you float without it rolling with a wooden or plastic float.
Other floats work the same, but you might need to water the wall or ceiling with something like a pump sprayer/garden sprayer to get the surface moist for floating.
How to plaster a damaged wall for minor fixes
Now, this is included for those that need to do minor fixing.
How to plaster a hole in the wall? If the hole is big, you don’t. You get a rough patching compound or make it whole like it was built.
The fix must be close to the hardness of the surrounding wall. If the patch is made with too hard a compound, it will crack and pop off the surface.
For small holes, everything goes.
You can’t do fine plastering before you fix the damage on your wall. Small and big holes will need to be fixed with cement compounds made for that purpose, like polymer fiber cement mixes if it’s concrete.
If it’s a brick wall, get some bricks and mortar for big holes. Try to fix it so that it’s level with the rest of the bricks, so you don’t need to grind it level.
When you’re done with the fixes, it’s like plastering any of the following walls. Here is also a guide on fixing holes in plaster walls.
I hope this clears up how to plaster a wall with cement plaster. The ceilings work the same way; you have to work upwards.
I like working with the polymer fiber cement renders as they can fill a bit, don’t crack that easily because of the fiber, and make a fine-looking floated surface.
Other mixes work as well; good workers won’t blame the product but update their skills to match them.