All about plaster cement mortar: characteristics, preparation, application

A versatile option that is frequently used in building and renovation projects is plaster cement mortar. This mixture has proven to be dependable and useful over time, whether it is being used for wall smoothing, covering brickwork, or creating a sturdy foundation for paint or wallpaper.

Achieving the best results requires an understanding of the properties of plaster cement mortar. It entails not only being aware of the components but also being proficient in their application and preparation. When carried out appropriately, it guarantees a robust, durable finish that is prepared for additional decoration.

The main components of plaster cement mortar will be covered in this article, from choosing the appropriate mixture to smoothly applying it to surfaces. Whether you’re a novice to wall finishing or a DIY enthusiast, the advice and insights provided here will help you achieve a strong, polished result.

Applications of cement plaster

Even tiny potholes can be filled with cement mortar since it sticks well to brick and concrete. There are no big flaws or cracks in the coating, which is fairly smooth.

Cement-based plaster is employed in the subsequent projects:

• facade finishing;
• plastering and leveling surfaces in rooms that do not have heating (balconies, loggias) or rooms with high humidity (bathrooms);
• sealing seams and cracks in external and internal walls;
• leveling surfaces with large defects and large dips;
• preparing walls for tiles.

In damp rooms, incomplete cement plaster may develop mold or mildew. In this instance, a neutralizing solution is etched onto the walls.

Cement-lime mixtures work better on stone and wood surfaces. Regular sand cement won’t adhere well to them.

A versatile mixture that is frequently used in construction to coat surfaces and walls is plaster cement mortar. It is renowned for being strong, resilient to moisture, and long-lasting, making it appropriate for both indoor and outdoor use. A smooth, durable finish is achieved by knowing the proper mix proportions, preparation methods, and application techniques. This guide will teach you everything you need to know to properly choose, mix, and apply plaster cement mortar, regardless of your level of experience.

Pros and cons

The following are cement compositions’ principal benefits:

• increased coating strength: unlike gypsum, it is not so easy to chip or crumble such plaster;
• resistance to temperature and humidity fluctuations;
• durability: even when finishing facades that are most exposed to adverse weather conditions, waterproof cement-sand plaster can last up to 15 years or more without repair;
• high adhesion to most types of surfaces, including concrete, brick, cinder block, stone;
• easy to make the solution: it can be prepared even at home, simply by mixing cement with sand and water in the right proportions;
• affordable price: ready-made CPS plasters are 15-20% cheaper than gypsum plasters, and if you mix it yourself, the price will be 2-3.5 times lower.

However, cement-based coatings also come with a host of drawbacks:

• work with a heavy viscous solution and it is difficult to level it;
• the surface is rough, so it requires applying an additional finishing layer of gypsum if you plan to paint the wall or wallpaper;
• cement-sand mortar makes the walls heavier, so the load on the foundation will also increase;
• poor adhesion to painted and wooden surfaces;
• it is not recommended to apply cement plaster to gypsum – a heavy layer will simply tear it off;
• it shrinks, so if too thin a layer is applied, it can crack; the minimum layer is 5 mm, the maximum is 30 mm. If a thicker leveling coating is required, it is applied with mesh reinforcement, plastering in 2-3 layers, drying each layer.

Composition of cement-sand mortar

A typical cement-sand mortar is made up of cement, water, and sand combined in a specific ratio to form the binder. The type of cement that is used directly affects how strong the coating is. Only interior work should use cement M150–200; plastering facades should use more durable grade M300 and above.

Keeping the proportions in check is critical. Insufficient sand will cause the mixture to dry faster and become less resilient. Sand-free cement is only meant to be used for small crack fillings; it is not a good mixture for leveling coatings.

It is also not a good idea to use too fine sand because that kind of plaster can break. The finish may become weaker and crack due to the presence of numerous impurities in the sand, such as clay and soil fragments.

The kind of sand that is used also affects the surface quality. Sand from rivers or washed-out quarries that has a fraction size of 0.5-2 mm is the best choice. The surface will be unduly rough due to the presence of large sand grains. Sand with a grain size of 2.5 mm or larger—up to 5 mm—is utilized exclusively for bricklaying and for the installation of reinforced concrete structures.

Lightweight cement plaster with lime and mineral fillers is an alternative to traditional cement-sand mortar. Its lower thermal conductivity is a result of its porous structure.

To make the solution plastic and improve adhesion to the surface, a variety of plasticizers are added. Typically, their portion of the solution doesn’t go above 1%. Cement’s characteristics are also enhanced by lime dough.

Technical characteristics

Density. The density of the plaster mixture directly affects its strength and thermal conductivity. Without any additional ingredients, pure cement-sand mortars are regarded as heavy and, when hardened, have a density of 1600–1800 kg/m3. This is a reasonably durable coating that can be used as a floor screed in addition to interior or facade decoration.

The ability to conduct heat. The cement-sand screed has a high thermal conductivity because of its high density. The thermal conductivity of cement and sand-based plaster is 0.9 W (m * K), which is higher than that of more porous gypsum, which has a thermal conductivity coefficient of 0.3 W (m * K) and retains heat well.

Permeability of vapor. The walls need to take up extra moisture and expel it outside in order to prevent condensation inside the space. Therefore, an indicator like vapor permeability is also considered when selecting a material for wall finishing. It is roughly the same for cement and gypsum mortars, equal to 0.09 mg/m h Pa in the second case and 0.11-0.14 in the first.

Time for drying. A 2 centimeter thick layer will dry in 12 to 14 hours at +15 to 25 °C. It is best to avoid touching the plastered surface for 24 hours because an increase in thickness naturally lengthens the drying period.

A comparison between gypsum plaster and cement-sand plaster is presented in this article. It also discusses a cement and gypsum mixture.

We will compile all of the attributes into a single table for clarity’s sake.

Consumption of cement plaster per 1 m2

Plaster consumption should be considered when estimating repair costs. Dry cement-sand mixtures cost less than gypsum, but they require more material per square meter—17 kg per m2 for a thickness of 10 mm—than gypsum does. For instance, two times less gypsum—only 8–9 kg—is required per square meter with a thickness of 1 cm. Information about the amount of material required per square meter to form a layer with a specific thickness must be provided by the manufacturer.

Let’s figure out how much water, sand, and cement are needed to plaster one square meter. With a thickness of 10 mm, the solution is consumed at a rate of 17 kg/m2. 0.15 to 0.17 liters of water are needed for mixing for every kilogram of dry mix. If we use a 1:4 ratio of cement to sand for plastering, the mass of the required materials will be:

• Cement – 2.9 kg
• Sand – 11.7 kg
• Water – 2.4 kg

Price of ready-made mixtures

Preparation of walls

It is essential to prepare the surface beforehand to prevent the heavy cement mixture from peeling off the walls. There are various methods:

On the wall, a thin coating of tile adhesive is put. It serves as a layer of filler in between the wall and the cement plaster. The glue has strong adhesion and good strength because of the additives in its composition. On top of it, a plaster mesh is applied, covering it entirely. There should be a 10-cm overlap between the mesh’s edges. Next, press the mesh into a layer of tile adhesive after smoothing it with a trowel with a notch. Next, use a trowel to create horizontal grooves. The adhesive solution will solidify into a base for leveling cement-sand plaster after it dries.

Reinforcement using self-tapping screws to firmly fasten a metal plaster mesh to the wall. This is carried out when it’s essential to apply a thick layer of plaster to walls made of clay and wood that are brittle.

There are notches all over the surface of concrete walls. Usually, an axe or hammer drill are used for this. An adhesive primer, such as Betonokontakt, is then applied.

An additional method for fortifying the wall is wire lathing. Either nails are driven in and tied with wire, or self-tapping screws are screwed into the wall at the same distance. It has the appearance of a plastered metal mesh. This is a labor-intensive, low-cost method that works best for small-scale repairs.

Prior to applying new plaster, the old plaster is tapped, any loose pieces are taken out, and the pits are brushed clean.

Their cellular concrete blocks and aerated concrete blocks typically have smooth walls that don’t need any extra preparation. To lessen the amount of water that the plaster mortar absorbs, they are coated with a deep penetration primer. The strength of the hardened layer will decrease as a result of the accelerated setting caused by dehydration of cement plaster.

Preparation of the solution

Purchasing a premade dry cement-sand mixture is a much easier option when finishing small surfaces. Preparing the work yourself is more profitable when there is a higher volume involved. The most crucial thing is to maintain precise proportions.

First, without using any water, thoroughly mix the sand and cement. The type of cement will determine the ratios used in the mixing. According to GOST, the resultant cement plaster is separated into multiple grades:

Tiny inclusions need to be removed by sieving even the purest sand. Cement that has caked from prolonged storage is not recommended for use. It can be sieved, if needed, to get rid of any solidified lumps, and the amount of sand in the mixture can be cut in half.

The dry ingredients are mixed and then liquid is added. Small amounts are added, thoroughly blending the solution after each addition.

Plasticizers are added to it to make it more flexible and mobile. This has already been discussed above. The completed solution needs to be evenly dispersed across the surface and gathered into a heap rather than being spread.

Here are more instructions on how to prepare sand-cement mortar for plastering.

Technology of plastering walls

Now think about the fundamental guidelines for positioning the walls using a cement mortar:

In order to increase adhesion, the walls are primed and completely dried;

Beacons are guides that help make a plane on the wall. They can be swapped out for mortar slaps, the height of which is determined by level, in small spaces.

As beacons, a unique metal profile can be employed. Putty is used to secure it to the wall. Wooden slats or bars can also be used to create beacons; screws are used to fasten them. The most important thing to keep in mind is that there should be 10–20 cm less space between beacons than there is between the width of the rule used to level the plaster.

Using a trowel, apply the plaster to the walls; a ladle can be used for a thicker layer. The splash layer is the initial layer and serves as the foundation for further layers.

It is best to apply the second layer a few hours after the first has dried. It is placed so that it completely covers the one before it, working from bottom to top. Plastering in narrow segments of one to one and a half meters is more practical. After that, a rule is used to pull and level the plaster. The rule is moved slightly from side to side as it is pressed firmly against the beacons and raised upward. Using a trowel, remove any extra mortar from the rule.

They proceed after plastering the entire space between the two beacons.

It is not possible to level minor flaws with beacons. This time, plastering is done with a different technology. Using a big spatula, distribute the mortar from the bottom up after spraying.

You can achieve a smoother surface by applying a second layer (extra coating) of liquid mixture. In this instance, the mortar’s composition will be 1:1 or 1:3 (cement, sand).

After setting, the cement-sand plaster is rubbed down before it hardens further. Using a trowel, remove small irregularities, grooves, and protrusions in a circular motion.

After drying, a wall leveled in this manner is ready for finishing. At typical indoor humidity levels, cement plaster dries in four to seven days. This can take up to two weeks for facade work.

Aspect	Description
Characteristics	Plaster cement mortar is durable, water-resistant, and provides a solid base for various finishes. It typically includes cement, sand, and water in specific ratios.
Preparation	To prepare, mix cement and sand in a 1:3 ratio, then gradually add water until the mixture reaches a smooth, workable consistency.
Application	The mixture is applied in layers using a trowel, ensuring each layer is even and smooth. It’s suitable for both interior and exterior surfaces.

A dependable choice for wall finishes that are resilient to both indoor and outdoor environments is plaster cement mortar. Its cement, sand, and water mixture provides durability and strength, which makes it a popular option for building projects.

Achieving a flawless application and strong adhesion requires careful attention to proportion and consistency. Plaster cement mortar mixed correctly makes it easier to cover uneven surfaces and prepare walls for further finishing.

When properly applied, this mortar gives your walls a more polished appearance while also adding a layer of resistance to weather, moisture, and everyday wear and tear. Even a novice can use this tried-and-true material to produce results of professional caliber with a little practice and attention to detail.

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