Plaster for external work: types, proportions and compositions

The correct plaster can make all the difference when it comes to protecting the outside of your house. In addition to improving the exterior of your building, external plaster provides vital defense against weather-related and environmental damage. Knowing the various plaster types and how to mix them correctly is essential whether you’re building a new building or remodeling an older area.

This post will examine the different kinds of plaster that are applied externally. We’ll go over the essential components and ratios required to get a long-lasting and efficient finish. We’ll go over everything you need to know to select the best plaster for your project and make sure it works well under all circumstances, from conventional lime-based plasters to contemporary cement alternatives.

Prepare to explore the fundamentals of external plastering and discover the best ways to choose and prepare materials for the outer layer of your home. With the correct information, you can confidently take on your plastering project and produce weatherproof results.

External plastering of the house – what you need to know about the structure of the wall.

In addition to serving as the house’s bearing and supporting structure, the exterior walls prevent heat from escaping. All of their components—interior design, masonry, cladding, and regular facade or exterior decorative plaster—obstruct the flow of heat.

However, in the winter, the building cools down significantly outside, producing a stark temperature contrast. The air’s water vapor eventually comes into contact with the cold as it passes through the structure’s thickness. They abruptly cool and condense, transforming into water. The wall becomes damp and wet.

The dew point is the temperature at which steam turns into water. In order to move the dew point as close to the street as feasible, it is crucial to attain this insulation balance.

The issue can be resolved structurally by raising the wall’s temperature and vapor permeability. The use of vapor-permeable plaster, appropriate for outdoor use, helps to partially address the issue from the perspective of the facade’s external decoration.

How to decorate the walls?

Steam faces some resistance when it passes through a solid wall because of the material’s density. The sandwich’s less vapor-permeable components are unable to remove all of the vapor that has already entered the wall. This is where the steam cools, moistening the building and lessening its ability to block heat.

External walls made of ordinary, decorative, and insulating plaster may present such a barrier if the layer below it permits more steam to permeate.

As such, specific solutions are appropriate for specific wall material types. and concluding in general.

1. Concrete, reinforced concrete. This includes concrete and slag-poured, cinder block, expanded clay and sawdust block structures. Cement-sand plaster, which has a composition uniform with the wall material, is quite applicable. Less dense ones – even more so.
2. Brickwork. A brick-like wall (thickness. 26 cm) at -10 degrees. will remain dry from the outside. But a layer of cement plaster of thickness. 2 cm will moisten it from the inside due to steam condensation. Therefore, it is important to have a clearer idea of ​​​​the dew point. Lime-sand finishing is more appropriate here.
3. Stonework. Depends on the density of the stone. For rubble stone, for example, external cement or lime-sand "protection" will be useless. The house will be damp from the inside even with a 10-centimeter thickness of the external coating. The best option for stone is a sawdust-clay mixture laid 3-4 cm thick (with reinforcement or shingles). It is not difficult to prepare such a composition of plaster for external, insulation work with your own hands.
4. Lightweight concrete walls (aerated and foam concrete blocks). Neither lime nor cement are applicable to cellular concrete. The best option from inexpensive ones is a gypsum-perlite mixture. But the most effective is the use of silicate mixtures.
5. Wooden houses plastered with clay. Only clay, sawdust-clay coating.
6. Open (unplastered) log houses. It is better to leave wood open, there is no plaster mixture through which steam passes better than through wood.

It’s not always a good idea to plaster a facade externally. Due to the walls’ excessively low density, thickness, and heat capacity, external decorative plaster is typically even prohibited. In this case, thinking about the external insulation device with ventilated facades makes more sense.

Layers of gypsum-perlite and clay need to be protected; they are not used as stand-alone exterior finishes.

Selecting the appropriate plaster type for exterior plastering is essential for its longevity and efficacy. This post will examine different kinds of plaster that are appropriate for outdoor use, outlining the precise proportions and compositions of each. By being aware of these factors, you can make sure that your external surfaces are both aesthetically pleasing and adequately protected from the weather.

Compositions of solutions for plastering external walls.

Mineral and polymer binders are the two types that enable the creation of solutions for finishing facades. While the second is more efficient, the first is less expensive. The developer’s budget directly influences their decision.

1. Cement-sand. A popular and cheap type of finishing. The disadvantage of the composition is its relatively low vapor permeability, low plasticity and decent mass.
2. Lime-sand. Cheap and easy to apply mixtures. But not very reliable for external finishing.
3. Gypsum plaster for external work is a common myth supported by unscrupulous manufacturers. Cannot be used for finishing facades without additional protection.
4. Acrylic. Strong, vapor-permeable, easy to work with and environmentally friendly. Used for plastering walls made of any materials. But expensive compared to mineral.
5. Silicate. A mixture of potassium (liquid) glass with lime. Has the greatest ability to pass water vapor. Applicable on any base.
6. Siliconeis characterized by maximum elasticity, resistance to destruction and high permeability. Reject dust particles, belong to the class of self-cleaning finishes. They are more expensive than plasters on other binders.

It’s crucial to take the surface’s composition into account in addition to cost. There are plasters that work for most surfaces. Others are only useful when combined with specific types of wall material.

Generally speaking, stronger solutions shouldn’t be applied to weaker substrates (previous finishes). For instance, if gypsum is placed on cement-sand mortar, it will undoubtedly tear off as it dries.

Do-it-yourself external plastering of the house.

After determining whether plastering is feasible and selecting an appropriate composition, they get to work. The facade should first be inspected to determine the extent and kind of surface damage, as well as whether any slopes or cracks are present.

Alignment with markers.

Special beacons, which are metal profile pieces fastened to the wall and leveled, are used for plastering. This method greatly reduces the amount of work. This is particularly crucial for novices who have chosen to embellish the facade themselves.

Beacons are positioned 1.2–1.4 meters apart so that they can subsequently be trusted as a rule.

Preparation of walls.

The entire old finish is removed, including paint remnants, lime, poorly adhering plaster layers, and facing elements like siding and slats.

The surface is primed before the solution is applied. Plaster primer is applied externally using a roller, brush, or spray.

It is best to use a penetrating primer for loose and cellular materials. It should be applied in two layers and completely dried between applications.

The surface is reinforced if it becomes necessary to create a layer thicker than what is allowed (each binder has its own norm).

Application of external plaster.

Starting from the bottom, the plaster mass is thrown into the spaces left by the beacons, covering the entire area from edge to edge. A rule with upward movements levels the mass.

Corners.

The last areas to be plastered are the corners and opening slopes. In this instance, the rule is guided by the dried exterior plaster.

In the latter case, two flat instruments—such as a spatula—are applied and pressed up against both mating planes. However, creating a template out of tin, plywood, or wooden slats is more practical.

For exterior work in corners, polymer decorative plasters are the best option because they are shockproof and never wear out.

Plinth.

Plastering of protruding and recessed plinths is done separately, while plastering of a flat plinth can be done in one piece with the wall. It is true that the waterproofing installed in the wall needs to extend to the basement plaster and wall’s edge.

It is unacceptable to compromise when finishing the basement if using "weak" solutions for the main portion of the wall is acceptable. This is the section of the house that is the wettest. Since only the roof covering is "wetter" than the basement, waterproof compounds are used exclusively during the work.

Preparing a solution for external plastering.

The type of binder, the quantity and kind of additives, and the necessary density of the solution determine the proportions of the mixture when plastering exterior walls by hand.

Since polymer exterior plasters are not produced independently, it is important to prepare these solutions in accordance with the manufacturer’s guidelines.

Mineral plasters are typically made on the spot and include cement-sand, lime-cement, and lime-sand.

1. Cement-sand. The proportion of cement with sand 1: 4 (when using Portland cement M-500). For external plastering, it is necessary to use plasticizers. For example, liquid soap.
2. Combined external. Mixture of cement and lime. A more plastic and waterproof solution.

It takes 280 kg of sand and 21 kg of lime to make one bag of M-500 cement.

1. Lime-sand. The components are mixed in a ratio of 1:4. A plastic, lightweight solution for budget external plastering.

Small amounts of the plaster mixture are diluted to make a volume that can be sold before it sets. The mixture’s viability determines this interval.

For exterior work, polymer plasters are prepared in accordance with the guidelines. which, in the end, come down to suggestions for how much water to add.

Simple DIY decoration.

Masses of homemade mineral plaster are applied and leveled on the wall. A decorative layer of the same composition completes the top.

Alignment.

The outermost layer of plaster. applied up to 1.5–2 cm thick to achieve the desired level of evenness on the wall. More substantial layers must always be reinforced if they are applied.

Occasionally, multiple thick layers of the exterior finish are applied and allowed to dry individually to prevent reinforcement. Nevertheless, layering is not very reliable; one of the primary causes of exterior finish cracking is uneven plaster thickness.

Decoration.

This is the second textured layer. Depending on the type, pattern, volume, and desired relief, it is applied using a variety of tools.

• Fur coatsare obtained when working with a roller. For this, the solution is made liquid and the decorated preparation is “painted” with this composition.
• Small fur coats are obtained by spraying the walls with a liquid solution using a brush. It is dipped in the composition and, directed to the desired area of ​​the wall, is drawn along the pile with a hard object. The straightening bristles (line) of the brush “shoot” the plaster mass.
• Stone texture is an imitation of the natural irregularities of natural minerals. It is applied in the form of a second layer with a cell or embossed material (crumpled piece of fabric, fur, cellophane).

The layer is partially laid, not removable, with the first layer’s gaps still visible in between the small fragments. The tool is used to "lubricate" the solution as it starts to take hold.

The solution’s proportions for the outer walls’ decorative plaster layer remain unchanged. The array ought to be uniform.

Waiting for the initial plaster to completely dry is not required for strong enough grasping. You need to moisten the dried wall.

Imitation of masonry.

Especially well-liked for decorating pillars, fences, supports, and basements.

Applying a print to external plaster is an easy DIY decoration project. Particular forms with masonry relief are pressed into the recently applied exterior plaster. It is painted once it has dried, which gives the "stones" a more authentic appearance.

You can only create a relief by sampling it in the wet plaster so as to avoid getting prints. Mark the rows of masonry on the wall, each with a single hewn or shaped stone. Using the spatula’s corner or another handy tool, choose the solution until it reaches the desired depth. A certain affinity for the fine arts is necessary for this technique.

Finishing with ready-made plasters for external work.

Mineral external plasters are less dependable than polymer ones. It’s true that their cost is higher. The mixture ratios with water can vary depending on the type of binder.

Since many compositions are already fully ready for use, they are frequently sold in buckets. Some just need to be diluted with water to make the plaster solution more workable and malleable.

Apply in accordance with the directions, which vary based on the mixture’s makeup and the desired texture.

What should not be done when applying external plaster.

There are a few typical errors that can lower the external finish’s quality.

1. Proper preparation. The solution will never “stick” to peeling, dusty surfaces. They need to be cleaned, unstable bases removed, primed.
2. Choosing the right finishing composition. For example, gypsum plaster is not for outdoor work. Gypsum is not waterproof enough to be used outside. It is also used indoors only in rooms with medium and low humidity.
3. You cannot make any solution yourself. For example, granite colored plaster for outdoor work is made only on the basis of synthetic resins saturated with plasticizers and other additives. They cannot be replaced with cement.
4. Following the instructions, designated by the manufacturer. Violation of them will lead to loss of money, because the finishing will quickly deteriorate. The composition of the polymer solution for plastering external walls is very durable, elastic. But requires careful adherence to the rules. Main damage:

• Defects. The result of unfair preparation of the wall, poor -quality primer.
• Delamination. Violations of the technology of application of the composition.

The plaster binder’s compatibility with the wall material is particularly crucial to consider.

It is not advisable to take chances or rely solely on luck if the instructions say that you cannot apply external plaster to a particular wall. The manufacturer would list such a material in the acceptable list if the likelihood of it happening was high.

Type of Plaster	Proportions and Composition
Traditional Lime Plaster	Lime, sand, and water. Typically, the ratio is 1 part lime to 2.5 parts sand. Useful for its breathability and flexibility.
Cement Plaster	Cement, sand, and water. A common mix is 1 part cement to 4 parts sand. It’s durable and resistant to weathering.
Gypsum Plaster	Gypsum, sand, and water. Commonly mixed in a 1 part gypsum to 3 parts sand ratio. Best used in dry conditions as it’s not water-resistant.
Hybrid Plaster	Mix of cement, lime, and sand. Proportions vary, but often 1 part cement, 1 part lime, and 4 parts sand. Balances durability and flexibility.

Selecting the appropriate type and mixture of plaster for external surfaces is crucial to attain longevity and safeguarding. Every variety of plaster has special advantages that are suited to various environmental factors and aesthetic tastes. Making an informed choice is aided by knowing these options, whether you choose for modern cement-based options for strength or traditional lime plaster for its breathability.

The performance of plaster mixtures is greatly influenced by their composition and proportions. Precise measurements guarantee the plaster’s correct adhesion and weather resistance. Whether you use pre-packaged plaster or mix your own, adhering to the suggested ratios is essential for a good application.

In conclusion, the right plaster selection and mixing are essential components of any external plastering project. You can attain a finish that is not only aesthetically pleasing but also long-lasting by taking into account the particular requirements of your project and adhering to recommended mixing and application techniques.

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