What insulation to choose for the walls of the house outside under the plaster

Choosing the appropriate insulation for your home’s exterior walls is essential to designing a cozy and energy-efficient living area. The best kind of insulation to use under plaster can be difficult to determine with so many options available. Every material has benefits of its own, and the choice you make will often rely on your needs, your financial situation, and the weather.

The most common insulating materials for external walls that need to be plastered will be discussed in this article. There is a solution that can satisfy your needs, whether they are related to eco-friendliness, high thermal performance, or simplicity of installation.

You can make an informed decision that not only increases the insulation in your home but also improves its overall durability and appearance by being aware of the advantages and disadvantages of each type of insulation.

Why insulate the facade

Achieving multiple goals at once is possible at times.

By putting insulation beneath the plaster on a facade, you can:

• effective heat conservation inside the building, and, consequently, saving energy and money on heating, creating comfortable, gentle conditions for residents;
• remove the place of active precipitation and settling of condensed moisture from inside the wall material outside of them, which protects the walls from dampness and destruction, prolongs the service life of the building;
• perform decorative design of the "exterior" of the building.

Plastering over insulation for interior walls makes less sense in terms of the second task than it does for facade insulation. On the other hand, there are circumstances in which insulation from the inside is the only option (e.g., local legislation).

Which insulation is better for the facade under plaster

Selecting insulation for a home’s exterior walls under plaster can be challenging for a novice, as there are many counters stacked high with contemporary goods from various manufacturers. Therefore, before selecting an insulation material, it is advisable to become familiar with the various types of insulating materials, as well as the primary differences in properties, characteristics, and application conditions.

The following qualities of insulating materials will be crucial for wet facades:

• thermal conductivity coefficient;
• density, and, consequently, the weight transferred to the wall, as well as the rigidity of the slab;
• water absorption;
• flammability;
• vapor barrier properties;
• environmental friendliness;
• durability;
• price.

Furthermore, density and heat-retaining capacity are related. Insulating materials can be categorized by density into:

• very light (for example, polystyrene foam, penoizol);
• light (mineral wool is conventionally included here);
• medium;
• rigid.

Thermal conductivity and density value are directly correlated. Heat escapes through thermal insulation more readily the higher the first, the less heat-saving air in an equivalent volume of insulation.

This implies that a layer of less dense material is taken thinner and a layer of denser material is taken thicker for the same capacity to retain heat.

Density (or specific gravity, usually expressed in kg/m3) influences the product’s cost, noise reduction level, installation method, application area, and installation method variations for materials of the same type, such as stone wool. Denser mineral wool therefore suppresses noise less but is easier to install because it resists applied loads and holds its shape better. Wet facades can use it (unlike less dense).

Initially, when they are making a decision, they consider:

• thermal insulation qualities;
• convenience of the shape of the slab material for installation;
• the possibility of installation without additional measures (ensured by the rigidity of the slabs);
• relatively low price.

Polystyrene and foam plastic

One of the varieties of construction materials made from polystyrene, a single raw material, using various technologies. Water vapor treatment of polystyrene granules yields foam plastic. As the granules get bigger, they adhere to one another to create a canvas with both closed and communicative pores.

• the slabs are light (do not load the walls);
• easy to cut;
• retain heat well;
• resistant to microorganisms;
• low price.

• almost zero vapor permeability, which forces to provide forced ventilation;
• unfortunately, the material is flammable, and toxic substances are released into the air during combustion;
• low mechanical strength, requires protection from external even medium-strength impacts;
• defenseless against rodents;
• does not tolerate solvents;
• not resistant to direct sunlight.

Mineral wool

Stone wool, another term for mineral wool, is insulation with a fibrous structure that is created by melting rocks and pulling out the lava-like mass that forms at 1500 degrees Celsius into fibers. The fibers are polymerized after plasticizers, water-repellent materials, and binding agents are added. The final product is divided into strips or slabs that are used as insulation for interior and external walls. Stone wool can be worked with without gloves.

The brand of mineral wool indicates its density. For plastering, stone wool from the PZh 125 and PZh 200 brands is appropriate. Wool with a density of less than 110–120 kg/m3 is not used for wet facades because it is less rigid and more pliable to loads.

Since 90% of basalt insulation is made of stone, this means:

• does not burn;
• does not rot;
• has high vapor permeability (probably the best insulation for wooden walls);
• resistant to solvents;
• can be installed all year round;
• easy to cut;
• does not require special skills for installation;
• durable.

The drawbacks of mineral wool are as follows:

• easily absorbs water, losing its thermal insulation properties;
• holds its shape worse than other heat-retaining materials;
• prolonged wetting can lead to loss of shape.

Ecowool

Seldom is this insulation placed beneath plaster used. The material is produced by processing secondary raw materials and waste paper.

Typically, the composition consists of:

• cellulose fibers ~ 80%;
• fire retardants (preventing combustion) ~ 8%;
• antiseptic (boric acid is used to prevent the appearance of fungi and other cellulose lovers in the mass) ~ 12%.

• is capable of absorbing up to 30% moisture without losing shape, continuing to retain heat;
• thermal insulation properties are 20-24% higher than those of mineral wool (for a dry state);
• allows walls to "breathe";
• forms a monolithic coating, which eliminates cold bridges;
• low price.

• complexity of application (equipment and spraying technology are required);
• smoldering is possible near fire sources;
• to eliminate shrinkage, it is necessary to strictly follow the technology;
• holds pressure worse than polystyrene foam;
• strong dust formation during dry installation, a long drying coating – during wet installation;
• big waste of time.

Either way, this is contentious material. Some even claim that the word "eco" means economical in translation but does not mean environmentally friendly on the Internet.

Penoplex EPS

An additional material composed of granules of polystyrene. By using an extrusion process, polystyrene is heated until it melts, and the resulting mass is then treated with steam to create penoplex, or polystyrene foam. Because of this, the pores are closed and tiny, which affects qualities like density, strength, and resistance to moisture.

With the exception of cost, penoplex is superior to foam plastic in nearly every aspect that matters for wet facades. Furthermore, because polystyrene foam requires less space, it is utilized for interior thermal insulation in buildings. Both types of materials work well for insulating facades and basements.

• lightness;
• water resistance (resistant to moisture);
• ease of processing;
• strength (withstands loads up to 4 kgf/cm2, which is unattainable for foam plastic with its 0.5 kg per the same area);
• durability.

• flammability;
• destroyed under direct sunlight;
• loved by rodents;
• more expensive than foam plastic.

Penoizol

An additional polystyrene foam modification.

• low thermal conductivity coefficient;
• does not support combustion;
• elastic (slight deformation with return of shape is allowed);

• expensive "pleasure".

Foam glass

Unusual substance made by frothing a blend of stone chips and glass. This insulation has undergone numerous inventions in modifications. There are vapor-impermeable, incredibly robust blocks. Blocks made of ETIZ gas glass have holes in them that let light flow through and allow the walls to "breathe." Since these are high-end products, we don’t give them any thought.

Sprayed thermal insulation materials

These kinds of compositions necessitate the use of specialized machinery in addition to a laborious component preparation and usage procedure. Materials that are sprayed shouldn’t be taken into consideration because their application and manufacturing technologies are complicated for novices. Likewise, for "wet" facades.

How to calculate the thickness of insulation

You need to know a little theory in order to perform calculations. The previous section covered thermal conductivity. To put it simply, let me use the analogy of filters to explain. The amount of water that seeps through a unit of area over time—for instance, an hour—is known as a product’s throughput. We can understand what the thermal conductivity coefficient means if we picture heat flowing linearly from a room through a wall (of unit thickness) per unit of time, instead of water.

We can compute the heat loss if we know the parameters, such as the wall thickness, the temperature differential inside the house, and "overboard," or the thermal conductivity coefficient (W * m / K). Alternately, determine the wall’s thickness to ensure that the intended level of heat loss is not exceeded. The inverse of thermal conductivity, or thermal resistance, can be calculated using a formula for this. The formula accounts for the wall’s resemblance to a layer cake due to the successive placement of multiple layers with varying thermal conductivity along the heat leakage path, as well as the thickness of each layer.

The formulas are used in the same order for the calculation.

We compute R min after determining the total resistance of all layers—there may be more than three. R min and R pr are compared. There is no need to insulate the wall if R min is less than R pr. If it is greater, we compute the difference and get ΔR by subtracting R min from R pr.

Due to the fact that the values of the units for the construction region must be found in the standards, this method is fairly complex. Online calculators are therefore typically used.

Insulation installation

Ideal circumstances for the production of installations:

• temperature +5 – +30 o C;
• calm;
• no precipitation;
• the place is shaded if the side of the house is illuminated by direct sunlight.

We explain their installation since craftsmen and novices typically use mineral wool or foam beneath the facade’s plaster.

1. Wall
2. Leveling layer of plaster
3. Insulation
4. Mesh
5. Top layer of plaster
6. Decorative finishing

These materials have comparable qualities, and installing them requires the same steps:

• purchase and prepare the required materials with a margin;
• prepare the walls for installation;
• install the thermal insulation boards;
• prepare the solution;
• do the reinforcement;
• prime the reinforced plaster layer;
• do the finishing.

An extensive explanation of the technology can be found in the "wet plaster" article. We will only discuss the primary phases here.

Preparation of materials

Ahead of time, stock up on all the supplies you’ll need.

• glue for insulation (corresponding to both the materials of the insulation and the wall);
• primers (for the wall and for the reinforced plaster layer, the compositions may be different);
• selected insulation (in case of external finishing of the house, we choose foam plastic marked F (for facades);
• mesh cloth (fiberglass or metal);
• plaster mixtures (base for creating a "shell", decorative for finishing);

• corners equipped with mesh on the sides;
• base guide profile (U-shaped);
• mushroom dowels (select the length based on the thickness of the insulation boards).

Mixtures should be prepared as directed on the label right before using adhesive or plaster compositions.

Preparing walls for installing insulation

This phase of the process is similar to priming a home’s walls for plastering:

• remove the worn-out coating of the plaster facade, leaving only what is strong and holds firmly, wash off the whitewash;
• revise the surface;
• cut off the drips, protrusions;
• clean from grease, rust, mold stains and soot;
• remove excess hardware, hide the wiring in the grooves;
• fill the grooves, masonry, interblock seams with foam glue;
• repair cracks, potholes;
• remove dust;
• if necessary, level the surface (prime, plaster);
• seal frames, window units with film;
• apply a primer;
• dry.

Install sturdy scaffolding for the aforementioned work and any further projects. Establish a location for cutting slabs and preparing solutions (plaster, adhesive). Make a surface mark. Install the base profile 30 cm below the level of the first floor slab but no higher than 60 cm above the ground.

Insulation installation

Applying adhesive mass to the sheets and gluing the first row of sheets (from the end of the building) is how we start installing insulation for the facade beneath the plaster. If the wall is not sufficiently flat, apply the adhesive mass continuously (with a flat wall surface) or in several flat cakes (diameter approximately 20 cm) and a strip along the sheet’s perimeter with an indent of 2-3 cm from the edge. If you want to spread continuously, use a trowel or notched trowel.

After pressing the "greased" plate firmly against the base to allow the glue to "stick," we move the insulation to one side and then put it back in its original location. Next, the space between the wall and the base will be equally filled with glue. Using a spatula, we remove the glue mass that has emerged at the edges, covering the areas where the slab’s edges are free of glue.

We push the slabs tightly together until the ends meet, joining each one after the other. If there are any gaps, we firmly pack insulating scraps into the empty areas. Cold bridges will form if the gaps are filled in with adhesive mass, which is something that shouldn’t happen.

You can move the slabs for a while until the glue sets. During this time, the insulation’s position is adjusted and corrected to create a flat plane on the slab’s surface. Using a wooden block or a rule, adjustments and checks are made.

After completing the insulation sheet cladding on the house’s facade, allow the glue to set for three days. Next, we use dowel-mushrooms to further secure each plate to the wall, pressing the sheet firmly at five points. One mushroom will fix the corners of adjacent slabs. The mushroom cap should "sink" into the slab by one millimeter and be covered in spread mortar to keep moisture out.

Reinforcement

Using a spatula, a layer of plaster or adhesive mortar is applied to the insulation’s previously primed surface (if glue was selected for the reinforcing layer). A notched spatula is used to line the surface before the mesh is applied and straightened. Using a standard spatula, push the reinforcing fabric over the mesh to push it into the mortar.

In the mesh "garment," gaps and butt joints between the sheets are not acceptable. A 10-centimeter overlap connects adjacent mesh pieces. For corners, profile corners are utilized. When reinforcement is done correctly, it will form a robust "shell" that holds in place so that the mesh tears off along the insulation rather than at the junction.

Types of plaster on insulation

Decorative plastering is most commonly used for the external finishing of walls that have been insulated in this manner. Here, a plaster that doesn’t chemically clash with the "shell" and insulation material composition is chosen for the plaster coating. Plastering is done in a manner akin to applying the solution to a standard wall that has been ready for plastering. Since the applied layer will be external (in comparison to the insulated one), it should serve protective purposes in addition to aesthetic ones.

The following combinations work well for plastering external walls’ insulated surfaces:

1. Mineral (neutral in relation to the listed insulation materials, but corrodes the plastic mesh). Fiberglass or metal reinforcement is used to create the "shell". Internal stresses that arise during the shrinkage of cement plaster can lead to damage to the heat-saving "pie". Therefore, high-strength foam plastic (marking above 35) or penoplex are chosen as insulation under the plaster.
2. Acrylic is suitable for any mesh. The inconvenience of having to quickly plaster the entire wall without interruption. After any break, color traces will appear on the wall at the junction of dried and fresh mixtures.
3. The only complaint about polymer plaster will be the cost of the mixture.
4. Silicone is also not cheap, very elastic, does not fade, does not conflict. However, you should not use compositions with stone chips based on silicone for weak mineral wool slabs. Want to try, make the reinforcement stronger by taking a fine-mesh metal mesh.

Insulation Type	Pros	Cons
EPS (Expanded Polystyrene)	Good thermal insulation, cost-effective, lightweight	Can absorb moisture, not very eco-friendly
XPS (Extruded Polystyrene)	Excellent moisture resistance, high thermal insulation	More expensive than EPS, can be less eco-friendly
Mineral Wool	Great fire resistance, good soundproofing, eco-friendly	Can be more expensive, absorbs moisture if not properly sealed
Polyurethane Foam	High thermal insulation, seamless application	Expensive, requires professional installation
Foil-Backed Insulation	Reflects heat, good for preventing heat loss	Less effective if not properly sealed, can be pricey

The comfort and energy efficiency of your home can be significantly improved by selecting the appropriate insulation for the external walls. It’s crucial to consider thermal performance, moisture resistance, and ease of installation when weighing your options. Popular options include expanded polystyrene (EPS) and mineral wool, each of which has advantages specific to your needs and local climate.

Because of its great thermal insulation qualities and reasonable price, EPS is a great option for a lot of homes. Its portability and ease of handling can make installation easier. However, depending on the fire safety regulations in your area, mineral wool offers both superior fire resistance and thermal insulation, which may be vital.

Consider the climate where you live and any unique difficulties that your house might encounter, like excessive humidity or very cold temperatures. This will assist you in selecting insulation that will not only maintain the comfort of your house over time, but also withstand changes in the surrounding environment.

In the end, installing the proper insulation will improve the energy efficiency of your house and possibly reduce your utility costs. You’ll benefit for years to come if you take the time to investigate and select an insulation material that meets your needs and your budget.

Selecting the appropriate insulation for your external walls prior to plastering is essential to preserving your home’s comfort and energy efficiency. Think about things like the type of wall construction, the climate, and the moisture resistance and thermal performance of the insulation when making the best decision. Understanding the characteristics of various materials and how they align with the requirements of your home can help you make an informed choice that improves insulation and the longevity of your plastered walls. Examples of these materials are mineral wool, foam board, and fiberglass.

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