Waterproofing a monolithic foundation slab

A slab foundation is a reliable and strong foundation. It consists of concrete, which is prone to absorbing moisture from the outside. Once inside the platform, moisture particles begin to interact with the components of the reinforcing frame, cause their corrosion, and remove cement from the slab. All this has a negative impact on the constructed base. Leads to its destruction and deformation changes inside.

Why do you need moisture protection for a monolithic foundation?

Measures aimed at protecting the load-bearing structure from the penetration of water drops into its structure are necessarily included in the complex of works for the construction of the foundation.

Not only groundwater causes moisture in a concrete structure, but also flood and rain moisture and accidental runoff. In this case, the liquid may contain acids, alkalis and salts, which accelerate the processes of metal corrosion and concrete destruction several times.

Requirements for waterproofing reinforced concrete structures are regulated by SP 28.13330.2017.

Cost of foundation waterproofing

Many people are familiar with the situation when a team tries to save on materials. This also applies to foundation waterproofing. As is known, the projects that are being implemented were developed by Union specialists and did not know new technologies at all. If, of course, you build a house for yourself, then most often it is done conscientiously and there is no talk of saving.

Basically, the cost of waterproofing work depends on the cost of the materials used, as well as the technology used by the specialists involved in this matter. It also depends on the surface area with which you will have to work, on the measures that will be applied. Most often, the costs are mainly spent on bitumen. And if we talk about large expenses, then these are the costs of coating materials, roll waterproofing and work on drainage arrangement on the site.

Of course, in the end, the choice to waterproof the foundation is yours. Is it worth spending money on materials and looking for an experienced team that is reliable and capable of doing everything properly? But remember, it may be better to incur the costs of all this now than when the time comes to save your home and carry out waterproofing in such a short time, it can cost you much more. And as mentioned above, it is necessary to take the specialists who will carry out this work more seriously. Once you make a mistake, you will have to do everything all over again, starting with finding competent people who know how to work in this area.

What can the lack of waterproofing lead to?

An unprotected monolithic foundation loses its performance when exposed to moisture . The process of destruction of concrete begins at the moment when the liquid penetrates the heterogeneous structure of concrete and begins to wash away the components of the cement binder.

As a result, the density and frost resistance of concrete decreases, and cavities and cracks form in the body of the foundation.

When the liquid penetrates deep enough to reach the reinforcement frame, metal corrosion begins and the rate of destruction of the load-bearing structure increases.

Steel is very sensitive to concrete moisture . The metal, under the influence of oxygen and substances dissolved in the liquid, transforms into a state of oxides and salts. Due to potential differences, stray currents arise, leading to electrochemical corrosion, which further destroys the remains of the reinforcement frame.

The effect of liquid on the foundation is aggravated if thermal insulation was not provided during the construction process. Repeated cycles of freezing and thawing of concrete lead to the breaking of bonds in its structure.

Thus, water penetrates even deeper into the body of the foundation, turning into ice at sub-zero temperatures. The liquid, the volume of which increases in the frozen state, contributes to the further opening of existing cracks.

If the surface of the slab is not protected from moisture, then the liquid penetrates into the material of the walls , which rest on the load-bearing structure. It leads to:

dampness in the lower rooms,
the appearance of mold,
fungus,
salt stains, etc.

Why is a slab foundation waterproofed?

The monolithic mass contains small pores, which act like capillaries at high humidity.

Unprotected concrete gradually absorbs moisture, which causes negative consequences:

the strength characteristics of the monolith decrease with constant waterlogging;
water is concentrated in the pores, which increases in volume during crystallization;
a damp base causes dampness in the room, which leads to the formation of mold.

In the absence of waterproofing, the foundation will gradually deteriorate. This will accordingly affect the stability of the building.

Whatever method of foundation installation you choose, it is important to remember that measures to cut off ground moisture from it are mandatory

Water protection solves a number of serious problems:

seals concrete, maintaining its integrity. The concrete mass is weakened when moisture freezes;
allows you to maintain a favorable indoor microclimate. Under normal humidity conditions, mold does not form;
increases the service life of the base. The rise of moisture through the capillaries stops, which has a positive effect on durability;
protects reinforcing bars from corrosion. Waterproofing the foundation preserves the strength properties of the reinforcement.

Methods for processing slab structures

A set of measures for waterproofing the slab base must be provided at the design stage and fully implemented during construction. Waterproofing methods:

Selecting a brand of concrete with optimal moisture permeability and frost resistance . The first indicator is determined based on the number of storeys of the house, the material of the walls and the method of construction:
- panel and frame houses up to three floors – W4;
brick and monolithic buildings - W8.

For screeding slab foundations, concrete with frost resistance from F35 to F35 is used. In this case, the content of clay particles in the mixture for the solution should not exceed 1%. Internal waterproofing measures may also involve the addition of penetrating (penetrating) compounds with hydrophobic properties into concrete at the stage of making the solution (the features of the waterproofing agent are discussed in the next section).

Design solutions that limit direct contact of the slab base with water:
- installation of a drainage system,

The design of the drainage system is aimed at collecting and draining melt, rain and groundwater from the building contour. The event is especially effective in areas prone to flooding and in regions with large amounts of precipitation. The drainage system consists of a set of perforated pipes connected to wells or collectors.

Building a slab foundation without excavating a pit and replacing the soil mass with a cushion made of non-metallic materials is allowed only if the work is carried out on sandy or coarse rocks with deep underground sources.

For other types of soil, which make up the predominant part in Russia (80%), under the foundation it is necessary to arrange a backfill that is not prone to heaving and will neutralize the effect of deformation forces on the structure as a result of temperature changes.

Treatment of surfaces with waterproofing materials - rolls, coating, putty, etc. Affordable and with high hydrophobic properties, modern materials help to implement high-quality waterproofing of slab foundations. The differences between the options are discussed in the next section.
Installation of “cold” seams . Simultaneous pouring of concrete into a large volume of space can take up to 5 hours. Due to the overlapping of layers, microcracks form in the body of the slab, into which moisture penetrates. To compensate for this circumstance, the joints are designed in advance - they are filled with waterproofing dowel , and then the screed is continued.

Types of foundation slab waterproofing

What technologies are used to waterproof a foundation slab?

Roll materials: membranes and films. The most common type, used in 90% of cases.
Penetrating compounds. They fill the pores of reinforced concrete and prevent capillary flow of moisture in the slab.
Additives to concrete leading to the effect of using penetrating waterproofing (for example, Penetron Admix).
Painting, coating and plaster waterproofing are used as additional ones: waterproofing the foundation slab from below in this way is impossible.

Roll waterproofing

Waterproofing a foundation slab with rolled materials has a number of advantages, among which it is generally accepted that it is an understandable and fairly simple application technology with high waterproofing quality. You can do this work yourself without any special professional equipment.

The result is a waterproofing layer of about 2 mm and capable of withstanding a pressure of about 0.5 MPa.

Sequence of process:

Creation of a cushion (layer of sand, layer of crushed stone 20 cm each) and concrete preparation.
Rolled waterproofing materials are laid on the hardened concrete preparation: in 2-3 layers using bitumen or bitumen-polymer mastic (the joints of different layers should not coincide, the material is joined with an overlap of 15-20 cm).
The release of the waterproofing layer beyond the aisles of the future slab is done by 30-50 cm.

After this, the formwork is installed, the reinforcement frame is made and the foundation slab is poured.

After removing the formwork, the waterproofing layer is wrapped on the sides and top of the slab.

There is no need to use any other materials for waterproofing the sidewalls (coating or plaster). This may prevent the roll waterproofing from being securely attached to the foundation in these areas.

Penetrating waterproofing

After the concrete has reached 30% strength, penetrating waterproofing compounds can be applied. Concrete with 30% strength already allows movement on it, which is necessary.

Stages of applying the penetrating composition:

Prepare the mixture. For Penetron, dilute the composition with water (0.4 liters per 1 kg of mixture) to the consistency of sour cream. It is convenient to use a mixer.
Apply two coats to damp concrete with a brush. The previous layer must dry before applying the next one. You can use a spray bottle.

Mixture consumption is approximately 1 kg/m2.

Additives for concrete

If you mix concrete at the pouring site, you can use special additives in concrete to increase its hydrophobic properties.

Using the Penetron Admix supplement as an example, we’ll look at how to do this.

The additive is added to the water for concrete mortar (1.5 parts by weight of the additive to 1 water. The rest of the concrete mixing technology does not change.

It makes no sense to combine roll waterproofing with penetrating waterproofing. There is no pressure pressure under the base of the slab and you can get by with one of the waterproofing options.

What is the best thing to do when building with your own hands?

At different stages of construction, waterproofing measures are taken, for which certain materials are used. Below are popular types of waterproofing, most of which can be used if you build a slab foundation with your own hands.

Roll materials

The method is suitable for protecting the base from groundwater. For this purpose, polymer films, profiled membranes and other rolled materials are used that are suitable for installation under the base of the slab.

In private housing construction they use for this purpose:

roofing felt,
Stekloizol,
Uniflex,
Linocrom,
TechnoNIKOL and more.

Among all roll waterproofing materials, TechnoNIKOL is widely used due to its affordable cost and high performance characteristics. The canvas is laid on a flat surface with an overlap of 15 cm. They begin to roll the material from top to bottom, securing the top edge with a special strip.

Coating waterproofing agents

Coating materials include:

special mastics based on bitumen,
liquid rubber,
polymer emulsion,
various resins,
pastes, etc.

Thanks to special additives, the mixture acquires an elastic structure, making it easy to apply by hand and retaining its strength characteristics for decades.

The entire surface of the slab foundation is covered with coating materials when the screed reaches the required strength.

Penetrating compounds

We are talking about a special impregnation that is added to the concrete solution to improve its waterproofness and frost resistance. The penetrating material can also be applied to the surface of the slab base after hardening, then the mixture is mixed with water immediately before use.

For this purpose, you can use impregnations such as:

Penetron,
Osmosis,
Hydrohit et al.

After application to the surface, the substances penetrate into the concrete structure to a depth of 12–17 cm, upon contact with water they turn into crystals and clog the pores, increasing the density of the material several times.

Liquid rubber

The material is applied using spray guns to the visible surface of the slab foundation, trying to form a protective layer in the form of an even coating.

Advantages of liquid rubber:

High water resistance.
Elastic structure.
Easy to apply.
Durability of the coating.
Good adhesion.
Wear resistance.

Private developers may be deterred from using liquid rubber by the high price of the material, but such costs are fully offset by high-quality waterproofing of the foundation for decades.

Plastering

The material is a mineral mixture prepared using clay and cement . Such a solution hardens very quickly in air, turning into a durable protective layer that is suitable for leveling the surface of a finished slab foundation and at the same time serves as a water-repellent base.

The advantage of the technique is the low cost of preparing the clay solution.

Shielded

The method is based on the use of special mats , which create a reliable waterproofing screen on the surface of the slab foundation.

The mats are attached to mounting foam or inserted into special locks installed along the edges of the structure. It is impossible to carry out the installation on your own; licensed specialists are involved in the work.

Sprayed waterproofing materials

A high-density protective film is obtained by spraying a special material (liquid rubber, Hydroplast, Technoelast, Gidroizol, etc.) onto a concrete surface.

The water resistance of a coating with a thickness of 2–3 mm is comparable to the properties of roofing felt or other rolled material applied in several layers.

Advantages of the technique:

high speed and ease of operation,
no seams in the finished coating,
elasticity,
without toxic substances in the material, etc.

Waterproofing a monolithic slab - methods of protecting the foundation

Builders prefer the following methods of waterproofing protection:

coating It is characterized by increased efficiency, simplicity and provides effective protection against moisture. It is carried out by applying special emulsions or mastics to the surface. According to the manufacturer's recommendations, the selected composition is applied to the surface to be treated in a heated or cold state;

It is known that water is extremely aggressive towards most building materials, and in particular to the concrete from which foundations are made

penetrating. This is a modern and promising method of waterproofing, providing an increased depth of penetration of the protective composition deep into the concrete mass. After application, the special mixture crystallizes in concrete pores and, as a result of the hydrophobic effect, makes it difficult for external moisture to access;
roll This is a fairly common method that involves the use of moisture-resistant materials supplied in rolls. The position of professionals regarding roll moisture protection is ambiguous. Some consider this method outdated, others focus on its effectiveness and simplicity.

The decision to use moisture protection technology is made individually, taking into account the following factors:

location of aquifers;
amount of precipitation;
the presence of drainage lines;
design features of the base;
financial opportunities.

What to choose and why?

High-quality waterproofing of a slab foundation is not limited to one of the known methods , since concrete must be protected both from the inside and from all sides. Replacing the soil with a cushion that is not prone to frost heaving is provided for by the technology.

The private developer can choose the remaining waterproofing methods himself, based on material capabilities and the necessary measures within the given conditions.

The easiest way to protect the foundation from moisture is to add penetrating additives to its composition , which plug microvoids in the structure of the material, preventing liquid from seeping into it.

But this measure is not enough in real conditions, so the surface of the sand-crushed stone cushion must be covered with a layer of waterproofing roll material, the web of which must be left with a reserve in order to then be placed on the walls of the formwork.

After the concrete gains strength and the panel formwork is dismantled, the surface of the slab must also be protected from storm water and sewage, on the one hand, and the walls of the house from soil moisture that penetrates through the body of the foundation, on the other.

In this case, builders choose the material for their own reasons, because for this purpose they can use:

impregnations,
coating and spraying agents,
adhesive roll materials,
shielding mats,
clay putty.

It is advisable for the owner to calculate the cost-effectiveness of different waterproofing methods, and when choosing a material, rely on its characteristics, including service life.

Features of waterproofing seams

The problem of waterproofing joints, as a rule, arises when they practice a prefabricated monolithic method of laying a foundation using factory-made slabs. Finished products are laid on layers of hydro- and thermal insulation on top of a sand cushion. No matter how tightly the slabs fit together, there are still gaps between them, which in the future may become a weak point of the foundation.

Complex waterproofing of joints between slabs is as follows:

At the joints, the surface of the slabs is coated with concrete mortar and the elements are joined to each other. The slabs are left in this position for several days.
The concreted joints are expanded again with a grinder or drill to fill the bottom of the cuts with liquid bitumen.
The remaining free space is filled with concrete mortar, and polyurethane fibers are laid along the upper joining edge, after which everything is sealed with a torch.

After waterproofing the seams, the next stages of construction of the slab foundation begin - reinforcement and the formation of a thin layer of concrete screed.

What is a slab foundation?

The article should begin with a description of the slab foundation, its structure and installation method. This type of foundation refers to non-buried or shallow-buried structures, depending on the type of soil. To lay it, you must first create a pit. The reinforced concrete slab is installed on a pre-arranged pad made of sand and crushed stone, which, in turn, was tightly compacted.

Slab foundations can be of two types: monolithic and prefabricated, each of them requires the installation of waterproofing. In the first option, the already prepared formwork is filled with ready-mixed concrete. A frame made of reinforcement is pre-installed. The second option for laying a slab foundation involves constructing a structure from pre-prepared reinforced concrete blocks, which may vary in structure.

Regardless of the type of foundation chosen, it is necessary to ensure reliable waterproofing of the slab to ensure its durability.