Basement waterproofing from the inside from groundwater

Recommendation points

• Effect of water on critical structures
• Waterproofing purposes
• Requirements for boundary planes
• Injection and penetration insulation techniques
• Roll materials
• Waterproofing coatings and mastics

Quite often, there is no access to the outer walls of the basement to protect it from flooding, and waterproofing has to be carried out from the inside, using a fairly wide arsenal of construction chemicals and technologies. Not surprisingly, mastering a suitable technique will not work without first studying.

Effect of water on critical structures

Basement waterproofing should be done not only to get rid of incoming water. Wall wetting is a very significant risk factor, because over time, the enclosing structures can significantly lose their strength.

The negative effect of water mainly lies in the washing out of binders, that is, in the corrosion of the cement mortar itself, which holds the masonry or concrete together. Such phenomena are most pronounced in those places where water comes from the soil under pressure and has a free outlet into the basement. When washed out, the concrete becomes even more porous, it is saturated with moisture even more, then through a chain reaction.

This is where two additional destructive factors come into play. The first is biological damage, the colonization of mold and fungus spores in the thickness of concrete, which only intensify erosion. The second factor is the appearance of gas exchange in the field of laying of reinforcement products. With relatively free access of moisture and oxygen, they corrode intensely, rust bursts the concrete and tears it.

The first to suffer are the upper zones of the walls and the ceiling. If the basement is partially located in the area of ​​soil freezing, the crystallization of water in the pores has a strong destructive effect. The forces of frost heaving can also add problems: a weakened structure can no longer withstand the pressure of the expanding soil. A properly organized blind area helps to significantly simplify the problem..

Waterproofing purposes

As you can imagine, it is not enough just to block the path of water into the basement. High-quality waterproofing creates a hydrophobic shell around the entire stone “bag”, excluding the saturation of concrete or masonry with water. However, this time we proceed from the fact that there is no access to the outer planes, which means that when installing internal waterproofing, one should adhere to two goals:

1. Stopping the flow of water, eliminating flooding;
2. Maximum protection of enclosing structures from moisture saturation, supporting the bearing capacity.

The less dense and inhomogeneous material of walls and floors is used to achieve these two goals. If concrete structures are easy enough to process with penetrating insulation, then with brick or block masonry such a technical solution is not very applicable. Also, injections and impregnations are practically useless when working with prefabricated foundations or monolithic structures with a large number of filling joints..

Requirements for boundary planes

The chosen method of waterproofing should solve the problem in the long term. It’s one thing when you have to work with good quality reinforced concrete structures and quite another – with dilapidated, partially damaged fences..

The best way out in the latter case would be, perhaps, the creation of a new load-bearing layer of the walls, and if the groundwater is entirely above the basement, the construction of a second floor. This is necessary for the reason that all types of waterproofing that are applied to the surface must be pressed against the pressure of the incoming water. Virtually no type of coating, roll or membrane material is resistant to back pressure. In addition, there is always a risk of destruction of structures already damaged by water, which will entail the formation of more and more gaps in the waterproofing.

Penetration and injection types of penetrating insulation are also not always applicable. The essence of their work is to saturate the array of walls with polymer, which increases in size in the presence of moisture and clogs the pores. For materials partially destroyed by erosion, this can only aggravate their condition, because water freezing in the pores acts in the same way. On the other hand, penetrating insulation does not fill through gaps.

Injection and penetration insulation techniques

Hydrophobic impregnations and injections are mainly used for internal waterproofing of basements in relatively young buildings in order to eliminate the filtration capacity of walls and ceilings. The main weak points of such waterproofing subsequently are cold seams, technological passages through concrete, formwork attachment points and seams between individual parts of the structure. Penetrating insulation works only in the solid, so all obvious gaps, cracks and seams must be thoroughly repaired.

The application of penetration compounds is performed on a well-cleaned and abundantly damp surface. The top layer of concrete must contain open pores that do not impede the penetration of moisture and chemicals, so it almost always makes sense to carefully sand the surface.

Impregnation takes place within 2-3 days, the composition can be applied 2-3 times after setting of each previous layer. During impregnation, the concrete must remain well moistened, therefore, water is periodically sprayed onto the walls and ceiling, or the humidity in the basement is maintained at 80-90%.

Waterproofing injections are used where penetration is not enough to completely saturate the entire thickness of the wall. Basically, there is a struggle for high-quality impregnation of the outer protective layer of concrete in order to prevent water from penetrating to the reinforcing elements.

The injection method is more technological: a lot of holes are drilled on the surface with a normalized distance between each other, and a water-repellent emulsion is pumped into them using a special syringe. Often, such work is not carried out independently, because even the slightest deviation from the technology can nullify the entire result. The effectiveness and durability of such waterproofing is higher than that of penetration, concrete retains its properties even after the formation of microcracks.

Roll materials

The situation with the use of all kinds of films and membranes for internal waterproofing is somewhat more complicated. Their main advantage is the presence of their own fastening base, thanks to which the insulation remains immune to cracking and deformation of the walls during the entire service life..

Since, with the use of retaining waterproofing, the enclosing structures remain exposed to moisture, it is necessary to completely or partially remove the bearing load from them. This is done by lining the basement from the inside with blocks of porous concrete or bricks. First, you should calculate the location of the beams that support the floor, and for large values ​​of the span – the supporting columns.

In this case, the installation of rolled waterproofing begins from the ceiling. Membranes have proven themselves in the best way for waterproofing the overlap. They are joined to each other without glue or heating, they can be temporarily supported by lathing on the scaffolds, or immediately glued to the old floor. It should be noted that waterproofing the ceiling is not always required, only if moisture penetrates inside from precipitation or with a high level of groundwater.

The edges of the ceiling membranes are lowered onto the walls about 50–80 cm, then the transition to wall insulation is performed. For it, both the same membranes and the more common roofing material, glass insulation, hydrobutyl and others like them can be used. After the installation of the hydro-barrier on the roof and walls of the basement, beams are raised to the ceiling on the repairmen, pressing the membranes to the ceiling through the polyethylene foam substrates. During installation, the slope of the ceiling is also taken into account to drain water towards the wall located at the bottom of the slope of the upper water carrier.

After temporarily fixing the beams, the inner box of the basement is laid out; if necessary, to avoid sagging of the waterproof membrane, it is provided with additional support by adding spacers between the beams or hemming the spans between them with sheet materials, but without fastening through the waterproofing. In conclusion, ceiling filing and interior decoration are carried out.

Waterproofing coatings and mastics

In fact, the use of coating insulation is not much different from the use of roll materials with one exception. Bituminous mastics, liquid rubber and similar products require preparation of the substrate to be applied. If the enclosing structures collapse over time, the insulation will retain its properties only if it is applied to a certain damper layer that levels out the effect of deformation phenomena.

Lime plaster is an example of such a layer. Under the influence of erosion, it will simply crumble, and at the same time the hydro-barrier will be tightly squeezed between the new strong lining of the basement and the destroyed, loose outer layer. To preserve the properties, the coating insulation must have residual elasticity, otherwise all cracks and defects in the base will affect the hydro-barrier.

The guarantee of the integrity of the waterproofing layer can be obtained using multilayer insulating materials. For example, on the applied and heated layer of mastic, a reinforcing fiberglass is rolled out, then another layer is applied, and so on. The number of layers and the final thickness depend on the stability of the soil and seismic conditions. In any case, the main idea is that the internal insulation over time begins to work as an external one, supported by the pressure of soil water..