We insulate the floors: Styrofoam on logs or on concrete under the floor screed and plywood on top: Step-by-step instructions + Video

We insulate the floors: Styrofoam on logs or on concrete under the floor screed and plywood on top: Step-by-step instructions + Video Is foam suitable for concrete screeds? The release of foam is carried out in the form of light, fine mesh plates of differentiated thickness and density. Plates are freely cut with any knife or special. tool. Considering their low weight (from 20 to 45 kg / m3), foam plates are very easy to carry, stick to, fit, they are easy to operate and perform various installation operations, from wall cladding to laying foam under the screed.

Before choosing the material and method of floor insulation with foam, it should be noted that not every brand of foam is suitable for laying on a floor under a screed, and not in all cases and under certain conditions.


Conditions for insulation

In order for foam insulation to work most effectively, the screed the floor on polystyrene turned out to be as strong as possible, it will be necessary to fulfill several conditions:

  • We insulate the floors: Styrofoam on logs or on concrete under the floor screed and plywood on top: Step-by-step instructions + Video To obtain high-strength insulation it is necessary to use foam plastic with a density of at least 25 kg / m3 for the floor screed;
  • The recommended thickness of the concrete screed above the insulation layer is more than 50 mm; as a base for floor heating, a grouting cement mortar up to 30 mm, with the additional installation of a fiberglass mesh;
  • Mandatory location of a layer of waterproofing and damping of the seam along the perimeter of the floor area.

The density of the insulation

The most important issue when using foam is related to the strength of the foam insulation. According to GOST, foam rubber corresponds to its maximum density, for example, for the 25th grade, the density of foam board can vary from 16 to 25 kg / m3. This means that the strength of a slab from one manufacturer may be satisfactory if the specific gravity exceeds 20 kg / m3, or be insufficient if the indicator varies from 16 to 20 kg / m3.

If you do not bother and take the usual handy foam, then there is a high probability that you will find yourself in a situation where, when you try to lay the screed, the foam will simply gag.

It is generally known that foam is a compressed mass of polystyrene in the form of balls. With prolonged exposure to the sun, the material rapidly ages and breaks up into many tiny balls. Therefore, before using the foam under the screed, you should clarify how and where it was stored. If the material has been stored outdoors for a couple of months, it should not be placed under a screed; alternatively, the floor in the barn can be insulated.

It is believed that foam is not hygroscopic, but this is not the case.

The lightest foam grades, which have the best thermal insulation, are able to absorb some moisture from the soil and air. After that, water foam can come off the screed, partially losing its insulating properties, and collapse even when frozen. Polymer foam can last up to 50 years without deterioration.

The best technology for laying foam under the screed

Based on the type of base that will be used under the screed, there are 2 options with foam as insulation on a soft base and on concrete black floor.

The screed on the bulk floor differs from the concreted version, only in the need to equip an additional filling cushion with two layers: a mixture of gravel screenings with clay and sand.

The two layers are carefully compacted and aligned in the plane of the floor.

The screed sequence is as follows:

  1. We insulate the floors: Styrofoam on logs or on concrete under the floor screed and plywood on top: Step-by-step instructions + Video Make a thick waterproofing film 7-10 cm larger than the wall;
  2. Lay out foam sheets in an even layer;
  3. Install beacons and pour concrete according to the planned level.

For screed on an earthen or gravel floor, before pouring concrete, it is recommended to lay a second layer of waterproofing on the laid foam.

Even when the floor is filled with the densest and most waterproof types of concrete or mortar, water vapor condensation forms on the back of the foam sheet. Therefore, when screeding a concrete floor in heated rooms, it will be necessary to lay the foam on a polyethylene base.

For other cases, one layer of waterproofing will suffice.

Preparation of foam insulation under a concrete screed

Laying of foam plastic should be carried out on a rough concrete floor, but first it is necessary to knock down all the cones and ridges on which can be broken relatively fragile sheets of insulation. When laying on gravel screenings, the plane of the future screed should be aligned as much as possible, better with a laser level.

Lay out a plastic film on the prepared surface, below, during the installation process, the foam is not crushed under the feet, the fabric is pulled in the corners with a load.

It is best to install foam sheets on tiles with glue, without the use of foam, assembly plugs, various acrylic paints and resins.

The adhesion strength of the slab mass is sufficient to fix the foam boards prior to pouring the concrete. Sheets must be laid out parallel to the joints so that they move in rows by at least half the width. On the back of each sheet, an adhesive mass is applied in the corners and around the entire perimeter, after which the foam is laid on the base and lightly clapped with the palm of your hand to improve adhesion.

Often the surface of the insulation is uneven or the foam has to be spread on gravel chips, in which case, in some places, bumps are formed due to the "hanging" of the material. To reduce the risk of damage to the insulation when pressing the leg or while filling the screed, the sheet in the hump zone should be divided into two or three parts so that the resulting elements fit as tightly as possible to the base.

The joints between the foam boards can be blown with a very small amount of professional foam and cleaned with a spatula.If the screed is planned for a serious load (for example, under a car), then it will be necessary in addition to lay a mesh of composite reinforcement. The grating rises above the foam layer, at a height of at least 2 cm.

Concrete screed execution

Before laying the screed, it is necessary to first install the guide bars of the beacons.

In order not to fool yourself with the adjustment of each flexible and unstable bar, you should use ordinary profiled square pipes 25x25 mm and cut reinforcing bars as a guide beacon.

Initially, we measure out the required number of bars in the insulation using the laser level. Cut off the excess with a grinder, put on a plastic fungus and attach it to the square tube of the lighthouse. The work takes 5 minutes, if you put the beacons under the screed on the foam in the usual way, then it will take much more time.

For pouring, an ordinary concrete mixture is used, but at the same time, 20% less water is used. The result is a mixture that is easy to spread on foam and seal with a tamper and spatula.

Put some more concrete between the beacons, with a small slide, and moisten the surface with water after preliminary leveling, then carefully pull the screed horizon. The result is a flat, perfectly smooth surface.

Not later than half an hour later, the profiled beacon pipe must be pulled out of the screed and installed on a new floor area. A completely filled screed is closed tightly for a day from drafts and heat. Then the traces of the lighthouses are sealed with a solution and cleaned.

For at least two weeks, the screed should gain strength, and by the 20th day it will be possible to clean it for laying laminate or warm floors.

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