There are two main ways to prepare a suitable horizontal base for the laying of floor coverings currently in use: screed and subfloor laid on load-bearing beams. In order for the flooring to be durable, not to change its geometry under load and at the same time serve for a long time, it is necessary to correctly fix the lag to the concrete floor or other supporting structures that are provided for in a particular situation. The article will discuss the devices with which you can attach wooden rails, as well as how to use them, some of which can be viewed in the attached thematic video materials.
How to choose a beam for a lag?
Proper selection of lumber that will be used for the construction of the flooring for laying the finish coating will guarantee the durability of the structure, and its ability to withstand the proposed loads without deformation of the surface. What should you pay attention to first of all?
- Humidity. The beam, which is usually used as a log, must be dry. The moisture content of wood, regardless of the species used, at the time of installation work should not exceed 18%. This is a natural moisture indicator for lumber. That is, the likelihood that moisture will occur or, on the contrary, further drying of the wood (both processes lead to deformation) with this moisture index is minimal.
- Type of wood. Logs, unlike beams, have more support points, the number of which can always be increased. So the type of wood does not play a special role. Grade 2 or 3 lumber is quite suitable. If a large knot or other defect affecting strength is found in the beam, it is enough to install an additional support in this place.
- Section. The main requirement is the shape of the butt. It is necessary that the cross section of the timber be rectangular, with an aspect ratio of ½ to 2/3. In this case, it will be correct to put the lag on the edge. In this position, the bar is maximally resistant to vertical load. The size of the section is selected so that its larger size allows you to lay a sufficient layer of insulation, and the smaller one allows you to easily lay and attach (taking into account the possible joining of fragments) a board, plywood or OSB. The strength of the lag can always be increased by installing additional supports.
- Type of wood. For the lag, they usually choose inexpensive coniferous timber - pine or even spruce will do. It is advisable to put larch bars where high humidity is expected.
- Treatment. The bars dried to the desired moisture content should be treated with protective impregnations. This will make the wood resistant to moisture, microorganisms and insects. If desired, it can be treated with flame retardants, which significantly reduce the combustibility of wood.
Important! Attention should be paid to the relief of the surface of the timber, to which the board or slab material will be attached. If there are irregularities on it, they should be removed with a planer. This must be done before installing the lag.
Properly selected and processed lumber is half the battle. Now let's look at how to properly attach the logs to the base, including concrete, in various situations.
Laying lag with slight floor insulation
This situation usually happens in apartments where the ceilings are low, so it makes sense to save space as much as possible. Moreover, there is a heated room below, so a small layer of insulation is enough, which is more needed as a sound insulator.
In this case, a small section of the log is selected, which are laid directly on a reinforced concrete slab or small regulating wooden stands. There is no special need for waterproofing in such a situation. An exception is when the apartment is located on the ground floor above a damp basement. Then it makes sense to cover the concrete surface with a polymer film or treat it with bituminous mastic.
In this case, metal corners or anchors can be used as fasteners. There is no need to firmly attach the bars. Such a fixation of the lag is enough so that they do not move during the laying of plywood or boards. Professionals sometimes do not fix the guide bars at all if they are in a stable position, since the lag frame does not experience other loads, except for vertical ones, during operation. An example of such a situation can be seen in the video below. The floor board or sheet material (plywood, OSB), when rigidly connected to the underlying supports, form a monolithic shield that does not have the possibility of lateral displacement.
How to fix the logs at a distance from the concrete floor?
This option for installing load-bearing beams is used if you want to lay a thick layer of insulation or simply raise the level of the floors. A similar situation arises when installing a wooden floor on a rough concrete base made on the ground, on loggias and balconies. This also happens in the living rooms of apartments, when, with large differences in the position of floor slabs, there is a desire to make the floor surface on the same level.
If it is necessary to significantly raise the log above the plane of the slab or concrete screed, two devices are most often used to help adjust the position of the bars and securely attach them. These include:
- screw adjustable supports;
- metal brackets.
Screw fasteners have an extended support platform that is connected to a vertical threaded pin. The lag is attached on top with nuts. By screwing in / out of the screw, it is possible to accurately and conveniently adjust the position of the bars, exposing them in the same horizontal line.
