How lag is mounted to the concrete floor

In modern construction or repair of a private nature, the question may arise how to fix logs to the concrete floor — after all, such a foundation can be called the most suitable for a plank floor. The advantage here is that the screed itself is a waterproofing barrier, and even when casting, a film or roofing material is used, moreover, it is usually insulated with expanded clay or even extrusion foam polystyrene.

If everything is done correctly, then the entire installation process will turn out to be simple and even interesting, which we will now tell you about, as well as demonstrate the video in this article on our topic.

Lies закреплены

Installation steps


Note. You can pour a cement-sand screed without adding crushed stone or sifting, but its strength will be much lower, especially if the base is ground. Therefore, such a simplified version is suitable only for those cases where the base is reinforced concrete floors.

Preparation of the base under the screed
  • Let's start with the fact that we need a smooth foundation and if this is done on the ground, then it needs to be planned and compacted, and after that we should fall asleep a sand-gravel cushion, as it was done on the top photo. Waterproofing is better to lay under the pillow, with a twist on the wall at the height of the entire screed and although many do it over the pillow - experience shows that the cut-off insulation is more effective at the very bottom.
Installation of beacons
  • Lighthouses are installed on the pillow, as required by the instructions for leveling any screed - they are best mounted on a cement-sand mortar, to which even some tiling glue is sometimes added for elasticity. The distance between the profiles should be about 10-15 cm less than what your rule is, which you will use at the moment.
  • For ease of leveling, you can first beat off along the perimeter of the room an approximate line along the height of the screed and install the ends of the beacons along it.. But in length, such profiles need to be leveled with a level with their own hands, because they are flexible, moreover, after the installation is completed, check them with the thread tension in several places so that their height completely coincides with each other. Start pouring concrete no earlier than the next day, otherwise you will knock down the lighthouses with a solution and a rule.
Concrete Ratio Table
  • For pouring, it is best for you to use M300 concrete grade, the ratio of components for which you see in the table above, although this is not a prerequisite, but advice. However, you can also order any brand at the nearest RC node, but its price will naturally be higher.

The recommendation is that cutting reinforced concrete with diamond circles and diamond drilling of holes in concrete is best done in a frozen solution, the operation of casting can be started only after 28 days. Otherwise, the mounting dowels will not hold, besides, the earlier laying of the wooden floor would entail the occurrence of dampness.


This distance is acceptable for a thick board.

Now, after the fill is dry, you need to determine the distance, since you will fix the logs to the concrete floor, taking into account the thickness of the coating. For example, if this is a plank floor of 40-50 mm thick oak, then the distance between the slats can be made about 50 cm, but if it is an inch board or the same OSB (OSB), let it be all 12 mm - this will be too much, and floorboards will sag. In such cases, the distance should be reduced to 40 cm, and sometimes even to 30 cm (learn here how to make fasteners for aerated concrete).

Учитывая то, что лаги будут укладываться на бетонную стяжку, то есть, плотно прилегать к основанию, вам не понадобится толстый брус - достаточно будет рейки сечением 50×50 мм. Но если монтаж будет производиться на бетонные перекрытия, которые не имеют ровной плоскости (обычно это происходит в многоэтажных домах), то тогда используйте брус 100×50 мм.


Итак, если у вас неровно установлены перекрытия, то монтаж можно производить при помощи анкерных болтов, где есть регулировочные гайки. Принцип выравнивания хорошо виден на фотографии - вы просто закручиваете или раскручиваете гайку, определяя тем самым высоту бруса. Учитывая, что он здесь будет 100×50 мм или 100×100 мм, то анкер вам понадобится не  менее 200 мм (читайте также статью «Concreteирование двора: советы новичку»).

Use of linings

A cheaper way is to use linings for timber to level it, which can be made of plywood, OSB or the same boards and slats. Here you can already use a regular screw 150 mm long in wood, only it will have to be drowned in sweat a few centimeters in order to create a large fixing area in concrete. Some also attach lags to impact dowels, but the author of this article believes that such fasteners are unreliable, experience suggests.

But if you poured a flat concrete screed, which has dried well, then you will not have problems with leveling the lag, the main thing is that they are all the same size (sometimes they allow for sawmills and spreads can be up to 5-7 mm thick).

Here you mount the rail on the screw on the tree, 100-120 mm long, it is only desirable to choose them with greater thickness. Take the dowel to these screws, 6-8 mm (not thinner), so that the self-tapping screw can be well spread across the walls - if the section of the screw coincides with the outer diameter of the dowel - everything is in order, the fixation will be excellent.


Вы теперь знаете, чем крепить лаги к бетонному полу - это буде зависеть, в первую очередь, от ровности самого основания, а также от толщины бруса. Расстояние между точками фиксации не должно быть более 50 см, а вот если лаги у вас получаются на весу, то это расстояние нужно вообще сокращать до 30-40 см. Итак, ровное основание, это залог простоты крепления обрешётки (см.также статью «Облицовка газобетона: способы и их особенности»).

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