In construction and repair, such material as plywood is very often used. It has several positive characteristics. Plywood is a durable, high-quality and environmentally friendly material, which, in addition, has a low cost and is versatile in use. In addition, the material is used to prepare the floor for further finishing. By laying plywood on a concrete floor, you can get the perfect platform for finishing. This is a fairly convenient and economical option.
How to lay plywood on a concrete floor? Before starting work, you need to pay great attention to the choice of the right material. There is now a wide range of products on the market. Plywood differs in its technical and operational characteristics.
How to choose the right material?
When buying, you need to know a few key properties of wood sheets. There are a couple of evaluation criteria:
- Moisture resistance. According to this indicator, there are materials of the following types: FSF and FK. The first type is characterized by increased moisture resistance. But, despite this, this material still cannot be used in the bathroom. Also, laying plywood on a concrete floor is not performed in baths and in the kitchen. As for the second category, it has average moisture resistance. To glue the layers of wood, the manufacturer uses glue based on carbide resins. This material is not dangerous to humans. Therefore, it is possible to lay plywood on a concrete floor both in industrial premises and in an apartment. But again, it doesn't have to be the bathroom or the kitchen.
- Material of production. There are conifers and hardwoods. The first type is highly resistant to fungi and other microorganisms. But, such material is not suitable for laying plywood on a concrete floor under a laminate in a residential area. But hardwood is the best option for arranging floors. It is better to choose FC series birch plywood.
- Formaldehyde levels. Although plywood is an environmentally friendly material, chemistry is used when gluing it. Therefore, it is always worth paying attention to the level of formaldehyde content. There are two classes: E1 and E2. The first group includes materials where 10 milligrams of formaldehyde is produced per 100 grams. In the second case, it may contain about 30 grams. For residential premises, experts recommend using E1 products.
Thus, iffinishing is being carried out in a house or apartment, you need to use plywood of the FC series. But it is not necessary to be guided only by this class. This material can be further divided into subgroups:
- Material where there are no external flaws (the most expensive of all).
- There are inserts of veneer and knots.
- Material with a large number of cracks.
But at the same time, the sheets will be glued together quite well. Therefore, it will not be financially feasible to use expensive and beautiful plywood for the subfloor. The best option, according to experts, would be the material that contains a small number of knots and veneer inserts. If we talk about brands, products based on E1 and FC wood receive positive feedback. The thickness of the sheet in this case should be from 12 to 16 millimeters. There are also exceptions. These are sheets for installation on logs. But we will talk about this point at the end of this article.
We carry out cutting and fitting plywood
So, we have decided on the desired grade and brand of material. However, it is important not only to purchase the right type, but also to calculate the quantity. So, the floor area needs to be increased by 10 percent (this part will go to the reserve). Sheet sizes are standard - 125 by 125 centimeters. But working with such large sheets is quite difficult. Therefore, we saw them into four squares with dimensions of just over 60 centimeters on each side. After that, we will be able to create the required number of expansion joints that will compensate for the moisture and temperature deformations of the wood. While the sheetssmaller ones don't expand as much as larger ones. To cut the pieces, use an electric jigsaw. This tool does not leave bundles and chips. Next, the cut sheet is laid out on the base for preliminary adjustment (we do not use glue and screws yet). This way we can roughly fit all the pieces with the existing ledges.
Experts recommend observing certain seams between the squares (their value is from 8 to 10 millimeters) and the gap between the wall and the extreme elements of the flooring (about 15-20 millimeters). The sheets themselves are placed as in brickwork, with offset rows. So we eliminate the possibility of crossing four seams at once in one area. What is done next? After adjusting the material, you need to number all the elements and draw a surface diagram, so that in the future the laying of plywood on a concrete floor under linoleum occurs quickly and without much effort.
Methods of attaching the material to the base
It is recommended to fasten plywood using a complex method - using self-tapping screws and glue. The choice of the first is determined simply - only the thickness of the wooden sheet is taken into account. But gluing plywood on a concrete floor is much more difficult. The main thing is to choose the right material. There are several options:
- Water based formulation. Among the advantages is environmental friendliness. Such glue is completely safe for humans and does not have a strong odor. Among the disadvantages is a long drying time. This nuance affects the speed of construction work.
- Glue onsolvent base. Its main advantage is the speed of drying. But, at the same time, the glue releases toxic substances, which are dangerous to exhale. The room should be as well ventilated as possible.
- Two-component adhesive. This is some kind of alternative between the first and second type. This composition is chosen by many because it dries quickly and does not emit an unpleasant odor. Also, two-component adhesive can be used to install plywood even on a screed that is not completely dry.
How is the concrete floor leveled with plywood? This operation consists of several important steps. Below we detail the procedure for attaching plywood to a concrete floor.
Checking the moisture content of the concrete base
Before starting the operation, you need to check the humidity of the room. If this parameter exceeds the norm, subsequently the material may simply exfoliate. It is not necessary to use special devices. You can use plastic wrap and a couple of suitable weights.
So, spread the film on the floor and squeeze the edges with any load. The center of the film must be free. In this form, the structure should stand for a couple of days. After this time, you can check. If condensation has accumulated under the film, it is impossible to lay plywood on a concrete floor under a laminate. Before this operation, an additional layer of waterproofing is performed. Only after that you can proceed to further installation.
Cleaning the base
It is necessary to grind all the bumps. How to do it? For thisuse a grinder with a special nozzle. Next, traces of old paint, putty are removed and recesses are made, if any. What if there are cracks in the floor? They must be removed with a cement-sand mortar. You also need to clean the surface of dust. To do this, use a powerful vacuum cleaner or broom. The latter must not be wetted, as the moisture content of the floor will increase, and the plywood will swell further.
Priming
Next comes the primer. As a consumable material, experts advise using a primer. This product should be applied with a short pile paint roller to the floor surface. What is the advantage of a primer over a regular primer:
- The primer has a good penetration depth, which ensures the strength of the top layer of the structure.
- The composition eliminates the presence of dust on the surface.
- Able to increase the adhesion of different materials.
Laying plywood
After cutting the sheets and applying the primer, you can start laying. It is necessary to focus on the previously performed numbering. The operation is performed in several steps:
- Concrete floor treated with plywood glue. The thickness of the layer should be up to two millimeters. Experts recommend applying glue in small areas so that you can have time to lay out the plywood before the composition grabs.
- On the treated base, you need to lay pieces of plywood in accordance with the established scheme.
- Next, the sheets are fixed byself-tapping screws. They are screwed around the perimeter and diagonally. The step should be from 15 to 20 centimeters. The maximum indent from the edges of the flooring is 2 centimeters. It is necessary to use self-tapping screws with a length that is 3 times the thickness of the sheets used. For example, for 12 mm plywood sheets, it is recommended to use self-tapping screws 40 mm long.
- The stacked sheets are processed by a grinder with the appropriate nozzle. You can also process manually with sandpaper (but if the area is large, it is better to use a tool anyway). Thanks to this operation, we will smooth out discrepancies in the height of adjacent sheets and eliminate burrs.
Checking the quality of work
After the plywood has been laid on the concrete floor, you need to carefully inspect the surface. It is important that the plywood sheets do not touch the walls. Expansion joints must be provided on all sides. You also need to make sure that there are no differences in height. A transition of 2 millimeters is allowed, but no more. In addition, after laying, you need to tap the wooden surface with a mallet. If there is a non-uniform thud, you will have to redo the work. This knock indicates that the plywood is peeling off the concrete.
Laying a log on a concrete floor under plywood
We have previously covered the installation method without lag. It is quite simple, but it can only be used if you need to hide minor irregularities. If the floor is too curved or the installation of a warm floor is envisaged, this method is chosen. It is important that the lags are installed correctly. To check their position, you need to use the building level and ruler.
As in the first case, surface preparation is preliminarily performed. If this is not a new screed, it must be completely cleaned of the old coating. Is it carpet, laminate or linoleum. It is important to check if there are cracks on the surface. If there are any, cement mortar is used and defects are sealed. Next, you need a substrate. As it can be used ordinary polyethylene. But the film must be solid and sealed, otherwise it will not bring any effect. The edges of the film are fixed with tape.
Next, work is performed in the following sequence:
- The lowest point in the room is determined. This is where you need to start installing the lag. How to fix plywood to concrete floor? They must be installed perpendicular to the incident light. In this case, the distance between the lags should not exceed 50 centimeters. It is also taken into account that the joints of plywood sheets will be located on the logs. To make the latter horizontal, you can put wooden blocks.
- The joists are attached to the concrete base of the floor by means of anchors.
- The crate between the lags is in progress.
- Thermal insulation is being installed. She pricks into the cells of the crate.
Please note that installing a log on a concrete floor under plywood has its own nuances. So, the thickness of waterproof plywood should not be less than 18 millimeters. A two-millimeter gap is left between the sheets. It subsequently needs to be filled with mastic. gapsare necessary in order to exclude warping of the base, as well as the occurrence of a creak when walking. As for the fasteners, self-tapping screws are used as such. As we said earlier, their length should be three times the thickness of the wooden sheet itself.
However, it is worth remembering that when laying plywood on a concrete floor by means of a crate, the height of the ceiling is reduced. But this is a minor deviation. However, if the ceilings in the apartment are low, it is better to refuse this method and level the surface differently.
Why is laying plywood relevant?
No matter how the plywood is laid, you end up with a practical, reliable and durable floor covering with good thermal insulation properties. The service life of plywood is more than 20 years, subject to the presence of expansion joints and waterproofing (if condensation has accumulated on the film after tests). Also, if necessary, it will be easy to dismantle the finishing floor covering (for example, laminate).
Conclusion
So, we found out how plywood is laid on a concrete floor with our own hands. As you can see, this operation is very laborious. However, as a result, you can get a fairly high-quality (and most importantly - even) flooring. Depending on the curvature of the floor, two methods can be used. As a rule, experts resort to the first method. But in the case of installing a warm floor or the presence of large defects, a lag is indispensable.
