Leveling a wooden floor with plywood. Working with plywood: fastening Fastening plywood to a wooden floor

Plywood is one of the most versatile materials invented by mankind. Plywood is also widely used in construction: in terms of ease of working with it, strength, cheapness and environmental friendliness, plywood is perhaps unparalleled. Plywood is especially widely used for laying and repairing floors. But the high functionality of plywood also determines a variety of techniques for working with it, so laying plywood on the floor with your own hands requires explanation for different cases practices.

Chipboard or plywood?

Plywood is not the cheapest of flooring and wall covering materials. Chipboard is even cheaper. But let’s leave phenol-formaldehyde resins alone for now - volatile carcinogens, on the basis of which chipboard is made.

Let's do the following experiment: put two pieces of pipe on the floor and lay a sheet of plywood 12 mm thick on them. Let's stand on it and get off. What happened? Nothing. He bent over and straightened up. What about chipboard? Most likely, it cracked at greater thickness. And it will definitely crack if you jump on it.

You can do two more experiments: hold scraps of plywood and chipboard in water and see how quickly they swell and become limp. There is no need to hit the edge with a hammer: everyone knows that chipboard is fragile. Therefore, the question: “chipboard or plywood?” The decision is definitely in favor of plywood.

What types of plywood are there?

There are many varieties of plywood. The following types of plywood are most often used in construction:

• FC is a moisture-resistant plywood based on urea resin, which is non-volatile and non-toxic. It has strength and elasticity comparable to BS aircraft plywood.
• NS – unpolished with casein glue. The cheapest, about 170 rubles/sq.m with a thickness of 12 mm. Before gluing parquet or other hard flooring onto it, it requires sanding.
• Ш1 is the main material used for the subfloor. Sanded on one side. The adhesive base is also casein.
• Ш2 – polished on both sides, on casein. For lightly loaded parts in dry rooms with a comfortable temperature it can be used as a substitute for FC.

What is contraindicated for plywood?

Nothing is perfect, and plywood is made from a hygroscopic material - wood. Therefore, plywood cannot be used in damp rooms: long-term air humidity should not exceed 68%; short-term within 12 hours – 78%. When laying untreated plywood, air humidity up to 60% is permissible.

The indicated values ​​are valid in a comfortable temperature range of 18-27 degrees Celsius. Outside these limits, the sensitivity of plywood, except for FC, to humidity increases: at 16 and 35 degrees and a humidity of 85%, plywood begins to delaminate after two months. Therefore, ordinary plywood for floors and walls should not be used in the kitchen, balcony, closet, hallway and bathroom.

How to improve plywood

The moisture resistance of plywood can be increased by impregnation with polyvinyl acetate (PVA)-based putty; it is similar to very thin PVA glue and is cheap. Soak first on one side until spots appear on the opposite side, then on the other twice. Dry in a horizontal position. It will take a long time to dry - at least 3 days at room temperature. After drying, the sheets are treated with any antiseptic-fungicide for wood.

The strength of the surface layer can be increased acrylic varnish. It is applied in two layers; the second - after the first has completely dried. If plywood needs to be stained for decorative purposes, paint it before varnishing.

Plywood acclimatization

Before describing how to lay plywood on the floor, we should talk about its acclimatization in the room. Plywood, like any wood material, requires acclimatization at the site of use. The acclimatization period depends on changes in temperature and humidity: if the conditions in a warehouse or store are the same as in an apartment, a day is enough; with a temperature difference of 2 to 8 degrees – three days; with more - a week. During acclimatization, the plywood is kept stacked in a horizontal position.

Checking the moisture content of the base floor

Before laying plywood on the floor, the base surface, and not only concrete, must be checked for moisture evaporation. To do this, 1 square meter of the base surface is covered with a solid square piece polyethylene film, pressing it along the edges with slats with weights and lifting the center a little. What happens next depends on the time at which condensation appears under the film:

1. The bubble fogged up from the inside within 24 hours - the room is unsuitable for covering the floor with plywood.
2. Small drops appeared within 3 days - the base concrete floor needs to be covered with glassine or plastic film, put a construction mounting mesh on it and make a screed. Wooden floor - disassemble; with such evaporation of moisture, the boards from the underside and the old joists are probably affected by rot. An option for 7-10 years is to cover it with plywood with improved moisture resistance using the home method (see above).
3. Condensation did not fall on the 5th day: you can lay plywood in any way.

Plywood base

Leveling the floor with plywood is a widely used construction technique. It is used both for laying new floors and for express repairs of existing ones. For various combinations base floors and top decorative covering Different plywood laying technologies are used.

On concrete

Laying plywood on a concrete floor is possible either directly along the screed or on joists. The first method is used if the base floor is fairly level and the finish is somewhat flexible; for example - under linoleum or cork flooring. Marmoleum can be laid directly on the screed without a subfloor.

Important: remember that after the concrete has set, it must be allowed to dry for at least 40 days at room temperature.

On a flat, dry screed

The room is thoroughly swept and vacuumed. The floor is treated with bitumen varnish or parquet mastic, diluted five times with solvent or kerosene (primerization). When working, they open the windows wide, work in a petal respirator, and in the apartment completely, by unscrewing the plugs or turning off the circuit breaker on the floor panel, remove the power supply: what is a spark in air saturated with vapors? organic solvent, no need to explain.

Plywood 8-18 mm is pre-cut into quarter squares standard sheet(1250x1250 mm) or stripes. They are laid out staggered, i.e. with a shift: there should be no four seams converging at one point. The sheets are cut with a jigsaw or a hand-held circular saw - this can be done in the next room an hour after priming. When cutting, you need to take into account that there should be a gap of 20-30 mm around the perimeter of the room.

Then the sheets of plywood are laid out on the floor, “dry”, adjusted without fastening and numbered. How to attach the plywood to the base floor in this case? Under linoleum or cork, you can simply use glue like bustilate or parquet mastic, without installation gaps - you get a floating subfloor. The ends of the sheets also need to be glued.

Under ordinary oak or similar parquet properties, plywood, along with gluing, is secured with 4-5x60 mm self-tapping screws in dowels. In this case, the sheets/strips must be laid out with mounting slots of 2-3 mm; For this it is convenient to use halves of toothpicks:

Note: It is convenient to use the insert of a combination screwdriver as a screwdriver insert for a drill (see figure above).

On concrete on joists

Under laminate, inlaid parquet or parquet valuable species wood plywood is laid on a concrete base. The same is done if the stability of the temperature and humidity conditions in the room is in doubt. The arrangement of the sub-floor plywood on joists is clear from the drawing; we will only give the necessary explanations:

1. Boards for joists are taken unplaned 100 mm (“weaving”).
2. The boards for joists are kept for at least a week in the room where they will be used, after which they are discarded: those that have warped with an arc are put on the bosses, and those that have twisted are completely discarded.
3. Plywood is taken from FC or self-improved, with a thickness of at least 12 mm; better - 18-20.
4. The preparation of the base floor is done in the same way as in the previous case.
5. Lathing from logs is made in increments of 300-600 mm so that all edges of the plywood sheets fall on the logs.
6. Sections of the sheathing are filled with polyurethane foam or other hydro- and heat-insulating material, but not with mineral wool - it will inevitably cause microscopic needles to appear in the air, irritating the respiratory system.
7. Plywood sheets are laid with an installation gap of 2-3 mm and a gap around the perimeter of the room of 20-30 mm.
8. Attach the plywood to the joists using “liquid nails” glue and fix it with nails; fastening with self-tapping screws in this case It does not significantly improve the quality of the subfloor, but it is more expensive.

Note: Recently, tongue-and-groove plywood with a thickness of 12-20 mm has appeared on sale specifically for subfloors. It is produced in the form of sheets from 300x300 mm and strips from 300x600 mm. For a floor made of valuable parquet, this is the preferable option: the cost of the subfloor in this case will still be a small fraction of the total cost of materials, and the likelihood of moisture vapor leaking from underneath is reduced by an order of magnitude.

Repairing wooden floors with plywood

Plywood is an excellent material for repairing cracked, cracked and creaky wooden floors. In this case, plywood is laid on a wooden floor in single sheets from the door, so that the most commonly used surface is continuous. The trimmings are allowed along the edges and in places under furniture. The plinth is removed as carefully as possible and then put back.

Plywood is taken from 12 mm thick. Installation is done with the usual gap of 20-30 mm around the perimeter, but without installation gaps between the sheets. The sheets are laid on bustilate, liquid nails or any other mounting adhesive; The ends are also glued.

This type of “self-improved” plywood floor, painted with any floor enamel, will last 20 years or more in a bedroom. But it is impossible to repair floors that are damp, swollen, with traces of rot and mold, and in rooms with biting weeds on the walls, with plywood. You need to remove the old floor, look for and eliminate the source of moisture, and only then lay a new one.

Warm floor on plywood

Lay under the plywood on a concrete screed on a mounting grid with waterproofing on the base floor. There is one nuance here: the edges of the waterproofing film must be brought under the baseboard. If they are muffled with a screed, the fumes from heating can concentrate in one place and cause delamination due to humidity.

When installing a subfloor under a warm floor on logs, this problem does not arise, but there is no point in complicating and increasing the cost of the work: a warm floor dries the room well. So it’s easier to leave a kind of vent around the perimeter for water vapor.

Plywood innovations

Plywood flooring is a branch of construction equipment that appears to be far from over. In the age of composites and nanotechnology, good old plywood does not retreat and finds new applications.

Adjustable floors

These floors are used as a base for wood inlays and other fine, exclusive work. Plywood flooring– double, made of high quality plywood. The sheets of the bottom layer have threaded sockets for bolts. The bolts are shaped: above the thread there is a flat widening in the form of a press washer, and above it there is a neck 3/4 high of the thickness of the sheet for a hexagon or with a Phillips slot.

The top sheet with holes for the necks of the bolts is placed on the screwed in bottom sheet bolts, and adjust with an open-end wrench or screwdriver. When using bakelized plywood, precision is achievable common surface quite mechanical engineering.

Plywood parquet

But plywood parquet is an invention of craftsmen. It revived the forgotten skill of artistic cutting from plywood at a new level. The technology of plywood parquet is simple and accessible to anyone.

Laying plywood on a concrete floor is carried out not only to level out minor surface irregularities, but also to create a heat-saving layer between the screed and the floor covering. A smooth and stable plywood base is ideal for laying materials that require horizontality such as laminate and parquet.

Leveling the floor with plywood will ensure a long service life of any covering. But get the best final result impossible without the correct choice and strict adherence to the technology for attaching plywood sheets to a cement base.

Laying plywood on a concrete floor is done in two ways:

For glue and self-tapping dowels
on glue

Important! Attaching plywood to the floor without gluing is unacceptable. Screws and dowels alone do not guarantee complete fixation. The glue fills all micro-irregularities of the surface and eliminates the slightest vibrations.

The next question that worries home craftsmen is: what glue should I use to glue plywood? The durability of the entire coating depends on the quality of the binder composition. Poor adhesion of plywood to cement base can soon lead to warping of the wood and shifting of sheets, which will cause the laminate to creak.

Plywood adhesive: types and features

Compositions on water based. Undoubted advantages This glue is environmentally friendly and odorless. The disadvantage is that it takes a long time to dry, which slows down the progress of the repair. Installation with water-based glue can only be used for moisture-resistant plywood and only in combination with additional fastening with self-tapping dowels.

Compositions based on solvents, including alcohol. The one-component solvent-based adhesive is fireproof and suitable for working with materials that are prone to deformation when exposed to moisture. Dries in 3 to 5 days. It has a pungent odor that disappears after drying. Glued sheets also need to be secured with dowels.

Two-component compositions (with hardener). Bonding of surfaces occurs in the shortest possible time. The very next day you can sand plywood and parquet work. Quick-setting adhesive provides strong adhesion to concrete and does not require additional fastening with dowels, which is especially important if there are communications at the base.

How to attach plywood to the floor? Let's consider the main stages of coating installation.

1. Using a notched trowel, apply a layer of a couple of millimeters of adhesive to the concrete surface.
2. Plywood sheets cut into squares are placed on the adhesive pad in a pre-designated sequence and rolled with a heavy roller.
3. The glued plywood must be screwed to the floor with dowel-screws or dowel-nails, observing a fastening pitch of 15-20 cm and edge distances of 2 cm.

Important! The length of the screws for plywood should be 3 times the thickness of the sheets being mounted, the diameter should be 6 mm. So that the flat heads of the fasteners are buried in the material, the top drilled holes countersinked with a large diameter drill.

The final stage of laying plywood under the laminate is sanding the surface with coarse sandpaper. Grinding smoothes out irregularities, eliminates burrs and height differences between sheets.

If for installation flooring you need a smooth and durable base, one of the fastest and simple ways- leveling the floor with plywood. Compared to screed, this method has many advantages: it does not require special skills and tools, repairs can be continued immediately after installation, and the price of plywood is cheaper. Depending on the thickness and impregnation used, the price per sheet of plywood varies from 300 to 1200 rubles.

Not every sheet material can be used on the floor.

• Plywood – best option. It consists of glued veneer sheets, each new leaf laid perpendicular to the fibers of the previous one, which increases rigidity. Moisture resistance, durability and environmental friendliness depend on the binding material used (it can be distinguished by its markings).
  • Most often, the FC brand is used for flooring. It is made on the basis of urea glue, and has lower moisture resistance and easily swells from moisture. Suitable for rooms with normal humidity, as it is safer for health.
  • The FSF marking has increased moisture resistance, but is not very environmentally friendly; it is made on the basis of phenol-formaldehyde glue. It is better not to use it indoors due to phenol emissions.

  

To level the floor, you can buy grade 3-4 plywood; the presence of knots will not affect the final quality; they will be covered by the floor covering.
Laying tiles on plywood is not recommended as wood has a high coefficient of expansion and may fall off as the season changes.

• DSP - ideal for leveling wooden floors under tiles.
• OSB - completely environmentally friendly material, theoretically, it can be used for leveling, but it is undesirable, because it bends more easily with the same thickness as plywood. In addition, OSB is usually slightly more expensive than plywood.
• Chipboard – has poor environmental friendliness and low strength.
• Fiberboard is not suitable for leveling, because it is too flexible a material and it will bend around all the irregularities.

Ways to level a floor with plywood

Depending on the requirements and initial data, plywood floors are laid in several ways.




Before starting work with any wooden materials, they must be left in the room where the renovation is taking place for at least two days.

Covering a wooden floor with plywood

This method has already been discussed in our article:.




One thick layer or two thin ones?


Plywood is a composite material, that is, the layers in it are initially laid crosswise with fibers, due to which the sheet is quite rigid. Therefore, two layers of 10 mm each, instead of one 20 mm thick, will not provide additional rigidity to the sheets.

In terms of price, the result is also almost the same.

However, if you lay one layer of plywood on a curved floor, it will smooth out the unevenness, but height differences will remain at the joints. If you put an additional layer, the height differences will be smoothed out, and the edges of the second layer will already lie in the center of the sheets of the even first layer.

Therefore, it is better to use two thinner layers for leveling.

What to do if there are large depressions in the floor?

If found on the floor big holes(which could have formed due to heavy load in this place), then it will not be possible to simply lay plywood here - it will follow the contour of the recess.




Gluing plywood to the floor

Laying plywood on a concrete floor allows you to hide minor irregularities in the screed and make it warmer.

To attach the sheets you will need glue and dowel screws. Tools: notched trowel, hammer drill, screwdriver or screwdriver.

The best glue is with the addition of pine resin (often it is not indicated in the composition, but its presence can be determined by the smell); this is, for example, Thomsit 200 or 400.

For better adhesion of glue to plywood and concrete, the floor is first primed.

The length of the dowels is selected so that they go 4-5 cm deep into the screed.


• Before starting work, carefully clean the screed from dust and debris and coat it with a deep penetration primer.
• Apply glue with a notched trowel to the plywood or floor and lay it with offset joints. We also leave technological gaps of 2-5 mm between the sheets and near the wall.
• For additional fixation, we drill holes with a hammer drill, insert dowels and tighten them so that the screw heads do not stick out.
• Seal the gaps between the sheets gypsum plaster. If you plan to lay the laminate on plywood later, you can leave them as is, or seal them with sealant.
• When the plaster hardens, it is treated with a grout mesh and the seams are taped with reinforced tape.

Adjustable plywood studs

Plywood on studs The next technology is the installation of an adjustable floor.



Laying plywood on the floor along the joists


In addition to leveling, laying plywood on joists allows you to additional insulation or soundproofing the floor. Compared to standard option When the logs are sheathed with tongue and groove boards, plywood allows you to speed up the process. With a standard lag pitch of 50-60 cm, plywood with a thickness of 15-22 mm will be sufficient.

• Uneven screeds can be corrected by filling them with fine sand. It is advisable to seal the cracks in the corners polyurethane foam(this is especially true in panel houses).
• When installing on a concrete floor, it is almost always important to use waterproofing, as concrete can release moisture even several years after pouring, and the wood will rot on the underside over time.

It’s easy to check this yourself: put plastic wrap on it for a day. If perspiration forms under it, then waterproofing is required. The easiest way to make waterproofing for such a floor is from ordinary polyethylene film, gluing it together with tape and overlapping the walls.

• If you wish, you cannot rigidly attach the joists to the floors or walls. It is advisable to install them on felt or rubber pads so that small vibration noises are damped. The joists should not touch the walls; step back 2-3 cm from them.
• Before installing the first log, you need to find the zero level, relative to which all other logs will be aligned.


• The timber for the logs is set according to the level for additional alignment You can use wooden pads. The main thing is that the beam stands stable: in the future it will be bound by the sheathing and it will not budge.


• Additionally, for plywood, it is recommended to make intermediate logs so that the cell size is small and the sheets can be pulled well to the frame. To do this, tie the logs together with crossbars made from scraps, screwing them with steel corners. It is advisable to select the size of the cells in such a way that they are a multiple of the dimensions of the plywood, and the edge of the sheet always falls on the joist.
• If insulation and sound insulation are necessary, insulation is placed in the cells between the joists on the waterproofing - mineral wool. It must be cut exactly to the size of the cells so that the edges are not bent. It is covered with a vapor barrier membrane on top, which will remove moisture but will not allow it to get inside. It is stapled to the joists.
• In any case, you need to leave a gap of at least 2 cm under the plywood so as not to interfere with floor ventilation. If after insulation and fastening of the vapor barrier there is no gap left, a 100*25 mm board is screwed onto the logs, which will serve as a counter-lattice.
• Important point - right choice self-tapping screws Regular black hardened screws will not do the job. Bad screwdrivers simply won’t screw them all the way, but good ones will break them. Therefore, you need to use special yellow wood screws with a powerful mounting hole.
• To prevent the floor from creaking in the future and to ensure that the plywood is better pressed against the joists, you need to pre-drill the scrolling area with a wood drill (with a sharp end).


• As in previous cases, the sheets are laid staggered to avoid cross-shaped joints (must be T-shaped).

This approach allows you to prepare a reliable base for laying linoleum, vinyl tiles, carpet, parquet, and if the differences are less than 2 mm per meter, you can even

During renovations, it is often necessary to replace the floor. In this case, select suitable covering is not difficult. Before laying the top layer, it is necessary to level the base, since the service life of any floor covering depends on this. Laminate and board, for example, have locking connections and when laid on a bumpy surface, cracks form.

In this case, the most favorable option for leveling the base would be plywood. And here, not very experienced repairmen are faced with the question of how to strengthen the plywood onto the base, and with what tools to do this. Before leveling the main floor, you need to assess in advance the condition of the surface and the degree of deformation of its “relief”. Sometimes the subfloor per 1 m² has differences of about 2 mm. Then you can achieve perfect evenness using putty made from wet sawdust mixed with PVA, or by covering the base with acrylic sealant. Old boards are renewed with a plane and laid back. All loose parts are simply nailed or secured with screws. But in order to smooth out significant unevenness, you will need to lay sheet material. Here again, information on how to attach plywood to the floor before finishing is useful.

Working conditions

Before you begin the repair process, you should prepare all the tools that you will need for the job. This list includes:

• perforator;
• hammer;
• notched spatula;
• electric jigsaw;
• roulette;
• drill;
• screwdriver;
• spirit level

To secure the plywood to the base, glue and dowels are used. The adhesive can be solvent-based, water-based, or two-part. What is the difference between these means? In short:

• the water base slows down the drying of the glue and can delay the repair for several days;
• glue, which is based on a solvent, dries very quickly, but has a pungent specific odor;
• two-component adhesive is used most often, especially if communications are laid in the concrete and the screed has not yet dried.

To lay plywood on the floor, you simply need a good screed.

This is where it begins labor process. It doesn’t matter what method (wet or dry) the screed is made, but it must be done with high quality and in perfect horizontal position. In order for the floors to remain in their original form, dry and warm, the following conditions are necessary:

• screed completed according to all rules;
• waterproofing;
• compliance with technological standards when installing thermal insulation;
• the presence of moisture in the base is not more than 1%.

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Mounting Selection

For the base under a parquet floor, it is best to choose material of grade FK 4/4 and higher. A thickness of 1 cm or 1.2 cm is suitable. It is these plywood sheets that have sufficient strength and the necessary flexibility. And this plays an important role, since laminated plywood bears quite a serious load when arranging furniture and when residents walk around. When choosing a material thicker than 1.2 cm financial resources will be wasted, since its properties are equivalent, but the cost is more expensive. If we take into account the price-quality ratio, then 2nd grade plywood is suitable. When marking on plywood sheets, it is indicated what type they are - sanded or unsanded:

• Ш1 ─ grinding 1 side;
• Ш2 ─ grinding of 2 sides;
• NS ─ without grinding.

Sanded plywood is marked with the free formaldehyde content:

• E1 ─ 100 g of dry plywood mass contains less than 10 ml of formaldehyde;
• E2 ─ 100 g contains 10-30 ml of formaldehyde.

To make the floor perfectly flat, you need to choose a 2nd grade plywood sheet, marked with the marks Ш1, ФК and Е1, the thickness of which is 10-12 mm.

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Cutting and fitting

Plywood consists of several layers, so high humidity does not have the best effect on it and delamination can be expected soon. Before you start laying, you need to determine the humidity concrete structure. To do this, during repairs, the worn out top covering is removed, and during construction the ceiling is cleared. Then on concrete slabs lay out a large piece of polyethylene and press it tightly around the edges, leaving the central part free. After 7 days, the film is examined. If no condensation is found on it, then you can safely lay the substrate. If drops of liquid appear on the polyethylene during testing, then the floors must be additionally covered with waterproofing.

When everything is ready to lay plywood, the room is measured and the sheets are cut according to the measurement results. In this case, you need to ensure that the seams between the sheets of plywood are 1 cm, and near the walls they are 1.5-2 cm. The plywood covering should not be allowed to touch the walls. This gap is left in case the coating parameters increase due to heat or humidity. If there is no free space, the floors may simply swell. In addition, the small format of plywood panels has greater stability and strength.

After cutting, check the ends of the workpieces. If they delaminate, they are rejected and new ones are prepared. Then the plywood sheets are laid out on the floor and adjusted to the base. It is very important that 4 sheets do not join in one place. To do this, all blanks need to be laid out using the method brickwork, that is, with a shift.

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Surface primer

Having adjusted the plywood, the sheets of blanks are numbered and a schematic representation of the layout is sketched out. Then the parts are removed and the base is leveled. To do this, remove any remaining mortar, paint, and construction debris. After this, dust is removed. It is better to do this with a special vacuum cleaner, but a simple broom will do. Cannot be carried out wet cleaning, because water will spoil them wooden parts designs.

Now the coating needs to be primed. A primer is required for this. It is prepared from an adhesive composition, diluted with a special solvent. The purpose of the primer is to:

1. Increase the strength of the bonding surface. This is achieved by penetration of the primer into the pores concrete base and gluing microscopic dust particles. All this increases the adhesion of plywood, glue and any dissimilar materials.
2. The primer holds the concrete surface together and protects against the formation of cement dust.

If the room has big sizes, then it is produced in sections. In this case, the primer should be applied in parts. The base for plywood covering in small rooms is primed entirely. In both cases, the primer is applied before laying the plywood sheets.

All photos from the article

In this article we will figure out how to level a wooden floor with plywood. We will study all the main stages of this work - from visiting the store for materials to laying linoleum or laminate on top of plywood. So let's get started.

General points

First, let's decide in what cases it makes sense to take on the leveling of an old wooden floor.

Here are the boundary conditions:

• At least three-quarters of the floorboards and all joists are in acceptable condition (that is, they have no visible signs of rotting and do not crumble under load).
• You are satisfied with the level of sound and heat insulation of the floor.
• The logs do not have significant deformations.

If any of these conditions are not met, our plans change.

We are faced with one of three operations:

1. Re-laying floorboards (sometimes accompanied by replacing joists).
2. Replacement with thick plywood along the joists.

1. Complete dismantling of the wooden floor and pouring insulated screed over the concrete floor.

Please note: in the latter case, do not forget about the maximum permissible specific long-term load on the floor slabs.
It is standardized at 150 kg/m2, which corresponds to a reinforced screed with a thickness of 5-6 centimeters.

Plywood selection

What kind of plywood should I lay on a wooden floor if all the above conditions are met?

First, let's list the characteristics by which it is classified.

Variety

Options range from elite grade to 3/4 grade (sellers usually do not separate them). In the latter case, there may be falling knots on the front surface in top layer veneer, traces of woodworm activity and other defects. Moreover, the price of a sheet, depending on the variety, can vary two or more times.

Since we need plywood as rough coating, the instructions are obvious: our choice is cheap, low-grade material.

Binder

This is indicated by the marking on the price tag:

What plywood should I use to level a wooden floor under linoleum or laminate? In this case optimal choice will be FC; its limited water resistance is leveled out by water-repellent impregnation.

Thickness

The thickness of plywood to lay on a wooden floor depends on the height differences between the floorboards and how much time you are willing to spend on repairs.

• Material with a thickness of 15-18 mm can even out differences of up to 5 mm per 30 cm of surface; at the same time, the thickness will not allow the flooring to sag under the weight of people or furniture. However, absolutely flat covering for obvious reasons it won't.