Preparing the floor for screeding

For any building or remodeling project, preparing the floor for screeding is an essential first step. In order to apply the screed—a thin layer of cementitious material—onto a smooth, level surface, preparation is required. An excellent adhesion and long-term performance of the screed are guaranteed by careful preparation.

Thoroughly cleaning the surface is the first step in floor preparation. This entails clearing away any dirt, dust, or other impurities that might prevent the screed from bonding properly. Vacuuming and sweeping the floor are typical techniques for obtaining a clean base.

After cleaning, it’s critical to look for any holes, cracks, or uneven patches on the floor. These flaws may have an impact on the screed’s ultimate finish. In order to guarantee a uniform and smooth substrate, small holes and cracks can be filled with the appropriate repair materials.

Checking the floor’s moisture content comes next after repairs. The integrity of the screed may be compromised by excessive moisture. Depending on the needs of the project, a variety of techniques for testing for moisture are available, including the use of a moisture meter and the calcium chloride test.

It’s crucial to apply a bonding agent or primer to the prepared floor surface before screeding. This increases the substrate and screed adhesion, guaranteeing a solid bond and boosting the flooring system’s overall durability.

Preparing the base

The base that the screed will rest upon must be properly prepared for a superior screed. It is preferable to remove the old screed when repairing the floor. It develops chips, cracks, and potholes with use and time. Expanded clay, which was poured beneath the cement screed in Soviet-built homes, speeds up the process of deterioration. Over time, the backfill compacts and leaves gaps beneath the cement screed that are nearly impossible to fill.

Even though replacing the floor will cost more, you won’t have to disassemble everything again because the screed won’t deform over the course of the new floor covering’s service life.

The old subfloor was removed with a hammer drill. Dust and other debris are removed from the concrete floor. It is advised to vacuum and give it a wet wipe after this. Every chip, peel, and damage to the ceiling has been fixed. Dents, joints, and surface impairments are sealed using a substantial cement mortar.

It should be kept in mind that without first preparing the base, cement mortar will not lie on concrete. After some time, he will simply fall behind.

Consequently, joints and damaged concrete are primed. If the cracks are too small to be rubbed with the solution, they must be opened with a puncher or scalpel.

Concrete primer

The following tools are used to fix the ceiling’s damage and seams before priming the entire surface:

• cement laitance;
• water;
• special primer (Ceresit ST 17).

As a point of comparison, other brands of factory primer are more costly, of worse quality, or have a shorter shelf life than Vetonit.

The primer’s job is to get as much moisture as possible into the concrete pores in the sealing regions. The solution won’t connect to the concrete base if this isn’t done.

The materials "How to make a floor screed with expanded clay?" go into great detail about the technology used to lay screed on expanded clay. and "Expanded clay in dry floor screed".

The chemical process of cement hardening will be interfered with by dry concrete, which will extract water from the cement-sand mixture. Furthermore, the primer binds dust particles and forms a film that strengthens the bond between cement mortar and concrete.

Cement and water are combined in a 1:2 ratio to create cement laitance. The restored areas are soaked two to three times with water and cement laitance, but no puddles form. It is advisable to use a paintbrush to hasten the hydration of the pores. Use a brush to aggressively rub the primer into the concrete in order to achieve this. A damp surface is treated with the repair solution (wet on wet) and thoroughly rubbed.

Wetting with water is not nearly as effective as priming with "milk." Its cement helps to strengthen the bond between the cement mortar and the repaired base by penetrating the pores of the concrete with water.

In the areas that need to be repaired, specific primers pierce the ceiling and crystallize, preventing the solution’s water from escaping. They create tiny scales on the penetration surface, which guarantee the patch’s adherence to the concrete.

One characteristic of pre-war homes in St. Petersburg and Moscow that makes floor repairs unique is the absence of concrete floor slabs. For the interfloor ceiling, strong metal T-beams are used. As a result, in these types of homes, the base for the screed is first prepared by filling the spaces between the beams with expanded clay, which is then covered in a layer of cement mortar.

Expanded clay base

Porous and light in weight is expanded clay. pure in terms of ecology. utilised as a space filler to lessen loads on the building’s load-bearing components, as well as for heat and sound insulation.

The base of the interfloor ceiling is covered with an overlapping film of polyethylene (thickness 100 microns or more) or another waterproofing material before the expanded clay is filled. Tape is used to glue the seams together. The film is positioned above the floor at the walls.

There are beacons being installed. After pouring expanded clay, a long rail is used to level the surface and keep it from rising above the beacons. Through the use of cement milk, the leveled layer of expanded clay is held in place and keeps the granules from moving when the screed is laid.

In individual homes or cottages, weeds are pulled either on the subfloor or the ground.

Soil base

The earth has been leveled and free of vegetation. To provide thermal insulation, expanded clay is poured on top of it, at least 5 cm thick, and is covered with a 10–15 cm layer of sand. The surface that results is rammed for dense shrinkage and wetted with water. This is the least expensive method of getting ready for screed; it is not less effective than more costly ones.

Wooden floor base (subfloor)

Several requirements must be satisfied by the wooden floor that serves as the screed’s base:

• not have rotten boards;
• be firmly attached to the logs;
• do not contain traces of glue, grease and paints;
• do not creak;
• don"t bend.

Drawbacks are easily overcome. It all boils down to replacing rotten and sagging boards before screed is poured. using sanding (a plane) or detergents to remove unclean stains. In addition, joists are fastened with squeaky boards. Potential mortar leakage areas, such as beneath baseboards close to walls, fractures, and fallen knots, are sealed using parquet putty, which is made of wood dust or oil paint diluted 1:1 with sawdust.

Important: Avoid using water-soluble putty as the solution’s moisture can ruin it.

Skirting boards can be taken off. In their place is a thin strip. Putty is used to seal the spaces between the lath and the floor. The lath is removed once the screed is installed, and the space left between the wall and the floor will allow air to circulate beneath the floor, preventing the joists and boards from rotting. A plinth will be placed over it once the flooring has been installed.

Sound and hydro-isolation preparation is the next stage of getting the base ready for installation. In the work "Waterproofing the floor before screeding," waterproofing issues are covered in detail.

Waterproofing

Many people associate waterproofing work with installing a damper tape when doing construction or repair work on floor installations by hand. Yes, the tape helps with sound absorption and waterproofing to some extent, but only where the wall and floor meet. It doesn’t shield the subfloor from leaks in humid rooms like bathrooms or moisture from the basement.

Important: in single-family homes without a basement, waterproofing the first floor is a must. The screed, the floor, and the foundation are all destroyed by capillary moisture and water evaporating from the soil beneath the structure. If the moisture is in an aggressive (acidic or alkaline) environment, the issue is exacerbated. It combines with the constituents of concrete to make it useless in a few years.

There are several approaches to waterproofing:

• Gravel-sand cushion. Used in private houses on the ground floors;
• Film. Suitable for all types of apartments and houses. It is easy to use, which allows a novice builder to perform such preparatory work. In terms of cost – a budget option. There is only one disadvantage: it cannot be laid on a base with many pipes;
• Coating waterproofing based on rubber or bitumen. Apply in several layers. Penetrates into all cracks, which guarantees the quality of the work performed;
• Impregnating waterproofing (Penetrat). A new type of insulating material. Its peculiarity is that it can be applied from any side of the concrete – by reacting with the components of concrete, the impregnation grows special crystals throughout the entire thickness of the concrete floor. Crystals and prevent moisture penetration.

Noise insulation

Apartment building occupants need sound insulation beginning on the second floor. For years, the upstairs neighbor found themselves bothered by noise from the TV, music, and screaming kids. Covering the floor with soundproof material is one way to solve this. In this instance, soundproofing material is applied either on top of the screed itself or beneath it on the slab (floating screed), depending on the type of flooring.

Floating screeds are made of a variety of materials:

• polystyrene;
• mineral wool;
• perlite;
• expanded clay.

Although its device is not very complex, it does require some skills and knowledge. Not suitable for some kinds of flooring. Soundproofing materials are placed between the screed and the floor in these situations. The article "Soundproofing the floor in an apartment under a do-it-yourself screed" provides instructions for soundproofing a floor screed.

Crucial: installing soundproofing virtually always resolves the issue of inadequate floor insulation.

Marking the subfloor

There are always flaws in the floor surface before the screed:

• slope, while in different rooms in different directions;
• bumps and protrusions in concrete that cannot be removed, etc.d.

In order to compensate for these drawbacks, a conditional horizon must be identified, above which the floor’s base will not be visible in every room. Drawing the zero level, or horizon line, and then the floor screed line with its assistance allows for this to be accomplished. These lines are either penciled in accordance with a rule or strip or marked with a construction cord along the room walls.

The next drawing step involves figuring out how many rows there are of beacons and how far apart they are from one another. Then, using chalk, mark each beacon’s location on the floor.

Installation of beacons

Beacon installation completes the finishing work that gets the floor ready for screeding. The kind of beacon is determined by:

• financial capabilities of the customer;
• construction experience;
• type of screed;
• urgency of work;
• availability of materials.

A sturdy floor is ensured by high-quality screed, which can be obtained with properly installed beacons.

For a smooth and long-lasting finish, careful planning and preparation are necessary when preparing a floor for screeding. In order to successfully apply screed, it is necessary to ensure that the floor is structurally sound, clean, and level. Through the management of moisture control, surface impurities, and appropriate substrate bonding, contractors can maximize the screed layer’s adhesion and durability. Proper floor preparation is essential to the overall success of construction and renovation projects because it not only improves the final flooring’s aesthetics but also adds to its structural integrity and longevity.

Conclusion

The following procedures are involved in preparing the subfloor for laminate flooring:

• cleaning the base from the old screed;
• surface repair;
• primer (if water and sound insulation work will be carried out on the surface of the screed);
• hydro- and noise insulation (modern materials make it possible to combine these technological operations into one);
• beacon installation.

It should be kept in mind that the caliber of the preparatory work affects how long the laminate lasts.

One of the most important steps in guaranteeing a smooth and long-lasting flooring finish is preparing the floor for screeding. The subfloor needs to be thoroughly cleaned and inspected first. Clear away any dirt, dust, or outdated glue that might have an impact on the screed’s ability to adhere.

Next, look for any unevenness or cracks in the subfloor. Use a self-leveling compound to level out uneven areas and fix cracks with an appropriate filler. In order to prevent any bumps or dips that could affect the final screed, this step is crucial to creating a flat surface.

To improve adhesion between the subfloor and the screed, prime the subfloor after it has been cleaned, leveled, and smoothed. In order to ensure a robust and long-lasting finish, the primer aids in surface sealing and bonding improvement.

As directed by the manufacturer, give the priming adequate drying time. By doing this, the primer is guaranteed to set completely and to sufficiently prepare the subfloor for the screed application.

By carefully following these instructions, you can make sure that your floor is ready for screeding. The flooring will last longer and be of higher quality thanks to this preparation, which also reduces the possibility of problems like cracks or uneven surfaces in the future. It is worthwhile to dedicate time to meticulous preparation if you want your screeded floor to have a polished and seamless finish.

Video on the topic

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8. Preparing the floor for screeding