Preparation of existing subfloors

Existing (or old) subfloors require particularly high skill from the installer. It is often difficult to determine what type the base should be classified as and how suitable it is for further use. Each base has its own specifics that must be used in its preparation. In addition, the surface of old subfloors is often contaminated with remnants of materials previously used when laying coatings: adhesives, mastics. Remnants of leveling compounds and floor coverings may also be encountered.

There are no absolutely reliable and reliable methods for assessing the materials remaining after removing old floor coverings, as well as any regulatory requirements for their quality. For this reason, significant elements of risk remain in the preparation of such subfloors. All counterparties (customer, management of the contractor) must be clearly aware of this circumstance.

To reduce risks, you must follow the following rules:

• Remove all weak, peeling and questionable areas of the subfloor.
• On floors with old coatings or adhesive residues, the layer of the leveling mixture should not be too thick (maximum 5 mm), otherwise the stresses arising when the mixture shrinks during its hardening can lead to peeling and destruction of the leveling layer. In this case, you can be guided by the principle - the thicker the layer, the greater the shrinkage stress.
• The existing subfloor may be sensitive to moisture. Therefore, it is necessary to minimize the impact of moisture contained in the applied materials (primer, leveling mixture). When in doubt, it is better to use a water-free primer such as epoxy.
• It is necessary to ensure favorable climatic conditions for the entire period of work, including preparation of the foundation. If the primer or leveling mixture takes too long to dry, the presence of adhesive or other material residues on the subfloor can lead to negative consequences.
• Preliminary mechanical treatment of the floor base should be provided as intensive as necessary, but with minimal loads if possible. For example, an incorrectly adjusted milling machine can destroy an insufficiently strong base - the shot blasting method has obvious advantages over milling. It is often wise to use drum cutters instead of disc cutters.

Water-dispersion adhesives

They often remain after removing elastic and textile coverings (linoleum, carpets). As a rule, they have a rubber-like consistency and color from light beige to brownish. Residues of such adhesives must be removed as completely as possible, otherwise cracks may appear over time on the leveling layer laid on elastic adhesive due to shrinkage deformations.

Solvent adhesives based on synthetic resins

They remain mainly after removing old carpets, tennis court coverings and parquet. These adhesives are light brown in color and tend to be brittle. When inspecting the base, the main attention should be paid to the condition of the adhesive layer. If the glue crumbles when scratched with a key, it must be completely removed.

Solvent adhesives based on synthetic rubber (neoprene)

They remain mainly after removing old PVC coatings and have a yellowish-brown color. Even after many years of use, such adhesives retain high elasticity and a rubber-like consistency. To prepare such subfloors, you must follow the same recommendations as for water-dispersed adhesives.

Bitumen mastics

Easily recognized by their black color. 30-40 years ago, bitumen mastics were used mainly for laying parquet and vinyl-asbestos tiles (hard PVC coverings). Bituminous mastics can be plastic (usually used for parquet) and relatively more rigid (used for vinyl-asbestos tiles). While leveling compounds can be laid over rigid mastics, plastic mastics must be completely removed. However, it must be remembered that bituminous materials may contain substances hazardous to health (for example, polycyclic aromatic hydrocarbons). Therefore, it is recommended to check them for toxic substances or, if this is not possible, to remove them in any case.

Mechanical restoration

Mechanical processing of floor bases is carried out using disc grinders, milling or shot blasting machines, depending on the nature of the contamination and the condition of the base. To remove old floor coverings, special machines called stripers are used. Disc grinders are the most versatile, thanks to a wide variety of replaceable attachments: discs with sandpaper, sanding meshes, carbide discs, metal brushes, discs with abrasive stones, system discs with carbide modules, star discs, grinding pads with diamond segments and metal rings. Drum milling machines are the most effective for processing concrete, allowing high productivity to remove the top layer of concrete to a depth of up to 5 mm. And finally, for processing high-strength, wear-resistant and difficult-to-process substrates (mosaic concrete, stone cladding, asphalt), it is recommended to use shot blasting machines.