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The state of the subfloor, be it of cement mortar (with or without a synthetic resin content), concrete, tile or terrazzo, steel or wood, has a direct bearing on the durability of the Epoxy resin based topping applied to it. Whether old or newly laid, subfloors must be painstakingly inspected for damaged areas. These must then be made good and the entire surface of the subfloor given a suitable pretreatment.

Cement mortar subfloors

Cement mortar screeds are usually applied to concrete floors as a levelling or finishing layer. The method of application, surface roughness, levelness, strength and post-treatment of such screeds must all be taken into account before applying an Resin based topping.

To utilize fully the high mechanical strength of an Epoxy resin floor topping the mortar screed on which it is laid must have at least the same compressive strength as the underlying structural concrete, i.e. 30 N/mm2 or more.

The adhesion of cement mortar screeds to the underlying concrete can easily be tested by tapping with a hammer. Hollow sounding areas should be chiselled out and repaired with fresh mortar.

Newly laid concrete subfloors should be allowed to set for as long as possible so that all excess water has evaporated and shrinkage of the concrete come largely to a halt before an Epoxy resin based topping is applied. The setting time required is usually about four weeks but depends on the water content and thickness of the layer of concrete, and on the prevailing weather. In any case the concrete subfloor should be dry before the topping is applied, particularly if there is no cellar underneath. Rising damp should be prevented by damp-proofing. Epoxy resin based toppings are impermeable to water vapour and damage can easily occur if the subfloor has not been correctly designed.

Concrete floors

Existing concrete floors should be examined carefully to make sure whether they are suitable as subfloors for Epoxy resin based toppings. Special care should be taken wherever a floor has been soiled repeatedly by deep-penetrating substances such as soaps, sugar, or cooking fats Like traces of mineral oil or asphalt, these substances act as release agents and must be removed by flame spraying or solvents.

Cracks or holes should be chiselled out right down to the sound substrate and then filled with cement mortar or a highly filled Epoxy resin based mortar (see below).

The decontaminated, repaired concrete floor must be cleaned thoroughly before the epoxy based topping is applied.

Tile and terrazzo floors

Damaged tile or terrazzo floors can be utilized as subfloors for Epoxy resin based toppings. The pre-treatment required will depend upon the type of tile present and the sort of traffic to which the floor has been subjected.

The best results are obtained by sandblasting or mechanical abrading, then vacuuming off all dust and particles. The floor can also be treated with acid.

Steel floors

If an Epoxy resin based topping is to be laid on a steel floor or deck, very good adhesion can be ensured by coarse sandblasting. If this pre-treatment is not feasible, the steel must be degreased, then abraded and cleaned with grinding wheels or steel brushes.

Repair of subfloors

Only epoxy based floor toppings laid on sound subfloors will exhibit high mechanical strength and very good chemical resistance. The damaged areas of worn floors must always be repaired before an Epoxy resin topping is applied.

Shrinkage induced cracks

Cracks always from when the water in a mix evaporates so quickly that stresses due to shrinkage build up before the concrete or mortar has attained adequate tensile strength. Such cracks may be 0.1 - 0.2 mm wide, usually form a network across the surface of the floor, and are readily visible at low temperatures. They can easily be traced by wetting the floor, the water in the cracks evaporating less rapidly than that on the surface.

Shrinkage induced cracks require no special pretreatment prior to the application of a thick Epoxy resin based floor topping.

Temperature-fluctuation cracks

Cracks induced by heat or cold vary in width with the ambient temperature. They should be converted into V-shaped grooves using a pneumatic hammer (Fig. 1), freed of all loose particles, and then filled with a flexibilized Epoxy resin system. If the mix used to fill the cracks contains a high proportion of filler, the edges and walls of the groove should first be coated with a low-viscosity Epoxy resin resin (Fig. 2). The deeper this priming layer penetrates into the substrate, the better will be consolidation of the peripheral zones an adhesion of the crack-filling compound (Fig. 3).

Expansion joint structure :

  • Epoxy based floor topping
  • Cement mortar screed
  • Concrete
  • Primer
  • Resilient joint filler
  • Compressible matarial, e.g. soft chipboard
    or rigid foam plastic