The compressive strength of the substrate should not be less than 25 N/mm2 (25 MPa). To meet defined loads, a higher strength may be required. It is advisable to take a number of measurements across the fl oor and in all parts of the proposed installation to confirm the compressive strength i.e. with a Schmidt hammer.
Concrete floors generally have some cement laitance with low cohesive strength in the top few mm. This weak layer must always be removed during the substrate preparation. Withstanding stresses from concrete shrinkage, thermal shock or loading requires a minimum cohesive strength. This should be: ≥ 1.5 N/mm2 (≥ 1.5 MPa) and this is usually measured by a number of Pull-off tests across the floor.
It is extremely important to measure the substrate moisture content because cement bound substrates should normally only be over-coated at a moisture level of 4% by volume, or visible rising moisture (condensation) on the bottom of the sheet, indicates the need for additional drying time or the use of Sikafloor® EpoCem® Technology.
If atmospheric and climatic factors are ignored, serious flooring defects such as poor adhesion, water marks, blistering, irregular surfaces and inadequate curing may occur.
The following must therefore be checked and recorded several times a day, before, during and after application to ensure that they are within the system limitations:
- Ambient temperature (air)
- Substrate temperature
- Relative humidity (air)
- Dew point
If not fully removed, any weak areas or cement laitance on the substrate will reduce the adhesion, performance and durability of any fl oor system.
Concrete surfaces must therefore always be mechanically prepared to a sound substrate. Any dirt, dust, oils, grease or any other contaminants will also reduce or prevent adhesion of any topping, so these must also be removed by thorough cleaning and vacuuming of all residues.