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Assessing the moisture content of concrete substrates for resin floors

04 of August '23

- Types and methods of measuring substrate moisture
- Effects of floor applications on a damp substrate
- Relationship between waterproofing and vapor permeability of floors

Moisture content, or water content (H2O) in a concrete substrate, is one of the most important parameters that determine whether it is properly prepared for resin flooring application on it. In order to properly evaluate the substrate, it is useful to know the basic methods of measuring the moisture content of concrete and to be aware of the relationship between water content and the "breathability" of the floor. Experts from the Flowcrete brand, a leading manufacturer and supplier of high-quality resin floors, outline the basic issues related to the moisture content of the concrete substrate on which such coatings are made.

Percentage, absolute and relative moisture content by weight

The most common moisture content in the construction industry is weight percentage moisture content, given in %H2O. Weighted moisture content presented in grams per unit of volume tested is absolute moisture content. Relative humidity, on the other hand, is expressed by the ratio of the actual measured water content of the test sample to the maximum water content of the fully saturated sample. For example - with complete, i.e. 100% water saturation of a concrete block we are dealing with when it is no longer possible to further saturate it, as evidenced by condensation of water on its surface.

Pomiar wilgotności podłoża

Measuring the moisture content of the substrate

© Flowcrete

When calculating the relative humidity, the difficulty arises in taking the correct value of the total saturation of the material due to the fact that it is highly dependent on the quality of the concrete, its grade, temperature, as well as air temperature and humidity. For this reason, it is more common to calculate the weight moisture content independently, with the simplest solution being the use of an electronic instrument that checks the relative humidity value.

The moisture requirements for the concrete substrate for Flowcrete floors are respectively:

  • up to 75% for the relative humidity of the substrate, according to BS 8204;
  • up to 5% in the case of the moisture content by weight, determined with a Tramex-type electronic instrument.

Methods for testing the moisture content of a concrete substrate

The aforementioned electronic method involves the use of equipment operating on the contact principle (application to the surface of the concrete). This method is the most convenient and easiest to use, but it does not work well when there is a large amount of steel reinforcement in the concrete substrate.

On the other hand, the dryer-weight method, or gravimetric method, is the most accurate method of measuring weight moisture, which is performed only under laboratory conditions.

In this method, the weight moisture content is calculated from the formula:
równanie Flowcrete

X - weight moisture content of the sample,
m1 - weight of the fresh sample,
m2 - weight of the sample after drying at 105°C for 30 minutes.

Thecarbide method (CM Gerät) uses the chemical process of decomposition of calcium carbide (carbide) in the water contained in the concrete substrate sample. During the reaction, acetylene is produced, causing an increase in pressure in the steel cylinder of the moisture meter. The carbide method has its own CM scale.

Under the so-called simple building method, a building film measuring about 1×1 m is spread and glued on the surface of the concrete substrate and left for several hours. After this time, there should be no signs of fogging or condensation on the film, and the surface of the substrate should be the same color as before the test, that is, the same color as the remaining surface not covered by the film.

Posadzki Flowcrete Flowcoat

Flowcrete Flowcoat floors

© Flowcrete

Effects of laying a floor on a soggy substrate

The condition that the weight moisture content of the concrete should not exceed a certain value is crucial. Failure to adhere to the moisture content of the substrate in the case of floors made with synthetic resins can result in the subsequent destruction of the floor. Damage to the floor under the influence of moisture usually occurs in two stages - during crosslinking, i.e. during chemical setting of the synthetic resin, and during subsequent use. Examples of types of damage to a resin floor laid on a soggy substrate include blistering, spalling, delamination, cracking, peeling, discoloration and tarnishing.

Posadzki Flowcrete Flowfresh

Flowcrete Flowfresh floors

© Flowcrete

Waterproofing properties of resin floors

Resin flooring is the outer, top layer of a floor, which serves, among other things, to protect a building's structure from outside elements - hence the airtightness requirements for flooring.

In the case of Flowcrete resin floors, water permeability, tested by the Karsten test, is zero. Related to this parameter, water tightness, is the limited vapor permeability of resin floors, and therefore their "breathability."

The vapor permeabilityof a floor is the ability of the floor to evaporate excess water penetrating into it from the concrete substrate. The higher the vapor permeability of the material, the lower its density after setting and channel structure, more similar to that of pumice.

According to EN 1504-2, the permeability of water vapor through the floor (vapor permeability), is defined in three classes:

  • Class I, Sd < 5 m, vapor-permeable floor,
  • Class II, 5 m < Sd < 50 m,
  • Class III Sd > 50 m, vapor impermeable floor.

The Sd coefficient indicates the thickness in meters of a stationary air layer that would put up an identical diffusion resistance to the floor sample under test. For example, Deckshield ID parking lot flooring has a vapor permeability capacity of Sd = 22.4 meters, while for a vapor barrier film the Sd factor is > 200 meters.

Posadzki Flowcrete Mondeco

Flowcrete Mondeco floors

© Flowcrete

The moisture requirements of the concrete substrate for resin floors are always related to the parameters of these systems - waterproofing and breathability. If the moisture level of the substrate is too high, it must be dried by gravity (usually for several weeks) or with fans and moisture condensers. Sometimes the waiting period for the substrate to reach the appropriate moisture level is too long and unacceptable to the construction management. In this case, a specialized material called Hydraseal DPM, which is resistant to static dampness of the concrete substrate, should be used as a primer. However, it is worthwhile to consult the solution used with Flowcrete's Technical Department.

For more information, visit the company's Tremco CPG Poland Sp. z o.o., posadzki Flowcrete page on the A&B portal.

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