Any professional who installs ceramic tiles will be familiar with this situation. Whether it is a concrete screed or a cementitious screed. This shouldn’t be a problem for seasoned pros. But when can we really say it’s ready at providing best products for Construction Companies in Dubai.
Residual Moisture as A Criterion
The supports only have to deform to a certain extent after the application of the coating material. Therefore, in the case of substrates subject to shrinkage, should apply ceramic coatings as late as possible. From 6 months for concrete to 28 days for cementitious screeds.
Otherwise, these are ready to cover concrete or mortar screeds with a residual moisture level of 2.0 CM% or less. In the case of unheated calcium sulphate (anhydrite) supports. A maximum humidity of 0.5 CM% requires. For heated calcium sulfate (anhydrite). With the maximum allowed value is 0.3 CM%.
What Impact Does Relative Humidity Have on The Residual Moisture Value of a Material?
Over time, a material reaches its equilibrium moisture content based on the relative humidity of the surrounding air. This time is determined at each previously set temperature (sorption isotherms).
The higher the relative humidity, the higher the equilibrium moisture content of the screed. For example, at 70% relative humidity, the equilibrium moisture content achieved by a cementitious screed (orange line) is approximately 3.7%, measured as oven-dry moisture content (left scale) or 2 .0 CM% (right scale).
Impact Of Relative Humidity on Screed Shrinkage
As drying proceeds, the moisture content falls and shrinkage proceeds until a limit reaches.
The following types of contraction distinguishes:
- Early shrinkage caused by improper treatment.
- Chemical shrinkage caused by hydration of the cement.
- Drying shrinkage caused by the release of excess water.
- Carbonation shrinkage caused by reaction with carbon dioxide.
- For the potter, chemical and drying shrinkage are the most important.
Hydration And Concrete
Hydration of the screed mortar mix produces concrete, which has a significantly smaller volume than the raw materials used: cement, sand, and water. Especially in the case of thicker components, complete hydration can take months or even years. However, most of the shrinkage caused by this process already occurs in the first few days (see graph 2). The chemical shrinkage process is irreversible. For complete hydration, a water-cement ratio of 0.4 would be adequate.
However, to ensure better workability, normally choose a water-cement ratio, which can be between 0.6 and 0.7. As a result, the screed releases excess water over time during the drying phase and shrinks as a result.
The ambient temperature and the relative humidity of the atmosphere determine the degree of drying shrinkage in a screed. Conversely, a very dry screed can absorb water and swell if exposed to high relative humidity. This means that drying shrinkage is a nearly reversible process. Could say Cement-based screeds to “breathe” based on the relative humidity of the ambient air.
Depending on the thickness of the screed and airflow, it can take months before the screed reaches its final shrinkage. As a general rule, the drying time quadruples if we double the thickness of the screed.
Can An Excessive Contraction of Our Screed Damage a Ceramic Coating?
Yes, especially if place the ceramic too early on the screed. And in a very special way. In the event that the floor is of the isolated or floating type. If the residual moisture content of the floating screed is too high.
The screed will slowly dry out and shrink over a period of months or even years. However, as the ceramic tile cannot shrink beyond the deformability of the cementitious adhesive type into the spaces left by the grouting, the center of the slab and floor covering structure will arc upwards (convex deformation).
This arch can cause the assembly of ceramic pieces and/or alteration of the flatness of the room, affecting doors or even the breakage of the slab in the center of the floor. See standard UNE 138002 General rules for the execution of coatings with ceramic tiles by adherence.
Does It Make Sense to Require a Residual Moisture Content Of 2 CM% In New Screeds?
As the sorption isotherm (graph 1) shows, a new screed can only reach an equilibrium moisture content of 2 CM% or less if expose it to an ambient relative humidity of 70% or less for weeks or months.
Depending on the time of year and the exposure of the screed, the relative humidity values vary, hence it makes no sense to contemplate the general residual humidity limit of 2 CM% or less. In addition to this, we can introduce errors in the measurement of the residual moisture value due to unfavorable weather conditions.
Furthermore, the remaining shrinkage after 28 days only represents a few tenths of a millimeter per meter of screed (Table 1 and Graph 2, dark gray area). Since the introduction of flexible adhesives, it has been possible to absorb this residual shrinkage.
An adhesive such as Master Tile; (deformable adhesive for laying all types of ceramics on facades, terraces, and deformable supports in general); It acts as a “flexible” joint between the screed and the ceramic floor covering (classification C2TE S1).
As a result, the reversible residual drying of our screed does not expose the floor covering to damaging forces such as those outlined in the screed shrinkage section.
Residual shrinkage after 28 days (dark gray area) is less than 0.1mm/m
Times required for Master Builders Solutions Master Tile ceramic range bonding products.
Master Builders and ages of concrete and mortar to be coated-1Table 2: Master Builders Solutions vs. minimum ages required F (type of floor).
In cases where it is not possible to let our concrete or cementitious screed dry for 28 days. Our company can offer proven solutions based on innovative waterproofing systems. Such as before laying the flooring.
With its corresponding cementitious adhesive is to make cementitious screeds based. A special binder for making fast-hardening mortar screeds. It can cover that with ceramic in just 3 days. Mortar for surface leveling prior to placement of ceramic on walls and floors. Coverable with ceramic after 24 hours.
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