A polymeric coating is created by the chemical polymerization reaction between simple premixed liquid-state compounds and the use of a hardener or catalyst, forming what are colloquially called solid-state polymeric resins. These leave a continuous layer as a protection on the concrete. The usual thickness of continuous flooring is from 0.1 to 5 mm and in particular applications a thickness greater than 5 mm may be necessary.
The chemical nature of the simple compounds, as well as the greater or lesser degree of polymerization, give rise to thermosetting polymeric resins with different physicochemical properties.
The most common resins are epoxy and polyurethane. Epoxy resins have good chemical resistance, but they are rigid and brittle and, due to their aromatic chemical nature, they are sensitive to UV rays, so they tend to yellow. On the contrary, polyurethanes have more resistance to humidity, wear, abrasion and are flexible. Due to their aliphatic nature, they are more resistant to UV rays. so they don’t yellow.
Knowing the nature and condition of our concrete is just as important as preparing the support before we can apply our continuous flooring system.
Once our resin has been applied, it is important to allow it to polymerize for the necessary time so that it acquires its definitive properties. During this initial period and after polymerization, visual defects may occur with a purely aesthetic nature, or in the most serious cases, with a functional nature.
We go on to comment on some of the most common defects.
Most common application defects
1. Differences in the color of the seal or Topcoat
The finishing layers of epoxy or polyurethane resins give added value to the flooring and are applied in low thickness.
a. Color variation problems appear when a pigmented resin is touched up after more than 15 minutes of application.
b. Change of manufacturing lot numbers. Batches can cause small differences in color compared to the same RAL.
2. Fish eyes in the epoxy
They are round and closed marks with the appearance of depression in the treatment. They usually show a small dot without a pore in the center, hence the name fisheye.
They are caused by insufficient consumption of resin, although it may be due to other more damaging factors, such as the presence of oil or grease on the support and contamination by silicones.
3. Light spots or white clouds form on the resin in fresh or cured state
Moisture in the concrete support or high ambient humidity can cause condensation during application or when the resin is fully cured. They are Blushing-type phenomena that come from chemical reactions during the polymerization of the resin.
a. Epoxy-amine crosslinking. Partial blends where the amine ratio is excessive. The use of solvents in the mixture can also cause a higher concentration of amine, giving rise to the aforementioned white marks and differences in tonality. Lastly, if the support is below the required temperature (+3ºC above the dew point) the migration of the amine component towards the surface can occur, generating the defects already described.
b. Contact with water, as well as condensation due to low temperature of the support and/or high ambient humidity.
c. Excessive consumption. Layers too thick and more visible on light colors.
4. Orange skin or stippling in the final layer of the system
It is possible to find it in both epoxies and polyurethanes. Consequence of cold or heat in the support and/or the material, which prevents it from self-leveling due to being in unsuitable conditions.
5. Peeling or delamination
The epoxy can become detached from the substrate or between layers.
a. Lack of cleaning of the support. The epoxy resin does not adhere if there is dirt, grease or other contaminants.
b. Lack of mechanical resistance of the support. Resistances of 1-1.5 N/mm2 are normally required depending on the products and mechanical stresses. This would be promoted by the existence of a laitance or surface layer in the low-strength concrete.
c. Concrete release agents or healers.
d. Lack of primer. If we do not prime the concrete, the penetration of the continuous coating will be less and its mechanical adherence will be clearly reduced. A good concrete primer will clog the pores and significantly increase adherence.
e. Moisture in the concrete support. In these cases, the concrete has a darker color when it presents this phenomenon.
If we talk about delamination between layers, this can be caused by:
a. Apply the layers beyond the time stipulated for it.
b. Dirt, presence of water, contamination by oil or grease or moisture between layers.
c. Improper resin and hardener mixing time.
6. Pinholes or bubbles in epoxies and polyurethanes
Pinholes are small bubbles or blisters that, once burst, leave a visible central crater behind a layer or thin film of material.
Among the most common causes are all those that are capable of generating air.
a. Degassing: The air (gdi) retained in the pores of the concrete passes into the lining without being able to be eliminated due to its partial permeability.
b. Temperature/Humidity: In case of high values of one or of the 2 factors, a rapid drying occurs that does not allow the solvents to evaporate, leaving them retained in the
resin. In polyurethanes, CO2 gas is generated by the reaction of moisture with the isocyanate present in its formulation.
c. Air currents or sunlight. If there are significant air currents or direct solar irradiation, rapid drying of the surface can occur before all the solvent in the resin evaporates.
d. Mixing of resins at high revolutions or extremely aggressive support preparation methods.
e. No use of a spiked roller in self-leveling systems. These help de-aerate the mixture.
7. Lack of resin drying
This defect is shown when the resin has 24 hours after its application. Most common in epoxy resins.
a. Environmental conditions: temperature lower than the minimum for the material to be applicable.
b. Inadequate mixing times.
c. Incorrect mixing methods.
Repairs are difficult, but involve removing uncured material with solvents or manual means such as scraping.
8. Mechanical resistance
It is important to choose the resins based on the mechanical requirements demanded. It is important to respect the charging times of the polymeric resins. 24 hours for pedestrian traffic and 7 days for heavy traffic.
a. Abrasion: Marks similar to burns may appear on the surface caused by excessive rubbing of heavy elements with little surface.
b. Scratched: epoxy resins scratch more than polyurethane resins. The use of rough systems considerably reduces and conceals the aesthetics of the scratches.
c. Impact: These are loads applied at high speed with greater or lesser weight than the normal of the coating. They can cause chipping, so the choice of elastic systems such as polyurethanes mitigate this mechanical variable to a greater extent.
9. Chemical resistance
Our polymeric resin systems must be resistant to exposed chemicals. If this is not the case, stains will appear that will be impossible to remove and possibly the chemical product will penetrate the coating, affecting its impermeability and even being able to affect the concrete, as shown in the following photograph.
The chemical agent, its concentration, the exposure time, as well as the contact temperature must be known. Based on this, the most feasible solutions will be analyzed.
The nature of the support must be known before starting to work, since this will largely condition the result. Once known, the appropriate mechanical treatments will be carried out on the coating to be implemented.
Appropriate primers will always be used.
The control of the working conditions and the use of the tools and methods described for each product will help to avoid major problems.
The provisions, times between layers and loading times are essential for a long-lasting solution.
It is useless to have a good polymer coating if proper maintenance is not carried out and a cleaning protocol is established according to needs. For the same reason, the cleaning products used in the polymer coating must be validated.
Thermally, the resins are thermostable, but beyond a certain value, the product begins to soften and after a certain temperature they lose consistency and degrade. In the case of requiring continuous coatings that are more stable at temperature and more chemically and mechanically resistant, we will opt for solutions such as the polyurethane-cements from the Ucrete range.