The characteristics of concrete and cement mortar floor and the selection of floor closed primers

In most cases, epoxy floor coating needs to be applied to concrete or fine stone cement mortar floor, therefore, it is of great significance to study and understand the characteristics of concrete and cement mortar in order to design and select the most suitable floor coating (especially primer) to improve the adhesion strength, anti-punch resistance and service life of the floor coating. The National Standard of the People's Republic of China GB50209-2002 "Construction Quality Acceptance Code for Construction Ground Works" and GB50212-2002 "Building Anti-corrosion Engineering Construction and Acceptance Code" for the construction of cement concrete and cement mortar surface layer made relevant provisions, the following mentioned cement concrete and cement mortar are based on the above-mentioned standards of construction of the ground.
1. The characteristics of concrete and cement mortar surface The composition of concrete and cement mortar is different, but they are cement as a binder, so there are some common characteristics:
1, due to the hydration reaction of concrete or cement particles, it takes some time, so the maintenance of . In fact, the continuous curing of cement can last for many years, but generally after 28 days, cement can achieve the initial performance, at the same time, the structure of excess water also need time to evaporate, so that the moisture content is reduced to a suitable level of coating.
2, concrete and cement mortar structure is porous. Since excess water needs to be added to the mixing and ground casting process, as the water evaporates, pores are left in the cement gel, known as the gel pores. The porousness of the entire cement material depends on the composition of the mixture (sand, stone, cement and water), curing methods and the use of certain chemical additives. The porous structure of concrete and cement mortar indicates that its surface is permeable, and its permeability depends on the compactness of its structure.
3, concrete and cement mortar is permeable, because its structure is porous, water in the form of steam is easier to pass through concrete or cement mortar structure, which is very important for the coating to be used. For areas with a higher water table, if a waterproof layer is not constructed in the ground structure, moisture from the ground floor moisture will penetrate the concrete or cement mortar structure and constantly push the floor coating to the back, unless the coating is extremely adhesive or the coating is also permeable Gas, otherwise it is easy to occur due to osmosis pressure caused by the coating bubble and peeling phenomenon, in addition, because the ground is constantly affected by moisture, so that its moisture content is difficult to fall to meet the level of coating requirements, coating and ground substrate attachment strength will be greatly affected.Although in this case can choose a good permeable coating (such as water-based epoxy coating) to solve the foaming problem, but because of the role of moisture, the alkali in the concrete (CaO) also gradually migrates with moisture to the surface under the coating, with the CO2 reaction in the air to produce a large number of white crystalline sediments, with the increase of this sediment, the film and substrate surface adhesion will gradually decrease until peeling, it is not possible to obtain a long-term good bonding effect.
4, because the cement is alkaline after curing, so the concrete and cement mortar is alkaline, usually pH between 12-13. 5, concrete or cement mortar ground has 10-40MPa pressure strength, but the pressure strength is relatively low, only about 3.45MPa, so it is easy to crack under the pressure.
2. The design of flooring primers according to the characteristics of the above-mentioned concrete and cement mortar floor, coatings applied to its surface should consider the following characteristics:
1, permeability of flooring primers for good adhesion, long coating life, better resistance to the external environment is extremely important. Coatings that can penetrate into concrete or cement mortar substrates can greatly increase the adhesion to substrates and extend the life of the coating compared to coatings that do not penetrate and rely only on coating bonding to the substrate surface. A good example is the penetration of some liquid epoxy coatings on a flat concrete surface, the penetration depth of the resin can reach about 6mm, which not only provides maximum adhesion, but also increases the density of the concrete surface. But not all epoxy coatings have these properties, those with high molecular weight solid resin preparation coatings, only with solvents to penetrate the surface, with the rapid evaporation of solvents and quickly become solid, penetration is very limited. Therefore, the penetration of the coating is mainly limited by the molecular size, viscosity and penetration time of the film resin, the solvent-free epoxy closed primer made of low molecular weight epoxy resin and low viscosity curing agent has excellent wetting on the substrate, and because it needs to rely on resin and curing agent The reaction increases viscosity and gradually cures, a process that usually takes a long time (4-8 hours), which ensures sufficient penetration time for the primer and therefore has a higher penetration depth, which increases if you add some solvents that wet the substrate surface when used. Below is the permeability comparison between solvent-free epoxy closed primer and solvent-based epoxy-enclosed primer: A, solvent-free epoxy-enclosed primer resin part Low molecular weight epoxy resin (molecular weight 194), low viscosity amine cure for liquid curing agent part 100% solid at room temperature Solids after mixing ≥98% after mixing viscosity ≤60S permeable time 4-8 hours B, solvent-based epoxy closed primer: resin parts Medium molecular weight epoxy resin (molecular weight 500), solid at room temperature, need to be solvent dissolved after painting. Curing agent component Polyamide or modified amine curing agent solution mixed solid parts are usually less than 70% after mixing viscosity ≤60S permeability time 15-30 minutes
2, alkaline resistance: epoxy resin coating inherently excellent alkaline resistance, in addition, some chlorine-containing polymers or ethylene resins also have good alkali resistance.
3, surface increased density and strength: epoxy closed primer seeped into the concrete substrate, in the paint epoxy resin and curing agent reaction curing, can anchor loose concrete surface, greatly increase the surface concrete surface strength.
4, adhesion: practice has proved that the separation of coating and concrete occurs in the concrete layer, check the back of the off coating, can be seen to the attachment of concrete. That is to say, the attachment between the surface concrete layers should be much smaller than the attachment between the coatings, if the deeper the primer penetration, the higher the surface concrete strength, then the stronger the combination of the coating and concrete.
3, the selection of flooring primers we recommend:
1, for the strength is not high, the surface loose porous and even sand-lifting concrete, should use a strong permeability of solvent-free epoxy closed primer, coating can also be added a moderate amount of thinner to reduce viscosity to further enhance its permeability.
2, for cost reasons, for dense concrete substrate surface, can also be used solvent-based epoxy closed primer.
3, for concrete with high moisture content, the use of good breathability of water-based epoxy closed primer, can reduce the risk of coating foaming.