There is a version of this conversation that happens constantly in the flooring industry. A facility manager specifies a coating — usually based on price or brand familiarity — and within two or three years it is peeling, dusting, staining, or all three. The product gets blamed. A replacement is specified. And within two or three years, that one is doing the same thing.
The coating is rarely the problem. The problem is what was going on underneath it — and what the coating was never designed to address.
Concrete looks solid, stable, and inert. It is not. At the surface level, concrete is chemically active, porous, and in a state of ongoing change. Understanding what that means is the starting point for understanding why most protective systems underperform, and what it takes to build one that holds.
What concrete actually is at the surface
Concrete is made by mixing Portland cement, aggregate, and water. During the curing process, cement hydrates — water reacts with the calcium silicate compounds in the cement to form calcium silicate hydrate (C-S-H), the crystalline compound that gives concrete its structural strength. This reaction is what makes concrete harden.
The problem is a byproduct. One of the principal products of cement hydration is calcium hydroxide (Ca(OH)₂), also called portlandite. It is soft, water-soluble, and chemically reactive. Because it dissolves readily into the bleed water and pore solution, it is carried upward through the slab as the concrete cures — via capillary action and evaporation-driven transport — concentrating at and near the surface, precisely where the coating will eventually be applied.
This is not an anomaly or a sign of low-quality concrete. It is a predictable outcome of normal cement chemistry. Every Portland cement slab contains free calcium hydroxide at its surface. And that calcium hydroxide is a primary reason concrete surfaces dust, absorb stains readily, and wear prematurely under traffic — a baseline condition that good mix design, finishing practice, and curing can reduce, but not eliminate.
The porosity problem
The second structural issue is porosity. During the mixing process, more water is typically used than the hydration chemistry requires — the excess is needed to make the mix workable. As the concrete cures and that excess water evaporates, it leaves behind a network of capillary pores running through the slab. These are not random voids. They are connected channels that run throughout the concrete, from the surface downward.
These pores mean that concrete is not a sealed material. It breathes. Moisture vapor moves through the slab continuously, driven by temperature gradients, humidity differentials between the slab and the ambient environment, and hydrostatic pressure from groundwater below. A coating applied to the surface does not stop this movement — it sits on top of a material that is actively pushing vapor upward.
When moisture vapor cannot escape through the coating, it accumulates at the bond line. The pressure it generates can overcome the adhesion holding the coating to the substrate. The result is bubbling, blistering, and eventually delamination — from beneath the coating, not through it.
This is why moisture vapor emission testing matters before any coating goes down, and why it is one of the most skipped steps in practice. The 72-hour calcium chloride test or relative humidity probe reading is not a box to check. It is the measurement that tells you whether the substrate is in a condition to hold a coating at all.
Carbonation and surface instability
There is a third process underway at the concrete surface that compounds both of the above. Carbon dioxide in the atmosphere reacts with calcium hydroxide to form calcium carbonate — a process called carbonation. Carbonation is slow, but it progresses from the surface inward over time, converting the calcium hydroxide closest to the surface into a compound with different mechanical properties.
A carbonated surface layer is typically harder and denser than the uncarbonated concrete below, which creates a condition where the surface and the substrate have different stiffness and expansion characteristics. Under thermal cycling — the floor warming and cooling through the day and through seasons — the two layers move at slightly different rates. A coating applied across that boundary has to accommodate differential movement that the bond was never designed for.
This is one of the reasons coating failures on older concrete look different from failures on new slabs. The chemistry at the surface has had more time to evolve, and what appears to be a well-prepared substrate may have a compromised transition zone that no amount of surface grinding fully addresses.
Why conventional coatings don’t address the root cause
Most conventional coating systems — epoxy, urethane, acrylic, and similar products — are formulated to sit on top of the substrate. They rely on mechanical adhesion: the coating flows into the texture of the prepared surface, cures into a film, and grips.
This adhesion depends entirely on a stable substrate surface. But the calcium hydroxide layer that coatings typically land on is not stable. It is soft relative to the concrete below, water-soluble, and chemically reactive with the environment. A coating bonded to a calcium hydroxide-rich surface is effectively bonded to the weakest material in the system — not to the concrete itself.
Add moisture vapor movement through the slab, carbonation-driven differential behavior between surface and substrate, and thermal cycling, and the conditions for mechanical bond failure are built into the system from the start. The coating is not failing because it is a bad coating. It is failing because what it bonded to was never a stable foundation.
This is not an argument against conventional coatings categorically. Many perform adequately on properly prepared substrates with well-managed moisture conditions and appropriate recoat cycles. The point is that coating performance is determined at least as much by substrate chemistry as by coating chemistry — and that applying a protective product without addressing the substrate is managing symptoms, not causes.
What addressing the chemistry looks like
Two approaches address the substrate chemistry directly rather than coating over it.
Densification.
A concrete densifier — specifically a silicate-based densifier — penetrates the slab and reacts chemically with the free calcium hydroxide near the surface. The reaction produces additional C-S-H, the same compound responsible for concrete’s structural strength. The calcium hydroxide that would otherwise sit at the surface as a soft, reactive layer is converted into a harder, more stable compound that becomes part of the concrete matrix. The surface becomes harder and less porous from within, not just protected on the outside.
This is why densification is a prerequisite for polished concrete systems and is strongly recommended before applying topical coatings to ground or high-porosity slabs. It addresses the root cause of surface weakness rather than applying protection on top of it. (Blog 2 in this series covers densification chemistry and application in detail.)
Covalent bond chemistry.
The second approach is the one Coval Technologies is built on. Rather than mechanically bonding to the surface, Coval coatings are formulated to form covalent chemical bonds with the substrate — molecular-level connections between the coating and the surface groups on concrete, stone, metal, or tile. The coating and the substrate are chemically joined at the interface, not simply in contact with it.
This changes the failure equation. The calcium hydroxide-rich surface layer is still present, but the coating is not relying on a mechanical grip to that layer to hold. The covalent bond is formed at the molecular scale, at and into the surface, rather than sitting on top of it. And because the bond is chemical rather than physical, it responds differently to differential thermal movement and the softness of the calcium hydroxide layer than a mechanical bond would. In lab testing (ASTM F1869), Coval’s concrete topcoat reduces moisture vapor emission by roughly 31% relative to uncoated concrete — not sealing the surface completely but cutting the pressure that builds at the bond line enough to matter.
The chemistry here links directly to what densification accomplishes. When a slab is densified before a Coval topcoat is applied, the calcium hydroxide near the surface has already been converted to C-S-H — a harder, more stable surface for the covalent bond to form against. The two steps are complementary: densification addresses the substrate weakness; the covalent bond topcoat provides protection that holds.
The practical takeaway
Concrete is not a neutral surface waiting to be coated. It is an active material with chemistry that directly determines what can adhere to it, how long that adhesion will last, and under what conditions it will fail.
Any coating specification that does not account for calcium hydroxide content, surface porosity, moisture vapor emission rate, and the age and condition of the carbonated surface zone is working with incomplete information. The best coating in the world underperforms on a substrate that wasn’t ready for it.
The question to ask before specifying any protective system is not just what product to use — it is what the surface chemistry is doing and what it will do under the conditions the coated floor will face. The answers to those questions determine the system. The product selection follows from them.
To discuss surface assessment and coating system selection for a specific substrate or environment: sales@covaltechnologies.com | USA: +1 281-566-4277 | Singapore: +65 9028 9174 | UAE: +971 54 588 11 77