What Is Crystalline Concrete Admixture and How Does It Work?

• Ahmet Toka
• 7 August 2026
• Waterproofing
• 5 min read

We usually think of waterproofing as a layer laid on top of concrete. Crystalline systems turn that logic around: they place the waterproofing not on top of but inside the concrete. The concrete mass itself becomes impermeable and dependence on an external skin layer disappears.

This is a significant advantage, particularly for structures whose surfaces cannot be reached again later. In this article we look at how crystalline admixture works chemically, which structures it is preferred in, how it differs from membrane systems, and what its limits are.

The most valuable property of a crystalline system is that it keeps working even on surfaces that can no longer be reached. A hairline crack forming years later can close again on contact with water.

Ahmet Toka, General Manager

Working Principle: Using the Concrete's Own Chemistry

Concrete is not as solid a material as it appears. During setting, part of the mix water does not react with the cement and, as it evaporates, leaves capillary voids behind. It is through this capillary network that water penetrates concrete.

Crystalline admixture reacts with the lime and moisture present in the concrete to form insoluble needle-like crystals. These crystals fill the capillary voids and micro-cracks, leaving no continuous path for water. The reaction continues while moisture is present, goes dormant in a dry environment and restarts when water returns.

This "reawakening" is the system's most striking feature: a hairline crack forming years later can close by itself as water contact restarts crystallisation. The limit is generally cracks of hair-like fineness; for wide and moving cracks this mechanism is not sufficient.

Two Forms of Application

Crystalline technology reaches the site in two different forms.

As an Admixture in the Mix (Integral)

The powder product is added to the concrete mix in the truck mixer or at the batching plant. As soon as the concrete is poured it acquires impermeability throughout its full section. No separate application labour, surface preparation or drying time is needed; it is the method that places the least burden on the programme.

The greatest advantage of this method is that it needs no protection layer. Unlike a membrane it cannot be punctured or torn and is not damaged during backfilling, because there is no separate layer to protect.

As a Surface Application

The powder product is mixed with water and applied to the hardened concrete surface by brush or spray. The active ingredients migrate inwards through the concrete's capillary network and crystallisation takes place within the section. In other words the surface layer is not a coating but a carrier; even when that layer wears away, the waterproofing remains inside the concrete.

This method can be applied on the negative side in existing structures, on the internal surfaces of water tanks, in lift pits and on basement retaining walls. Details: crystalline concrete admixture applications.

Where Is It Used?

• Water tanks and reservoirs: Certified products can be used in drinking water reservoirs; it reduces the need for a separate coating on the internal surface.
• Basements and retaining walls: Its ability to work on the negative side on surfaces that cannot be reached from outside is the decisive advantage.
• Lift pits: It offers ease of application in narrow, hard-to-reach and permanently damp spaces.
• Swimming pools: As a permanent impermeability layer beneath the finish.
• Tunnels, underpasses and retaining structures: In structures where later intervention is very expensive.
• Concrete beneath car parks and terraces: As a second line of defence complementing the membrane system.

Comparison with Membrane Systems

The most important row in the table is the third from the bottom: a crystalline system cannot solve moving joints and wide cracks. These areas must in every case be addressed separately with waterstops, joint sealing applications and, where necessary, injection .

Critical Points for Correct Application

• Dosage and mixing time: The admixture must be distributed homogeneously in the concrete; insufficient mixing creates local weakness.
• Curing. Crystallisation requires moisture. Early drying of the concrete stops the reaction; curing time and method must not be neglected.
• Surface preparation (in surface application): Laitance and form release agent must be removed and the surface opened up so that its pores are exposed. Active ingredients cannot penetrate a closed surface.
• Damp surface: Before surface application the concrete is brought to a saturated surface-dry (SSD) condition; this is necessary for migration to begin.
• Joints and penetrations: Cold joints, construction joints and pipe penetrations require separate detail solutions; crystalline admixture does not seal them.

For an overview of waterproofing as a whole see our waterproofing page.

Common Misunderstandings

Because crystalline systems work invisibly, expectations are easily set wrong. The misunderstandings we encounter most often on site are these:

• "We used a crystalline product, so nothing else is needed." Integral impermeability does not solve moving joints and wide cracks. Joint details, waterstops and pipe penetrations must be addressed separately in every case.
• "The surface layer has worn away, so the waterproofing is finished." In surface application the layer is only a carrier; the active ingredients have already migrated into the concrete section. Wear of the surface layer does not remove the impermeability within the section.
• "It closes every crack by itself." Self-closing applies only to very fine hairline cracks and only in the presence of moisture. For wide and moving cracks the mechanism is insufficient.
• "It was applied, we checked it visually, that's it." Visual inspection is impossible because the waterproofing is invisible. Verification is done with flood testing, permeability testing and dosage and mixing records.
• "Curing doesn't matter, the chemistry works anyway." The opposite is true: crystallisation requires moisture. In concrete that dries early the reaction stops and the expected performance never develops.

When these expectations are set correctly, crystalline systems provide a very valuable layer of assurance, especially on surfaces that cannot be reached again later.