Crystalline Waterproofing
For many years, membranes have been used for basement waterproofing, but that has changed significantly with the advent of Cementitious Capillary Waterproofing (crystalline admixtures) gaining a much larger share of the underground waterproofing market. These waterproofing admixtures – often referred to as “crystal growth” or “capillary waterproofing” – are the fastest-growing segment of the world waterproofing market.
Membranes are still very common, but there are other forms of waterproofing that are growing at much quicker rates than membranes.
Below-ground structures are the area of a building that most often has leaks. It is also commonly known that leaks in basements are much harder to fix than leaks above the ground in any structure.
Used for water tanks
Crystal growth is also perfect for waterproofing water tanks – whether they are above ground or below ground.
Used for tunnels, underpasses, and subterranean passageways
Because tunnels are thermally protected, this type of waterproofing is perfect for waterproofing such structures.
Development of hydrophobic concrete
Hydrophobic concrete was developed to counter the problems of membranes, which would blister, tear, and puncture. But they were only moderately successful and soon replaced by crystal growth, which offered several advantages.
A Great Advancement
Crystal growth was developed in the mid-20th century
It was originally applied as a surface coating to the concrete, thereby blocking the penetration of water into the concrete. It is still applied this way today in restoration situations (and is an excellent way to stop leakage in existing buildings that may have waterproofing problems), but for new projects it is more commonly added to the concrete as an admixture.
There have been numerous scientific studies done on this subject over many years. These include ASCE (American Society of Civil Engineers) and MDPI.
Below-ground applications
Under a microscope, concrete can be seen to have millions of voids, capillaries, and pores. It could be said that it is similar to a sponge.
After initially being used as a surface coating, crystalline later began being used as an admixture in the concrete.
Whilst there are two or three different types of admixtures put into concrete for waterproofing, this has been by far the most successful and is now used in virtually every country in the world.
Today crystal growth is the most widely used waterproofing admixture in the world, and in 2026 the worldwide market is estimated to exceed 5 billion USD.
Accordingly, we are now going to look at the use of crystalline admixtures for below ground.
Crack-sealing properties
Concrete itself is porous, and of course low-MPA concrete is more porous than high-MPA concrete. Although some claim that very high MPA concrete is waterproof by itself, that does not consider the fact that nobody can stop concrete cracking. So even if the concrete is, say, 60 MPA, if it develops cracking, it is undeniable that water can penetrate to the rebar regardless of the concrete’s strength.
This is one of the advantages of crystalline. Crystal growth products react with free lime and moisture within the concrete to form millions and millions of insoluble crystals. These grow throughout the concrete and can seal cracks that may develop in the future. Thus, even in high MPA concrete, which can develop cracks and leak, these cracks can be sealed through crystalline.
The crystals actually grow towards moisture and remain reactive in the concrete for the life of the structure. Thus, if leaking develops in future years due to cracks, the crystals will grow towards these cracks and automatically seal them (with certain maximum limits, of course, depending on each individual product).
The chemical process that makes it happen
The performance of these admixtures in the design mix is caused by the reaction between the active ingredients of the admixture and the calcium within the mix design.
Addition to the concrete
The admixture, which is often a blend of active ingredients with other cementitious materials, is added to the concrete during production (hence it is often referred to as integral waterproofing) or later, in the hardened state, as a coating applied on the surface by brush.
The formation of crystals
After its addition to the concrete, the active chemicals react with cement hydration byproducts and moisture, in particular Ca(OH)₂ (calcium hydroxide or lime). This results in the formation of millions of insoluble crystals in the shape of needles. These grow within the concrete and actually continue to grow for the life of the structure; hence, they are called reactive.
Permanent sealing of concrete
These millions and millions of crystals eventually block the capillaries and voids within the concrete. This massively reduces permeability… Although, of course, as with everything, some products are more effective than others. Because of this, the structure becomes highly resistant to water ingress, even in conditions where the concrete structure is exposed to or subjected to substantial hydrostatic pressure. Resistance to hydrostatic pressure is a prerequisite for good integral waterproofing, given its use in so many underground structures.
No crystal growth at 10 µm.
Crystal growth at 10 µm.
The benefits
The use of these products for the waterproofing of concrete establishes several key advantages of this technology when compared to traditional external coatings and membranes:
Lifetime Concrete Protection
The crystals that grow within the concrete continue to grow for the life of the building. They do not deteriorate, and they stay reactive within the concrete for the entire lifespan of the building. This has been proven over many, many years of use. This means they avoid many of the problems of membranes, which encounter blistering, de-bonding, and mechanical damage, among other problems.
It works through the entire mass of the concrete, and thus, whichever direction the water is trying to enter the structure from, the concrete is protected. When added into the concrete (hence, as we said above, why it is also known as integral) it works both positive side and negative side.
Self-Healing Properties
The active ingredient, which has been added to the concrete during construction, remains in a reactive state for the entire life of the structure. At later stages if there is water entering the structure, crystals will grow towards that water and create millions and millions more crystals, thus effectively blocking the passage of water.
During this period it will also seal hairline cracks in the concrete that may have occurred over time.
Vapor Permeability
It is impermeable to liquid water but does allow the transmission of vapor from the concrete. This helps to minimize moisture increasing within the concrete structure.
Future protection
Not only do these millions of crystals block water, but they also block the passage of chlorides and sulfates into the concrete. This protects the steel, which would otherwise begin to rust, possibly expanding into seven times its original size, and this will result in not only leakage of water into the concrete but also spalling the concrete and eventual degradation of the structure. This can be seen in several catastrophic building collapses lately that did not adequately protect their basements with good quality waterproofing.
Environmentally Friendly
Most of these products are very friendly to the environment. They contain no VOCs (volatile organic chemicals) and are safe with potable water. For example, CWS Admix has several internationally recognized approvals for drinking water.
Where is it used?
Applications include the following:
Subterranean Waterproofing (including basement waterproofing and below-ground car parks)
Ground slabs
Drinking water tanks
Elevator pits
Foundation walls and footings
Sewage plants
Tunnels
Industrial wastewater
It’s primary use is for below ground applications but NOT rooftops
These products are composed of millions and millions of tiny, needle-like crystals. These crystals are rigid and are therefore better used in areas where there is little movement of the concrete. Thus, areas of low thermal stress such as water tanks, basements,, and tunnels are perfect applications.
On the other hand, it should not be used on concrete areas where movement can be expected. This includes suspended slabs to some extent but definitely applies to rooftops that will have movement from thermal stress.
The American Concrete Institute said in a document published some time ago that “temperature fluctuations after application of these sealers can cause unstable crystal growth; they are therefore best suited for interior or below ground applications”.
Another said: “Crystalline waterproofing should not be applied to suspended structural decks because it is not elastic and will not withstand movement in the substrate”.
If there is movement in the substrate, the crystals will break. Eventually, due to the nature of the product,, further crystals will be formed. Therefore, if the movement were a one-off situation – e.g. an earthquake – there would be leakage for a period of time until further crystals formed and the building would then be watertight. So in short, it should be used for basement waterproofing and other situations such as water tanks but not where there is thermal stress. If there is thermal stress regularly, the crystals would not have time to reform, and so leakage would be constant.
So for rooftop applications where only one form of waterproofing is being used, a product such as CWS100, which has flexibility and resistance to thermal stress, is a far more suitable product.
Effects on concrete
The first question most specifiers ask for products added to the concrete is “What is its effect on concrete”?
Does it affect strength?
Of course the exact answer varies from product to product, but in general it has minimal effect on concrete strength. In the case of CWS Admix, with which we are most familiar, repeated testing has shown little or no effect on concrete strength. Testing being what it is, there is always some variation, but almost every test has proven that it has a nil to one or two MPA increase in strength. As with all testing, if repeated testing shows a similar result but one test shows a massive difference – e.g. a 25% increase in strength or similar – it is reasonable to assume that it is testing error rather than reality.
Does it affect slump?
Generally, the answer is yes. It generally has some plasticising effect and it is advisable to check the effect with each particular design mix via a trial mix.
Does it retard setting times?
Generally the answer is yes. The amount of retardation will vary from product to product but most will retard concrete setting times by something like 1 to 2 hours. Of course this can be offset by using an accelerator if that is beneficial in the applicable climate.
How does it react with other additives that are also in the mix?
Generally it does not react adversely with other additives used in integral concrete waterproofing. However, being cautious – there are so many additives around the world that it is impossible to give a 100% totally categorical answer. However one thing we do know is that often it will react with water reducing admixtures and may cause increased retardation and an increase in setting times.
We would always recommend that it is good practice to perform a trial mix with the relevant mix design.
Crystal growth versus other technologies
Hydrophobic versus Hydrophilic
When discussing crystalline, many people refer to it simply as integral, whereas, in fact, integral encompasses some other categories as well.
Above we referred to hydrophobic waterproofing and hydrophilic waterproofing.
The real difference between hydrophobic and hydrophilic is that, whilst hydrophobic waterproofing rejects water (such as water beading onto a leaf), hydrophilic will absorb a small amount of that water and use that water to create the chemical reaction that produces crystals. So crystalline is hydrophilic. Hydrophilic waterproofing is technically referred to as a PRAH, whereas hydrophobic waterproofing comes under the category of PRAN. The H and the N stand for hydrostatic and nonhydrostatic, respectively.
The effects of hydrostatic pressure
When designing below ground structures, obviously hydrostatic pressure can be a crucial factor. Some basements that go into the ground, particularly where there is a high water table, consultants need to be assured that the waterproofing will stand the hydrostatic pressure that will be encountered in the basement.
The most common hydrophobic waterpoofings are silanes, siloxanes, and what are commonly called “pore blockers.” These products have been around for quite a few years and are a stearate: essentially a fat that reacts with calcium hydroxide and gradually blocks the pores. While they do this quite well, none of these products can withstand hydrostatic pressure. Hence, they are good for vertical applications such as columns supporting a bridge where silanes are sometimes used but not on a bridge deck itself because it won’t resist the hydrostatic pressure.
Crystal growth, on the other hand, has an excellent ability to withstand hydrostatic pressure. For example, CWS Admix has outstanding testing to 14 bars of hydrostatic pressure… This is the equivalent of 142 meters—approximately the height of a 40-story building.
Most of these products meet the European standard for waterproofing under EN 12390–8. In this case the product is tested for 72 hours under 5 bars of hydrostatic pressure – approximately 50 meters (roughly the height of a 15-story building).
Comparison with pore blockers
Crack sealing versus no crack sealing
Another significant difference with pore blockers is that these products can seal static cracks in the concrete. The importance of crack sealing cannot be overstated. Additionally, as crystals remain “alive” in the concrete for the entire lifespan of the building, they can seal cracks that may develop many years later, which would otherwise result in leaks.
The converse to this is that pore blockers, silanes, and siloxanes have no such ability, so if the concrete develops any cracking, there will be leakage into the building and the resultant issues such as damage to property, disgruntled clients, and problems that need fixing.
CWS Admix ® - a proven solution backed by a 25 year warranty
This technology was developed more than 40 years ago, and today CWS Admix is still the most advanced implementation of the initial concept. Several advantages set it apart from its competitors. Firstly, it has been successfully tested to withstand 14 bars of hydrostatic pressure (equivalent to 140 meters of waterhead or a 40 story building), whereas most other products are tested to only 5 bars hydrostatic pressure. Additionally, it is dosed at a fixed dosage of only 0.8 kg/m3, regardless of cement content, when other admixtures are dosed as a percentage of the cement content. That makes the dosing much easier and eliminates the risk of mistakes of constantly changing the quantity of admixture per cubic meter, especially during the time when the decision about the final mix design is based on several calculations and modifications. Contact us now to see how we can help protect your project. |