Concrete Waterproofing with Crystalline Technology

Crystalline chemicals improve concrete durability, lower maintenance costs, and extend building life cycles

From foundations, floor slabs and exterior pre-cast panels, to water treatment facilities and underground urban infrastructure, concrete is one of the most commonly used building and construction materials. However, due to its composition, a mixture of rock, sand, cement, and water, concrete is often susceptible to damage and deterioration from water and chemical penetration.

These deleterious effects can be avoided through the use of crystalline waterproofing technology, which effectively improves the durability and lifespan of concrete structures, thereby reducing long-term maintenance costs. This article explores how crystalline technology provides a high level of performance to concrete mixtures, materials, and structures, and what design professionals need to know in order to specify and understand how this chemical technology will enhance building projects.

The Nature of Concrete

The aggregate base of a concrete mixture is formed by rock and sand. This cement and water mixture creates a paste that binds the aggregates together. As the cement particles hydrate, or combine with water, they form calcium silicate hydrates. The mixture then hardens into a solid, rock-like mass.

Concrete is also a water based product. To make this mixture workable, easy to place, and consolidate, more water than is necessary for the hydration of the cement is used. This extra water, known as the water of convenience, will bleed out of the concrete, leaving behind pores and capillary tracts. Although concrete appears to be a solid material, it is both porous and permeable.

Water reducers and superplasticizers can be used to reduce the amount of water in the concrete mix, and maintain its workability. However, pores, voids, and capillary paths will remain in cured concrete and can carry water and aggressive chemicals into structural elements that will corrode steel reinforcement and deteriorate concrete, thus jeopardizing the structure’s integrity.

Concrete deterioration due to rusting of reinforcing steel Photo courtesy of Xypex

The Porous and Permeable Nature of Concrete

Concrete is best described as a porous and permeable material. Porosity, which refers to the amount of holes or voids left in concrete, is expressed as a percentage of the total volume of a material. Permeability is an expression of how well the voids are connected. Together, these qualities allow pathways to form that allow the movement of water into, and through, along with the cracking that occurs due to drying shrinkage.

Water chart of permeability size scales Image courtesy of Xypex

Permeability, a broader term than porosity, is the ability of liquid water under pressure to flow through porous material. Permeability is described by a quantity known as the permeability coefficient, commonly referred to as D’Arcy’s Coefficient. The water permeability of a concrete mix is a good indicator of the quality of the concrete for durability reasons. The lower D'Arcy's Coefficient, that is the more impervious the concrete, the higher the quality of the material. Although concrete with a low porosity may be relatively durable, it may still need a waterproofing agent to prevent leakage through cracks.

Despite its apparent density, concrete remains a porous and permeable material that can leak and deteriorate rapidly when in contact with water or solutions containing chemicals such as chlorides, sulfates or other substances. But there are other ways in which water can be transported through concrete.

Vapor Flow and Relative Humidity

Water also migrates through concrete in the form of water vapor which is water held in air as a dissolved gas. The direction of vapor flow occurs s from high vapor pressure, generally the source, to low vapor pressure, by a process of diffusion. The direction of flow can vary based on environmental conditions.

The direction of vapor flow is critical when applying waterproofing treatment in situations where an unbalanced vapor pressure gradient exists. Typical examples include:

• Applying a low vapor permeable membrane, such as a traffic deck coating over a damp concrete surface (even if the very top surface is dry) on a warm day will result in pressure vapor pressure build-up and pin-holing or blistering.
• Applying a coating or sealant to the outside of a building wall may trap moisture into the wall if the sealant is not sufficiently vapor permeable.
• Applying low vapor permeable flooring over a slab-on-grade where there is high subsurface moisture content may result in delamination of the flooring.

Generally, a low vapor permeable sealant or coating should not be placed on the downstream face of a building or structure. Either the vapor pressure or water pressure will act to damage and blister the membrane. Some types of coatings and water permeability reducing admixtures in the concrete accommodate considerable vapor movement, thus allowing them to be placed successfully on the downstream side. Primary examples are cement-based waterproof coatings and water permeability reducing admixtures.

Vapor flow through a foundation wall Image courtesy of Xypex

How Crystalline Waterproofing Technology Works

Crystalline technology improves the durability and performance of concrete structures, lowering their maintenance cost and extending their lifespan by protecting them against the effect of aggressive chemicals. These high performance qualities result from the ways in which the crystalline technology works, when used with concrete.

Crystalline Technology waterproofs and improves the durability of concrete structures by filling and plugging the pores, capillaries and micro-cracks with a non-soluble, highly resistant crystalline formation. The waterproofing effect is based on two simple reactions, one chemical and one physical. Concrete is chemical in nature. When a cement particle hydrates, the reaction between water and the cement causes the concrete to become a hard, solid mass. The reaction also generates chemical by-products such as calcium hydroxide, sulfates and carbonates of sodium potassium and calcium as well as un-hydrated or partially hydrated cement particles all of which reside in the capillary tracts of the concrete.

Crystalline waterproofing introduces another set of chemicals to the concrete. When these two chemical groups, the by-products of cement hydration and the crystalline chemicals, are brought together in the presence of moisture, a chemical reaction occurs. The end product of this reaction is a non-soluble crystalline formation.

This crystalline formation can only occur where moisture is present, thus it will only form in the pores, capillary tracts, and shrinkage cracks of the concrete. Wherever water goes, crystalline waterproofing will form filling the pores, voids and cracks.

When crystalline waterproofing is applied to the surface, either as a coating or as a dry-shake application to a fresh concrete slab, a process called chemical diffusion takes place. The theory behind diffusion is that a solution of high chemical density will migrate through a solution of lower chemical density until the two equalize.

Thus, when concrete is saturated with water prior to applying crystalline waterproofing, a solution of low chemical density is introduced into the porosity concrete. When crystalline waterproofing is applied to the concrete surface, a solution of high chemical density is created, triggering the process of chemical diffusion. The crystalline waterproofing chemicals must migrate through the water (the solution of low density) until the two solutions equalize.

When the crystalline waterproofing chemicals spread into and through the concrete they become available to the by-products of cement hydration thus allowing the chemical reaction to take place forming a non-soluble crystalline structure. As the chemicals continue to diffuse through the water, the crystalline growth will form behind the advancing chemical front. The reaction will continue until the crystalline chemicals are either depleted or run out of water. Chemical diffusion can carry these chemicals up to 12 inches into the concrete. If water has permeated two inches into the substrate, then the crystalline chemicals can only diffuse to this depth but, they still have the potential to penetrate 10 inches further.

Instead of reducing the porosity of concrete, like water reducers and superplasticizers, the crystalline formation fills and plugs the voids in concrete becoming an integral and permanent part of the structure.

Scanning electron microscope (SEM) view of a concrete pore Image courtesy of Xypex	SEM view of a concrete pore filled with crystalline formation Image courtesy of Xypex

Because these crystalline formations are within the concrete and are not exposed at the surface, they cannot be punctured or otherwise damaged like membranes or surface coatings. Crystalline waterproofing is highly resistant to chemicals where the pH range is between three and 11 under constant contact, and two to 12 under periodic contact. Crystalline waterproofing will tolerate temperatures between -25 degrees Fahrenheit (-32 degrees Centigrade) and 265 degrees Fahrenheit (130 degrees Centigrade) in a constant state. Humidity, ultraviolet light, and oxygen levels have no impact on the products ability to perform.

Crystalline waterproofing offers protection against the following agents and phenomena:

• Inhibits the effects of CO, CO2, the gasses responsible for the corrosive phenomenon known as ‘carbonation’ a process in which exterior gasses create a corrosive phenomenon that softens the surface layers of the concrete. Carbonation testing shows that the crystalline formation in the capillary tracts reduces the flow of gases into concrete, thus significantly retarding carbonation.
• Protects concrete against alkali aggregate reactions (AAR) by denying water to those processes affecting reactive aggregates.
• Chloride ion diffusion testing shows that crystalline waterproofing reduces the diffusion of chlorides in concrete structures. This helps protect reinforcing steel and prevents deterioration that could occur from oxidation and expansion of steel reinforcement.

Michael Brown, P.E., principal with Golder Associates in Seattle, has used crystalline waterproofing in numerous applications, but notably on the Blackbird mine remediation project near Salmon, Idaho, which has very low pH acidic mine water flowing through concrete structures. "We use crystalline waterproofing technology as an additive to concrete to reduce permeability and provide protection for the epoxy coated reinforcing bar," said Brown.

More traditional methods of protecting concrete still leave it open to chemical and water damage. Membranes and other coatings are susceptible to errors caused by faulty workmanship such as pinholes, improperly sealed seams, blistering, delamination and damage during backfilling. Unlike crystalline waterproofing, they also deteriorate over time and lose their effectiveness.

Type of Construction and Appropriate Crystalline Technology Application

Crystalline waterproofing and protection technology is available in powder form. There are three different application methods:

• Applied as a coating to the surface of an existing concrete structure, for example, a foundation wall or a floor slab.
• Mixed directly into the concrete at the batch plant as an admixture.
• Shaken as a dry powder onto fresh concrete and trowelled into the surface.

Methods and Procedures of Crystalline Waterproofing Coating Applications

Crystalline waterproofing can be applied by  brush or with spray equipment.  To ensure the success of the application, care must go into the conditions under which the material is applied, i.e.  surface preparation, surface wetting, coat thickness, and curing time. 

Because the crystalline waterproofing coating system has a unique chemical diffusing characteristic, proper surface preparation of the concrete is critical to the performance of the material.  Concrete surfaces that will receive the crystalline waterproofing coating need to have an open pore texture to allow the transfer of the reactive crystalline chemicals from the coating into the concrete substrate. The surface also needs to be clean and free of dirt, form oil, and other foreign matter as this can potentially cause de-lamination of the coating.

The three common methods of concrete surface preparation are water blasting, sand blasting and acid etching. When water blasting, the pressure should be 3,000 pounds per square inch (psi) to 4,000 psi. Sand blasting is normally required when steel forms have been used and the concrete has a tight, mirror like finish. Acid etching can be accomplished using either muriatic acid or citrus-based products when the use of an acid is not environmentally acceptable.

Wetting the Surface

The coating systems require that the concrete be in a saturated, surface damp condition for the waterproofing to be effective. The active chemicals in the coating use water as a migrating or diffusing medium that allows the chemicals to transfer from the coating into the capillary tracts of the concrete. To make sure that concrete on vertical surfaces is saturated, wet the walls with clean water and allow the moisture to be drawn into the substrate for approximately ten minutes. Re-wet the walls a second time and allow to stand for 20 minutes.

In hot weather, when evaporation rates are high, it may be necessary to soak the concrete overnight. This can be accomplished using  soaker hoses at  the top of  walls that allow water to flow down the vertical surfaces, or a series of sprinklers if walls are less than 12 to 15 feet.

If water is not readily available on the job site, the saturation of the concrete should be done early in the morning when evaporation rates are low and before the concrete begins to heat up. In difficult conditions with  hot sun and wind it is better to attempt small areas that can be controlled rather than large areas at one time. In hot weather the use of an evaporation retarder to help keep moisture in the concrete can be considered.

In cold weather, saturation of the concrete should only take place when the ambient temperature is going to be above 33 degrees Fahrenheit for 24 hours.

Coating Application

The crystalline waterproofing coating materials are mixed with water at a ratio of five parts powder to two parts water by volume for brush application, and five parts powder to three parts water by volume for spray application. The coverage rate is 1.25 to 1.5 pounds per square yard per coat. At this rate, a 60 pound pail of material will cover 360 to430 square feet, and a 50 pound bag will cover 300 to360 square feet of surface area.

Coatings can be applied by brush, hopper gun or specialized spray equipment. When using a standard six inch masonry brush, one person can mix and apply approximately 80 to100 square feet per hour. A hopper gun or texture gun requires  a two-person crew with one  mixing the material and the other  doing the spraying. The gun uses a 3/8  inch nozzle and operates at roughly 25 psi. A two-person crew can apply the coating at a rate of 400 to500 square feet per hour per coat.

Specialized spray equipment is operated with a three-person crew. At application rates of 1,200 to 1,500 square feet per hour per coat it is necessary to have all materials pre-measured in order to keep up with the spray equipment capacity. When using this type of equipment, the best procedure is to pre-measure the powder into at least five or six large buckets (five gallon pails) and pre-measure the water. This is done on the basis of five parts powder to three parts water by volume.

Sprayed on surface application Photo courtesy of Xypex

On vertical surfaces, the standard application procedure is to start at the top of the wall and work down. When using spray equipment, the first coat  should  be “back-brushed” using a 20 inch wide janitors broom with a soft bristle or a finisher’s broom. This helps ensure an even coverage rate and minimizes any run down of the coating.

When a second coat is specified, it needs to be applied no later than 48 hours after the first coat. Under normal conditions, the crystalline waterproofing coating will begin to set up in two to three hours and application of the second coat should be done at this point. If the first coat has dried out, it must be lightly sprayed with water prior to the application of the second coat. Failure to do so may result in lack of bond between the two coats.

When applying the coating materials to a large concrete structure, it is better to break the job up into manageable segments rather than try to complete large areas at one time. This is especially important when the weather is hot or windy.

Curing

Moist curing of the crystalline waterproofing system is essential for proper performance and is extremely important for two reasons:

First, crystalline waterproofing uses water as a diffusing medium which allows the reactive chemicals to transfer from the coating into the saturated concrete substrate. If adequate curing of the crystalline waterproofing does not take place, evaporation will first dry out the coating and then begin to pull moisture from out of the concrete. As the concrete substrate dries, further chemical transfer into the substrate will be compromised thus limiting the effectiveness of the application

Second, the crystalline waterproofing coating uses a sand and cement as a carrying agent for the active chemicals so curing is necessary for proper hardening of the coating and  adhesion to the concrete surface. Curing of the treatment is achieved either by spraying with water or through the use of a specialized evaporation retardant.

Curing the crystalline waterproofing coating should begin as soon as it has hardened sufficiently so as not to be damaged by a fine spray. Under normal conditions, the treatment will be ready for moist curing two to three hours after application. This is accomplished by misting with a fog spray of clean water at least three times a day for two to three days to prevent premature drying.

In warm climates or on hot windy days, increased curing will be required to keep the coating from drying out. This can be achieved by misting the coating five or six times per day for two to three days. Curing should be carried out if 70 percent of the coating is dry and 30 percent is still damp. In this case, the next fog spray should be done.

During the curing period, treated surfaces must be protected from damage by rain, frost, and freezing temperatures. If plastic sheeting is used for protection, it must be raised off the waterproofing coating to allow sufficient air circulation. The overall process of crystalline formation may take two to three weeks to reach full maturity.

Use of Crystalline Waterproofing as an Admixture for Concrete

Admix soluble bag Photo courtesy of Xypex

Adding crystalline waterproofing chemicals  to the concrete mix at the batch plant ensures that the crystalline formation occurs uniformly throughout the structure, rather than penetrating from the surface as would be the case with a coating application. Crystalline waterproofing admixture can reduce concrete shrinkage and increase compressive strength. When the crystalline chemicals are added directly to the concrete mix, the same chemical reactions take place but construction costs are significantly reduced because labor associated with a surface treatment application is eliminated and the construction schedule can be accelerated.

The crystalline waterproofing admixture is added to concrete at the time of batching. The sequence of procedures for addition will vary according to the type of batch plant operation and equipment. For most mixtures, the dosage rate is two to three percent, based on the Portland cement content.

Crystalline waterproofing admixtures are compatible with superplasticizers, air entraining agents and water reducers. In addition, fly ash, and other supplementary cementing materials may also be used with crystalline waterproofing to improve the performance of modern concrete mixes. When specifying crystalline waterproofing as an admixture, design professionals should verify that all elements in the concrete mix are compatible with each other.

Dry-Shake Application of Crystalline Waterproofing for New Slab Construction

Crystalline waterproofing can also be applied by the dry-shake application method, like floor hardeners to new slabs while under construction. This process requires the crystalline powder compound to be sprinkled onto the surface of slabs with the use of a mechanical spreader after concrete is placed, consolidated, and leveled. The powder is then worked into the surface of the slab during the normal finishing process with a power trowel. Crystalline waterproofing is also available combined with synthetic floor hardeners to both waterproof and harden floor slabs. Typical applications for the dry-shake application are basement slabs and warehouse floors.

Negative Side Waterproofing

Existing basements that are subject to water seepage through foundation walls and floors can be treated by the application of crystalline waterproofing on the negative side, or inside, of the structure. Coatings that depend on their adhesion to the surface will blister and peel when moisture seeping through the concrete dissolves soluble minerals and deposits them on the surface, under the coating, in the form of efflorescence, a white powdery substance that forms on the concrete surfaces. Because crystalline waterproofing penetrates into the concrete, plugging the pores beneath the surface, it does not depend on surface adhesion and will therefore not blister and peel off, like surface coatings. "I specify crystalline waterproofing on virtually every one of my projects as an admixture for the retaining side of walls where applied membranes cannot be used," says Mel Cole, FCSI, an architectural specifier in Soquel, California.

Vapor transmission through basement floors and walls is a common problem that may lead to damp, musty odors. Testing has shown that the application of crystalline waterproofing under these conditions can reduce vapor flows as much as 50 percent, which in most cases, will result in a drier environment.

Three Case Studies

The effective use of crystalline waterproofing technology products is illustrated by the following projects.

As an Admixture

The triple tower development designed by architect Hijjas Kasturi as a new headquarters  for Maybank in Kuala Lumpur, Malaysia involved the use of diaphragm wall construction incorporating a nine level underground parking garage. A crystalline technology admixture was selected to control of the heat of hydration, reduce shrinkage cracking, give the slab enduring 'self healing' capacity, waterproof the concrete, and increase strength and durability. The basement slab required approximately 24,000 cubic meters of concrete with crystalline waterproofing admixture. In September 1997, the initial pour of approximately 13,200 cubic meters was conducted over a 60-hour period. This project was the third largest continuous concrete pour conducted in the world, and the largest in Southeast Asia.

Excavation and diaphragm wall for Maybank Headquarters, in Kuala Lumpur, Malaysia. Architect: Hijjas Katsuri Photo courtesy of Xypex

As an Applied Product

For the National Aeronautics and Space Administration (NASA) Neutral Buoyancy Tank, a two-coat application of white crystalline waterproofing was applied to the 50,000 sq. ft. Lab Tank. This tank is used to train astronauts for space walks necessary during construction of the space station. The white crystalline waterproofing coating was chosen as a replacement for a white pool paint finish because of its longer life span and lower maintenance requirements.

NASA Neutral Buoyancy Tank Photo courtesy of NASA

As a Dry-Shake Application

The slabs of the a 110,000 sq. ft. distribution facility for Duracell in Cleveland, Tennessee, were waterproofed with a dry-shake application of crystalline waterproofing incorporating a floor hardener to increase the abrasion resistance. Due to the presence of a high water table and unstable ground conditions, there was a requirement to use a negative side waterproofing system which also had to be capable of handling fork lift traffic.

Shake Application on Fresh Concrete Slab Photo courtesy of Xypex

Other Applications

The material produced in dry powder from crystalline waterproofing products reduces shrinkage and cracking to a wide range of other concrete elements. Crystalline technology can improve the performance of bagged mortar mixes, stuccos, and concrete. The performance of precast concrete panels, as well as precast elements, such as pipes, box culverts, and manholes can also be enhanced.

Technical Glossary Admixtures – These are chemical ingredients that can be included in a concrete mix to enhance performance and modify characteristics. They include plasticizers, water reducers, set retarders and accelerators. Aggressive Chemicals – These include a wide range of chemicals that often come in contact with concrete. Examples include chlorides in coastal zones, sulfates often found in soils, and effluents in wastewater. Calcium Silicate Hydrate – A substance formed by the hydration of cement in concrete and is the material that binds aggregates together. Chlorides – Salts that will penetrate concrete structures carried by moisture in coastal zones or de-icing salts. Delamination – A process that occurs when a surface application of crystalline waterproofing does not adhere properly to a concrete surface. Usually due to improper surface preparation, inadequate wetting of the substrate or premature drying in hot weather. Efflorescence – A substance caused by the deposit of soluble salts and calcium on the negative side of concrete surfaces after they have been carried to the surface by moisture flow through the concrete. Green Concrete – Refers to concrete that has reached an initial or final set but is not yet fully cured. Concrete will remain green for 7 to 28 days. Heat of Hydration – The heat generated by the reaction (hydration) of Portland cement and water. In mass concrete pours, this reaction can generate very high temperatures. Ice is sometimes used in concrete mixes to reduce the heat produced by hydration. Plasticizers – Chemical ingredients used to improve the workability of concrete mixes without resorting to adding more water to the mix. Retarders - Set retarders are used in hot weather to delay the initial set of concrete mixes. Saturation Level – Refers to the amount of water in concrete, expressed as a percentage of the porosity or void space.

Conclusion

Although concrete may appear to be a simple product to put together, it requires a highly engineered approach. In an increasingly competitive design and construction environment, where high performance requirements, such as longer life cycles, more durable concrete, and value engineering are expected, careful consideration must be paid to basic requirements, such as the concrete, water, and cement ratio; cementing materials, and more sophisticated chemical admixtures.

Effective use of crystalline waterproofing technology will reduce the porosity and permeability of conventional concrete, and provide the high performance advantages and benefits that building owners and design professionals have come to rely upon in design and construction projects.

XYPEX Crystalline Concrete Waterproofing Penetrates and permanently plugs concrete’s pores and micro-cracks. Becomes an integral part of the structure. Will not deteriorate like coatings and membranes. Also available as an admixture for new concrete. Non-toxic. No VOC. www.xypex.com