How to use crystalline waterproofing
Crystalline waterproofing and protection technology is sold in powder form and is typically used in four main ways:
- as an admixture that is added directly to the concrete mix during batching and used in precasting concrete products or for cast-in-place structures;
- as a cementitious coating that is applied to a cured concrete surface that is saturated, surface damp (SSD) such as foundation walls, slab floors, or water containing structures;
- as a repair mortar for patching or resurfacing deteriorated concrete such as often found in water and wastewater treatment facilities, dams, sea walls, and drainage structures; and
- as a dry-shake powder applied to green concrete and trowelled into the surface.
Crystalline waterproofing admixture
The addition of crystalline waterproofing to concrete at the time of batching provides the maximum benefits while eliminating the need for and cost of trained applicators and reducing any delays or application time, and providing structural benefits such as increased compressive strength. By adding crystalline waterproofing to the concrete mix at the batch plant, in the ready-mix truck, or in an onsite mixer also ensures the crystalline formation occurs uniformly throughout the structure rather than penetrating from the surface as would be the case with a surface application.
The admixture also reduces bleed water loss resulting in less plastic shrinkage and increased compressive strengths. For most mixtures the dosage rate is two to three per cent based on the Portland cement content.
Coating and repair applications
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 (Figure 3). The coverage rate is 1/2 to 2/3 kg (1.25 to 1.5 lb) per square yard per coat. At this rate a 27-kg (60-lb) pail of material will cover 33 to 40 m2 (360 to 430 sf) and a 23-kg (50-lb) bag will cover 28 to 33 m2 (300 to 360 sf) of surface area.
Crystalline waterproofing coatings can be applied by brush, hopper gun, or specialized spray equipment. When using a standard 152-mm (6-in.) masonry brush, one person can mix and apply approximately 7 to 9 m2 (80 to 100 sf) per hour per coat. A hopper gun or texture gun uses a two-person crew with one person mixing material and the second spraying. The gun uses a 9.5-mm (3/8-in.) nozzle and operates at roughly 172 kPa (25 psi). A two-person crew can apply the Xypex coating at a rate of 37 to 46 m2 (400 to 500 sf) per hour per coat.
Specialized spray equipment such as Quick Spray, Hy-Flex, or equivalent is operated with a three-person crew. At application rates of 111 to 139 m2 (1200 to 1500 sf) per hour per coat it is necessary to have all materials pre-measured in order to keep up with the spray equipment’s capacity. When using this type of equipment the best procedure is to pre-measure the powder into at least five or six large buckets (19-L [5-gal] pails) and pre-measure the water. This is done on the basis of five parts powder to three parts water by volume.
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 of material can be back-brushed using a 508-mm (20-in.) 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 one. Under normal conditions the crystalline waterproofing coating will begin to set up in two to three hours and application of the second coat can be done at this time. If the first coat has dried out it should be lightly moistened with water prior to the second coat being applied. Failure to do so may result in lack of bond between the two coats.
When applying the coating materials to a concrete structure it is better to break up the job into manageable segments rather than try to complete large areas at one time. This becomes even more critical when the weather is hot or windy.
All information listed in this section was submitted by Xypex Chemical Corp.
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fact or omission. The publisher nor CSC does not endorse any products featured in this article.