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"Dry" Cast Stone and "Wet" Precast Concrete
Which product to use on hardscape furnishings?

Dry Cast Stone and Wet Precast Concrete

Deficiencies in the manufacturing process of dry cast stone products make them less ideal for hardscape designs.

The answer is "Precast," and it has to do with the manufacturing process and mix designs. Dry cast stone (DCS) is a mixture of sand and cement and has a very low water content - zero slump. This mixture is a lot like the sand you would use on the beach to build a sandcastle. DCS is manufactured from zero slump concrete using the Vibrant Dry Tamp (VDT) casting method. The VDT method uses a ramming tool against an earth moist, zero-slump concrete, against a rigid mold in layers until it is densely compacted. Since these layers are compacted together it results in entrapped air which creates capillaries or voids in the mix. These voids create pockets of bad air that lessen the DCS mix integrity and results in absorption of water, which causes cracking during freeze-thaw cycles.

DCS mix, by design, has high compressive strength, up to 10,000 PSI. However, this high compressive strength makes it susceptible to chipping or breaking during installation. DCS cannot be reinforced with rebar or steel mesh, which is typical of wet precast concrete (WPC). DCS is only available in a limestone finish since the mix is only sand and cement. Therefore, DCS is not an ideal stone product for hardscape designs because of these deficiencies in the mix due to manufacturing. Color can vary by +/- 30% in hue in DCS. The product is used in hardscape designs but should only be used on small details like window surrounds, water tables, etc.

Dry Cast Stone and Wet Precast Concrete

Wet precast concrete (WPC) is a mixture of sand, cement, aggregates and admixtures. The WPC mix is manufactured from measurable slump concrete. The wet casting method for production of WPC uses a mix of moist concrete which is poured into a mold and vibrated until it is densely consolidated. Since the mix is wet it adheres easily to the rebar or steel mesh, which adds strength and durability. WPC's properties are more effectively controlled. Properties such as air entrainment can be controlled for product that is needed in higher thermal change environments. WPC can be used for all types of hardscape furnishings both large and small. Planters, wall copings, fountains, bollards, benches, countertops, and stair treads are just some products ideal for WPC.

Designers also enjoy the variety of finishes which are available. WPC is available in a light sandblast finish (similar to a sidewalk), medium or heavy sandblast (exposes more of the cast in aggregate), polished finishes for countertops, benches, and table tops, and acid wash finish texture. WPC also provides the ability for custom colored aggregates to look like granite, which often is value engineered out of designs due to high costs.

So, select precast concrete for your hardscape furnishing designs. You'll be glad you did and will provide your project with the best material to keep your designs looking great for many years to come.

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October 16, 2019, 1:35 pm PDT

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