Can You Cover Aggregate With Carpet?

Definition of Aggregate

• Aggregate is a component of concrete and is composed of sand, crushed stone and gravel. Aggregate comes in two sizes or grades — fine and coarse — and is created by crushing boulders, quarried rock and large gravel; washing and cleaning the stone; and screening it for size. Recycled and crushed concrete is another source of aggregate. Sand used in aggregate is dug from a riverbed, lake, seabed or pit. Aggregate makes up 60 to 75 percent of a cement's total volume.

Concrete Versus Aggregate

• Alone, aggregate does not make a good surface for carpet to be installed on because of its coarse, rough and bumpy nature. Aggregate is not typically mixed with a binder; instead, it is placed loosely on the ground or within a border or edging material. Concrete, on the other hand, provides a stable, hard surface for carpet. Concrete floors are created by mixing aggregate with the correct proportions of cement and water, pouring the mixture into place, leveling the surface of the concrete and allowing it to harden.

Proper Adhesion

• Although carpet can certainly be placed over aggregate, without the right surface leveling and proper adhesion, you really are not installing carpet. The porous and rocky nature of the aggregate does not allow for a strong adhesive bond. Although some of the aggregate may adhere to the carpet backing, because the carpet is not being adhered to a solid surface means the carpet may bunch, twist and shift under foot. In contrast, properly cured and prepared concrete does provide a surface that carpet adhesive can bond to.

Recommended Floor Preparation

• The Carpet and Rug Institute recommends a clean and prepared concrete surface suitable for installation according to the carpet manufacturer's instructions. Holes, cracks and irregularities in the concrete should be repaired before installing the carpet, which will ensure a smooth and level feel once the carpet is installed. The CRI also recommends selecting a polymer-fortified patching or filler compound, as directed by the carpet manufacturer. Primer used over patched areas to cover porous or alkaline surfaces will need to be compatible with the adhesive used to lay the carpet. CRI recommends reading and following the American Society for Testing and Materials publication E1155-96, dated 2008, for information about test methods for determining overall floor flatness before laying carpet.