How long should concrete dry before fitting a laminate floor?

Concrete is a stable, convenient subfloor for laminate wood. But it's important to wait until the concrete is fully dry before installing your laminate. Floors that are still releasing moisture could cause serious damage to the finished floor. Learn how to tell when your concrete is ready to build on to prevent serious problems down the line.

A fully cured concrete floor isn't the same as one that's fully dry. Many people think that they can lay their laminate floors as soon as the cure time is up. While most 10 cm (4 inch) slabs take around 28 days to cure completely, they could release moisture for some time after this. Don't rely on a vapour barrier to keep water out of the flooring -- this material is meant to keep water from wicking up from the ground. Drying concrete may release more water than the vapour barrier can handle.

An improperly dried floor can seriously damage the laminate on top of it. Floors that are still releasing moisture can cause the wood laminate to warp and deform. They can also loosen glue and create mould issues under the laminate. Concrete is very alkaline, which tends to disrupt the adhesive action of many flooring glues, causing individual pieces to shift and pull up. Modern low-VOC adhesives are more sensitive to water and other adverse conditions than older materials, according to the National Ready Mixed Concrete Association.

According to the Ready-Mix Concrete Association, concrete can take six weeks to a full year to dry enough to accept flooring. Concrete dries faster in warm, dry conditions but has a higher chance of cracking or shrinking. It may require occasional misting.

Most homeowners aren't willing to wait a full year to install new flooring. To speed up drying, use dehumidifiers, fans and heaters. Measure the moisture in the slab, using a polythene sheet, commercial test strip or moisture meter before you install your flooring.