Assessing Moisture in Concrete Subfloors

There are many avenues for moisture to enter a concrete slab, examples include:

  • Ground moisture can enter through capillary action or as water vapour
  • Groundwater might be present due to a high water table or poor drainage
  • High air humidity
  • High relative humidity in the environment
  • Leaking plumbing that goes through the slab

Installing any type of floor over concrete that isn’t sufficiently dry can be disastrous and cause short and long-term issues. For instance, for wood floors, slabs with excessive moisture can cause:

  • adhesive failure
  • wood warping or cupping
  • gaps
  • creaking
  • Floor coatings can suffer from blistering and delamination
  • Mould and mildew are also common problems

You cannot look at the surface of a concrete slab and know if it is sufficiently dry to install a floor, it must be tested! Learn more about moisture in subfloors from the ATFA. This is an excerpt from Assessing Concrete Moisture by the ATFA:

“A great proportion of timber floors are installed over concrete these days and it’s a vital element of your subfloor preparation to assess the concrete moisture. Your subfloor preparation is the key to a successful install. Having the correct moisture meters and following the correct procedures are highly important. Likewise, don’t assume that an old concrete slab is a dry slab.”

Click here to view the Information Sheet #43, July 2014, published by the ATFA which will aid in clearly understanding these essential procedures.