Moisture meters and humidistats are the most critical tools of the trade. If your installer does not have either of these tools, they are obviously not aware of the very important relationship between wood and moisture. Continuing with an install constitutes acceptance of the jobsite conditions by the installer.
The wood based subfloor must be within 2% moisture content of the hardwood flooring. The relative humidity of the home must be between 30% and 50% for solid hardwood and 35% and 55% for engineered before, during and after the install. A minimum of 10 moisture readings taken per 500 square feet no closer than 4’ apart recording the highest and lowest measurements.
There are many types and brands of moisture meters. Pin types penetrate into the wood to obtain the moisture reading. Pinless, non-destructive meters obtain moisture readings without penetrating the wood. The pinless meters give a reading which is not necessarily accurate, but offers an approximate reading of the moisture content. The more expensive meters have adjustable settings that are more accurate, but are affected by the glues in the subfloor. The only true method to measure the moisture content of wood is to weigh the piece of wood; dry it until there is no moisture left; weigh the now dry piece; subtract the dry weight from the green weight; and divide by the dry weight. MC = [(initial weight- oven dry weight)/oven dry weight] x 100% for example: 400 grams - 370 grams = 30 grams, divided by 370 grams x 100 = 8.1% moisture content.
Humidistats, or hygrometers, are readily available for purchase. Purchasing and using 2 units will keep accurate results. Take and record these measurements throughout the job.
Before testing a concrete slab it must be at least 45 days old. Use the Calcium Chloride test which is available at the Big Box stores. The moisture level using the calcium chloride must not exceed 3lb/1000 square feet.
The length of time it takes for concrete to cure can create delays on the construction site. A concrete slab or wall in perfect drying conditions with a large dehumidifier operating will dry at approximately 1” per month. Without those conditions the concrete may only dry ¼” per month. Concrete cures by hydration when water reacts with the cement powder, giving concrete its strength. However, the mix always contains more water than the hydration reaction requires. This has become more prevalent with the use of lightweight aggregate, which tends to retain moisture. In typical floor slabs, there could be up to 50 gallons of extra water in every cubic yard of the pour. Using a dehumidifier with constant air flow over the slab surface will speed up the process. When the slab is dry it is recommended to use a concrete sealer or a recommended adhesive with moisture barrier.
Radiant heating in concrete slabs must be turned on to a minimal temperature of 22o C, 7 days prior, in order to drive out residual moisture before wood flooring can be installed.
Since there are many types of radiant heating systems, please contact us for more detailed information for your project at firstname.lastname@example.org, or see chapter 12.