Tim McAdoo of J.J.Haines Co., and I were recently having a conversation regarding the benefits of the proper temperature for the installation of floor covering. It quickly dawned on me: why just keep it between the two of us?

In today’s world of new construction it is a constant fight to control the temperature of the jobsite. Fast-track construction has pushed the flooring world backward as contractors face the daily battle of trying to obtain recommended job site conditions from the flooring, adhesive, and patching manufacturers. When the flooring contractor gets on the jobsite to install the flooring, the permanent windows and doors might not yet be installed, let alone the HVAC system be up and running.

Why is having the HVAC up and running so important? Let’s look at this from the ground on up. After the concrete is poured with a vapor retarder in place directly beneath the slab, without a controlled air space the drying time of the concrete can be greatly extended. If the air in the newly constructed building is saturated with moisture, the saturated air can hold very little excess moisture.

This will affect the evaporation of the mix water the newly poured concrete can get rid of and slow the drying process down. Drying and stabilizing the newly constructed buildings air space allows the concrete to get rid of the excess water mix water and begin the drying process.

We don’t put just-washed clothes out to dry on a damp/wet day, do we? Why? Because it won’t dry under those conditions…and neither will concrete or the other subfloors we install on.

Poured gypsum underlayments require – before, during and after installation – that the building interior be enclosed and maintained at a temperature above 50 degrees F and below 100 degrees F until structure and subfloor temperature are stabilized. The general contractor shall provide continuous ventilation and adequate heat to rapidly remove moisture from the area until the gypsum underlayment is dry. Again, if the air is saturated with moisture, it can absorb little to none of the moisture being emitted from the gypsum underlayment.

Moisture testing requires a controlled air space. The Calcium Chloride (ASTM F1869-98) states that the “site should be same temperature and humidity expected during normal use, but if not possible, then 75 + 10 degrees F and 50 + 10% relative humidity.”

The RH Probe (ASTM F2170-02) states: “Concrete slabs shall be at service temperature and air space above the floor slab shall be at service temperature and relative humidity for 48 hours prior to measuring concrete RH.”

Have you ever run a Calcium Chloride test and get an acceptable reading, then run an RH Probe test and get a very high reading? The reason for this is that the air is saturated and does not allow the slab to emit the extra water. This gives you a low reading on your Calcium Chloride test, which reads the amount of moisture being emitted from the concrete. The slab is retaining the extra water, which gives you a high RH Probe reading.

Patching compounds, self-leveling underlayments and adhesives also require a temperature range to be installed in. If it is cold and damp, it retards the drying and curing process of these products and does not allow them to dry and cure properly before the floor covering is installed.

Flooring is greatly affected by temperature. Too cold and it is stiff, can crack and break, and it can shrink when cold. Too warm, it is very soft and tends to grow. Having the building at service conditions is ideal for flooring installation. 40 degrees F is not service conditions. Acclimation is key to flooring products prior to installation. Let the products get used to the environment they will be installed in – 60 to 70 degrees F.

Having temporary heat in buildings can also affect the drying of the subfloors. Propane heat can add more moisture into the air. A 20-pound cylinder of propane adds 3 gallons of moisture to the air. Diesel and kerosene add almost a gallon-to-gallon burned. Temporary heat systems tend to heat the air, but the slab remains cold as the hot air rises. The relative humidity can remain high retarding the drying of the environment.

Having the HVAC up and running stabilizes the building environment and allows things to dry and cure properly.

That is why I think slab temperature is so important. It is the true temperature of the slab, not the ambient temperature of the room. There is no telling when the ambient temperature was turned on and left on. The tests we conduct that require the relative humidity of the slab to be a certain stage can be thrown off by temperature and humidity.

I have had experience with jobs using temporary heat and found the concrete dry near the heaters, but wet further away from the heaters. The contractor showed some disbelief, but the testing was accurate. In all directions the outcome was the same.

In certain areas they don’t permit the use of HVAC units until the occupancy. That is a shame; that policy does the flooring professional an injustice, and I think it ought to change.