Specs matter

Managing the end at the beginning

Chris Maskell

Yet another construction manager called me recently, distressed and looking for answers. He shared the details of his situation: Fifty thousand square feet of 5-inch-thick concrete slab poured eight months previously, half of which was on grade, the rest poured into second floor Q -Deck (steel pan).

Moisture test results confirmed a 99 percent Relative Humidity (RH) when tested using the In-Situ Probe Test according to ASTM F-2170. The QDeck space, lower at 90 percent which was unusual since a slab poured into a steel pan should take much longer to dry.

The adhesive and floor covering manufacturers’ installation guidelines called for test results to confirm 75 percent RH.

With deadline looming, now what?

The problem is usually a combination of issues. This particular case was no different. Now, with everyone paying attention, the problem appeared to have stemmed from the instructions set at the beginning of the whole process in the written specifications.

These were followed to the word, which ultimately guided process on site as they should. But in this case, that meant an overly smooth, power-troweled concrete surface was delivered. Now, the general contractor was left with a terrible problem. With an overly tight dense concrete surface, the water ingredient used in the concrete mix could not escape as it would normally.

With time running out, spare budget long spent to afford any kind of Plan B, what is the general contractor to do?

Kill five birds with one stone

It’s scenarios like this that we are all trying to avoid. No one wants to see the construction team go through project hell trying to figure something like this out. The best thing to do is to be proactive. That means working with the spec writing community wherever possible so that they have access to correct language that drives correct actions on site. We also know that concrete slabs deflect, shrink and change shape, and therefore some measure of Hydraulic Cement Underlayment (topping material) will just about always be required.

• NFCA installation guidelines specified on every project. These assign responsibility to the correct party for the provision of acceptable conditions, including a flat surface, to the floor covering trade.
• Replace (or add quantifiable terms to) typically used language in the specifications such as ‘Provide a smooth and un-burnished surface, free of ridges’, with quantifiable terms such as ‘General Contractor to provide a Concrete Surface Profile of 3’ and surface porosity according to ASTM F-3191, or as required by the next scheduled product before placing any Hydraulic Cement Underlayment.
• Replace steel blades on power troweling machines with plastic blades designed to build the desired (or close to) profile into the concrete surface at time of curing.

The result:
• The slab dries faster as a profiled slab has more surface area for vapour emissions to escape.
• No shot blasting to profile an overly smooth surface.
• Conversation starts early around the obvious, such as ‘all windows installed and main heat on’ prior to any flooring products being delivered to site.
• Thoroughly dry concrete, needed by the floor covering trade, will more likely be provided.
• Porosity automatically built in for mechanical bond of adhesives.
• Overall less chance of slab rejection.

It should be noted that no one solution will fit all scenarios and that in some cases shot blasting is likely a necessary process prior to floor covering installation just to remove surface contaminants and months of surface use and abuse from general construction activity.

The National Floor Covering Association (NFCA) promotes industry standards for resilient, carpet, hardwood, laminate, cork and bamboo floor covering installations.

Speak Your Mind