Cut Finish Times and Save $6 Per Square Foot by Rethinking Climate Control

Construction schedules continue to compress. Years ago projects would shut down for the winter and restart in the spring when weather conditions became more favorable. Now the average contract time has shrunk to 9-10 months from breaking ground to occupancy. Add in continuously tightening regulations and the resulting product changes, and extra expenses and delays quickly become the norm rather than the exception, especially when it comes to finish times.

Turnaround times for projects are shorter than ever.

The Expanded Shale, Clay, and Slate Institute (ESCSI) tried to discover why this is so common.

In a study titled CONCRETE DRYING TIMES FOR NORMAL WEIGHT AND LIGHTWEIGHT CONCRETE IN REAL WORLD APPLICATIONS - Bill Wolfe of the Norlite Corporation explains:

Since the 1980’s there have been several high profile cases of sick building syndrome. The Environmental Protection Agency (EPA) has identified indoor air pollution as one of the four greatest risks to human health. The World Health Organization estimates that 30% of new and remodeled buildings worldwide experience indoor air quality problems. In an effort to improve indoor air quality the EPA mandated that volatile organic compounds (VOC’s) be limited in flooring adhesives .This September 1999 action sent shock waves through the construction industry which prompted development of many new flooring adhesives that were low in VOC’s.

Increased health and safety restrictions can lead to compensating in other areas.

These low VOC adhesives are water based as compared to the previous solvent based adhesives. The interaction between substrate, adhesive, and flooring had little room for error and failures on all types of substrates and flooring types increased. Adhesives were much more susceptible to degradation from alkalinity. Flooring adhesive manufacturers came out with specific recommendations for substrate moisture and pH levels prior to placing the flooring down.

A study was designed to evaluate the interaction between the concrete substrate, flooring adhesive, and the flooring. The rate at which the concrete dried was a key component evaluated. To achieve the real word conditions, the assemblies used in this study were large, 12 feet by 12 feet, and use construction methods and materials found on jobsites. The assemblies used commercial corrugated decking and were constructed with a minimum of 10” of air space below the assemblies to allow air to circulate.

The conclusion outlines something we all unfortunately experience far too often:

In an effort to better understand the drying characteristics of real world concrete flooring assemblies, three comparable test assemblies were constructed. The assemblies were constructed as specified by commonly used 2 hour fire rated deck designs. These assemblies indicated that both lightweight and normal weight concrete assemblies dry at very similar rates. The study also indicated that the drying characteristics are heavily dependent upon the ambient conditions surrounding the slabs. All of the slabs fell below accepted moisture vapor emission rates for only a short period of time. This only occurred when the ambient conditions were suitable to allow the concrete, which was at equilibrium with its surroundings, to achieve the industry accepted values. Once the ambient conditions changed the concrete followed and raised above the accepted levels.

In order to eliminate VOCs from projects many contractors had to compromise their finish schedules.

The internal relative humidities that were measured in the normal weight and lightweight slabs never achieved the recommended values for floor covering placement. The readings followed the same trend lines mirroring the ambient conditions. The values reached their lowest point when the ambient conditions were the driest. After the ambient relative humidity increased, all of the concrete slabs followed.

The normal weight and lightweight slabs dried at the same rate and mirrored the ambient conditions in the study area. Unless the environment is controlled after concrete has reached equilibrium with its surroundings, the slabs may never reach the currently accepted values for flooring placement.

More buildings are facing fast track construction schedules to get early occupancy in the structure. We need to understand the drying characteristics of all flooring systems to make informed decisions concerning construction and occupancy schedules.

(Read the full article here)

Managing water-content in concrete can quickly become expensive.

The rule of thumb for our industry is that concrete requires 30 days of cure per inch for proper hydration. The study, however, lays out a convincing case for why that is unlikely to be enough time. Lower VOC content may make a structure safer, but it will also hurt finish times. Many choose to add an expensive admixture or just plan on mitigating all critical floors to stay on schedule. A solid plan for sure, but not without the significant cost of $5-6 per square foot of treatment.

There is, however, an easier, simpler remedy for your winter projects, though in an area you might not expect.

There are two main ways to handle humidity-related delays: with chemicals or with climate control.

Without changing the chemical makeup of the concrete, the right climate control system can greatly reduce finish times. An open flame source contributes moisture and an indirect fired unit incurs high fuel costs to operate. A hydronic system does neither. By recirculating the air within the structure, it reduces humidity rather than increasing it. For every 10 degrees above ambient conditions the system cuts humidity in half. Furthermore, it drastically cuts lowers costs by intelligently regulating energy consumption.

With the right temporary heat you can kill two birds with one stone: heat the structure and dry out concrete.

Controlling both temperature and the humidity with a hydronic system allows the concrete to cure at a safe normal rate. In most cases, this eliminates the need for mitigation. VOC regulations are here to stay, but that doesn't mean your projects have to suffer unexpected delays and expenses. Make the right climate control choices and find your budget and finish schedule back under control.