Maxx Minutes Blog

A New Approach to High-Rise Concrete Construction

Markets across the country are experiencing an uptick in high-rise concrete construction starts. These projects are going up fast, some at the rate of one floor every two days. This rigorous construction schedule puts a tremendous amount of pressure on concrete contractors because of the necessity of meeting specific floor flatness criteria.

Adding to the challenge, concrete and floor contractors have battled for years over the different floor flatness criteria found in Division 03 and Division 09.  Flatness is measured by the concrete contractor within 72 hours of the pour. Meanwhile the flooring contractor may not be able to install the floor goods for weeks or months in order to allow the concrete to dry adequately. By then the concrete has deflected and curled, often to the point where hard surface floor goods cannot be installed. This causes further delay in the construction cycle, as the floors need to be brought to the necessary floor flatness criteria.  In order to keep projects on track, or even accelerate the construction schedule, contractors across North America are turning to a relatively new system.

In the new system, the concrete contractor is installing the concrete below the specified height. Instead of finishing the concrete, it is left at a rough screed finish.  In as little as five days, a surface-applied moisture vapor barrier is installed over the new concrete, preventing the moisture in the still-curing concrete from migrating to the top of the slab.  A self-leveling underlayment is then installed over the moisture vapor barrier, resulting in a moisture vapor-protected flat floor. 

A Success Story for All Parties…

Moisture is released from a concrete slab over weeks or months and using mechanical dehumidification to accelerate the dry time can cause cracking, curling, and physical property loss.  Installation of a surface applied moisture vapor barrier blocks the movement of moisture vapor through to the top of the slab where it would otherwise collect. This eliminates the possibility of floor good failures due to moisture vapor emissions and speeds up project timelines by allowing floor goods to be installed sooner. Plus, since moisture is prevented from moving through the concrete, adding a surface applied moisture vapor barrier limits the warping and curling of the slab. It also addresses moisture concerns early in the construction process, providing peace of mind that future delays due to moisture emissions have been avoided.

A self-leveling underlayment can be installed from a featheredge to several inches deep, allowing the new system to correct any undulations that might have developed in the concrete. This flat, level substrate provides an ideal surface for most finished floor goods. Concrete contractors also appreciate the system because they can rough screed the concrete and move on to the next floor. This saves time and money by eliminating the need for laser screed and power trowel equipment as well as skilled concrete finishers. And since the self-leveling underlayment is fast-drying, this system allows floor goods to be installed weeks before traditional high-rise concrete construction, resulting in overall project cost savings.

The expense of the new and old systems are comparable, however the new system provides greater flexibility by giving other trades access to the slab sooner, significantly speeding up the construction schedule.  While not essential to the system, a surface applied moisture vapor barrier is strongly recommended due to the prevalence of moisture sensitive adhesives and flooring. It is common for manufacturers to offer both the moisture vapor barrier and self-leveling underlayment. Such a system should offer the benefit of being covered by one warranty; this should be confirmed prior to proceeding with any system.