Building Management Hawaii April/May - (Page 14)

3 Steps For A Solid Spalling Job How to prevent premature failure of concrete repairs. By Sean Dunham RestoRation A ll too often, concrete repairs fail quicker than they should. Have you ever noticed that the areas you repaired five years ago are once again a key problem for your building? While concrete repair and steel reinforcing construction are still evolving sciences, there are some simple steps that you and your contractor can take to minimize recurring problems. As part of the repair process, deteriorated concrete is removed and create a void that needs to be filled with new concrete. An uninformed or inexperienced repairer might be inclined to use the latest and greatest, off-the-shelf mortar promising “no cracking,” “flows like water” and “easy to finish.” However, what is being overlooked is that this particular “easy solution” might not be compatible with the adjacent older concrete. It is important to keep in mind that all concrete—depending on its composition—contracts and expands at different rates when it’s exposed to heat and moisture ... even the concrete mix that promises no cracks will do so over time. And, when it does crack, it will do so all along the perimeter where the newer concrete abuts against the older concrete. The cracks will allow water to penetrate to the rebar, causing the process of deterioration to start again. An equally critical concern is that the chemical electrical process that causes steel to rust can actually be accelerated by CRACKS a new repair patch. A new patch typically has higher alkalinity compared to the surrounding area. The higher alkalinity will actually create a cathode and push electrical current into the surrounding rebar. This process, in turn, produces an anode, causing rust to start. This phenomenon is known as the “ring effect,” whereby the concrete surrounding the new patch starts to deteriorate much quicker than other areas. At this point, you’re undoubtedly wondering how to avoid these problems. There are several easy steps you can take either during the contractor bidding or pre-selection interviewing process. • First, select a licensed contractor with the necessary expertise and track record to capitalize on their knowledge. • Second, pick the right concrete aggregate mix and top coating. Confirm with your contractor that the proposed aggregate mix ratio closely mimics the material adjacent Cost/Sq Ft Effective Reapply Membrane $6-$8 100% > 5-7 yrs Overlay $12-15 95% > 15 yrs Sealer $2.50 85-90% > 3-5 yrs Seal Cracks $6-7/lin ft Local April - May 2013 BMH REBAR CATHODE COMPARISON OF WATERPROOFING OPTIONS 14 CORROSION CURRENT FLOW > 5 yrs to the intended patch area. Also confirm with your contractor that the material meets the industry standards for your particular application: a) lack of shrinkage; b) elasticity; c) proper thermal coefficient; and d) tensile strength. Note, there is no need for greater compressive strength of the patch relative to the adjacent material. For example, an 8,000 psi patch is unnecessary when the rest of the building is 3,000 psi. • Third, select a coating material (painting or waterproofing with membranes) that can bridge hairline cracks. This coating will slow down the process of water and calcium ion intrusion. Without a protective coating, the reinforcing steel will corrode and cause hairline cracks to expand. While this approach may be ideal, it may not always be affordable for a large repair area. In this type of situation, another option is to saw-cut a groove along the perimeter of the repair. This groove is then filled with sealant that prevents water from entering where cracks may occur. Sean Dunham of Kawika’s Painting Inc. graduated from the University of Denver in 2010 with a degree in accounting and a minor in construction management. He helps Kawika’s with its bookkeeping, estimating and project management.

Table of Contents for the Digital Edition of Building Management Hawaii April/May

Lifts: Elevators & Escalators
Service Providers Leverage Cutting-Edge Technology
Time To Modernize?
Ready To Switch Gears?
Concrete: Restoration & Repairs
When To Test For Lead
3 Steps For A Solid Spalling Job
Deep Secrets
Phase The Work
Concrete Restoration
Tips On How To Reduce Spalling On Newer Buildings
The Difference Between Repair & Restoration
Equipment Breakdown Insurance
High-rise Hotspot
Toolbox Talk: How to choose the correct ladder for the job.
Industry News and Movers & Shakers
On Site: Saving Staff

Building Management Hawaii April/May