Secondary Containment: Start With the Chemical

A secondary containment area is the concrete basin around a chemical tank. It can sit empty for years, then one day it has to hold something aggressive for as long as cleanup takes. That is an unusual job for a coating, and it has to be specified in reverse.

Start with the chemical, not the concrete

Most coating decisions begin with the substrate. Containment begins with what is stored:

• What is the chemical?

• At what concentration?

• At what temperature?

• How long could it sit before cleanup: 72 hours, a week?

Sulfuric acid at 93 percent and sodium hydroxide at 50 percent are both common in containment, and they call for different chemistries. Areas that hold several chemicals need a system that survives the most aggressive one in the area, not the average.

Then the substrate

Once the chemical exposure is defined, the usual concrete questions follow: condition, cracks and joints, surface profile (CSP), moisture and thickness. Joints and moving cracks need flexible detailing. A rigid coating over a moving joint will crack and leak.

Containment systems are usually thick, 60 to 125 mils of novolac epoxy or vinyl ester, sometimes reinforced with fiberglass mat.

It is also a compliance item

EPA rules under 40 CFR require secondary containment to be impervious to the stored material. That puts the coating in a compliance role, not just a protective one.

What to check in your spec

• Attach the safety data sheet for every stored chemical, with concentration and temperature.

• State the required chemical resistance duration.

• Detail joints and cracks with a flexible treatment.

• Specify moisture testing and CSP before application.

Further reading: Tnemec Technical Bulletin 00-28, Avoiding Coating Failure Due to Cracking Concrete. Standards: 40 CFR 264.175, 40 CFR 112, NACE SP0892.

Talk to a consultant. Atlantic Coating Consultants helps owners, engineers and contractors in PA, NJ, DE, MD, DC, WV and OH with specification writing, on-site condition assessment, training, product recommendations and field support. Call 484-644-5303 or email atlantic@tnemec.com.