If you talk to enough people on the subject of site preparation and flooring issues eventually the question of fly ash concrete and bond failure will crop up. I’ve heard the question from all corners of the industry and there are few definitive answers.
As a result, many commercial flooring contractors are not warrantying their installations over such concrete. Instead, they add a disclaimer in their terms of contract stating that no installation warranty is offered over substrates that contain a greater than 20% fly ash content. Yes, the flooring product warranty will be in place but that’s no good if the adhesive fails.
SO WHAT’S THE PROBLEM?
1. The general consensus is that concrete, with a high fly ash content, results in a denser, less porous product, which in turn interferes with the flooring adhesive and/or leveling compound’s ability to bond. Hard trowelling of the concrete surface to a super smooth finish exacerbates the problem.
2. Collectively, manufacturers have not come out with a clear position on the subject. Is there a bonding problem? If there is, is it slab density related or some other ingredient in the concrete effecting bond? Moisture testing? Should Calcium Chloride (MVER) tests be recommended over this type of concrete? Answer, not sure... many manufacturers call for both RH Probe and Calcium Chloride tests to be taken simultaneously.
WHY IS FLY ASH USED?
Fly ash as an additive in concrete has been around for a long time and will continue to be used for a number of reasons: 1. It helps produce a stronger, more durable concrete product that is less permeable.
2. It aids in the reduction of efflorescence, a white chalky substance that develops on concrete surfaces.
3. It’s use in concrete is LEED driven because:
As a result, many commercial flooring contractors are not warrantying their installations over such concrete. Instead, they add a disclaimer in their terms of contract stating that no installation warranty is offered over substrates that contain a greater than 20% fly ash content. Yes, the flooring product warranty will be in place but that’s no good if the adhesive fails.
SO WHAT’S THE PROBLEM?
1. The general consensus is that concrete, with a high fly ash content, results in a denser, less porous product, which in turn interferes with the flooring adhesive and/or leveling compound’s ability to bond. Hard trowelling of the concrete surface to a super smooth finish exacerbates the problem.
2. Collectively, manufacturers have not come out with a clear position on the subject. Is there a bonding problem? If there is, is it slab density related or some other ingredient in the concrete effecting bond? Moisture testing? Should Calcium Chloride (MVER) tests be recommended over this type of concrete? Answer, not sure... many manufacturers call for both RH Probe and Calcium Chloride tests to be taken simultaneously.
WHY IS FLY ASH USED?
Fly ash as an additive in concrete has been around for a long time and will continue to be used for a number of reasons: 1. It helps produce a stronger, more durable concrete product that is less permeable.
2. It aids in the reduction of efflorescence, a white chalky substance that develops on concrete surfaces.
3. It’s use in concrete is LEED driven because:
- It reduces the energy intensive use of Portland Cement.
- Fly ash is a by-product of burning coal and its use in concrete is one way to use this waste product up.
The reality is that fly ash as an ingredient in concrete will likely increase over time as LEED projects continue to grow in number. So what do you do when faced with an instal- lation over this type of substrate?
- As the flooring contractor you should understand the concrete surface you are installing over before proceeding. Ask questions about the concrete mix.
- Consult the adhesive / leveler manufacturer before you proceed. Fully understand the limitations of adhesive or leveler that is expected to bond to the concrete surface.
- Understand your options regarding possible product upgrades that work better with concrete of this type.
- Communicate in writing with the general contractor and building owner regarding voided warranties before you proceed because the industry standard states ‘Installation implies acceptance of conditions’.
5. Shot blast or scarify the concrete surface to increase mechanical bond. Concrete specifications should call for a broom or textured finish of the slab. This work is the responsibility of the general contractor.
6. Take a bond (or pull) test before proceeding. Document the test by video recording it.
7. If you have a choice then choose the RH In-Situ probe moisture test (ASTM F-2170) over the Anhydrous Calcium Chloride (MVER) test (ASTM F-1869). Moisture Vapor Emission Rates (MVER) in fly ash concrete are reduced because the concrete product is denser. This increases the risk that an acceptable MVER will be recorded at the surface while excess moisture is still present deeper in the slab. When an MVER meets the manufacturer’s warranty requirements yet fails to reveal the true moisture content of the concrete at deeper levels, the floor installation will be given the go-ahead risking problems later on. Note that moisture testing is the responsibility of the general contractor.
For clarity on this issue, the industry requires manufacturers to lead the way and replace opinion with scientific, test-based fact. With this done the end user will stand a better chance of receiving their new floor with product and installation warranties intact.
6. Take a bond (or pull) test before proceeding. Document the test by video recording it.
7. If you have a choice then choose the RH In-Situ probe moisture test (ASTM F-2170) over the Anhydrous Calcium Chloride (MVER) test (ASTM F-1869). Moisture Vapor Emission Rates (MVER) in fly ash concrete are reduced because the concrete product is denser. This increases the risk that an acceptable MVER will be recorded at the surface while excess moisture is still present deeper in the slab. When an MVER meets the manufacturer’s warranty requirements yet fails to reveal the true moisture content of the concrete at deeper levels, the floor installation will be given the go-ahead risking problems later on. Note that moisture testing is the responsibility of the general contractor.
For clarity on this issue, the industry requires manufacturers to lead the way and replace opinion with scientific, test-based fact. With this done the end user will stand a better chance of receiving their new floor with product and installation warranties intact.
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