Minimum Grout Thickness
Minimum Grout Thickness
(OP)
I'm interested in others' opinions regarding a disagreement I've had with a coworker. This involves non-shrink grout for leveling/bearing beneath steel column base plates.
Most of the major non-shrink grout manufacturers, such as MasterFlow, FiveStar, etc, list a minimum application thickness, often 1". Despite how carefully I detail my design drawings, with relative frequency I have scenarios where the gap between the column base and the concrete foundation below needs reduction, sometimes down to 1/2", to result in the correct top-of-column elevation.
My coworker believes we should never vary from the manufacturer minimum for liability reasons. My thought is that if any aggregate in the mix is small (say, less than 1/3" the gap thickness), there should be no problem getting full coverage in the tight space, especially if the plan area of the base plate is not great. It would seem that a gap reduction does not compromise the structural integrity provided the grout achieves full coverage. The grout will still provide the bearing strength, and the manufacturer minimum most likely relates to ease or difficulty of workability. I contend that if you want extra reassurance, you can specify a small hole or two in the base plate to aid in verifying grout coverage. Despite the effort this takes, usually the contractor still prefers to go this route as opposed to some type of steel column modification.
This flexibility usually buys some good will with the contractor, though ultimately my main concern, and highest responsibility, is prudent engineering design that will last. I'm interested in others' opinions.
Most of the major non-shrink grout manufacturers, such as MasterFlow, FiveStar, etc, list a minimum application thickness, often 1". Despite how carefully I detail my design drawings, with relative frequency I have scenarios where the gap between the column base and the concrete foundation below needs reduction, sometimes down to 1/2", to result in the correct top-of-column elevation.
My coworker believes we should never vary from the manufacturer minimum for liability reasons. My thought is that if any aggregate in the mix is small (say, less than 1/3" the gap thickness), there should be no problem getting full coverage in the tight space, especially if the plan area of the base plate is not great. It would seem that a gap reduction does not compromise the structural integrity provided the grout achieves full coverage. The grout will still provide the bearing strength, and the manufacturer minimum most likely relates to ease or difficulty of workability. I contend that if you want extra reassurance, you can specify a small hole or two in the base plate to aid in verifying grout coverage. Despite the effort this takes, usually the contractor still prefers to go this route as opposed to some type of steel column modification.
This flexibility usually buys some good will with the contractor, though ultimately my main concern, and highest responsibility, is prudent engineering design that will last. I'm interested in others' opinions.






RE: Minimum Grout Thickness
RE: Minimum Grout Thickness
GROUT FOR BEARING PLATES AND BASE PLATES OR FOR DRYPACKING SHALL BE 'M-BED' AS MANUFACTURED BY SIKA, 'IN-PAKT PRE-MIX' AS MANUFACTURED BY CC CHEMICALS OF CANADA, OR APPD EQ. MIN THICKNESS [1" | 25MM]
FLOWABLE GROUT FOR BEARING PLATES, EQUIPMENT BASES AND TRANSFORMER BASES [SIKAGROUT 212 (1") | SIKAGROUT 300PT (1/8")] AS MANUFACTURED BY SIKA OR AN APPD EQ. PROVIDE CONFINEMENT AS REQD
RE: Minimum Grout Thickness
RE: Minimum Grout Thickness
RE: Minimum Grout Thickness
Dik
RE: Minimum Grout Thickness
If you deviate from their spec and something bad happens- it is on you
As long as you are willing to take liability for their product, do whatever you want.
RE: Minimum Grout Thickness
RE: Minimum Grout Thickness
RE: Minimum Grout Thickness
Our contractor ended up watering down the mix for flowability, pumping it into a steel formed edge under pressure, then providing us breaks for the final compressive strength.
Granted, this was a very strange application -- not a typical building base plate. So we were willing to accept an off the wall solution (and the contractor was willing to spend the extra cash required), as long as it could rationally calc out in the end.
You could also look at finger shims, perhaps? Or is that a long-term corrosion/durability concern?
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The name is a long story -- just call me Lo.