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I have a electronics assembly company, and we run two assembly lines. They consist of several machines, with the heaviest being around 4000lbs, on 6 metal casters. We currently have the line on a concrete slab, inside a large converted warehouse.

The concrete slab is badly spalled, and apparently didn't have a vapor barrier when originally poured. If we leave anything heavy on the floor (cardboard box), it will be dripping with water the next day. We maintain a humidity level of 45%, which probably brings more water up also. We are located in Florida, so have a high water table.

The landlord is willing to work with us to fix this issue, and a contractor recommended we do a vapor barrier on the slab, then a grid of 2x4's, then tongue and groove plywood. On the plywood we would install ESD safe vinyl tiles. They said this is common in gyms and dance studio's. They use rubber strips under the 2x4's to help dampen noise and vibration.

It's hard to find information on this method, is this suitable for this amount of weight, in an industrial environment? I really don't see of many other options if this isn't acceptable to do. I would assume we would do the 2x4's either 6" or 12" on center.

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The use in gyms and dance studios is not a good reference. Those floors are designed for dynamic impact loads from people dropping gym equipment and dancers jumping around. They need to be able to absorb the impact energy by deflecting under load, and therefore the plywood is introduced as a "soft" element which is able to bend with relative ease so the dancers don't hurt their knees and ankles when landing. The distance between the 2x4's is not just a maximum distance but also a minimum distance to prevent the floor from becoming too stiff.

This is generally not the best way to design floors for heavy machinery especially if the machinery is able to induce vibrations in the underlying structure. Then it will be dancing around. But assuming the machinery won't be moved around all that much, it is an option to create hardpoints to support it — supports that don't rely on the stiffness of the plywood. And by reducing the distance between the 2x4's and increasing the thickness of the plywood, it is possible to design it for fairly large point loads. So it is possible to do it right, but don't accept a design that has been copy-pasted from a gym or dance studio. Demand that is redesigned for the weight as well as any vibrations of your machinery and it should be okay.

For this type of use, I would normally recommend an epoxy-based coating applied directly on the concrete, but in your case it may be impossible to get the concrete dry enough for the coating to stick properly. So maybe a bitumen-based membrane on top of the concrete, a concrete screed on top of the membrane to protect it and then an epoxy-based coating on top of the screed could be an alternative approach capable of supporting very heavy machinery.

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  • $\begingroup$ See ASTM D2718 for plywood rolling shear test. Vinyl tiles hate rolling loads even moreso than plywood. +1 for fix floor then epoxy. (Or move). $\endgroup$
    – Phil Sweet
    Jan 19 '20 at 22:30
  • $\begingroup$ Thanks guys. Actually had a acquaintance come out today who is a structural PE, and mimic'd your comment. Going to try and find a solution for the water, and then decide from there. $\endgroup$ Jan 20 '20 at 0:44

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