Should the slab be scrubbed before or after racking goes in?

Before, for the heavy scrub. Racking install usually kicks up a second, lighter round of grit, so a quick re-scrub afterward is common. If the schedule only allows one scrub, do it before racking and ask the racking crew to sweep behind themselves.

Can you scrub a slab that has just been sealed or densified?

Once the product has cured per the manufacturer’s instructions, yes, with products safe for the finish. Scrubbing before cure can damage the finish. Ask the sealer applicator for the cure time and schedule the scrub after it.

Will scrubbing remove the white haze on a new slab?

If the haze is dust and light laitance, usually yes. If it is efflorescence or a curing-compound residue, it may need a specific chemistry or mechanical removal. A test area during the walkthrough answers it before the whole floor is quoted.

Post-Construction Concrete Floor Cleaning: A Checklist

A new concrete floor should be machine-scrubbed after the last dust-making trade and before racking, striping, or fixtures go in. An auto scrubber lifts drywall dust, slab grit, and light haze; cured adhesive, heavy mortar, and paint fields need mechanical removal. Timing and scope are what separate a slab that looks finished from one that still looks like a jobsite.

By Brandon Maddox, Maddox Surface

When in the schedule

The floor scrub belongs after the last trade that makes dust and before anything that makes the floor hard to reach. In practice that means:

Drywall finish, paint, and ceiling work are complete.
Overhead trades are out and their lifts are off the slab.
The slab has been dry-swept and the piles removed.
Racking, striping, fixtures, and FF&E have not gone in yet.

If racking install happens after the scrub, expect a second round of grit from the anchors and the forklifts. A lighter re-scrub after racking is common, and it is quoted below the first visit.

What a scrubber removes, and what it does not

An auto scrubber lifts:

Drywall and joint-compound dust, including what has been walked into the pores
Slab grit, sand, and the fine laitance a new floor sheds
Light mortar and grout haze from tile and masonry work
Joint-compound drips and small adhesive spots, with the right chemistry
General residue: footprints, coffee, sawdust film, the gray of a months-old jobsite

A scrubber does not lift:

Cured flooring adhesive fields
Heavy mortar or thinset buildup
Paint fields or heavy overspray
Curing-compound residue on some slabs
Anything that needs a surface profile for a coating

Those are mechanical-removal jobs, usually a grinder, and a floor contractor should say so during the walkthrough.

What a complete clean includes

A walkthrough with the superintendent to confirm what is left on the slab, which trades are still coming, and what the punch list means by “clean”
Anything that needs a grinder, named in the quote so nobody expects the scrubber to handle it
Pickup of the screws, wire, banding, and debris the final sweep left behind
A full-slab machine scrub, including the offices, restrooms, and corners, with the dirty water recovered
Treatment of mortar haze, joint-compound drips, and adhesive spots
A dry floor with no film, ready for the next crew, the striping, or the owner’s walkthrough

Common mistakes

Scrubbing too early. Paint and drywall work after the scrub put dust back on the slab, and the floor has to be scrubbed again.
Hosing the slab. Water without recovery pushes the dust into the joints and leaves a floor that dries hazy.
Acid on a new slab. Muriatic acid has no place in a post-construction clean.
Assuming the scrub preps for coatings. A coating needs the profile a grinder or shot-blaster leaves. A scrub before the coatings crew arrives removes the dust that would otherwise be ground into the slab; it does not replace the prep.
Skipping the dry pickup. Screws, wire, and dust piles left on the slab add time and cost to the scrub.

What to send a floor contractor for a quote

Square footage, the floor type (bare, sealed, densified, or coated), what trades have been on it, your turnover date, and a few photos of the worst areas. For most shells that is enough to quote from plans; occupied buildings and heavy-residue floors get a walkthrough so the number is right.

How Maddox handles it

For general contractors, construction managers, and incoming tenants in Houston, Maddox schedules post-construction floor cleaning to the turnover date. A turnover date that moves by a day or two is absorbed without re-quoting.