Polished Concrete Guide for slabs

This is intended to help create a best case scenario for a finished polished concrete floor. Overall a polished floor is dependent on proper placement and design mix.

90 % of owner complaints on polishing work are due to factors outside of the polishing contractor.  Concrete by nature is an industrial look that is never going to be perfect (relative) Most budgets restrict the amount of time and care required to get things right.

We should, however, attempt to achieve the best case scenario through communication.  This communication starts pre-construction.  Much of the discussion involves polished concrete protection.

Polished concrete should be specified by architect or engineers that include a proper design mix for concrete contractor pouring the slab.  This is especially important with integrally colored concrete surfaces.

Communication must start at a pre-construction meeting and follow the through-out project as many people that set foot on a job do not know the concrete will be the finished floor. Post signs. these are general guidelines, for design its best to consult with the ASCC for a more detailed polished concrete specification.

Polished concrete design mix guidelines

  • Higher PSI concrete is best. 3500 PSI or higher.
  • Stay away from lightweight concrete or aggregates
  • Avoid using Air-entrained concrete (pin holes)
  • Slump 4 ½- 5 in (high water-cement ratio makes a weak surface susceptible to spalling)
  • Admixtures should be verified with the polished contractor. (staining)
  • Avoid fly ash in mix design (makes the surface less glossy)

Slab placement

  • Min FF 50 (floor flatness) Laser screed for best results (humpy rolling floor will be present in high gloss polish)
  • Curing Agent. Use only dissipating cures. This cure the concrete, then break down and deteriorate traffic and UV light.
  • No acrylics, no sheets on 7 days damp curing. (Can leave a terrible pattern on the floor due to differential curing.)
  • Best to avoid walking on a slab,(boot marks after the slab is cut) keep finishing reserved for a ride-on helicopter, hand troweling will present a different tone and porosity then field (machine troweled) Also causes a difference in aggregate exposure.
  • Avoid burning cement cream by over troweling. (Leaves black marks)

Tilt-ups

  • Dayton Superior T-66 Tilt Brackets or any that avoids busting holes in concrete. (ugly patch marks in the finish)

Spills and contaminants of all trades and GC

HVAC, the framing of shell

  • Diaper all scissor lifts; avoid leaking hydraulic fluid on the floor. (+electricans)
  • Spilled energy drinks or coffee
  • Do not stack material directly after pour (30 days) Will cause differential cure stain
  • Do not leave metal (framing, HVAC) directly on the floor (will cause rust in the floor)
  • Permanente markers or paint on the floor

Plumbers and fire sprinkler trades

  • If trenching concrete to move a pipe or add plumbing after the pour, please consult polishing contractor. Avoid trenching through the center of the room, keep trench against the wall (as much as possible) even if it requires more pipe & concrete (change order OK, the owner would rather have trench on the side then an ugly trench through the middle of the room.
  • Don’t cut the black pipe on concrete (saw cut marks in the floor)
  • No rolling or storing black pipe directly on concrete (grease on concrete)

Electricians

  • Avoid trenching and keep electrical coming down from the ceiling whenever possible and trench along the wall if necessary.

Painters

  • Avoid cleaning spills with solvents (de-gloss)
  • Do not tape anything directly to the concrete slab

Polished concrete maintenance

  • It must be determined who is responsible for covering the concrete floor. This expense can run around 0.50 per SF plus labor. Do not tape anything directly to the floor.

Cleaning polished concrete

  • Do not use “clean sweep” (red sawdust and sand) which will de-gloss and impregnate oils in the floor.
  • Use only a PH neutral concrete cleaner to avoid etching the floor. For stained concrete floor cleaning products test a small area first.
  • Better to use automatic floor scrubbers then a pressure washer that can damage a floor

Maintaining polished concrete is pretty easy. For normal traffic:

  1. You should start with daily dust mopping. I prefer the use of a microfiber mop. They attract dust. Keeping the floor clean will prevent micro abrasion that leads to areas that dirt can stay.
  2. Next wet mopping the surface with clean water. Change water as it becomes dirty or you will leave streaks.
  3. To really clean this type of floor requires a cleaning solution that is neutral PH. There are plenty of eco-friendly cleaners that I don’t recommend. These may have orange citric acids which are bad for the surface.  We use Cement Shine Polished concrete cleaner for cleaning concrete.
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