If the concrete slab is soft, can it be polished?

soft concreteIn my experience, ANY concrete slab can be polished. The limitations though to ANY concrete slab being polished is usually budget and time.

The general rule of thumb is that the softer the concrete is when you start the process, the more work and materials it will take to make it look good. More labor, more diamond tools, more chemical will all be required to make a soft slab look like a show-piece and all these extras cost time and money.

If the project can afford more of both, then it's no problem whatsoever to polish a soft slab.

Before considering undertaking a project that has soft concrete, clearly understand that:

  • Aggregate exposure cannot be controlled. The depth to which a slab must be ground depends on which amount of surface needs to be removed to expose strong concrete.
  • Color differences and linear marks may appear. During installation of the slab, some of the aggregates may have been pushed together differently leaving concentration and arrangement variation.
  • Porosity and micro-pitting will be prevalent. After the first 1/32" (.5mm) of concrete is removed, air holes will become more common and likely need to be filled.


Should a grout be installed on every polished concrete floor?

grouting concreteNo.

Grout is used to fill in small pits and porosity of the concrete slab's surface. Holes and crazing less than 2mm are perfect to be filled by the grouting material, but any holes or cracks larger than this should be treated with patching materials suited to that application.

Concrete slabs that have a good density and consolidation of the fine aggregates will have very little porosity or crazing and therefore would be redundant if a contractor were to apply a grout.

Make Side-by-Side Mock-ups to Know for Sure

The only way to know for sure if a slab will benefit from a grout coat will be to install a grout coat sample during mock-up phase and a sample that has no grout. Side-by-side and quantitative analysis (gloss meter) of the final results will tell if the grout coat helped or made no difference at all.


© 2016 Substrate Technology, Inc.

For any clarification of the above or to discuss your unique situation, please do not hesitate to contact STI or any of its authorized dealers for more help and advice. We are all here to supply solutions that save you time and make you money.

Is the size of the machine related to the quality of the polish?

PM-machine-bottomsIn the most general terms, no.

The size of the machine only has a bearing on how quickly the work can be done. For the quality of the polish, this has everything to do with the tools being of a given quality and matched to the physics of the machine.

For the purpose of our context, the physics of the machine would be items like weight, speed, surface area, wet, dry, etc. and the resultant effects on the tools. If someone says that a machine is too small to make a good polish, they may be accurate in that the polish does not look good, but that has more (if not all) to do with the abrasives being used.