Concrete Slab Evaluation
The concrete slab evaluation process must include the condition of the surface, the flatness of the slab, whether there will be another flooring material removed, whether water be used to wet cut the floor if needed, and how much concrete repair is required, to name a few. All of these will dramatically impact the outcome.
Concrete Flatness
If the owner does not want to see any coarse aggregate after it has been polished, the floor must be flat, with minimal undulation (rolling hills and valleys). If the floor is bumpy, the grinder will cut the highs (hills) and miss the lows at first. When the floor is uniformly cut, the areas where the highs were, will show larger aggregate, and the lows will show fine aggregate. This floor is not a good candidate to not show any large aggregate.
The flatness of a new floor is measured within 72 hours after it has been placed. This is when the concrete has taken its initial set, is stable, and dimensionally not changing. There are several ways flatness is measured. The values obtained from each method will be very similar. Floor flatness is measured using FF/FL (floor flatness/floor levelness) values. Typical FF and FL values generally fall between 12 and 45. There are four classifications of floor flatness based on FF/FL.
- FF 25/FL 20 – moderately flat
- FF 35/FL 25 – flat
- FF 45/FL 35 – very flat
- FF 60/FL 40 – super flat
The ideal flatness values to obtain a polished floor with minimal to no large aggregate shown will fall in the Very Flat category. All the categories can be polished but the amount of aggregate exposure will be dictated by the floor flatness. The flatter the floor, the more even the aggregate exposure will be able to be obtained.
When you have an old, existing floor, you can do a simple test to check how bumpy the floor is. Take a 10’ to 16’ straight edge and lay it on the floor in several areas. There will be voids between the straight edge and the floor. If these voids are less than a ¼”, you have a moderately flat floor. This will give an idea of what you must work with.
Always check the joints for curling. Curling is when the joint shoulders are higher than the area 2’ to the sides of the joint. Every time the joint is a bit higher, you will observe exposed aggregate down the joint once polished. There is very little you can do to eliminate this.
Concrete Repair
As you walk the slab checking the flatness, you will have an opportunity to determine if there will be a need for some concrete repair. Cracks and spalls will be amplified once the floor has been polished. Unless you are skilled at matching color and aggregate when performing the repair, these areas could be a concern to the client. This will need to be discussed with them and then determine how to approach each defect.
Hand Work
With most projects, there will be some hand work required. Edges, drains, partitions, and pipe protrusions all need to be addressed. Do they want the floor polished wall to wall, or will they accept coated, solid-color borders? Borders are much easier to install for someone with less experience than hand-polishing edges.
Tile Ghosting
Tile ghosting will show up when you remove VCT (vinyl composite tile) from a floor that is to be polished. There are several theories why ghost lines show up, no matter why they are there, you will not be able to get rid of them once you have them. If you are doing a pre-bid walk-through and there is VCT that needs to be removed, you must explain to the client there could be ghost lines from the tile that will show after the floor has been polished. We suggest printing off images of ghost lines and presenting them to the client before starting so there are no surprises.
Job Site Evaluation
Walking the floor is important but walking around the site can also be beneficial. Access to the building, access to the floor, available power, water, and dumpster location - All of these will impact your job and efficiency.
Floor Access
Access to the floor might sound trivial but if you can’t get your grinder on the floor, it can’t polish. What size grinder do you need to perform the work, and can it be brought into the area? The polishing area might be on the 3rd floor with no elevator or crane to swing the grinder in. At that point using a grinder that can be taken apart and safely carried up the stairs is the only option.
Building Access
If it is new construction, is the parking lot paved? Is there a usable road going into the site? Can you park outside the building once unloaded? Is there a safe area to leave a trailer or does it need to be removed every night during the installation?
House Power
The first question concerning power is who is responsible for supplying it. Industrial facilities typically will have what is needed but it must be determined before you show up with the equipment. Not all commercial or residential facilities will have the power requirements needed to run big grinders and vacs. A portable generator might need to be brought onsite to provide enough power. If that’s the case, where can you park the generator?
If you are using a propane grinder, power usually is a nonconcern. Check with the client to make sure propane is allowed in their facility. Some cities do not allow propane equipment to be on job sites.
Dumpster Location
If you are dry polishing, you will be generating cement dust. This needs to be removed from the site by you or the client. Having a dumpster near the polishing area will save you time and effort. If you are on an old, soft concrete slab, there will be a considerable amount of dust generated.
Water
Even if you decide to polish dry, having water to fill your auto-scrubber is essential. The auto-scrubber will be used to clean the floor between cuts. It’s not going to be as much water as there will be if wet grinding, but you still need access to water.
Conclusion
Although many projects have been bid sight unseen, you should now have a sense that there is much more to a project than show up and grind. Having input from the client before you start will minimize future issues that could arise. Aggregate exposure allowed, defect repairs, getting the equipment in, and where to dispose of the debris, are concerns not only to your client but to you as the contractor as well.
DiamaPro Systems has concrete preparation equipment, tooling, accessories, and most important of all, expertise to ensure your floor evaluation is accurate and the surface preparation job is efficient. Contact us for information or support – our products are available for purchase at Niagara Machine.