Overview
Overview
Specifying proper floor prep starts at understanding what you have to start with and what you want to finish with. DMA Floors has been properly preparing floors to receive floor covering for as long as we have been installing floors. In over 30 years of installing floors and through extensive training we have developed best practices for proper preparation. We have the knowledge and with our grinders and shot blasters we have the equipment to do it right for you.
Slab Curing and Finishing
Curing and Finishing
If you are specifying a floor on a new project, you need to consider your slab finishing and curing methods. We were able to save a customer over 25% on a job by changing the slab finishing and curing methods to a moisture cure and light trowelled finish thereby eliminating a great deal of expensive floor prep.Boilerplate slab specifications do not take into account finishes and when left up to the concrete contractor substantial floor prep expense may be the result. It is important to consider what you plan on putting over the slab, but most floorcovering adhesive and resinous system manufacturers recommend avoiding curing compounds and over trowelling the slab.
Mix Design
Mix Design
Some lightweight aggregates are very absorbent and can retain significant moisture during curing. This increase the amount of time needed for the floor to adequately dry and contribute to Alkali-Silica reaction (which can cause spalling and structural damage) so lightweight aggregates should be selected carefully. Some lightweight concrete and gypsum based concretes can also be incompatible with certain systems so these should be selected carefully and with consideration of planned finishes.
Water/Cement Ratios
Water/Cement Ratios
Cement requires a .25 water/cement ratio for the hydration reaction. A .42 to .5 will typically provide adequate workability for placement. Ratios above .5 can drastically increase drying times, weaken the concrete and increase potential moisture vapor issues.
Water/Cement Ratio |
Gallons/yd |
Gallons/1000 Sqft |
Water of Convenience/1000 Sqft |
0.4 |
23 |
283 |
111 |
0.5 |
28 |
344 |
172 |
0.6 |
34 |
418 |
246 |
0.7 |
39 |
480 |
308 |
0.8 |
45 |
554 |
382 |
0.9 |
51 |
627 |
455 |
1.0 |
56 |
689 |
517 |
After you have taken the .25 water mix required for hydration into consideration, a .6 water/cement ratio a 1000 sqft slab would need to shed a percentage of the remaining 246 gallons of water to “dry” to the point where it meets the RH requirements for floor installation.
Floor Flatness
Floor Flatness
Historically we have been happy with specifying 3/16” in 10’, but what does that really tell you? Standard methods of determining floor flatness ignore the frequency of the troughs and peaks. This inconsistency can have an impact on the appearance of the floor and may increase your costs by requiring extensive patching to achieve a smooth appearance. If polishing concrete, it may make your slab unsuitable for polishing without an overlay. The American Concrete Institute recommends testing floor flatness in accordance with ASTM E1155 (link) and specifying the level of flatness required for your specified finish. There is some ambiguity as to when the flatness should be tested (some suggest testing as soon as you can walk on the floor,) but testing will provide the most accurate readings after the floor has cured. Waiting until cure allows you to account for slab curl during curing, which will affect finishes.
Existing Conditions
Existing Conditions
What is on the floor (sealers, glues, mortars, epoxies, etc.) can have a monumental financial impact on the project if proper procedures are not utilized to abate the current conditions. While some of these can be easily removed, some may require shaving the slab and removal of significant material. Whether you need to remove ¼” of epoxy or simply a cure and seal there is still a financial impact on the project that needs to be considered and specified. It is important as well to know what may lie under current finishes that are to be removed. We worked with a general contractor on a small project that required a polished concrete finish, but as they removed the carpet they discovered that the floor was well beyond any conditions that could be polished and would require an overlay.