Most polished concrete specs require that a certain system be used. They require that only certain products can be used and that only certain companies can install these products. Ours is different.
Most polished concrete specs have no measurable standards. They specify an arbitrary grit level or call for a certain sheen (high gloss, matte finish, etc.). But when the floor doesn’t meet the anticipated expectations, architects and owners have no recourse. Ours is different.
Our spec is designed to act as a template for specifying polished concrete on your project without eliminating competition. It is not limited to any particular system, products, or installers, and is fully customizable to fit the needs of your project. When utilized properly, it guarantees that you will get the floor you desire. It will look like the pictures. And that is guaranteed by objective measurable tests, not someone’s opinion.
Modifying the Spec for Your Project
First things first. Have you downloaded our master spec? If not, click here to download. Particularly if you do not have much experience specifying polished concrete, these guidelines will be easier to understand if you follow along in the spec.
As an architect you would probably agree that the most important aspect of spec writing is having measurable standards. Take a standard concrete specification, for instance. It typically includes a minimum PSI requirement, which is measurable with a strength compression test, and floor flatness and levelness requirements, which are measurable with a floor profilometer. If there is ever a question with the finished product, the architect and/or owner always have these tests to rely on for contractor accountability and recourse, if necessary. Concrete polishing is no different.
Most concrete polishing specifications require that a contractor start at a certain grit level and end at a certain grit level. The idea behind this method is that the starting grit level should indicate how much material is to be removed initially, typically to achieve a certain aggregate exposure. The ending grit level is used to achieve a certain gloss level. The problem with this method: not all polishing machines, polishing tooling, and polishing contractors are created equal. One contractor’s 16 grit diamond tool can vary greatly from another. If a contractor runs a large, heavy polishing machine very slowly over the floor with a 50 grit diamond, he is going to remove much more material than a contractor who runs a light machine very quickly over the floor with that same diamond. This method is not measurable, nor is there any way to hold a contractor accountable. The solution: two measurable standards.
Gloss Level: ASTM D523 - Standard Test Method for Specular Gloss
Aggregate Exposure: Simple measurement done with a standard ruler
Both of these measurements will be discussed in more detail, but let’s start at the beginning of the spec with the concrete placement properties.
Section 1.03: B – Design Requirements
Hardened Concrete & Placement Properties
You may be thinking the hardened concrete properties belong in the concrete placement specification, and they should be. It should also be placed in the polished concrete specification. The foundation of a beautiful floor starts with the flatwork. We recommend 4,000 psi for best results, but a minimum of 3,500 psi is required. Anything below that is simply not strong enough to sustain a good polish. The flatness and levelness requirements are also very important. A floor with high or low spots results in varying aggregate exposure and an uneven polish if not ground flat.
Although it is not written into our spec, this is also the section to include seeding requirements or special aggregate mixes. One of the beautiful aspects of polished concrete is that you can achieve many different designs with what you put into the concrete at the time of pour. “Seeding” is a process of adding aggregate to the surface of the concrete at the time of placement and hand troweling it in. The advantage to this process is the aggregate remains very close to the surface and a consistent heavy exposure is much easier to achieve. You can also add a variety of materials including colored rock or glass to the mix. We’ve seen very beautiful floors which achieve their color and design not from coloring the concrete, but from leaving the concrete natural gray and adding color with materials in the concrete. We recommend if you choose to seed or add a special aggregate to your floor that you specify a heavy (level 3) exposure.
Slab protection is extremely important. In fact, I cannot stress how important it is throughout the entire construction process. These are some guidelines, which the general contractor is primarily responsible for, about protection in the 28 day curing process before the grinding machines ever touch the floor.
(Skip ahead to Section 1.07. Everything in between should be straightforward, but please contact us if you have any questions.)
Section 1.07: Quality Assurance
A mock-up is the best way to ensure prior to the polishing process that you have a qualified contractor who can meet the spec and stay on schedule. The most expensive mistake you can make is to getting to the end of the project and realizing the polishing contractor cannot produce a floor that meets the spec, and most importantly a floor that is acceptable to the owner or architect. This typically requires another contractor to step back several steps and redo most of the work.
We recommend that you request an estimated time schedule and monitor performance of the mock-up to ensure timely progress. Remember that this is typically only a very small portion of the project and should not take more than half to a full day, depending on the extent of polish, exposure, dye work, etc. If a standard size mock-up cannot be completed in a day, it is very likely the contractor will have difficulty staying on schedule. We also recommend, if possible, that you personally approve the mock-up. While these tasks should ultimately be the general contractor’s responsibility, a general contractor may not know your expectations. Trust us, a floor can make or break your project.
(Skip forward. Again, if you have any questions regarding sections in between, please contact us)
Section 2.02: Polished Concrete Finished Products
There is no reason to specify a specific product or manufacturer. The only thing this will achieve is limited competition. Instead, specify the type of product to be used.
We have written our spec to allow only true silicate densifiers, which produce the highest abrasion resistance and strongest surface. These products will greatly increase the longevity and shine of the floor. For a more in-depth discussion on densifiers including why they’re important and how they work, please read our densifier discussion.
Oil Repellent Sealer
All polished concrete sealers are penetrating. Some products are semi-topical while others are full penetrating. Semi-topical sealers leave a thin film on the surface and will increase the gloss characteristics of the floor. Full penetrating sealers leave no topical characteristics and will not alter the gloss characteristics of the floor. If a semi-topical sealer or “guard” product is to be used then gloss testing needs to be done prior to the application of the sealer as this will provide inaccurate testing results. This is crucial to the longevity of the floor as the film left behind is a thin layer of acrylic that will wear away quickly exposing the underlying polish on the floor. If a sealer has been used to achieve the gloss, then the gloss will disappear as the sealer wears away. If a full penetrating sealer is used, then gloss testing can be performed before or after the application of the sealer as it will not impact the aesthetics of the floor.
Semi –topical sealers are relatively easy to identify. Prior to gloss testing a floor you will want to identify if a guard was used. To do this, you can simply find a piece of copper wire or use a brass key and attempt to scratch the floor. The acrylic topical component is relatively soft and can be scratched by softer metals, the concrete however cannot. If a scratch appears, then the surface most likely has a guard on it and you will need to have the contractor remove the guard prior to testing.
The floor finish is the gloss level. This is one of the most important aspects of this spec and will ultimately determine the look of the floor. This is also one of the two measurable standards. Almost every facet of the polishing process will contribute to the gloss level. If the densifier is not applied correctly or if an inadequate amount of densifier is used it will ultimately affect the gloss level. If the polishing machine was run too quickly over the floor or if the contractor skips diamond steps, the gloss level will be affected. All these factors contribute to the aesthetics and longevity of the floor.
The test, ASTM D523, is a specular gloss test. A gloss meter is an instrument that projects a laser onto the floor at a 60° angle and returns a gloss unit (GU). In layman’s terms, it reads how shiny the floor is. This test is to be taken from 10 sample areas throughout the floor, and ideally should be done by a 3rd party. We recommend this test be performed on every project, whether the floor is accepted or not, and the results be kept on file. These results will provide the owner or contractor recourse in the event the floor deteriorates or issues arise.
Be sure to spec the gloss level you are truly after. Matte Finish is 30 GU @ 60°; Semi-Goss is 45 GU @ 60°; High Gloss is 60+ GU @ 60°.
Aggregate exposure is the second measurable test of polished concrete and also greatly affects the look of the floor. Particularly if additional or special aggregate mixtures are added, specifying the level of aggregate exposure to a measurable standard is extremely important. This test is easily performed with a ruler by measuring the size of the rocks exposed. Our spec is written for a 1” minus (-) river rock aggregate, which is fairly standard in New Mexico. This section may need to be altered to reflect the size of aggregate used. For assistance altering the aggregate size, please contact us. For examples of each level of aggregate exposure, please click here.
Section 3.03 Installation
Sequence of Polishing
The sequence of polishing is primarily a budgetary concern, but can greatly affect the final floor so should be chosen carefully. Some architects may choose to leave this decision up to the contractor, in which case this section should be removed. We recommend the architect specify the sequence of polishing on competitive bid projects. This ensures a competitive bidding environment as all contractors will be bidding to do the floor at the same point in the project.
Polished concrete scheduling can be a headache. The slab must cure a minimum of 28 days prior to grinding, but the polishing process is faster and less expensive if done prior to interior framing. Many general contractors do not have time to wait 28 days for curing, and additional time for the polishing process. Moreover, a finished floor that has to sustain the abuse of the entire construction process will never be what it was new.
So, our recommendation is to meet somewhere in the middle. Perform the initial grinding steps prior to interior framing (before partition studs are erected, per the spec). Perform the resin steps, the actual polishing, after interior framing but prior to drywall (after partition studs are erected, but before gypsum board is installed, per the spec). The floor will still need to be protected after the initial grind, but not as heavily as a finished floor.
This has everything to do with the end use of the floor. Typically, we recommend using a full penetrating sealer as it provides the best traction characteristics and does not alter the abrasion characteristics or appearance of the floor. However, in certain instances where the floor may be exposed to above average levels of contamination (i.e. school cafeterias, restaurant dining rooms, bars, etc…), semi-topical sealers or “guard” products may be a better option as they provide a thin film barrier for added stain protection. For more about topical sealers, refer to the “Oil Repellent Sealer” section earlier in the discussion.
Section 3.06 Protection
Floor protection is commonly overlooked but is vital to the well being of the floor. Depending on the scheduling, the level of floor protection will vary (another reason it is a good idea to include scheduling in the spec).
Typically the general contractor should be responsible for floor protection, as they are overseeing daily operations and all other trades. In all situations, we recommend taking measures to ensure the slab is protected from potential staining both before and after polishing. This means diapering any hydraulic equipment to be utilized in the polished areas, not allowing pipe cutting or any other operations involving the use of oils or solvents to be performed in polished concrete areas, and requiring the use of drop cloths or masking materials for any operations requiring the use of chemicals (i.e. drywall mud, paint, pipe sealants, fluxes, etc…). One item that is often overlooked is overhead plumbing and fire sprinkler systems in which various chemicals are often used for the bonding together of pipes and fittings which can potentially stain the floor.
For more information or if you have any remaining questions regarding the spec, please feel free to contact us via email or phone at 800-523-2245.