Method and material specifications are NOT suitable for polished concrete and this paper is to explain the reasons. However, first, before that explanation, it is probably best to have an understanding of the different types of specifications for construction projects and their implications for contractors. For architects, engineers, and many others, this may be redundant, but it is necessary to understand the legal concepts behind each of the 3 primary specification types before diving into the reason method and material specifications are not appropriate for concrete polishing.
Method and Material Specifications (a.k.a. – Prescriptive Specifications)
Method and material specifications instruct the contractor on which methods to use for installation of materials that are listed in the specifications. For example, the specifications may say, “Apply 1 coat of XYZ Brand liquid densifier, at 400 square feet per gallon, keep concrete wet with densifier for 20 minutes, and use a low pressure sprayer followed by a microfiber mop. Thinning of the densifier is strictly prohibited”. If the contractor does this exactly, and the job is unsatisfactory, then the contractor is not at fault. If the contractor thins the densifier 10%, he has violated the specifications and is responsible for correcting the unacceptable work at his own expense.
Many other variables will come into play in the example given above, such as the requirement to perform to “Industry Standard Practices” and the requirement to follow the manufacturer’s product data and application sheets for the specified product. An overly simplified example of an industry standard practice for painting may be, “Don’t paint in the rain.” An example of a manufacturer’s requirement may be, “This paint must be applied between 45° and 90° F. Do not apply this paint within 5° of dew point.” Acceptable industry standard practices, the manufacturer’s instructions, and the concept of “good workmanship” will typically apply to the contract by specific mention, legal statute, or by reference. These requirements may also be located in the specifications, General Conditions, or Special Provisions of the contract. Regardless, these requirements are typically incorporated into the contract.
For the contractor, method and material specifications are helpful as long as the contractor follows them to the letter. The reason they are good for the contractor is that if he follows them exactly, he has the right to expect that a satisfactory product will result. This means, if the contractor followed the specifications and there is an unsatisfactory result, then the contractor is under no obligation to fix the problem. Oftentimes, this will result in a change order for the contractor. If the fault is the architect’s because he specified the wrong material or the wrong way to install it, then it may fall under the architect’s “errors and omissions” insurance, or the architect may pay from his own pocket. The payment to correct the problem may come of any number or combination of other sources. In the event of a problem, each party has the right to mitigate its own costs, so the guilty party is not obligated to hire the original contractor to correct the defect.
Sometimes the materials will be exactly specified, or a list of options may be provided. The contractor may safely choose from the listed options and expect a satisfactory outcome if he follows the method and materials specifications. Many specifications will also allow “or equal” products to be submitted by the contractor. If the contractor submits an “or equal” product to those listed, he most likely is then responsible for the results of that product. Here are some of the implications for the contractor should he choose to submit an “or equal product.”
“Or Equal” Substitutions by the Contractor
When a contractor submits an “or equal” product, the contractor may be assuming the design responsibility for the successful performance of that product. That could mean even if the product is stamped “Approved “or “Reviewed” by the general contractor (GC) or architect, the contractor may have taken on design responsibility for that product and responsibility for the successful outcome of his work. This is an area of much legal dispute. It is recommended that prior to submitting an “or equal” product that the contractor fully understand the implications of making such a submission. If a contractor is considering making an “or equal” product submittal, it would be wise to get the advice of an attorney who operates in the jurisdiction where the work is being performed. Please read carefully the two example stamps below, one from the general contractor and the other from the architect. Note the use of exculpatory language in their “Approval” or “Reviewed” stamps for product submittals.
- “Or equal” clauses are typically found in government projects as it illegal to specify a “sole source” and limit completion on these projects.
- In private industry, proprietary specifications are often used. A proprietary specification lets the property owner choose either a specific product or a specific contractor, or they may select from a group of products and contractors. These may specify the job as method and material specification, a performance specification, or a design build specification. Proprietary specifications carry all the same implications for each party (owner, designer, contractor) as the other specification types, but they may limit the competition to one or a few chosen vendors. In many instances, propriety specifications are used by an owner that wants to maintain consistency of materials, quality, or brand identification, or possibly the owner or designer simply prefers a specific type of product or contractor. Also, in highly complex installations where there is only one specific piece of equipment that will accomplish a specified task, a proprietary specification is required. Typically, designers attempt to avoid using sole source or proprietary specifications, as they may increase costs.
A performance specification requires that certain functional criteria are met. For example, in polished concrete, it may not tell the contractor what methods (machinery, diamonds, number of passes, etc.) to use, but it may simply state something like:
“The polished concrete floor shall be natural grey, be ground deeply enough to have a uniform light sand exposure, and have a minim gloss of 50 when measured by a Tasco light meter using the 60° reflectivity mode. The contractor shall polish in subsequent grits so and not to leave scratch marks in the concrete. Skipping grits or mixing grits on the machine is not permitted. Polish the concrete to a minimum of 3000 grit even if the 50 gloss reading is obtained at an earlier grit. The 50 gloss must be attained prior to the application of any guard product or other shine enhancing product. The polished concrete floor must certified by the NFSI or a NFSI certified walkway auditor to meet the ANSI/NFSI B101.09 Standard for ‘High Traction’ in a hard surface floor. The contractor will be responsible to provide the certification either in the form of being an NFSI certified product or by hiring and NFSI certified walkway auditor to audit the project. The contractor will not be permitted to certify its own work.”
“If there are defects in the concrete that are noticeable prior to beginning work or if defects are discovered during the performance of the work (such as uncovering foot prints beneath the concrete’s top cream, the concrete polisher shall stop work and notify the owner, general contractor, or architect (whomever hired the polisher) and ask for direction on how to proceed.”
Performance specifications can apply to almost any construction discipline specified. These specifications leave the methods and materials selection up to the contractor.
Design Build Specifications
A design build specification requires that the contractor provide both the design and construction of the project. The owner sets forth certain standards that are desired and the contractor is responsible for delivering a satisfactory product. The design build contract is very similar to the performance specification, with the additional requirement that the contractor design the entire project and make it work to the owner’s satisfaction. The design build contract is a two-way relationship where the contactor is both designer and builder for the owner. Method and material specifications and performance specifications involve three parties:
- the owner,
- the designer, and
- the builder or contractor.
Method and Material Specifications are Not Suitable for Polished Concrete
The reason method and material specifications are not suitable for polished concrete is because there are many concrete pours in every floor. In fact, some of the larger floors require many truckloads of concrete over multiple days, and each truckload of concrete has its own characteristics. The factors involved in each truckload of concrete are infinite. Here are some examples:
• The pour started a 2 a.m. and ended at 10 a.m. There are temperature and humidity differences between daytime and nighttime that affect the poured concrete.
• A concrete truck was delayed by traffic. Heavy traffic and delivery times can usually be accounted for, but it is impossible to predict traffic accidents.
• The concrete from one truck was dryer or wetter than concrete from other trucks.
• There was a pop-up rainstorm when finishing the slab.
• An uncooperative neighbor decided to cut down a pine tree during the pour, and pine needles blew into the cream.
• The pour was performed inside a building, and fossil fuel-powered equipment caused carbonation of the slab.
• One concrete slab is wavy; another is flat; yet another is flatter still.
You get the idea. There is a human factor in specifying the mix design, the setting of the rebar or wire mesh, or the choice and amount of fiber to use. Humans choose the batch plant, humans dispatch and deliver the concrete, the men doing the work have good and bad days, and the contractor may have committed to working shorthanded or inexperienced workers. Then there are the environmental factors that change from hour by hour, and sometimes within minutes.
There are just so many factors that affect each pour on each project that it is impossible to say all concrete is the same. For that very reason, it is impossible to write a method and material specification that will work on every piece of concrete to be polished.
- Some concrete is hard, and some is soft.
- There are soft diamonds for hard concrete, and hard diamonds for soft concrete.
- Some grinding and polishing machines are gear-operated and work with counter-rotating heads.
- Some grinding and polishing machines are belt-driven and work by planetary rotating actions.
- Some polishing machines have heads mounted by rubber grommets that will better accommodate a wavy floor.
- Smaller machines work better on wavy floors than very large machines.
- There are machines that are better grinders, and machines that are better polishers.
- Some densifiers are better for water resistance, some penetrate better, and some are substantially less expensive, yet quite suitable for the intended environment.
- Some diamond tooling manufacturers have a much higher diamond content than others, and provide a more refined scratch pattern and thus a higher shine.
- The weight of the machine affects the grinding ability of the tooling.
- The number of diamonds and their size affect the down pressure of the machine.
- The speed at which the machine tooling turns greatly affects its polishing ability.
It is because of the infinite number of variables in both the concrete, combined with the infinite possible combinations of grinding and polishing machines, tooling, densifiers, and guard products that one set of specifications with precise methods and materials is not the best method for specifying all polished concrete. Using the wrong combination of methods and materials often leads to disappointment and disputes.
The Most Suitable Spec for Polished Concrete
The most suitable specification for polished concrete is a specification that allows the concrete polishing professional to adapt his machinery and tooling as he performs the work. If there is a curing compound on the floor, then the polisher may need to change from dry to wet grinding. In severe cases, the curing compound may require chemical stripping.
It is typical that the hardcap (the super compacted concrete cream and fines on the top 1-2 millimeters of the slab) is considerably harder than cement paste at the aggregate level. The hardcap may require soft diamond tooling, and the cream and aggregate just below may require medium hard diamond tooling.
Flat and wavy floors will have more even aggregate exposure if the proper grinding machinery is used. Very flexible heads that are smaller in diameter do the best job of polishing wavy floors.
Based on the above and many other factors, method and material specifications do not allow the latitude to the concrete floor polisher that a performance specification does. That is the reason why Titus considers a well-written performance specification to be the best type of specification for polished concrete.
In some cases, a combination of methods and materials and performance specifications is acceptable. OSHA recommends that wet grinding and polishing concrete should be used whenever possible, and Titus agrees. This method not only provides a more refined cutting and polishing action, but resins from the diamonds do not create a false shine on the slab. Perhaps most importantly, wet grinding and polishing the safest method for both the building’s future occupants and the workers performing the construction. Silicosis is an incurable occupational disease caused by breathing in small particles of silica dust.