The benefits of physical mock-ups

From an engineer’s perspective, mock-ups—detailed, full-scale, site-constructed samples of part of a project—are an important part of today’s construction process. Typically, mock-ups are requested as part of the submittal process in order to verify the contractor’s ability to install a given product in accordance with the specifications, but they also provide the owner with a means of comparison by which to judge the acceptability of the required work.

Additionally, mock-ups serve as a means by which an engineer can review the constructability of the design and also test the system for various levels of compliance with the specifications. However, because of time and budget constraints, mock-ups are too often omitted from practice. Unfortunately, neglecting the use of mock-ups can be detrimental to project success. Not only do mock-ups provide a sample of the work to be completed, they set the standard for quality workmanship on a project-specific basis, help alleviate concerns that might arise during the actual construction, provide a comparison basis for final appearance for the project, as well as, test the integrity of the design and construction solution.

The process

In most cases, the process of developing a mock-up begins with a need to demonstrate how a portion of the project will be assembled. This need may be outlined in the specifications by the architect or the engineer, identified by the owner, or insisted on by the contractor. Engineers and architects specify mock-ups as a means of quantifying items in the design that may not be easily submitted or approved by means of a paper submittal. For example, an engineer or architect may wish to specify an exposed aggregate concrete for repairs to a sidewalk, but the existing sidewalk is difficult to match. The engineer or architect can specify a mock-up by including the following language in contract documents: "Contractor shall provide on-site mock-ups of exposed aggregate sidewalk in minimum 3-foot by 3-foot panels for owner approval. A total of four (4) mock-up panels shall be included in the contract sum. Mock-ups shall match existing sidewalk in color, texture, and finish."

The contractor is then obligated to install a sample of the finished product and a determination can be made as to whether that sample matches existing. If the sample does not match, the engineer or architect and the contractor can revise portions of the design mix, or the installation process, in order to achieve an acceptable sample.

In some cases, an owner or an owner’s representative may not be able to access the installed work to review it—such as on a façade project where swing-stages are used. In this case, the owner may request a mock-up that can be reviewed at a convenient location. For example, a recent façade project necessitated the installation of a sloped metal cap at a gutter on the 9th and 11th floors of a 13-story building. The contractor provided a mock-up of the copper roof section in order to obtain owner approval without the owner accessing the work areas at the 9th and 11th floors.

The contractor can insist on mock-ups being installed for a variety of reasons. In some instances, the contractor may want to verify that what is shown in the drawings can actually be constructed (constructability). Other times, the contractor may want to train their less-experienced personnel in the installation of certain products. Additionally, contractors may want to install mock-ups as comparison samples in order to have a basis for determining the acceptability of installed work.

The money myth

Although frequently an accepted solution for those seeking to resolve an aesthetic issue or to test a material/building product once it arrives on the jobsite, mock-ups should be integrated into both new construction and renovation projects much earlier in the design process, giving all team members a chance to capitalize on lessons learned. General contractors, architects, and engineers are accustomed to seeing mock-ups and appreciate the time and effort which goes into preparing them. However, owners often need to be sold on their importance since they may appear as an unnecessary, or extra, line-item in the budget. In reality, the money spent upfront usually pays for itself. In fact, without a mock-up, most contractors are more likely to bid risk into their proposal as they know that there is a likely chance there will be disagreement about the method or materials. As such, it has been proven time and time again that mock-ups need to be in-place and approved before the actual work is completed, an in some cases it is even beneficial to have the mock-ups installed as part of the design process in order to provide a basis for the bidding documents.

If planned correctly, mock-ups don’t need to break the bank. In many instances, the product supplier will supply the necessary materials for a mock-up constructed early in the design process in order to secure the job. However, depending on access issues, material availability, manufacturer willingness to provide small quantities, and a host of other factors, it can often be difficult to get mock-ups installed before work begins. Therefore, adequate schedule time should be allowed for the mock-up process. Coordination with product representatives ahead of time also is crucial.

Ensuring quality

The most common reason to create a mock-up is to ensure the construction method and materials will be acceptable to the owner. For example, mock-ups are especially important with regard to ensuring consistency in the color, texture, and finish of masonry and decorative concrete as well as other colored and textured installations. When a contractor provides an on-site mock-up of a concrete or mortar installation, the owner can approve and ensure that the materials create the desired effect. Once approved, everyone on-site has a sample of the specific color, texture, and finish of the material and the owner can be assured that the finished product will coincide with the quality of the sample provided. Because each job is unique, it is important not to use mock-ups from old jobs for a new project. The result of using an old mock-up could be as dangerous as not having one at all. And, having a better established mock-up will lead to a better start and progression of the project.

Case in point is a recent project in which the contractor created a mock-up that was approved by the owner. Later, the owner changed their mind about the mortar color. Without the mock-up, the contractor would have been left to re-do the project and a claim likely would have resulted since there was no agreed upon visual definition at project onset. Because of the mock-up, the contractor was entitled to a change order for the additional time and materials associated with successive mock-ups and lost time due to the subsequent submissions. Both the engineer and the contractor were protected by the mock-up process. Even when a sample is given before-hand, an owner can change their mind. In providing a mock-up, the contractor and engineer protect themselves and allow for necessary owner approval before the installation proceeds. This is especially important with regard to historic restoration. In such projects, mock-up approval by historic review boards can help the owner, engineer or architect, and contractor ensure that the work is completed in accordance with the necessary precautions to preserve the historic integrity of the building.

Once the mock-up is approved, it must be treated as a project record. Although it remains on-site as a comparison sample, the physical mock-up must be marked in some way as approved, while being careful to ensure that the marking does not obscure the attributes of the mock-up necessary for comparison. Further, transporting the mock-up to and from the site for comparison purposes is discouraged due to possibility of damage and/or loss. If the approved mock-up is preserved, and all installed work matches it, the mock-up should be able to be left in-place an incorporated into the project.

Making choices

The mock-up process is not only beneficial in ensuring that all members of the design and construction team have the same expectations, but often it can be used to determine expectations. For example, consider the difficult restoration task of replacing 100-year-old wood windows that have been painted time and time again atop chipping and flaking paint. To restore these windows, the contractor can carefully remove the paint and perform restoration of the wood, which is likely warped and at the very least, rough, based on a century of use and all of the layers of paint, which can be a costly process. Or, the contractor may be able to maintain the historic integrity of the windows by simply painting over the window-frame or stripping a layer or two of paint. In a project such as this, it is very difficult for the Contractor to determine the optimal approach without a mock-up since it is very difficult to ascertain how the latter approach will look once complete. As such, a mock-up of each option will help the owner make a better decision that isn’t solely based on price.

Mock-ups as test samples

Mock-ups themselves can become test samples for performance testing. A mortar tuck-pointing sample can become a water test area, a sample installed fastener can become a pull-test, or a sample of installed flashing can be leak tested to determine the effectiveness of its design. When several components come together, there can be the need for larger scale mock-ups that allow for testing of the interaction of these multiple components. For many projects, this is still referred to as a mock-up, for others it can be considered a test specimen, and still for others it may be called a prototype, but the essence of the ideal remains the same, installation of a component or a combination of components to demonstrate the constructability and installed appearance of the work.

Success with mock-ups

Mock-ups help minimize risk because the contractor has been exposed to information from the first stages of the building process and the owner has been given a tangible, measurable basis of comparison. Although some believe mock-ups slow the construction process, it has been proven that they typically lead to greater project success, especially when utilized early in the design process. The establishment of committees related to mock-ups in organizations such as the American Society for Testing of Materials (ASTM) and other such standards writing groups suggests that the further refinement of mock-up practice is in the works. ASTM is working toward publishing a standard in the next few years that will address some mock-up procedures.

As an industry, it is important for all members of the design and construction team to embrace mock-ups and make them standard on our projects and in our specifications. Engineers and architects should consider revising standard front end documents to include a section on mock-ups, consolidating the required samples from the individual technical sections into one section for ease of reference and clarity. By making it part of our industry cultural norms, paying close attention to the details of the mock-up process, and creating effective mock-up programs within project documents we’ll all benefit.

Steven Bentz, P.E., R.R.C., is a project manger specializing in building envelope repair and assessment at the Fairfax, Va., office of Facility Engineering Associates, P.C. He can be reached at Steven.Bentz@feapc.com. Mark K. Howell works with Structural Preservation Systems in Baltimore, Md. He can be reached via e-mail at mhowell@structural.net.

Photo: Mock-ups are often considered unnecessary budget items, but if the mock-up is successful, it should be able to be left in-place an incorporated into the final project, such as with this concrete repair mock up.
Credit: Structural Preservation Systems