Planning
Before specifying mortar testing it’s essential to carefully determine what information you want to obtain from mortar analysis and how you plan to apply it. Testing options vary widely as to cost, lead time, and data produced so establishing the test goal is important to clarify early in the project. The most common reasons specifiers contact us for mortar testing are:
- To identify the original for restoration
- To determine if an existing replacement mortar is contributing to building deterioration
- To provide documentation to support restoration plans for a historic preservation commission or other oversight group.
If mortar testing is indicated, we strongly encourage the restoration team to undertake it before creating specifications or soliciting bids. Testing is often is part of the bid package fso that contractors provide samples for testing after they have bid on a project. This means that the winning bidder did not base his or her numbers on a specified product and instead relied on his or her experience and judgment. If testing then indicates that a lime mortar is the more suitable replacement mortar there is often pressure to permit an OPC or to accept change orders. This scenario can be avoided if the building owner commissions the testing early and the specifications are then driven by test data.
Mortar Testing & Project Bidding
Sometimes it’s simply not possible to perform testing before issuing specifications. In these cases, we recommend including a bid allowance for both an OPC mortar and hydraulic lime mortar to allow for the final results of the mortar testing. Comparing bidders’ numbers for historic lime mortar will also give some insight into their relative experience; inexperienced bidders tend to go either very low or very high. Very low bidders usually haven’t familiarized themselves with the material costs and additional labor, and high bidders often provide extra contingencies to cover unknown factors. If you receive bids that vary dramatically you should further qualify the bidders.
Selecting a Testing Laboratory
Commissioning testing early in the process allows the architect and/or the building owner to choose the laboratory. This is an important consideration since testing labs vary widely in quality, capability, and experience in analyzing historic materials. Some labs rely exclusively on acid digestion testing, which is a very basic analysis that offers only a general picture of mortar composition. New construction labs may not have technicians who are familiar with the idiosyncrasies of historic mortars, and some labs advertise exclusive proprietary tests that achieve results that standard ASTM tests cannot. We don’t recommend these proprietary tests claiming to achieve results that ASTM testing can’t since the test methods are opaque, as is the process of analyzing and interpreting the results.
Centurywerks is please to partner with a renowned AASHTO-certified aboratory that is well-qualified to perform ASTM material testing, and we work with their team of engineers and scientists to coordinate testing for our clients.
Identifying Testing Procedures
Clearly identify the ASTM procedure you want to use to reach your objective. If testing is to be performed by the contractor, identify the specific test protocol. We regularly field calls from contractors who are asked to perform testing “to identify the composition” or to “determine the compressive strength” of the mortar. These kinds of instructions are too vague and many contractors will gravitate toward the fastest and cheapest option to fulfill these kinds of requirements. The quality and usefulness of the test results will be in proportion to the quality of the specifications.
An Important Note About Compressive Strength
One important note: one of the most common problems we encounter are specifications that call for testing the compressive strength of mortar. There is no ASTM standard test to determine the compressive strength of an extracted historic mortar sample. The standard test for compressive strength is ASTM C-109 “Standard Test Method for Compressive Strength of Hydraulic Cement Mortars” which involves compression testing a set of two-inch cubes. This procedure doesn’t translate to smaller, irregular samples pulled from a wall, nor does it account for the numerous other variabilities of extant historic mortar.
Some testing facilities offer compressive strength testing for historic mortars but such proprietary tests rely on undisclosed methods, meaning that the results can’t be independently verified or analyzed and it’s impossible to determine how sound the methodology is.
For more information about mortar testing, please call us at 773-598-4300.
Need Assistance?
Contact us at 773-598-4300 for more information and assistance.
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