NEW ASTM MORTAR STANDARD

With 2010 being the new year and the start of a new decade, it also marks the beginning of a new ASTM mortar standard: C1714. The official title for C1714 is the Standard Specification for Preblended Dry Mortar Mix for Unit Masonry. After several years in development, C1714 was ratified during the December ASTM meeting, and first made available as an official standard on December 28, 2009. At present it is only available from the ASTM website because the collection of standards volume 04.05 won’t be published until June. More information is available on the ASTM website at www.astm.org.

C1714 is really a subset of the reigning mortar standard C270. In fact, most people in the industry know C270 by its 1800psi strength requirement. C270 was first published in 1951, so it was developed during a time when mortar mix materials were batched on jobsite at the mixer. While C270 governs the mortar’s physical characteristics necessary for a structure’s engineering requirements, the spirit of the standard is still rooted in mortar mix materials batched on the jobsite.

The majority of the mortar used today is a preblended dry mortar mix in 80lb small bags or 3000-3500lb bulk bags, all of which is designed to meet the requirements of C270. The industry has switched to preblending mortar due to the many advantages it offers over mortar mixed on a jobsite including consistency from batch to batch, consistency of ingredient ratios, the ability to combine ingredients of extremely small dosages, custom sand blends, confidence that the mortar mix complies with the ASTM standards, etc. Preblended mortar simplifies material handling on the job site; everything is “ready to use” all in one bag; “all you have to do is open the bag and add water.”

One particularly useful advantage, Preblended mortar offers the ability to directly compare the test results from the mortar mix sampled at the manufacturing facility to the mortar mix sampled at the jobsite. The preblended mortar mix is delivered to the jobsite dry and therefore can be sampled dry and taken back to the lab to be tested alongside mortar sampled from the plant using the exact same laboratory test methods. On the other hand, with mortars batched at the jobsite, where the sand already contains moisture, the mortar mix is wet as soon as the sand is added, which starts the mortar setting process, and therefore requires different test methods. The results from these test methods are not directly comparable to those of the laboratory test methods.

The mortar test that causes the most misconception about comparable results is the mortar strength test. C270 requires a Type S mortar to have a minimum strength of 1800psi. The number 1800 is easily remembered; however it is not the only part of the requirement. The rest of the requirement places specific, controlled restrictions on exactly how the mortar is to be tested, in a laboratory. One of these controls is water content, which plays a huge role in defining the strength of the mortar. The amount of water in the mortar required for a C270 strength test is anywhere from one third to a half of the amount of water used on the jobsite. (Side note: In general, the lower the water content of the mortar the higher the mortar strength. So, why the difference in water contents between lab test mortar and mortar used on the jobsite? The jobsite mortar has more water to make it easier to place in the wall. When the mortar is placed in the wall, the masonry unit absorbs some of the water out of the mortar thereby increasing the strength of the mortar. The lab test is designed to loosely simulate the strength of the mortar after placement in the wall.)

Specification C270 doesn’t directly address the characteristics and practices associated with preblended mortar, which makes specifying the preblended mortar process more complicated. That is where C1714 comes in.

Under the umbrella of C270, there are five main components to C1714: traceability of ingredients of the mortar mix, ingredient blending consistency, testing frequency, allowance of additives based upon performance, and all ingredients are to be dry. Specification C1714 requires the ingredients and their corresponding dosage in a batch be recorded for every batch, and every mortar mix package receive a traceability marking linking it to the corresponding batch from which it was made, and all of this information is to be recorded and retained. C1714 places calibration requirements on the batching equipment for ingredients added in large and small quantities as well as tolerances on the ingredient dosages.

C1714 really defines a subset of mortars available under the umbrella of C270, so one of the biggest challenges in developing C1714 was in the area of admixtures. In C270 admixtures are only allowed if specified. From the overview standpoint of C270, the concern regarding the use of admixtures without being specified centered on a lack of real control of how and what type of admixtures are added in the field. In C1714 the as specified restriction was removed. The approach to admixture use in C1714 required three things. One, a clearly stated requirement that all ingredients of the mortar mix be dry. Two, a clearly stated requirement that all ingredients be added at the manufacturing facility, where the dosage can be precisely controlled and the resulting mortar mix can be tested. Three, the definition of admixture needed to be modified. Admixtures for masonry mortars have had a standard for several years, C1384. C270 even recognizes it. The only problem with using C1384 was the definition of admixture includes liquid ingredients-combining liquid materials with dry materials for long term use as a dry material is tricky. Instead of placing modification requirements on the use of admixtures, the task group decided to develop a new term for our desired type of ingredients: additives. C12 does not have a specific definition for additives, so we developed one. The C1714 definition of additive is essentially the same as for admixture only restricted to dry materials, so as a result these ingredients must comply with the requirements of C1384. For reference, some of these additives have dosage requirements that are extremely small, for example 30g of additive may be added to batch with a total weight of 4500lb. That type of dosage is just not practical for a jobsite mix.

C1714 has only been an official ASTM standard for a few weeks, so it’s going to take time to find its way into the industry.

Sincerely,

Jeff Thompson
QC Manager of Dry Mix Plant