Expansive grout as anchor fill

by Katie Daniel | November 27, 2015 10:27 am

[1]FAILURES
Deborah Slaton, David S. Patterson, AIA, and Kenneth M. Itle
In stone veneer construction, the panels’ lateral support is typically provided by anchors connecting the stone veneer to a backup structure. Some lateral support anchors project from their attachment at the building structure, and are engaged within a slot or kerf cut into the stone thickness—typically at the panels’ top and bottom edges. Dowel anchors inserted into drilled holes are also commonly used.

The space surrounding the anchor within the kerf or drilled hole is typically filled by a material acting as part of the lateral support system. The fill also limits the amount of moisture entering the kerf or drilled hole. (In freezing environments, water collecting in these spaces can freeze, expand, and crack and spall the adjacent stone.) Materials used to fill the void space surrounding the anchor include cementitious grout, epoxy or other resin products, or sealants.

In the example shown, Indiana limestone was used as architectural ornament on the granite masonry façade of a building constructed in the early 2000s. Various types of lateral anchors set in grout were used to hold the limestone units in place. Within a decade, cracks and spalls were observed at individual limestone units throughout the façade. The observed stone distress was investigated by the removal of cracked or spalled stone units, each of which corresponded to an anchor location with a grout-filled kerf or hole.

[2]

Laboratory analysis of the grout confirmed the grout contained a significant proportion of calcium sulfate dihydrate (i.e. gypsum). Due to its rapid setting characteristics, gypsum is commonly used in grouts intended for dry, interior locations. However, when exposed to moisture, gypsum is an expansive material that can exert force on the stone, resulting in cracks and spalls.

Industry standards such as those of the Indiana Limestone Institute recommend either mortar or sealant be used to fill kerfs and anchor holes. Cementitious grout is popular for this application as it provides a flowable, fast-setting fill material. However, grout products containing added gypsum are inappropriate for stone veneer systems. If grout is used as fill for the project, the material safety data sheet (MSDS) should be thoroughly reviewed in order to confirm the actual grout constituents.

The product literature for the grout used in the example shown described the material as 
a “fast-setting hydraulic cement.” The MSDS further indicated the grout contained quartz silica, sand, portland cement, and “calcium salt.” Research using the CAS Registry Number—
an identifier provided for individual chemical substances by the American Chemical Society’s Chemical Abstracts Service—provided on the MSDS identified the “calcium salt” as Plaster of Paris—gypsum, in other words. This illustrates the challenges specifiers face in identifying inappropriate grout materials proposed for these applications. Products claiming to be ‘fast-setting’ or containing ‘calcium salt’ would benefit from further scrutiny prior to use.

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect those of The Construction Specifier or CSI.

Deborah Slaton is an architectural conservator and principal with Wiss, Janney, Elstner Associates (WJE) in Northbrook, Illinois. She specializes in historic preservation and materials conservation, and can be contacted via e-mail at dslaton@wje.com[3].

David S. Patterson, AIA, is an architect and senior principal with WJE’s Princeton, New Jersey, office. He specializes in building envelope investigation and repair, and can be reached at dpatterson@wje.com[4].

Kenneth M. Itle is a preservation architect and associate principal with WJE in Northbrook, Illinois. He can be contacted via e-mail at kitle@wje.com[5].

Source URL: https://www.constructionspecifier.com/expansive-grout-as-anchor-fill/

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