Tilt-Up Warehouse Exposures

A tilt-up warehouse in El Paso, TX, was renovated in the Spring of 2005. As part of this renovation, the failing 20 year old sealant used in the original construc­tion was removed and replaced with the acrylic and polyurethane sealants de­scribed above. To directly compare performance, these two sealants were ap­plied in alternating joints around all four elevations of the warehouse, for a total of 62 joints. The sealants were applied by a moisture-proofing contractor with over 60 years in the business using two applicators with over 48 combined years of experience in the field. One applicator installed all of the polyurethane sealant, and the other installed all of the acrylic sealant.

The warehouse was constructed of concrete tilt-up panels with a decorative aggregate surface finish (Figs. 1 and 2). The aggregate finish is made up of a large aggregate embedded in a soft friable concrete mortar. Because of the size of the aggregate, the aggregate layer is roughly 3/4 in. (19 mm) deep. Although it would have been preferable, from an adhesion point of view, to install the sealants against the underlying concrete panels, it was not possible to do so

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FIG. 1—El Paso, TX, tilt-up warehouse used for exposure of high performance acrylic and polyurethane sealants.

 

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FIG. 2—Example of a prepared joint 1 in. (25 mm) wide. The underlying concrete slab and exposed aggregate surface layer are readily visible.

 

because of the depth of the aggregate layer. In both the original installation and in the retrofit described below, the sealants were installed flush with the build­ing exterior and against the aggregate layer.

The joints for the replacement sealants were formed by cutting out the old sealant, widening the joints where necessary, and then smoothing the inner edges of the joints with a grinder (Fig. 2). The dust generated by the grinding process was cleaned off with a blower, and the joints were brushed off prior to the application of the sealant. The resulting joints varied from 1/2 in. (13 mm) to over 1.5 in. (38 mm) in width (Fig. 2). A closed cell backer rod was used for all sealant applications and was carefully inserted so that it remained convex and untwisted. The sealant was applied with a bulk loading gun. Since much of the application was done on a ladder, the applied joint lengths were generally limited to 4-6 ft (1.2—1.8 m) at a time. Each section of sealant was tooled immediately after application. Although tilt-up buildings in the El Paso area are often painted, the warehouse used for the current exposure was not top-coated due to its decorative aggregate finish.

During the initial construction of the warehouse, the tilt-up panels were welded together at built-in weld plates, theoretically limiting the movement of the panels relative to one another. However, movement indicators attached to representative joints at the roofline indicated that some joints exhibited sub­stantial movement while others exhibited none. Measured movements ranged from 14 to 22 % (total) of the initial joint widths, substantially below the 50 % total movement capabilities of the applied sealants. The contractor felt that the amount of movement measured in these joints, and the variable nature of the movement, was typical for tilt-up construction in the El Paso area.

Applicator comments about the use of acrylic sealants were noted through­out the installation process and reported below. To assess application quality, sealant adhesion, and sealant cure, small sections of sealant were periodically cut and pulled from representative joints. To assess aesthetics, durability, and functional performance, the sealants were visually inspected and photographed at irregular intervals over a period of 3 years. Sealant dirt pickup, gloss, and crazing were visually assessed and readily captured in photographs. Sealant chalking was gauged by rubbing the sealant surfaces with an index finger and assessing the amount of white residue transferred from the sealant to the finger. Sealant softening and tack were subjectively gauged by digging at the sealant joints with a finger nail and pressing with fingertips.