Accelerated Weathering

In addition to the warehouse exposures described above, the durability of the two sealants was also evaluated using standard accelerated weathering proce­dures and ASTM C1519-04, Standard Practice for Evaluating Durability of Building Construction Sealants by Laboratory Accelerated Weathering Proce­dures.

Weathering of Plaques in Xenon Arc and Fluorescent UV Weathering Apparatus-Specimens for accelerated weathering were laid up as 5 X1^ X ^in.3 (127 X 38 X 3.2 mm3) thick wet plaques on 3 X 6 in.2 (76 X 52 mm2) aluminum panels. The specimens were cured for 3 days at 23±2 ° C, 50±5 % relative humidity, and then placed in either the xenon arc or fluorescent UV accelerated weathering apparatus, following the procedures described below. Changes in sealant surface appearance (e. g., crazing, pitting, and chalking) were monitored periodically over a minimum of 2000 h. Changes in sealant color, as measured by changes in L*a*b* [3], were measured as a function of time in the fluorescent UV apparatus using a Minolta CR-231 portable Chroma Meter color analyzer.[24]

Procedure for Exposure in Xenon Arc Light Apparatus-An Atlas Ci65A Xenon Weather-Ometer[25] was equipped with daylight filters conforming

to ASTM Practice G155 [4]. The exposure cycle was 102 min of light followed by a wet period of 18 min light with water spray. The irradiance was set to 0.51 W/(m2 ■ nm) at 340 nm and the chamber air temperature to 45 ° C. The uninsulated black panel temperature was measured at 68 ° C.

Procedure for Exposure in Fluorescent UV Apparatus-A QUV Accelerated Weathering Tester (model QUV/basic) from Q-Lab[26] was equipped with

fluorescent UVA-340 lamps that comply with the spectral power distri­bution specifications in ASTM Practice G154 [5]. The exposure cycle consisted of 8 h of UV exposure at an uninsulated black panel tempera­ture of 60 ° C, followed by 4 h of wetting by condensation at an uninsu­lated black panel temperature of 50 ° C. Irradiance was not controlled. ASTM C1519-04 [6] Durability-Three aluminum H block specimens, as de­scribed in Test Method C 719-93 [7], were made for each of the two sealants tested. The acrylic sealant specimens were cured for 1 week at 23±2 ° C, 50±5 % relative humidity, followed by 2 weeks at 50 ° C. The two part polyure­thane sealant was mixed immediately prior to sample preparation with a paddle mixer and following the manufacturer’s instructions. The resulting specimens were cured for 3 weeks at 23±2 ° C, 50±5 % relative humidity. Fol­lowing cure, the specimens were placed into either a xenon arc or fluorescent UV weathering apparatus. After 4 weeks the specimens were subjected to six room temperature cycles of ±25 % cyclic movement at a rate of 1/8 in. (3.2 mm)/h. They were then evaluated for overall appearance and amount of adhe­sive or cohesive failure. The cycle of weathering followed by joint movement is an ongoing process, and the test will continue until significant failures have occurred. Results to date, through a total of five cycles, are reported.

Exterior Exposure in Static Joints-Channels for static joint exposures were fabricated by nailing pine strips to a plywood base to form a series of 4 X 2 X 30 in.3 (19 X 13 X 762 mm3) channels. To prevent degradation of the sub­strate, the wood was first primed and then painted with a high quality exterior paint. After the paint was dry, the channels were filled with sealant. The seal­ants were tooled flat and flush with the tops of the channels and then cured for 4 weeks under ambient conditions. To assess sealant coatability and the appear­ance of overcoated sealants, half of each sealant was coated with a 38 pigment volume concentration (PVC)[27] all acrylic elastomeric wall coating (EWC). The coating was brush applied in two coats to the sealant and channel surfaces at a combined coating weight which resulted in a calculated final dry film thickness of 20 dry mils (0.5 dry mm). The first coat was dried for 24 h before the appli­cation of the second coat, and several additional days elapsed before the EWC coated channels were taken outside for exposure. The filled and coated chan­nels were exposed horizontally in a south-45° direction at the Spring House Farm in southeastern PA. After 1 year of exterior exposure the channels were brought back into the laboratory, and the coated and uncoated sealants were assessed for dirt pickup, crazing, and chalking.