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Two identical specimens of mineral wool board were cut from the same shipment. Each was a standard 1" specimen 2 1/2" wide and 48" long. The specimens were gently placed across two tables 46" apart for the test, first on one side and then the other so that if any natural bow existed in the samples, the average of the two numbers, one from each side, would give an accurate account of their sag. One specimen was then matted with the standard Dura Glass 7511 glass fiber mat. A straight edge suspended between the two tables measured a distance from floor to straight edge in the center at 36 1/8". The first sample, the one without the Dura Glass 7511 glass fiber mat, but identical in every other way, measured a sag of 35" on one side and 34 7/8" on the other side. The sample with the Dura Glass 7511 glass fiber mat measured a sag of 35 3/4" on one side and 35 3/4" when turned over to the other side.
Therefore, the average sag of the specimen without mat was 1 3/16" while the specimen with mat was only 3/8". This is extremely significant when considering that in the field handling of acoustical panels, sag, and flop creates delamination of the fabric to the core and excess sag can thus relate to an unusable acoustical panel. Once the panel is on the wall and fastened securely, sag no longer becomes a factor, but in the handling of these materials, it is critical.
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