b'TECHNICAL & RESEARCHDimensional Stability of Polyisocyanurate InsulationRandy Adams, R Adams Roofing IncD uring 2017, the MRCA T&R Committee conducted a survey of Knit Line issues with Polyisocyanurate Roof Insulation.Reports from the field indicate the irregularities or indentations, in the surface of polyisocyanurate roof insulation continue to be a concern. Lets start by understanding a few points about the grooves created within the surface of the insulation:Knit Lines occur during the manufacturing process of polyisocyanurate insulation. The expanding foam used in manufacturing, is sprayed via multiple heads on to the bottom facer.If the foam spray meets incorrectly, a knit line may form. Knit lines may be unsightly on the roof surface, particularly when a fully adhered single ply is installed. Depending upon the direction of roof slope, dirt may accumulate in the depressions, as a consequence to drainage issues.There are three ASTM Criteria pertinent to theprescribes measurements to be made 1 production of Polyisocyanurate Insulation. to 3 in from the board corners.Two ASTM C1289-16applies to theadditional measurements shall be taken Standard Specification for Rigid Cellularnear the center of the long dimension Polyisocyanurate Thermal Insulationof the board, between the corner Board.There is further stipulation formeasurement locations.Type I and Type II products. The MRCA conducted a survey while ASTM C1289 Section 8pertains tolooking in to the manufacturing challenges of dimensional tolerance criteria.Thispolyisocyanurate insulation.The following standard stipulates length and widthquestions were asked:tolerances shall not exceed +/- .The1.Have you observed knit lines in thickness tolerance shall not exceed 1/8,polyisocyanurate insulation?and the thickness of any two boards shall79 % of respondentsYesnot differ more than 1/8ASTM C303Standard Test Method for2.Have you measured the board thickness for Dimensions and Density of Preformedvariance from the specified thickness?Block and Board Type Thermal Insulation. 50 % of respondentsYesTo measure board thickness, ASTM C303The range of thickness variance as a 46 www.mrca.orgMidwest Roofer'