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Canada Mortgage and Housing Corporation (CMHC) completed during 1994 a research program that investigated, amongst other aspects, joint design and sealant bond to EIF Systems. Eight different joint designs were tested as well as sealant bond strengths to the EIFS lamina (either finish or base coat). Polyurethane and silicone sealants as well as an impregnated expanding foam sealant composite were selected for testing based on the presumption of having either a “low modulus” characteristic, or of being representative of industry wide usage. Bond strength results indicated, that for the uniform samples tested, loads (stress) greater than 670 N (the cohesive strength of the EIFS lamina/EPS foam interface), will initiate substrate failure. Due to over-stressing of the EIFS lamina joint movement may occur without external visual signs. Capillaries or voids may be created either within the lamina or between basecoat and EPS foam that will effect short or long-term life expectancy. Of the joint design configurations tested, several could overly damage the EIFS lamina, even with limited movement. A series of joint designs has emerged based on either a binary sealant configuration or double joint with vented cavity (rain-screen principle) that show low lamina stress values. While these joints may not be fully pressure equalized rain-screen designs, the net effect is to prevent further moisture penetration into the EIF System.
low modulus, polyurethane, silicone, impregnated expanding foam sealant composites, binary sealant, EIFS lamina, substrate failure, double joints, over-stressing, barrier wall, vented cavity
President, Emseal Corporation, Mississauga, Ontario