Reduced tension sealant systems-eifs joint design properties and lamina stresses intiating substrate failure

摘要

Canada Mortage and Housing Corporation (CMHC) completed during 1994 a research proram that investigated, amongst other aspects; joint depsign and sealant bond to EIF Systems. Eight different joint design were tested as well as sealant bound 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 o f 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 sings. Capillaries or voids may be created wither winthin 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 inary sealant congiruation 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.