Archive through June 13, 2006

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Author Message David R. Combs, CSI, CCS, CCCA Senior Member Username: davidcombs Post Number: 145 Registered: 08-2004 Posted on Monday, June 12, 2006 - 04:40 pm:    This is a new one to me; anyone else heard of this?: Project architect has been told by structural engineer that this may be a problem: "a condition where I have a rubberized asphalt adhesive/sealant flashing that is being used in a masonry wall. Our relief angles and lintels are galvanized and are not compatible with the flashing" and . . . "The issue comes from a situation when the asphalt is adhered to the galvanized steel. The chemical reaction with the zinc coating/water/asphalt causes the zinc to become soap and then dislodges from the steel." Has anyone heard of this before? Is it truly a concern? What approach was taken to alleviate the problem? Thanks all. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 534 Registered: 03-2002 Posted on Monday, June 12, 2006 - 05:46 pm:    I have not heard this. I have also seen many details with rubberized asphalt flashing on galvanized steel. I have heard of the asphalt oozing out under certain conditions of temperature and pressure, though the standard nowadays seems to be to use a rigid flashing component that extends past the exterior face of the masonry with the remainder being rubberized asphalt. Saponification occurs as a reaction between an oil and an alkali, for example, with alkyd coatings (oil) on hot plaster or concrete. (This, of course, is how soap is made - lye and fat, or as I prefer, olive oil.) I found some references that suggest that zinc hydroxides (one of the corrosion products of zinc) are alkaline, so it could be feasible that, in the failure that this engineer experienced, the galvanizing had become more corroded than may be typical, and this reacted with oils in the rubberized asphalt. I would not expect asphalt itself to be "oil", but there may be shorter-chain petroleum additives that are oils added by some flashing manufacturers to their product. Thus, I can see that this would be theoretically possible, and perhaps has occurred in certain circumstances. However, this is such a common application of these products I would expect some unusual situation to be the culprit. "Banning" these products outright without a thorough understanding of the failure mechanism experienced in this case is not very good engineering. We need a knowledgeable response from a peel-and-stick manufacturer on this issue, I think. Margaret G. Chewning FCSI CCS Senior Member Username: presbspec Post Number: 102 Registered: 01-2003 Posted on Monday, June 12, 2006 - 06:20 pm:    I've heard this "theory" floating around for quite a while. I've forwarded David's question to our local galvanizing plant here in VA. Hopefully Stewart will refute or confirm these statements. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 353 Registered: 07-2002 Posted on Monday, June 12, 2006 - 07:46 pm:    I'm curious about the use of galvanized metal in that condition -- in a hidden condition where you have flashing, we always use stainless steel with the rubberized asphalt (I call out finish 2B with dead soft temper). I think putting galvanized metal in a cavity wall is just asking for a problem. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 536 Registered: 03-2002 Posted on Tuesday, June 13, 2006 - 08:52 am:    It is the lintel that's galvanized, not the flashing. We'd use copper or stainless for metal flashing in a wall, but our relieving angles are always "galvy." Wayne Yancey Senior Member Username: wyancey Post Number: 136 Registered: 05-2005 Posted on Tuesday, June 13, 2006 - 01:42 pm:    David, This a first for me also. If you are using a self-adhering membrane flashing such as Henry Blueskin TWF or comparable, the contact surfaces of the galvanized product will be liberally primed for adhesion. Alternatively, the S.A.M. will be applied to a stainless steel backing. The end of these thru-wall flashings should always be trimmed 1/2" behind site lines and a metal drip edge projecting beyond the face of the masonry. Like Anne, we spec stainless steel flashings because of our climate and proximity to salt water. What is the brand name of the flashing you are using? I will post this on our company building science forum for input. Wayne David R. Combs, CSI, CCS, CCCA Senior Member Username: davidcombs Post Number: 147 Registered: 08-2004 Posted on Tuesday, June 13, 2006 - 03:44 pm:    John B. is correct; the lintel is what is galvanized. The flashing that was specificed is the standard 40 mil peel-and-stick rubberized asphalt (by Henry, Grace, Polyguard, and others). Project is in Arizona, so there shouldn't be a "salt" problem. The structural engineer is the one who first raised the issue with the project architect. Someone else wrote the specifications; I'm just assisting with the research, so my knowledge of particulars is somewhat limited. Thanks again for the feedback. I'll provide additional info as it becomes available.