• Field Notes 18.11.2009

    It has recently been pressed upon me that I’m now, officially, old. For the first time professionally, I’m now the old man of the office. There’s only one other guy in the office older than me, and he owns the place. He can retire; I can join AARP. I don’t know how getting this old happened. 

    But, I’m not as old as dirt, contrary to what my kids or some of the guys in Engineering will tell you. I was NOT there when the first caveman cut a wheel from stone. To put my age in a curtainwall perspective, I’m as old as urethane sealants, but not as old as polysulfide. (If you have to ask what either of these are, you’re still young.) Your office old guy can tell you what they are – see, we do have SOME value. 

    When I got into this business, everything we used to seal curtainwalls was two-part urethane sealant. Then, the first structural silicone glazing job we did came along, and we had to put a slide-in, alodine-finished, aluminum extrusion in the mullion design because the silicone sealant manufacturers were not yet comfortable with allowing silicone adhesion to Kynar-based paints. Some time after that, in the mid-80s, that obviously changed – and in short order, too.

    But one thing hasn’t changed in all these years:  Sealants are such a small part of any job, but they play as critical a role as any other single component in an effective installation. If you don’t believe me, surely somewhere in your experience there’s been a missed or improperly installed seal that later became a leaker. If it was just one, you were lucky. Missed a whole bunch, and you just shot the profitability of that job, if not for the whole year. I know some (a LOT) of people to refer you to with firsthand experience, if you need any on this one.  

    Nothing made that clearer to me recently than in reviewing the Glass Association of North America’s latest re-write of the Sealant Manual. And, after having been in the consulting end of things, nothing seems to get less attention paid to it. It’s too important an element of what we do to shortcut in any form. 

    And then came along structural sealant. If you want to scare your friends, tell them there’s a tall tower in your town using only silicone to hold the glass to the building, nothing else. I got a dollar that says they come back with, “What, the stuff I buy at the local hardware store to seal up my tub and shower at home?” And then tell them yes, and watch the look on their faces. Ok, it’s not that simple, but it’s good for a laugh or two at the next holiday party. 

    Aluminum, glass and panels usually don’t leak, but the joints between them do. Sometimes you use sealant to plug those gaps. It’s usually one of the first and last lines of defense to air and water penetration. I got a dollar that says you better understand completely how the sealant you use will work. Or, face the loss of revenue that my dollar won’t begin to cover. Some examples: 

    • I saw a unitized curtainwall assembler tooling wet sealant with soap and water about three years ago, something they had been doing for more than 20 years because “they had always done it that way and the company WE both used to work for had done it that way.” Even though the specifications clearly prohibited that practice, he thought it was ok. It had been prohibited for about 15 years, and had ceased at our prior company because the sealant manufacturers had come out and said that soap on the substrates would compromise adhesion. 
    • Installations are often erected and put into the opening with perimeter seal joints smaller than the dimensions shown on the shop drawings. Just because a window can fit inside the opening doesn’t mean that everything’s ok. Tolerance for both the opening and for the window can contribute to that smaller joint, but such a joint is a leak waiting to happen. The sealant will most likely be overworked. The joints shown on the details are MINIMUMS, and smaller joints should NOT be allowed to occur. Please point this out to your installers!!!
    • I know of a manufacturer (not in the U.S., but from a country that Max Perilstein knows and loves) that shipped a unitized, factory-glazed, structural silicone project without any sealant manufacturer testing, drawing review or approved quality control procedure. When asked for the sealant company warranty, one was not forthcoming because none of this REQUIRED, BASIC legwork had been done prior to manufacturing. The curtainwall manufacturer then had to find a warehouse at or near the jobsite to completely deglaze and reapply the silicone AFTER the testing had been SATISFACTORILY completed. Bet they lost their shirt on that job. Wonder how much repeat work THAT got them?   

     So, boiling this all down, here are one well-aged glass guy’s thoughts on what to keep in mind when sizing a joint:

    1. What are the sealant’s capacities for handling movement? For curing? For staining? For adhesion, will primer be required? What special cleaning/prep work has to be done to the substrate before sealant is applied?

    2. What are the amounts of building or wall movement that will impact the joint?

       a. From seismic? Is the window opening going to be racked?

       b.From thermal – both of the window or curtainwall, as well as the surrounding substrate?

       c. From building frame movement – most notably structural deflection of floor beams or surrounding materials? Long-term or shot-term creep?

       d. From the wall deflection of framing members? A ½” joint won’t work if the jamb mullion’s going to deflect ¾” with a sealant that has 50% movement capacity. 

     3. And, what are the tolerances of:

       a. The opening in which the window or curtainwall sits?  Masonry and concrete tolerances can dramatically impact sealants. The tolerances of these materials will surprise you, and rival that of structural steel.

       b. Even though windows and curtainwalls have pretty tight tolerances, they still have them, which can impact the sealants if they run to the plus size. 

    It’s critical to know all there is to know about sealants. And if you don’t, the sealant manufacturers have expended a lot of effort in setting up technical support staffs, and done an excellent job of training their in-field personnel in offering to assist in planning your sealant use on the next project.

    I had an owner tell me in Dubai that one could erect curtainwall without sealant. Yeah, right. Go ahead, try. Tell me the name of the contractor, window or curtainwall manufacturer, glazier or ironworker that’s never used sealant on a project. I’d like to call the owner and see how THAT worked.

    Posted by Blogger @ 8:18 am

  • Leave a Reply

    Your email address will not be published. Required fields are marked *

USGlass Magazine

USGlass Magazine