Archive through August 23, 2011

Log Out | Topics | Search Moderators | Register | Edit Profile

Author Message Unregistered Guest (Unregistered Guest) Unregistered guest Posted on Wednesday, July 13, 2011 - 09:55 pm:    Does anyone know about this stuff? Polymethylmethacrylate(sp?) How does it compare to other fluid-applied roofing (e.g. polyurethane) and to other sheet membranes (i.e., PVC, TPO, etc.)....in both cost and performance? Lynn Javoroski CSI CCS LEED® AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1278 Registered: 07-2002 Posted on Thursday, July 14, 2011 - 09:45 am:    And what about its use for flashings? (especially with an SBS mod bit roofing). Robert Dye, FCSI, RRC Senior Member Username: crazyguydye Post Number: 8 Registered: 03-2007 Posted on Thursday, July 14, 2011 - 02:15 pm:    It is my understanding that PMMA technology has been around a long time. I heard the Germans developed it as a liquid plastic during WW2. The chemistry is not new, its use by the roofing and waterproofing industry is. Performance-wise, it would compare favorably with other fluid-applied membranes. Without going into the application method, I like it because it is fairly easy to install correctly. When it comes to roofing details that is essential. Manufacturers of sheet-goods are always stumped when it comes to edge and penetration details. They are great at the field of the roof; it’s the details that trip them up. And the details are where the leaks are. I would think that the cost of PMMA would limit its use to details and small, difficult to access roof areas. The chemistry is not cheap and the labor to install is higher (compared to sheet goods). It is basically a field-fabricated single-ply membrane. There is a base coat, and reinforcement layer, and a top coat. Performance should be excellent, especially for those awkward details. Soprema and Siplast both have branded versions of PMMA. I am familiar with a company called Liquid Plastics that does nothing but PMMA type stuff. I'm not sure how many other manufacturers have adopted PMMA as an approved detailing system. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 1213 Registered: 03-2002 Posted on Thursday, July 14, 2011 - 02:22 pm:    What would you like to know about it? PMMA (Parapro) and polyurethane (Kemper) are very similar products in installation, application and performance. My specification lists both companies. Parapro and Kemper are both high quality roofing systems and therefore expensive. These systems can be self-flashed. That is your can use the system to create flashings. The roofing system can also be used to tie into existing mod bit roofing systems. I am currently working on a project where we are installing structural steel bracing for parapets. We are using Parapro to patch the roofing where we cut for supports. We are using Parapro to flash around the support penetrations. We are also running Parapro up the back side of the parapet wall and onto the top of the parapet in lieu of a wall cap. Brian E. Trimble, CDT Senior Member Username: brian_e_trimble_cdt Post Number: 49 Registered: 08-2005 Posted on Friday, July 15, 2011 - 10:08 am:    David, Don't you worry about not letting the parapet breathe when you run the roofing up the back of the parapet? I have always heard you want the wall to breathe (maybe I'm just talking about masonry). Also, is there some allowance for differential movement between the parapet and the roof? Unregistered (Unregistered Guest) Unregistered guest Posted on Friday, July 15, 2011 - 05:52 pm:    Thanks to everyone for the information. At this point in time, since project is new construction and D-B, I am thinking that GC will likely opt for less-expensive roofing solution...maybe single-ply sheet membrane, as that was also "suggested" in the same sentence? David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 1217 Registered: 03-2002 Posted on Friday, July 15, 2011 - 07:08 pm:    Brian, Please explain. Our parapet is brick masonry on the backside and decorative (Limestone looking) cast stone on the front side. Also we have not allowed for differential movement between the roof and parapet. Thanks. I will check into this. Brian E. Trimble, CDT Senior Member Username: brian_e_trimble_cdt Post Number: 50 Registered: 08-2005 Posted on Tuesday, August 02, 2011 - 09:56 am:    Back from vacation... I have always been told, and I agree with, that the parapet needs to breathe. Since this is a very exposed location, water penetration is likely to happen. How does that water then get out of the parapet? Does it flow downwards exiting the wall somewhere else? Partially. Does it evaporate out through the coping? Not likely if you use a flashing material under the coping as generally recommended. Does it evaoprate out through the front or back sides of the parapet? Yes, but if you cover the back side with a roofing membrane, you have just limited the surfaces that evaporation can occur. If you think you are stopping water entry with the use of the roofing membrane, you are only partially doing that. Condensation is a real problem in parapets that the roofing membrane doesn't help. So if you have an exterior cladding that breathes well, then maybe the back side of the parapet doesn't matter, but in most cases you don't have that condition. Read some of Joe Lstiburek's info on parapets as well as Justin Henshell's articles on the subject. ken hercenberg Senior Member Username: khercenberg Post Number: 85 Registered: 12-2006 Posted on Tuesday, August 02, 2011 - 03:34 pm:    Great point Brian. Regarding MMA, keep in mind that while it is a very hard and durable product, much harder to damage than urethane, it is also much less flexible and has limited elongation. It's not for every application but may work at traffic decks as long as you properly design and detail enough joints to handle expansion and contraction. Jim Sliff Senior Member Username: jim_sliff Post Number: 79 Registered: 08-2010 Posted on Monday, August 08, 2011 - 04:46 pm:    "I have always been told, and I agree with, that the parapet needs to breathe." Yep. I've looked at many a "waterproofing" problem that wouldn't exist if someone hadn't noticed that gap under each side of the parapet cap and decided those big ol' holes running around the top of the building better be caulked shut! Normally the weatherproofing *should* shunt any water penetration to the outside, which *should* breathe (and have weep holes in certain situations). But as Robert said the details can confuse some contractors; I had a 21-story building where the water was shunted to the *inside*, causing all sorts of grief. It was discovered long after the GC was out of business, so a decision was made to seal the whole parapet cap shut, leave the roof...which was fine...alone, and R&R about 8 miles of 3/4" urethane panel joint, using closed-cell rod (the "skin" was brick veneer and water was penetrating and soaking the original open-cell rod). I haven't seen much PMMA on the west coast; most fluid-applied specs I've run across are urethane or polyurea. Polyurea is what I prefer as it's easy to flash with simple fabric reinforcement, it's fast, pretty much bulletproof when applied properly - and applicators have had to make a huge investment in equipment and training, meaning they're less likely to screw it up! Gerard Sanchis Senior Member Username: gerard_sanchis Post Number: 39 Registered: 10-2009 Posted on Monday, August 08, 2011 - 05:26 pm:    I have no experience with PMMA, but I should share my experience with liquid-applied roofs over foam. We seldom specify this type of roof, except for one client, and then it's applied directly to concrete. It happens that birds, especially sea gulls, love the stuff. What they do with it, I have no idea, but on at least 2 roofs that we were asked to re-roof, the birds picked and picked at the roof until it looked like a Swiss cheese. Needless to say, the owner did not want to replace the failed roofs with the same system. Regarding venting of parapet walls, I've never heard of it. Could someone explain the logic for doing it, and why parapet walls and not the building walls? Wayne Yancey Senior Member Username: wayne_yancey Post Number: 483 Registered: 01-2008 Posted on Monday, August 08, 2011 - 06:15 pm:    Like Gerard, I'm also confused about venting parapet walls. My only experience with venting in a parapet was in wood frame buildings with insulation under the roof deck with air spaces above vented up through the parapet. The Lstiburek article (INSIGHT-050) I have on parpapets only discusses venting for balloon framing (Figure 14). Figures 12a, 12b, 13, and 15 make the parapet as air tight as possible. Balloon framing should be avoided in my humble opinion. Figures 12a, 12b, 13 are preferred. Go to www.buildingscience.com for Insight-050. Brian E. Trimble, CDT Senior Member Username: brian_e_trimble_cdt Post Number: 52 Registered: 08-2005 Posted on Friday, August 12, 2011 - 11:21 am:    I'm not sure that anyone is recommending venting the parapet wall. What I am recommending is that the natural characteristics of a masonry parapet be allowed to work which is the natural absorption and evaporation through the face of the masonry. What I don't think is a good idea is the seal the wall with a bituminous coating or other waterproof membrane. That would trap water in the wall and force any evaporation to occur through just the exterior facade elements, and that may not be enough surface area. Having said that, I am a proponet of vented brick cavity walls. I also agree with Lstiburek's recommendations for parapet walls. Wayne Yancey Senior Member Username: wayne_yancey Post Number: 486 Registered: 01-2008 Posted on Friday, August 12, 2011 - 11:43 am:    Brian, You raise a good point about mass wall parapets built-up with burned clay brick, however, at my firm, we don't design in mass brick walls unless it is plant-cast or site-cast precast (tilt-up). Concrete is not as absorptive as clay brick. For precast we protect the roof side face of the precast with the cap membrane and the exposed face with a water repellent. No issues at this time. Masonry mass walls do occur in the odd renovation, such as the one I am currently specifying for. In this case the roofing membrane terminates 8" above the toe of the cant to permit the mass wall to breath (I assume). Mass parapet walls on this project are varied: composite of stone and brick, all stone, and some with 3 wythes of brick. Anne Whitacre, FCSI CCS Senior Member Username: awhitacre Post Number: 1189 Registered: 07-2002 Posted on Friday, August 12, 2011 - 12:56 pm:    Gerard: the original membrane roof on the now departed KingDome (Seattle) also was regularly attacked by seagulls. the offgassing of the roof apparently made them slightly drunk so they just sort of hung out there a lot. (Seagulls were not permitted in the neighborhood bars.) as far as venting, I regularly like to see vented parapets and vented walls -- I think that air movement through those spaces makes for a better assembly. even in a wet climate like Seattle's, the RH remains in the healthy level rather than in the mold-forming level. Jim Sliff Senior Member Username: jim_sliff Post Number: 84 Registered: 08-2010 Posted on Monday, August 22, 2011 - 10:12 pm:    Gerard - We had several to repair in Santa Monica - and inland crows like urethane as well. I don't specify foam without a heavy elastomeric roof coating - generally 80mils and up or polyurea or hot-applied polyurethane with granules - to prevent the bird issues. Haven't had any problems with a good membrane on top, which IMO is a good idea with foam anyway - no matter how well you write maintenance specs workers will break through the coating exposing the "snack". Jim Sliff Senior Member Username: jim_sliff Post Number: 85 Registered: 08-2010 Posted on Tuesday, August 23, 2011 - 12:42 am:    I neglected to add that in the 80's I worked a lot with Verizon (it was General Telephone in those days) - they'd specified foam for several years with acrylic roof coatings, discovered the stuff was bird food, and tore 'em off, replacing them with nothing but Hypalon...which ended up having more problems (as I recall mostly installation-related, with seam failures). So they started tearing THOSE off - and replaced them with SPF again, except with the high-build elastomers now available. Each of the 3 systems required a different system for handling parapet caps, flashing and other variations-on-a-theme...with each manufacturer seemingly having some unique (or bizarre) twist that caused the subcontractor to reinvent the wheel. Which brings to mind my previous life; only one company I worked for pushed similar faux "product standards", but it's pretty common knowledge in the applicator world that manufacturers come up with their own quirks to gain an edge. Sometimes it's one unique, sole-source product shown on the details that is not vital, but also not part of anyone else's system. If they get it "sold" to the Project Architect or Specifier chances are the other will go along for the ride, eliminating competition (if there's no "equal" and no protest it's often a slam-dunk). Waterproofing details, both in fluid-applied roofing membranes and deck coatings are two of the applications where these attempts at gaining "sole-source" status still show up regularly. It takes a lot of study and research just to prevent these problems from occurring. It's really annoying.