Extruded vx Expanded Polystyrene in EIFS

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Author Message Robin E. Snyder Senior Member Username: robin Post Number: 91 Registered: 08-2004 Posted on Friday, February 23, 2007 - 10:47 am:    A client recently asked me about a spec written by another spec writer (who is no longer available to question). In the EIFS section they specified extruded Polystyrene and said "Expanded polystyrene is not acceptable", but, when I look at a manufacturer's website (IE, Dryvit) they call out for expanded polystyrene. Any ideas why I wouldn't want to allow EPS? Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 318 Registered: 05-2003 Posted on Friday, February 23, 2007 - 02:28 pm:    EPS is actually a bad term as EPS can be either expanded or extruded polystyrene. Extruded due to its manuf processes is resistant to moisture, its closed cell structure resists the movement of moisture we use it for insulation all the time. Expanded polystyrene is manuf in a totally different manner and will allow moisture to pass thru it. We specify Expanded for decorative ornamentation because it can be easily shaped into all kinds of crazy profiles, but in doing that we always specify a modified cement wp over the substrate to receive the profile. Extruded is sometimes called blue board (expanded is always white and looks like bead board) and is much more expensive than expanded. It really depends on the assembly for the EIFS product and how the manuf deals with the moisture issue. George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 257 Registered: 11-2004 Posted on Friday, February 23, 2007 - 02:44 pm:    I have heard the terms EPS (for expanded) and XPS (for extruded), but am not sure if those acronyms come from some standard or if they are just manufacturer's jargon. I agree it is confusing, and am in the habit of spelling it out in the specification. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 319 Registered: 05-2003 Posted on Friday, February 23, 2007 - 02:51 pm:    Yes George, I too prefer to spell out terms, and yet my clients still are confused - like with ESP, its like banging heads to get them to understand its a process not a paint. I believe there was a good article in the Specifier on Extruded Polystyrene a couple of months ago, perhaps someone could dig up a link for that for Robin - I'm swamped today on deadlines, otherwise I would. Wayne Yancey Senior Member Username: wyancey Post Number: 287 Registered: 05-2005 Posted on Friday, February 23, 2007 - 05:16 pm:    Robin, Manufacturing may have changed since my experiences occured, but extruded polystryene (or Styrofoam Blue as it was regionally called) had large lettering and logos printed in the surfaces and over time would telegraph through the basecoat, mesh and finish coat. This phenomena required rasping of the face skin of the XPS which was labor intensive with resultant cost implications. XPS did have the advanatage of superior compressive strength but this may be offset with additional reinforcing at lower elevations. I will try to dig up the past when I am able. Wayne Sheldon Wolfe Senior Member Username: sheldon_wolfe Post Number: 231 Registered: 01-2003 Posted on Friday, February 23, 2007 - 05:49 pm:    ASTM C578 refers to "cellular polystyrene boards...made by molding (EPS) or extrusion (XPS)" George A. Everding, AIA, CSI, CCS, CCCA Senior Member Username: geverding Post Number: 258 Registered: 11-2004 Posted on Friday, February 23, 2007 - 06:29 pm:    Thanks, Sheldon. I was quite embarrassed to learn that the definition is right there in the reference standard we use all the time, (PRM says "know the standard"). So I decided to look it up in my copy of C578-03 and surprised to find it wasn't there at all. Then I checked the ASTM website and found the current standard is C578-06. More embarrassment. (PRM says "use the current standard") Sure enough, XPS and EPS have been added in the more recent version. Enough knowledge for one week. It’s Friday evening and I’m going home. Ron Beard CCS Senior Member Username: rm_beard_ccs Post Number: 171 Registered: 10-2002 Posted on Friday, February 23, 2007 - 06:33 pm:    The polystyrene industry has certainly expanded [no pun intended] the design professions' available choices. My first recollection of extruded polystyrene was when DOW introduced it as a part of their IMRA "upside-down" roofing system. XPS had a high compressive strength, 40-psi, and could survive quite well in standing water. The hype then was if you specified expanded polystyrene you get a coffee cup. Most architects, however, are not aware that DOW makes some very high-compressive strength XPSs. They have a civil engineering line that has products starting at 100-psi. I have specified 100-psi XPS in terraced gardens where very large "potted" trees [tons of weight] where supported waterproofing membranes [to avoid problems with mfrs roofing warranties]. I have also specified one of DOW's 100-psi XPS specialty products with an asphaltic top coat where a hot asphalt driveway was applied right to the XPS [had very limited space available over a boiler room to receive a driveway for ambulances at a local hospital]. But the expanded polystyrene industry has likewise improved. The EIFS industry product line for example. EPS is being used now in multiple product lines in both interior and exterior applications: interior moldings, inserts in wood/composite doors, SIP's, belowgrade drainage panels, highway construction, and many other applications to numerous to mention. I have even specified very large blocks of highway EPS to fill-in large voids over terraced to substantially reduce weight on structure [see: http://www.geosyscorp.com/noframes/products.htm]. This product was used quite extensively on an Interstate highway out near Colin's place. Jeffrey Wilson CSI CCS Senior Member Username: wilsonconsulting Post Number: 6 Registered: 03-2006 Posted on Saturday, February 24, 2007 - 11:40 am:    Masterspec uses "molded polystyrene" rather than "expanded." I prefer the former term because it is easier to distinguish from extruded-polystyrene. I, too, spell out the terms for both these products in specs, but use "MPS" and "XPS" in correspondence w/ clients to discuss the differences. I avoid "EPS" because it can easily be confused for either product. ASTM C 578 uses "RCPS" (rigid cellular polystyrene) as the abbreviation for both molded & extruded polystyrene. How's that for confusing? According to Masterpec's Evaluations for EIFS, MPS (which they refer to as EPS) is the most common insulation type recommended by EIFS manufacturers. I suspect that the prohibition against the expanded (molded) product in the original post related to what the specifier might have known about the differences between MPS and XPS in below-grade or other moist environments. Phil Kabza Senior Member Username: phil_kabza Post Number: 235 Registered: 12-2002 Posted on Sunday, February 25, 2007 - 02:05 pm:    Does anyone have expanded (sorry) information about long-term performance of MPS compared to XPS with respect to moisture absorption and the related reduction in thermal resistance value? This is an interesting topic if the thermal performance is a reason for selecting EIFS in the first place. My hot tub cover (MPS) has gotten considerably heavier over its 4-year life. I'm certain the added weight is all moisture, and that it no longer insulates as well as it used to. I imagine there are EIFS walls around doing the same thing. Anyone have probes and data? Wayne Yancey Senior Member Username: wyancey Post Number: 292 Registered: 05-2005 Posted on Tuesday, February 27, 2007 - 10:55 am:    Akrilon Industries Inc. reports molded polystyrene or expanded polystyrene "...has good adhesion because it is an open cell board, whereas if we were using extruded polystrene we'd have to take the skin or the face off in order to gain proper adhesion for application of the board." John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 661 Registered: 03-2002 Posted on Tuesday, February 27, 2007 - 03:27 pm:    EIFS is quite out of favor in New England, still, after the well-known problems of a number of years ago (which pre-date the famous Atlantic coast problems in residential). Thus, it is rarely used in this harsh climate. A common approach when it was used: extruded polystyrene used with mechanical fastening and mesh reinforcing. When this is done, the adhesion of the "finish" to the insulation is not an issue. However, my information is out-of-date. Concerns centered around failure of adhesion to gypsum sheathing (I'm talking of the original gyp sheathing, here, not glass mat), and the higher absorbtion of expanded PS. My personal view is that the density of the insulation is not very important in this environment, but moisture absorption is. Wayne Yancey Senior Member Username: wyancey Post Number: 296 Registered: 05-2005 Posted on Wednesday, February 28, 2007 - 06:06 pm:    In my first posting, I mentioned the lettering/logo subliminally showing through the base and finish coats. Before, [insert manufacturers name] started planing the surfaces of their extruded polystytrene, the name XXX STYROFOAM could be seen across the street from a school in Edmonton, Alberta Canada. New to the EPS market is a high-density EPS that provides 40 psi compressive strength. It is marketed by Beaver Plastics under the trade name TERRAFOAM. MeetsASTM C578-05 Type 14 – 276 kPa (40 psi) Compressive strength. This is the product now used by Akrilon Industries Inc. in the EIFS system.