Archive through August 22, 2005

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Author Message David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 494 Registered: 03-2002 Posted on Friday, August 12, 2005 - 12:23 pm:    Does anybody have any good or bad experiences on self-leveling gypsum underlayments? (We normally specify cementitious underlayments.) John Regener, AIA, CCS, CCCA, CSI, SCIP Senior Member Username: john_regener Post Number: 222 Registered: 04-2002 Posted on Friday, August 12, 2005 - 08:10 pm:    Are you referring to gypsum cement floor fill, such as Gypcrete, and cellular concrete floor fill, such as Elastizell? Or, are you referring to thin section floor leveling compounds such as the high-strength portland cement products produced by Ardex? The criticism of gypsum-based floor fill is its alleged breakdown over time due to point and rolling loads. But it doesn't shrink and crack like cellular concrete. For leveling and filling concrete slabs, I only specify portland cement base underlayment. I'm leary of gypsum-based products because of less than desirable resistance to degradation from moisture. There's also an issue of sealing a gypsum product so that adhesives will make effective bonds. (Unregistered Guest) Unregistered guest Posted on Friday, August 12, 2005 - 07:15 pm:    David, check with the manufacturers of the floor coverings you plan to put over the underlayment. A few years ago some of them told me that gypsum was unsuitable for adhesion of their products. It needed some sort of hardener. I don't remember the details, but I remember that there was a problem. I agree that cementitious is better. Anonymous   Posted on Friday, August 12, 2005 - 05:12 pm:    we specify gypsum underlayment routinely. never had a bad experience (10 years running), not sure what would qualify for you as a "good" experience with this product. I mean, i didn't lose my virginity on a floor covered with gypcrete, have never experienced any sort of euphoria walking over one... anon Anonymous   Posted on Thursday, August 18, 2005 - 02:52 pm:    The only self-leveling underlayment our firm specifies is a cementitious underlayment. Gypsum based products have most of the problems indicated in these posted messages. Brett M. Wilbur CSI, CDT, AIA Senior Member Username: brett Post Number: 58 Registered: 12-2004 Posted on Thursday, August 18, 2005 - 04:32 pm:    Just like Unregistered Guest states above, check with the flooring manufacturers recommendations. Some may not warrant their flooring products if used over gypsum underlayment. Especially on ground floor. We use Ardex K-15 routinely as our basis of specification but have seen other good products by Pre-blend Products, Inc., or Degussa Chemrex Inc. All three have portland cement based products. The Pre-blend is a portland cement based modified polymer underlayment. We are trying not to use any gypsum based products anymore, fireproofing and such, for IAQ reasons. The organic compounds are too susceptible to bacteria growth and may soften if exposed to moisture. David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 499 Registered: 03-2002 Posted on Thursday, August 18, 2005 - 08:34 pm:    Okay I will name names. USG has really been doing the full court press on my firm to specify Levelrock. Years ago my firm had a failure with a gypsum based levelling compound. Since that time the partners have been very gun shy about using any gypsum based levelling compound. Portland cement based products are fine and we regularly specify about a dozen different brands. Anonymous   Posted on Monday, August 22, 2005 - 02:39 pm:    We recently were called in to do some forensic and remedial work for a client who was experiencing substantial bond failures in a slate tile floor installed over gypsum underlayment. The flooring and underlayment had been installed over both new and existing concrete slab on grade. When exposed to water, gypsum can react with some elements present in portland cement to create an expansive salt known as ettringite. See the CTIOA field report at http://www.ctioa.org/reports/fr100.html Since being involved with this project, we have only specified cementitious underlayments. Posting anon. because the project is still active, but I'd be willing to share additional information offline, if you wish. Doug Brinley AIA CSI CDT CCS Senior Member Username: dbrinley Post Number: 87 Registered: 12-2002 Posted on Monday, August 22, 2005 - 02:47 pm:    Ardex is marketing 'moisture control solutions' = epoxy. Does anyone have experience with this epoxy system? We specify cementitious products (no gypsum) but we place emphasis on the workmanship of the concrete pour, and appropriateness of the concrete mix (with respect to the weather as much as anything). David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 503 Registered: 03-2002 Posted on Monday, August 22, 2005 - 03:29 pm:    Anon, Yes please share info on gyp underlayments. I'm at daxt AT bassettiarch DOT com. Thanks! David Axt, AIA, CCS, CSI Senior Member Username: david_axt Post Number: 504 Registered: 03-2002 Posted on Monday, August 22, 2005 - 03:40 pm:    I'll throw this out there for what it is worth. My understanding is that Gypcrete had so many failures that they changed their company name to Maxxon. Same stuff, different package. Anonymous   Posted on Monday, August 22, 2005 - 03:51 pm:    Judging from the postings, it appears that folks are of the opinion that gypsum and cement based underlayments are interchangeable, which is not my position, nor have I ever specified these products in that way. I specify cement based underlayments as floor repair and as (rarely) floor finishes. I specificy Ff anf Fl requirements for slabs and require self leveling cement based underlayment products if the contractor is unable to meet the spec for the slab. I only specify gypsum based underlayments for wood framed floor assemblies that need hourly ratings. I have never had a problem with these products specified in this way. The USG product is comparable to Maxxon products. anon