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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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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:   Edit PostDelete PostPrint Post

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

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