Question for a Chemist?

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Author Message Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 481 Registered: 05-2003 Posted on Friday, December 21, 2007 - 05:46 pm:    Is "Anhydrite" (calcium sulfate) in non-shrink cement grout considered as gypsum - we specified the high strength grout to be "gypsum-free", the MSDS shows it to contain Anhydrite. Should we be concerned? Marc C Chavez Senior Member Username: mchavez Post Number: 264 Registered: 07-2002 Posted on Friday, December 21, 2007 - 06:50 pm:    just add water to CaSO4 and you get...gypsum CaSO4-2H20. I remembered most of that from my geology days AND I looked it up to confirm. SO I'd say; yes! The product will have gypsum in it when you add water. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 39 Registered: 10-2005 Posted on Friday, December 21, 2007 - 07:27 pm:    Hi Jerome, You should not be concern Anhydrite is used in very small quantities in our grout. I am sure it is the same for our competitors. It will not support mold growth if that is your concern. Even Portland cement contains a small amount of anhydrite. It is not like gypsum in wall board. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 482 Registered: 05-2003 Posted on Friday, December 21, 2007 - 09:45 pm:    The question is if the grout is exposed to moisture would the grout eventually fail due to distinigration of the Anhydrite? For example grouting around pipe railing posts, we call out for a non-shrink, non-metallic, Gypsum-free grout. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 821 Registered: 03-2002 Posted on Wednesday, December 26, 2007 - 08:58 am:    I have read about failures such as Jerome describes, though I don't recall what percentage of gypsum was in those products, or if the articles I read had that information. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 40 Registered: 10-2005 Posted on Friday, December 28, 2007 - 05:20 pm:    I can speak for our (Custom Building Products Prism) grout 118.7 will not fail if it comes in contact with moisture There is no residual gypsum or anhydrite after curing, the calcium sulfate reacts chemically with other components to form Ettringite. Ettringite is not water soluble, nor is it reactive after hardening rendering the cured material extremely durable in virtually all environments. This is why gypsum is added to cement. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 41 Registered: 10-2005 Posted on Thursday, January 03, 2008 - 10:29 am:    Jerome i just wanted to make sure you were talking about grout for tile and stone. There are some differences between grout to be used with ceramic tile and “non-shrink, non-metallic, gypsum free machine grout”. This type is generally used to fill voids that are considerably larger that the largest tile joint. Because of this it is very important that the grout does not shrink away from the pipe or post, nor should it expand so much as to break the surrounding concrete. my advice has been for tile and stone. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 483 Registered: 05-2003 Posted on Thursday, January 03, 2008 - 10:49 am:    Dale, the query was for "non-shrink, non-metallic, gypsum free machine grout" not tile grout. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 42 Registered: 10-2005 Posted on Thursday, January 03, 2008 - 11:31 am:    Sorry 118.7 is for tile my apologies for my misunderstanding. Dale Roberts CSI, CDT Senior Member Username: dale_roberts_csi Post Number: 43 Registered: 10-2005 Posted on Thursday, January 03, 2008 - 11:41 am:    When machine grouts are used, you expect a slight expansion to help reinforce the positioning of the post in the concrete. Ettringite expands during curing, which is why it controls shrinkage. Ettringite is not water soluble, nor is it reactive after hardening, rendering the cured material extremely durable in virtually all environments. I still think you should not be concerned about the Anhydrite in the grout.