Integral water repellents in CMU

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Author Message David G. Axt, CDT, CCS, CSI, SCIP Senior Member Username: david_axt Post Number: 2076 Registered: 03-2002 Posted on Thursday, May 02, 2024 - 01:53 pm:    There has been some discussion lately about integral water repellents in concrete masonry units. Do they affect the mortar bond strength? Do they affect the application of surface-applied water repellents? David G. Axt, CDT, CCS, CSI, SCIP Specifications Consultant Axt Consulting LLC (Unregistered Guest) Unregistered guest Posted on Friday, May 03, 2024 - 10:47 am:    My understanding is that most manufacturers add this to the CMU mix whether you specify it or not. Since units are not marked, the only way to verity if this has been done is do put a couple of drops of water on it to see if the water soaks in or beads up. What this means is that you would have a significant number of bond failures, and I suspect this is not the case. ken hercenberg Senior Member Username: khercenberg Post Number: 1627 Registered: 12-2006 Posted on Friday, May 03, 2024 - 02:17 pm:    We always specify the matching mortar admixture to ensure compatibility. When not specified, I understand that it's added in lesser amounts to aid in form release.