Cast-in-Place Concrete or Architectur...

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Author Message Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1544 Registered: 05-2003 Posted on Wednesday, January 06, 2016 - 07:20 pm:    I am working on a job with poured in place concrete balconies, CBS envelope and flat concrete slabs. The architect wants to expose the underside of the concrete balconies, sandblast them and than paint them. The Concrete spec has been written by the Structural Engineer. The architect want me to create an Architectural Concrete spec to address the finish of the underside of the balconies. I am perplexed, why can't the Structural PE just modify their spec to include sandblasted finishes. I forsee confusion in adding an Architectural Concrete section. Not sure how to paint a sandblasted concrete finish? Bizarre job? Help? Dave Metzger Senior Member Username: davemetzger Post Number: 619 Registered: 07-2001 Posted on Wednesday, January 06, 2016 - 07:59 pm:    Jerome, Architectural concrete is typically used for exposed concrete finishes. I agree with you that an architectural concrete specification section is not needed in this instance. But what's the point of sandblasting the concrete if the concrete then will be painted? Why not just use a smooth-form finish, eg MDO (medium density-overlay plywood)? And depending on the paint selected, a typical (rough-form) plywood formwork finish could be used. There are heavy-bodied acrylic paint available specifically intended for concrete. ken hercenberg Senior Member Username: khercenberg Post Number: 972 Registered: 12-2006 Posted on Wednesday, January 06, 2016 - 08:11 pm:    A decent high performance coating may need some form of blasting as surface prep. I presume you're going to use some type of acrylic coating (TexCote, Miracote, or similar). Perhaps check with them as to what their surface prep is. I agree with Dave; definitely not architectural concrete. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1545 Registered: 05-2003 Posted on Thursday, January 07, 2016 - 01:25 am:    Dave, the structural engineer is refusing to revise their specs to specify a smooth form finish, IMHO, the structural PE does not know how to specify this, please don't ask why, this engineer is a thorn in my side, doesn't write specs well, reuses archaic specs, won't take direction, and is one of the largest engineers in FLorida...difficult to work with. Since the structural engineer will not revise their specs, I need to come up with a work around solution. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1546 Registered: 05-2003 Posted on Thursday, January 07, 2016 - 01:30 am:    I have had success with a product similar to Texcote, BASF's Masterprotect HB (formerly Thorocoat) its a high build 100% acrylic coating, its perfect for this area, but selling it to the developer, not so easy. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 774 Registered: 10-2007 Posted on Thursday, January 07, 2016 - 08:51 am:    There is no good work around if the structural consultant will not cooperate. That said the CIP Concrete specification prepared by the engineer should address decisions that need to be made prior to the casting of the concrete. This includes the need for a smooth form finish and the tolerance in the offset at plywood edges. An architectural concrete specification section should address post casting treatments and coatings. Let the Project Architect know of the problem so it is now his problem. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1547 Registered: 05-2003 Posted on Thursday, January 07, 2016 - 08:58 am:    THANKS MARK, GREAT EXPLANATION Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP Senior Member Username: specman Post Number: 1376 Registered: 03-2003 Posted on Thursday, January 07, 2016 - 10:08 am:    I suggest using Section 03 35 00 "Concrete Finishing" to address only the finishes and not the concrete itself. I know this section is intended for finishing after placement of concrete, but you can try to address form finishes here, too. If the structural engineer won't address form finishes, then have him remove anything regarding finishes (formed and hand finishing) he does have in the specification and replace it with a reference to your finishes section. Ron Geren, FCSI, AIA, CCS, CCCA, SCIP www.specsandcodes.com Wayne Yancey Senior Member Username: wayne_yancey Post Number: 772 Registered: 01-2008 Posted on Thursday, January 07, 2016 - 12:42 pm:    I 2nd Ron. I follow his recommendations just as he described for the past 25 years. Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 106 Registered: 10-2003 Posted on Thursday, January 07, 2016 - 02:35 pm:    Take a look at Wonderfixx by CTS Cement as an alternative to sandblasting. It can cover a lot of defects in a concrete surface and is very paintable. Michael Chusid, RA FCSI CCS www.chusid.com www.buildingproduct.guru John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1663 Registered: 03-2002 Posted on Saturday, January 09, 2016 - 04:44 pm:    Sandblasting may be intended to address potential incompatibility with form release agents(?). But, there may need to be other prep to remove fins and other defects, or to fill holes. Use of architectural concrete does seem to be overkill because it's costly, but this level of prep also is pretty costly. J. Peter Jordan Senior Member Username: jpjordan Post Number: 883 Registered: 05-2004 Posted on Sunday, January 10, 2016 - 11:10 am:    I am of the opinion that if the concrete surface is to be sandblasted and painted, it should be "regular" structural concrete. The intent of designating it "architectural" may be to reduce the "defects" such as bug holes and honeycombs. These can be patched before sandblasting. The primer is important since it will "normalize" the concrete surface so the finish coat(s) will be uniform in terms of color and sheen. Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1552 Registered: 05-2003 Posted on Thursday, January 14, 2016 - 04:54 pm:    Michael, do you know if Wonderfixx is stainable? Michael Chusid, RA FCSI CCS Senior Member Username: michael_chusid Post Number: 110 Registered: 10-2003 Posted on Thursday, January 14, 2016 - 05:39 pm:    1. If you mean stains from organic debris, copper run-off, rust, urban pollution, etc., the the answer is yes, it will stain. 2. I doubt it works well with reactive stains that depend on a reaction with lime. Wonderfixx is based on an calcium alumino silicate cement, not portland cement, and does not produce as much lime when it hydrates. 3. If you mean a dye type of stain, it probably will accept dye. However, the thickness of the Wonderfixx varies from 0.5 inch to nothing, and areas of the underlying portland cement remain exposed, so the dyed surface will be visually inconsistent. I see it mostly as an alternative to rubbing and sacking for an exposed concrete finish and as a surface prep for painted concrete. I wrote an article about it in Specifier in 2006 - see http://www.chusid.com/pdf/The%20Construction%20Specifier,%20Giving%20the%20Sack%20to%20Concrete%20Sacking%20and%20Patching,%202006-12.pdf For additional info, contact Matt Sambol at CTS, the co-author: msambol at ctscement dot com. Michael Chusid, RA FCSI CCS www.chusid.com www.buildingproduct.guru Jerome J. Lazar, RA, CCS, CSI, SCIP Senior Member Username: lazarcitec Post Number: 1553 Registered: 05-2003 Posted on Thursday, January 14, 2016 - 05:44 pm:    Thanks Michael Steve Gantner, RA, CSI, CCS, CCCA Senior Member Username: sgantner Post Number: 45 Registered: 08-2007 Posted on Wednesday, January 20, 2016 - 05:12 pm:    I'm just getting caught up on my 4specs reading. Why not include the prep work required (sandblasting, etc.) in the painting/coating spec, by-passing the structural engineer?