Archive through November 06, 2013

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Author Message David J. Wyatt, CDT Senior Member Username: david_j_wyatt_cdt Post Number: 35 Registered: 03-2011 Posted on Tuesday, November 05, 2013 - 10:26 am:    I am doing CA for an exterior restoration project. It includes restoring spalled areas of pre-cast concrete wall panels with exposed aggregate finish. The panels were cast in the early 1970s. The contractor has made several attempts to patch the spalled areas with an aggregate-and-mortar mixture, but is having trouble matching the aggregate color, size, and workmanship of the original panels. I am about to recommend an epoxy and aggregate mixture to effect a better match. Does anyone have any recommendations? Ralph Liebing, RA, CSI, CDT Senior Member Username: rliebing Post Number: 1444 Registered: 02-2003 Posted on Tuesday, November 05, 2013 - 10:46 am:    Matching the aggregate is a losing battle as aggregate is natural materal and has an unbouded array of colors and no set palate where color is within a constant range. Matching, I think, is a problemn without solution. Whatever you use as setting material is not going to solve this problem either. ken hercenberg Senior Member Username: khercenberg Post Number: 641 Registered: 12-2006 Posted on Tuesday, November 05, 2013 - 02:04 pm:    I'd be hesitant to use an epoxy as your matrix since your chances of spalling will be pretty high over time. Have you considered using a repair mortar designed for this type of work? I usually use either Jahn Mortars by Cathedral Stone or Edison Coatings. Used more often for stone and masonry but no reason why you couldn't use them for precast panels. As Ralph pointed out, matching the exposed aggregate can get tricky but it is usually possible. Ellis C. Whitby, PE, CSI, AIA, LEEDŽ AP Senior Member Username: ecwhitby Post Number: 209 Registered: 03-2003 Posted on Tuesday, November 05, 2013 - 02:12 pm:    Matching the aesthetics of existing concrete is not something that the average GCs and concrete contractors can do, notwithstanding how good they are otherwise. This is a fairly specialized talent. John Bunzick, CCS, CCCA, LEED AP Senior Member Username: bunzick Post Number: 1542 Registered: 03-2002 Posted on Tuesday, November 05, 2013 - 02:15 pm:    Another down side of patching with epoxy in particular, and to a lesser extent with polymer modified Portland cement, is that the materials have very different rates of moisture absorption from the original concrete. This can result in the patches being extremely visible during wet weather, perhaps in an undesirable way. David J. Wyatt, CDT Senior Member Username: david_j_wyatt_cdt Post Number: 36 Registered: 03-2011 Posted on Tuesday, November 05, 2013 - 02:15 pm:    Gentlemen, Thank you for your responses. There is a vein of wisdom in each of them. Lynn Javoroski FCSI CCS LEEDŽ AP SCIP Affiliate Senior Member Username: lynn_javoroski Post Number: 1721 Registered: 07-2002 Posted on Tuesday, November 05, 2013 - 02:25 pm:    I'd start by contacting ChemMasters, BASF, and maybe Prosoco. Ask each what they would do, what products they have and would recommend. Ronald J. Ray, RA, CCS, CCCA Senior Member Username: rjray Post Number: 124 Registered: 04-2004 Posted on Tuesday, November 05, 2013 - 05:44 pm:    I would suggest you encourage the contractor to try and determine the original precast plant, and attempt to obtain aggregates from their orginal source. It is unlikely that their source has changed even after 40 years Justatim Senior Member Username: justatim Post Number: 55 Registered: 04-2010 Posted on Wednesday, November 06, 2013 - 07:27 am:    It may also be useful to have the "sound" remaining concrete tested to determine the likely mode of failure of the spalling and the depth of carbonation. This can guide your selection of repair methods. If any of the panels are beyond repair, consider using them as a source of raw aggregate... it's a bit expensive, but the color should match... at least the surface aggregate should match. Also consider that, on older panels, you may see as much or more sand as aggregate and cement matrix. Until the surface paste wears away or is abraded, the patch may not match the original. David J. Wyatt, CDT Senior Member Username: david_j_wyatt_cdt Post Number: 37 Registered: 03-2011 Posted on Wednesday, November 06, 2013 - 08:47 am:    Thank you, all. I took Ron Ray's suggestion and contacted the original pre-cast panel manufacturer, who is sitting on the same quarry. We really could not do better in the client's eyes.