Course Objective PRECAST CONCRETE REPAIR: ARCHITECTURAL CONCRETE. Precast Show 2018 NPCA 1

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1 PRECAST CONCRETE REPAIR: ARCHITECTURAL CONCRETE Course Objective Matching concrete colors and finishes in architectural precast repairs. Barry Fleck CEO, ALP Supply 1 2 The Difference Between Commercial and Architectural Concrete Repairs Commercial Finish Repairs Commercial Finishes Sound Walls, Median Barriers, Warehouse Walls, etc Functional concrete performance Aesthetics, color and finish match is what the customer is paying for Not acceptable for architectural repair 3 Standard structural concrete mixes use plain grey cement for color. Color consistency from panel to panel may vary slightly. Steel form finishes are typical Standard concrete color determined by cement and aggregate Color ranges from white to dark grey or even a light beige 4 Architectural Repairs Architectural concrete mixes use white cement and grey pigments to maintain consistency from panel to panel. Color and texture need to match closely Use original ingredients Repair material not pre-mixed Different finish tools needed 2 Types of Repairs 1. Structural Defects Cracks Spalls Dimension Issues Block Outs Delamination 2. Aesthetic Defects Finish Issues Bug Holes Texture Chips Color Variations & Efflorescence Do repairs prior to shipping. Much cheaper than on job sites. 5 6 NPCA 1

2 Start at the Beginning Establish a written procedure Repair Process Evaluation: Is it Cosmetic or Structural? Damaged surface? Finish difference? Color difference? If Structural: Identify cracks that could impact performance Repairs near connections can be an issue 7 8 Commercial Finishes Structural Concrete Cosmetic Repairs Variations occur with non-architectural concrete mix from panel to panel Requires matching the average color/shade of the panels Can be accomplished using prepackaged repair products > Blending gray and white patching cements from the same manufacturer > Blending job mix using a rich mix of cement and sand on site 9 10 Premixed Patching Cement Provides consistent color from bag to bag Placement consistency Water ratio dependent Set time allows for placement and finish of the repair NPCA 2

3 Structural Gray Color Matching Can blend white patching cement with grey patching cement from same manufacturer Different ratios provide different shades Prepare 4-5 different blended mixes to compare against product you re repairing Job mixing, use white and gray together with sand Less workable consistency No set time harder to place Requires precise mixing of ingredients Repair Mix Design Cement to Sand Ratio Typical Repair Mix Ratio Cement: 42-50% Sand: 50-58% Critical Factors Cement Range Below 30% - Bond failure / low strength Above 43% - Shrinkage range but higher strength Sand Range Above 70% - Low strength Above 73% - Sandy mix Repair Mix Design Grey / White Cement Ratios Grey Cement: 50-90%. White Cement: 10-50% Blended Cement Ratios 42% Cement Ratio for 5 lb Mix Gray % Gray (lbs) White (lbs) White % 50% % 60% % 70% % Batching of the Repair Material for Architectural Concrete Repairs 80% % 90% % Must control consistency in paste, aggregate and environment: Physical differences in cements, sands and aggregate Environmental differences in curing conditions Weigh the amount of water used to control W/C and maintain consistent color Fresh Cement Settled Cement Repair mix must closely match the original concrete mix: Tight control over ingredients by weight not volume Use dry sifted aggregate to control moisture and W/C to be consistent NPCA 3

4 Mix 1 part cement to 1 or 1-1/2 parts of No. 16 screened sand Richer cement mix = better workability, more mix shrinkage Leaner cement mix = less bond strength, workability Sand should not be too fine Do not use Air-entraining admixtures Latex bonding admixtures increase workability, tensile strength and patch bond Ratios 1 part water to 1-2 parts bonding agent Mixing time and method must be consistent Water/cement ratios influence colors One batch at a time Add pigment after the water to prevent clumping and streaking Trowel trick to gauge mix consistency Job Mix Design Develop repair mix before production Compare to approved mock-up Get approval for patch color on mock-up NPCA 4

5 Job Mix Design Job Mix Design Original mix design is the starting point. No aggregate in mix alters finished color when matching Gradually increase white cement, add pigment if necessary Add white cement to offset the lower W/C ratio of patch vs. concrete Less water = darker patch, so use white cement to offset the curing difference The density of the patch is different than the concrete being repaired. Trial mixes should go from darker to lighter to provide matching options Use pigment as control, do not change the weight of the mix Job Mix Design For color adjustments change amount of sand and cement Put sample in a mold for placement consistency and finish the top surface Make several samples from lighter to darker Set Times vs. Cold Temperatures Mix Temperature 72 F 51 F 49 F Curing Temperature 72 F 72 F 40 F Vicat Initial Set 19 min 36 min 59 min Vicat Final Set 23 min 43 min 71 min #1 Red #2 pink #3 Salmon 500 grams sand 600 grams sand 650 grams sand 250 grams white cement 300 grams white cement 325 grams white cement.5 grams red pigment.5 grams red pigment.5 grams red pigment Color Matching Which one do you want us to match? Choose one shade lighter, as repairs darken with curing Color matching is not instant Mock-up repairs Seek approval of patch color Factors Color Matching Cement Dominant factor Sand Larger particle size Dominates color range Increasing lightens / decreasing darkens Placement Finishing NPCA 5

6 Color Matching Color Matching Issues Natural Colors Blend grey and white Shading differences Pigmented finishes Blend pigments for desired color Patches must fully cure Concrete absorption rate, moisture exposure Time from fabrication to patch During product repair: Maintain consistent curing environment Imitate the production environment Document curing environment Longer cured/darker and lighter if patch dries out faster Repair texture must duplicate the product finish Color Matching Issues Repair prior to shipment AIA standard for verbal approval is 20 feet Only repair if appearance is improved Allow sufficient cure time Staining is another option It requires curing time, days for final color Repair Process Installation Installation Establish a Repair Procedure The 3 biggest items for all successful concrete repairs: The single biggest factor in repair failures is improper preparation. Preparation, Preparation, and Preparation NPCA 6

7 Repair Depths Repair Depths Depth should be 1.5 times the maximum aggregate size Use mechanical anchors for large repairs Add larger aggregate as filler Use forms with large patches Determine if bonding agent is required Square cut to a minimum depth to eliminate feather edging Minor repairs cut 1/4"-1/2 for blemish repairs 3/4" depth provides smoother finish eliminating need to feather edge Remove any dust or debris that will interfere with bond of the patch Mechanically remove all loose or fractured substrate Application Conditions Repair weather conditions are a factor: Cold Weather Requires protection procedures Consider using an accelerator Do repair work in a controlled environment Force initial set with a heat gun Hot Weather Keep product in cool place prior to use Cover mixing bucket with a wet towel and keep out of the sun Application Conditions SSD (Saturated Surface Dry) surface to control suction issues Saturate with water to equalize suction Hot weather can create false set of patching material Thinner patch areas dry out faster Do not leave puddles of water on the surface Mixing Procedures Dry blend material Slowly add water while hand mixing (only use enough for a no slump consistency) Repair mortar should stick to the side of the trowel when tapped twice Cover the mixing bucket with damp cloth Let material sit for 5 minutes Note: Pre-mixed patching cements have a set time and must be placed immediately after mixing. Apply the product in a thixotropic consistency Be consistent in materials and placement procedures NPCA 7

8 Do not over work the cement paste beyond the patch edge. Eliminates patch halo issues. Do not let repair material sag Scratch finish area prior to applying the next lift Level patch immediately with straight edge Do not apply material in direct sunlight Leave repair surface slightly higher & let sit until initial set Restrike surface and level it smooth Remove excess mortar with a damp sponge Finishing Do not over trowel or use steel trowel for architectural finishing Texture repair while surface is wet Finish with wood or plastic trowel Immediately brush out patch with damp sponge or spray bottle NPCA 8

9 49 50 Finishing Finishing Moist cure repaired surface for a minimum of 2-3 days Curing and Finishing Procedures Curing of the repair Repairs require time to complete the curing cycle It could take weeks depending on weather and job site conditions Curing and Finishing Procedures Do not view repair when light illuminates the surface from an extreme angle View at a distance no less than 20 feet Repair if visible at a casual glance Repairs should improve appearance, not accentuate flaws Determine if engineering approvals required NPCA 9

10 Color Options If patching does not produce proper color match, consider staining the surface Panel blending Color correction through exposure, staining or toning Use tea mix for color toning of the panel Moist cure patch to prevent premature shrinkage or cracking Temperature limitations for extreme conditions during placement and curing Thank You Presentation Sources Metro Precast & Stone Services, Inc. Manassas, Va. Kiley Marcoe Architectural Precast Associations Manual PCI Architectural Precast Concrete Production Workshop Manual 2013 NPCA Architectural Repair Guide Thank you Barry Fleck CEO, ALP Supply NPCA 10