Problem Clinic & Troubleshooting

Problem Clinic & Troubleshooting

• Battling Graffiti

  Q: We have a concrete tide gate that was recently hit by graffiti, covering much of the surface. We could paint over it, however, then we would have the ongoing maintenance of the paint. Can you recommend the best cleaning methods? If we sandblast it, will it harm the integrity of the concrete?

   

• Dealing With Burlap Stains

  One problem with trying to remove this type of stain is that you may find yourself left with a nonuniform appearance--the areas of cleaner, brighter concrete standing out where dark stains used to be. You might try blasting lightly using blast media that'

   
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  Decorative for Existing Slabs

  I am a California architect and read your article about decorative concrete at the World of Concrete. Are there processes that can be used on existing concrete floors to make them more decorative? I know you can use dyes and then stamp it with wet concrete. Is there a polishing process using dyes...

   

• Problem Clinic: Colored Concrete Shrinkage

  How does coloring affect concrete shrinkage?

   

• Rust Stains

  We have some concrete that has developed rust stains over a period of about a year. It appears to be caused by the aggregate.

   

• Removing Lime Stains

  What is the best way to remove the white calcification from my colored concrete patio? We have very hard water here, and the sprinklers spray onto the patio.

   

• Black Concrete

  We are considering the use of integrally colored black concrete for a downtown sidewalk. How much more would the colored concrete cost than standard concrete? And should we consider using both integral color and black aggregate? If so, what's the cost of black aggregate vs. standard aggregate?

   

• Coloring flatwork after it's in place

  We wrote a job specification calling for application of a colored dry shake to 50,000 square feet of concrete floor. The contractor didn't read the specification and finished the concrete without applying the colored dry shake. Workers applied a membrane curing compound to the concrete. Is there...

   

• Can Acid Cleaning Cause Driveway Deterioration?

  I run a pressure-washing business in Georgia. To remove the red clay that stains many driveways, I wet the driveway, then use a low-pressure hand sprayer to apply a dilute solution of muriatic acid (one part commercial-grade muriatic acid to three parts water). After that, I immediately rinse the...

   

• Adding latex paint to concrete

  We're bidding a job that requires a white concrete floor. Another bidder has proposed mixing white latex paint in with the concrete. Can this work?

   

• Patching with black concrete

  We sometimes patch existing asphalt parking lots with concrete. On a couple projects, we sawcut the area to be patched, removed the bad material, and replaced it with air-entrained concrete. This seems to be economical. The one drawback is the patches are so noticeable. Has anyone else done this...

   

• Stains From Straw

  We read your recent article on cleaning concrete (November 1992, page 791) thoroughly but failed to find any recommendations on the removal of straw stains from concrete. In the past year we've had several requests for help with yellowish brown stains cau

   

• Stains in precast panels

  We're making precast panels using integral color in the concrete. The panels are covered with a tarp at night to hold in the heat and make them cure faster. Our problem is that moisture condenses on the underside of the tarp and drips on the panel. When the drops evaporate they leave a white powder...

   

• Painting Concrete in Bright Colors

  Where can we get a deeply colored paint for concrete, one that is highly saturated with primary color? We need it for a multiuse building 600 feet tall. The owner wants several bright colors, not the stains, pastels, and earth tones commonly used on concr

   

• Preventing Rust Stains

  We were very pleased with our architectural concrete office building until ugly rust stains appeared on several surfaces. Did the contractor make a mistake, or is this unavoidable? What can be done?

   

• Bluish stains will fade

  On an architectural concrete job where we used plastic-coated plywood to get an especially smooth finish, we were shocked to find random bluish stains marring what should have been a beautiful, smooth surface. On areas near form joints and where plain plywood was used, the concrete color was mostly...

   

• Sparkling Aggregate for Flatwork

  While visiting downtown San Francisco recently, we noticed that the concrete sidewalks appeared to have a sparkly substance in them. We really like this effect. Can you help us identify the substance and tell us how it can be made available to us? Is this

   

• Colored Traffic Lanes

  While planning the offramps for an expressway the question has come up whether these can be colored to distinguish them from the regular traffic lanes. If so, can you suggest how much color to use?

   

• Black Concrete Driveways

  A job calls for 200 cubic yards of black concrete for driveways. We have been told that this would require 10 percent black pigment by weight of cement. If we use lampblack as pigment will it knock out the entrained air? What can we do to be sure the job

   

• Removing Oil Stains

  What is the best way to remove motor oil stains? The oil has probably soaked pretty deeply into the concrete.