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Hot weather practices for stamped Concrete. Acid Staining and Overlays

 

Since it has been so hot this summer I went ahead and revised an article I wrote a few years ago and added a section on Vertical Overlays.

Stamped Concrete:  Stamped Concrete in summer brings many challenges due to ambient heat, high concrete temperature, windy conditions and low humidity, all these factors contribute to premature setting and the development of shrinkage cracking. Although not all is always preventable, if you follow some good practices you may be able to avoid many of these pitfalls.

  • Always wet the sub grade, forms and anything that will be in contact with the concrete to prevent moisture loss.
  • Many times I placed plastic sheathing over the sub grade, much like a moisture barrier to keep the moisture in the concrete. I also noticed that since there was less water shifting within the mix the color came out more even.
  • Try to pour early in the morning, it is easier to control and finish a job when the heat is still manageable.
  • Work with your ready mix company regarding your mix design. Most concrete producers have already developed special hot weather mix designs for stamped concrete applications.
  • Learn about the use of retarders and water reducers. There are companies that sell specially packaged additives to retard concrete either by the full truck, in stages or one yard at a time.
  • Add fibers to your mix, the fibers will help in reducing shrinkage cracking while adding strength to the mix.
  • You may use a surface retarder that does not interfere with the use of color hardeners and release powders and will not affect integral colors.

Acid Staining in hot weather also presents some problems. If you are working inside under AC and in a controlled environment then you shouldn't have much to worry about, but if you are working outside in the summer or in a non-ac interior job, then it is another story.

Acid Stain works by a chemical reaction that occurs between the mineral salts in the stain and the lime and cement in the concrete. In order for this chemical reaction to reach its full potential, the stain must remain wet and reactive for some time. If it's too hot outside when you spray the stain on the concrete it will dry almost instantly, then you will not get much of a reaction and the resulting color will be splotchy and very uneven. To prevent this from happening just follow some of these suggestions:

  • Stain in the morning or evening after the concrete has cooled down.
  • You can flood the concrete with cool water to lower its temperature and to saturate it with water so the stain will not dry so quickly.
  • Pre wet the concrete and immediately follow up with the stain; this will keep the stain wet longer.
  • After the stain application mist the area with water to keep the reaction going.
  • Apply more stain than usual, this will result on longer working time but will cost more.

Overlays:  Depending how the overlay is applied and which system one is using it will run into different problems.

For all overlays the main issue is rapid moisture loss, this is especially true for thin applications such as Skip Trowel and Bond Coats. If the concrete is very hot and the temperature is high, the product will dry too fast leading to incomplete hydration, lower performance and a less than desirable finish.

Different manufacturers have different overlay systems, though at the end of the day the product may look the same, the application methods change. Here we list some general steps on how to deal with heat when installing decorative overlays.

 

  • Apply the product early in the morning if possible.
  • Cool the surface by flooding with water, squeegee off excess water before placing overlay.
  • Use a primer if recommended by the manufacturer.
  • If no primer is used, dampen the surface before applying the overlay to saturate substrate and reduce rapid moisture loss.
  • Keep the bags in the shade as well as the resin if using a two-part system.
  • Use cold (ice) water in the mix. A good system I used many times was to get a 30 to 40 gallon clean trash can, fill it with water and put a couple of ice blocks or ice bags in it to keep the mix water cool, ice cubes work well but may melt too fast so you may want to keep the bag closed so they last longer, ice blocks last a lot longer but are more difficult to get (you could make your own in your freezer). Another way is to do the same thing but instead of using the water from the trash can you coil a length of water hose inside the trash can to cool the water as it goes through the hose.
  • Add a little extra water to your mix to compensate for rapid evaporation.
  • Some Overlay suppliers sell a retarder to use when weather is very hot, these are very helpful as they can actually “revive” a mix that has become too thick and gives you an extra 30 minutes to an hour working time.

Vertical Overlays

Many of the things that apply to horizontal overlays will work for vertical as well, on difference though is that vertical products are applied much thicker which may create other issues when it is too hot.

  • Try using an evaporation retarder after you apply your mix, these usually come in concentrated form and are sprayed on the surface, they help hold the water in the mix which will greatly reduce shrinkage cracking and, they do not interfere with stamping and or carving techniques and do not affect coloring either.
  • As most stucco guys do, you can spry water on the mix as it dries to prevent shrinkage cracking, or rapid set. An issue with spraying water on the surface is that it will discolor it, especially noticeable if you have a pigment in the mix.
  • Add more water to your mix, in really hot weather water evaporates too fast; a little extra water will not affect the performance of the mix.
  • Use cool water to mix (see above in overlays section)
  • Use a set retarder in your mix

 

Art Pinto

Decorative Concrete Forum Contributor Writer

Copyright © 2012 Decorative Concrete Forums Inc. All rights reserved. No portion of this article may be reproduced without the express consent or permission from Decorative Concrete Forums Inc.

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