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Contractors have two options to choose from when it comes to sealers: penetrating and non penetrating (or topical). A topical sealer resides on the top of the concrete, often producing a shiny look. A penetrating sealer penetrates into the concrete to help protect it. Unlike topical sealers which enhance colors, a penetrating sealer darkens the color of the concrete. This is an important fact to share with a customer so he or she is not surprised if the color of the stain changes.

McKinnon Materials' Product Specialist Glen O'Steen, or Buster as he is known throughout the industry, says he uses penetrating sealers exclusively for outdoor projects. "Anything that penetrates is going to have a lot less likelihood of having a bond failure," O'Steen says. "Moisture is being sucked down into the concrete. And if that moisture is a sealer, once it's sucked into the surface then it polymerizes and turns hard, creating a good adhesion to the surface."

Topical sealers may have the tendency to be slipperier, so many manufacturers suggest a penetrating sealer for all outdoor decorative concrete, especially areas that may get wet.

O'Steen points out sealers have different hardness factors, which also needs to be considered. "The harder a sealer is, the slipperier it will be," O'Steen says.

With VOC requirements becoming stricter, some contractors are moving toward water-based sealers only. Water-based sealers allow the concrete to breath rather than trapping in all the moisture, says Jerry Bodie of Surebond. Another sealer option that works well in the outdoors is an epoxy-modified sealer, Bodie adds.