Question
Hi Sean, thanks for helping me out.  I live in Denver, CO.  We are putting in a concrete walkway around from our fenced side yard to our backyard ~6' long and 3' wide.  I would like to put some decorative stone into the concrete along the edges to add some interest/style.  I like washed river rock in the 3/4-1" size and was thinking of pressing it into the concrete after it is poured to add the accent.  Will this work?  How should this be done so that the rocks don't fall out sometime down the road? Thanks!

Answer
Peggy:
The best way that I know of is to press the rocks in immediately after pouring and screeding the concrete while it is still very workable. They need to be pressed in 3/5ths of the way to ensure they won't pop loose. Then after pressing them all in you must let the concrete begin to set up. After a few hours you wipe the concrete haze off the top or exposed parts of the decorative rocks. But it is a real trick to know when to do this...if its too soon you'll break stones loose and roughen the surface of the concrete. If you wait too late the haze and excess will become very difficult to remove. The first wipe down should be done with a large soft sponge (like you use on a car) rids the rock of the major excess. The second takes the fine haze off (use a smaller slightly harder sponge). So be sure, the next morning you should wipe down the stones a second time. You might also consider an acid spray down. Using a small hand held pump sprayer (no metal parts) add muriatic acid and water together to make an acid wash. Spray down the stone and let it set for half hour before washing the acid off. Don't do this for at least one week.

Finally, you should seal the concrete and stone with an appropriate masonry sealant. See your local paint store or masonry store for best recommendations. Be careful before using a gloss finish as some people love it and other hate the glossy plastic look.

I recommend doing a test area first. Sealants protect the concrete from breaking down from water penetration and also bring out the colors.

Best of Luck
Sean J Murphy, LA,ISA, LEED AP
Please check out my blogs and articles on landscape topics like this on my websites.
http://www.seanjmurphy.com
http://amenityarchitects.com