Expert: Dan Griffin - 6/16/2009

Question
Hello Dan, I currently have a 12 x 20 raised aggregate patio in excellent shape but do to the addition of top soil the grade is wrong and the patio floods. I would like to use the existing pad, not break it up, as the base for a thicker and larger patio to correct the grade issues and increase square footage. Can and should this be done? What precautions need to be taken to ensure the concrete pad extending past the older pad doesn't break/crack off?

Answer
Rocky, I see no problem capping the existing patio.  My normal reccomendation is to always add control joints so that no block of concrete is greater than 12'.  Your existing patio is well settled into the ground, any new additional concrete beyong this base will not have the same support, so you need to make extra efforts at subgrade compaction.  I would still consider a pattern of saw cuts or joints that coincide with the old patio perimeter.  You can cetainly create a pattern of joints that cover the old patio also.  With sufficient compaction of a select fill, the new slab should be quite stable.  You may want to put down a layer of sand on the old patio to prevent having the new slab bond to it, so the new slab can move as it needs.

Are you planning to pour it yourself or have a finisher involved.  A good mason will be able to offer excellent advice.