I am building a composite deck over a flagstone patio. The patio is about 2' off the ground and measures 8'x 10'. I am going to take up the flagstone, break up the 3 inch layer of concrete that sits on top of 2 layers of concrete block and put 2 x 4s onto the concrete blocks --- this will allow the decking to set at a height that is then just a short step down out our back door.

It is a 60+ year old patio. I plan to use concrete screws to put the 2x4's into the concrete block. Do you you think it is realistic that the blocks were filled or will I be able to put the concrete screws into the webs that surround open voids in the concrete blocks??

Also, thoughts on clips vs. screws for composite decking?? I would rather go with clips, but did not know if there are major downsides.