Solution 1 : Packing strips under decking
- Rip a piece of treated lumber (packing strips) at the required thickness to pack the decking boards level on the concrete patio. Place the packing strips in a line continuing out from the joists.
- Fix the decking (see fig.1) with 6.5mm (1/4″) anchor wedge screws or similar fastenings. 6.5mm (1/4″) holes will need to be drilled through the decking, packer, and into the concrete with a masonry bit. The holes will need to be countersunk to take the heads of the screws.
- Place the anchor wedges into the pre-drilled holes and tighten.
- The decking should not be touching the concrete and any water on the concrete patio should be able to drain away.The screw heads, albeit very big, could be a feature of the deck if they run in a straight line.
Solution 2 : Create channels in concrete to take joists
- Create channels in the concrete patio in lines continuing from the joists.
- The channel should be deep enough and wide enough to take a piece of lumber (joist) at least 50mm x 50mm (2″x2″).
- The channels can be made with an electric kango which can be hired from any building hire center.
- Place the treated joists in the channels at the right height (pack if necessary) and fix to the patio with galvanized dynobolts, anchor wedges or similar fastenings.The decking can now be laid in the normal way.The decking should not be touching the concrete and any water on the concrete patio should be able to drain away.