Expert: Dan Griffin - 3/1/2011

Question
I have concrete attached to my house wall (siding).patio lengh is about 30 ft. The gap (space) between siding wall and concrete floor is about 2" wide and 30 ft long. how can we fix this gap?
I am confused because it is siding.

Answer
David, I'm not sure I am following your question.  here is my guess about what you have:

You have a patio that runs along the back of the house for 30 feet.  The house has siding on it, probably wood or man made material.  The siding should have been installed in such a manner as to just barely cover the the joint between the top of the concrete footing and the bottom of the wall/floor framing.  The top of the grass/grading on the outside of the building should have been 6" lower than the bottom of the first siding board.  This dimension is to help prevent bugs and termites and to allow the siding to be able to breathe and release water and condensation that formss on the back of the siding.  Your patio and its concrete should have followed exactly the same rules.  It sounds as if your patio was poured way too high.  I have no explanation for the 2" gap at the siding other than a that a 2x4 is 1 1/2" and may have been set with some thin stakes when they were forming the concrete.

My personal opinion would suggest NOT sealing or filling the gap.  I have known people to pour a patio up at finish floor and against the siding.  I strongly suggested not doing so to one man in particular.  He had someone else pour the patio where he wanted it.  The place has not fallen down, but rot and mold may take quite a while to show up.

If you do decide to seal the gap an effective method would be to get some suitably sized backer rod and seal the gap with one of the self leveling polyurethane caulks like SL-1.  Another less expensive approach would be to fill the gap with bagged asphalt which is self consolidating and self leveling.