View Full Version : Picing in new concrete to old

Daniel Sapp
05-10-2011, 12:09 PM
I'm converting my attached garage to a family room, and I need to pour a new section of concrete so that the concrete foundation, which is ~6" above the floor slab, is continuous across the 8' section where the garage door was.

My plan was to dig down 36", place rebar vertically and horizontally (drilling holes and attaching it to the existing foundation on either side), building my form and then pouring in my concrete.

Do I need to do anything to the old concrete surface (aside from roughing it up and making sure it's clean) before I pour the cement? It doesn't seem too difficult, but I have a rather spendy 10' patio door that is going to end up resting across that new section, so I want to make sure I do it right.

John Kogel
05-10-2011, 08:55 PM
Ready Mix, Sakrete or you-mix? Concrete work is fun and very rewarding if you do the prep right and use a good mix. There are some good websites out there dedicated to working with concrete.
I wouldn't worry too much about the cold joint.
You will want to tamp the wet concrete along the edges of the forms so there's no voids or honeycombs. You could set some pins or bolts in to hold the 2X6 sill plate. I wish more people bothered to do what you're planning. I see a lot of wet wood sills where the garage door used to be.

Daniel Sapp
05-11-2011, 09:48 AM
I was just planning on mixing it myself. Do you think I should put in any fiberglass, or will the rebar be enough for strength? I just want to make sure it doesn't crack.

One good thing is that I live in Portland, OR, so I don't have to worry about a freeze/thaw cycle.

John Kogel
05-11-2011, 12:01 PM
It's just a little footing. Nothing special needed. Use a good mix of sand and gravel, or 'navvy jack'. Too little sand, you get a porous concrete with less strength.

Craig Cook
05-13-2011, 12:42 AM
Coat the existing concrete with a latex additive for concrete or thinset, this will provide and additional bond for the new concrete.

Daniel Sapp
07-15-2011, 09:21 AM
I just wanted to update you on my project. I used the latex coating for good bonding, and ended up just getting a ready-mix truck out (it was worth the little extra cost). I'm very pleased with teh results. I ended up with a little bow because my form wasn't braced quite enough, but it turned out to be a good thing because it adds some additional support under the doors sill plate. The best part of it though, is that it makes it look like an addition to the house instead of a garage turned into a living space. Thanks for the advice.

James Duffin
07-15-2011, 07:09 PM
That looks nice....