Need concrete tips and suggestions

spaceman spif

I'm getting ready to pour some concrete to help finish up a cruddy looking edge on a concrete slab and would appreciate some help.

It's an outdoor slab that my deck sits on. The edges on one side are crooked and look awful, so I'm going to put in some rebar and then smooth out the edges by pouring 3-4" of concrete and extend the edge. First question is what type of concrete do I use? Standard Quikrete? Second question is should I apply some adhesive between the old and new concrete?

The concrete slab sits on my driveway, so my forms are sitting on blacktop, not ground, so I couldn't dig a little trench to set the forms in. The driveway obviously isn't perfectly smooth, so there are gaps here and there under my form boards that I'm worried concrete will run through. Largest gap is around 1/4"-3/8" high. Someone once mentioned using plastic sheeting to fill in the gaps, but I don't want to spend $20-$30 on the sheeting, if possible. The forms I'm using are 2" thick styrofoam insulating boards I had laying around. If I cut some thin pieces of foam and try to fill the gaps with that, will it work? Or will the concrete just push those out?

spaceman spif

Btw, the foam pieces are supported by placing boards behind them plus some heavy blocks and stones as well.

johnnyconcrete

My kind of project. Standard Quikrete is a 4000psi concrete mix which is probably stronger than the concrete in your existing pad. When you say you are going to put in some rebar does that mean you are drilling into the existing slab to tie the two together? That's my recommendation. As for the concrete running through the gaps, it isn't like water. Concrete plugs up real well (especially when you shovel it in place) and 3-4 inches won't exert much pressure on your forms. Just add enough water to your pre-mix to get it like thick gravy. You want to be able to work the mix after it's in the forms with out pulling a muscle. Good luck.

spaceman spif

Thanks for the reply! Yup, I'm going to put in some pieces of rebar into the existing slab and extend those out into the new pour. Should I put a few pieces of rebar down into the driveway as well?

If I go with standard Quikrete, how long do I let it sit? Is there a point where it's firm enough to remove the forms but still be able to trowel smooth any rough spots?

jomama45

I wouldn't get my hopes too high if I were you, as this may just be a temporary fix, at least if I'm understanding what you're doing. Not to mention, the new concrete will stick out like a sour thumb next to the old. As for stripping & "facing" the edge of the pour, it will be difficult with foam. This is where the plastic would come in handy. You really could put anything smooth & dense next to the form to aid in this though. I can't exactly explain to you on the web "when" to pull the form off, as it's fairly objective depending on a number of factors, but it can almost always be done with a little caution.