How to spec concrete flatwork/steps?
I’m a HO preparing a spec for a contractor to pour new concrete landing and steps over exiting 20 year old landing/steps. Existing concrete is in very good shape (no cracks or scaling).
The new steps and landing will be WIDER than existing and my question is how to spec the job so that the new concrete doesn’t develop a crack where the two sections (old an new) meet. Contractor has proposed drilling holes horizontally into sides of existing landing and steps for short sections of rebar. Note that there will be at least 3″ of new concrete spanning both the new and old sections at the surface to “tie” the two together (since new steps and landings will be higher than existing ones).
While I’m at it, I plan on asking for 8″ deep of up to 3/4″ compacted gravel base underneath the new concrete. I think that is pretty much standard right?
I just want to make sure that I spell everything out in the contract to avoid a dissapointment later. I just had a landscape contractor till, regrade and resod my yard and I wasn’t careful to write everything out. Result was that he made new grade flat (as opposed to slight slope away from house as it was before). At back of yard, the bottom of my fence ended up 8″ below grade (it was 2″ above the grass before he started)! Finally got resolved although I’m not 100% happy but that is another story 😉
Replies
I would include in the specs a provision for power-washing the existing concrete, acid washing the existing concrete and the use of a bonding agent before the overlay is poured.
While nothing is foolproof, these steps will reduce the likelihood of the new concrete not adhering properly to the old. The power-wash will remove built up grime, etc. The acid wash will etch the concrete to allow for better adhesion. The bonding agent is just that... a bonding agent that encourages bonding of the new and old concrete.
The addition of the rebar is good... as long as the rebar is epoxied into the holes. If it is just fre-floating... it may as well not be there.
You also want to consider if you want reinforcement in the overlay.
Thanks. Good recommendations. I'll do that.
How are you going to compact under the existing stairs? Do you think a couple tons of concrete won't want to settle? I would break up and haul off the existing stairs. I would also consider precast products if they fit your design.
Not sure I understand your point. I'm not worried about the existing steps settling. They are being widened at one end by about 6" and it is that new section that I want to ensure doesn't settle.
Or maybe that was your point - that the new section will likely want to settle no matter how well the base is compacted which will result in the two sections cracking apart?
E2,
Are you only widening everything 6"? Only one side? How important$$ is it to you that you have no cracks?
If you are going any wider, it could make a difference in what you need to do.
What are the dimensions of the old work (WxL and depth of the extended side(s)) and which dimension are you extending? You mention old and new sections. Dimensions?
Bonding the new pour to the surface of the old will encourage cracking if any dimension of the old work is over 6'.
SamT
Sorry if we appear dumb, but your description is a little short without a picture or diagram. I'm getting the idea of two additions - one on the side to widen and another step on top. Is this right?