Pouring new concrete on top of an older concrete patio?? (fireplace, pool)

[Lauren0319]

We are about to begin the process of expanding our tiny & worthless patio into something much larger and more useful. Our current concrete patio is aggregate (with little pebbles) and is about 12x12. It is pretty thick and in good condition w/ rebar. We are wanting to basically double the size with stamped and stained concrete. Here is where I am SO confused... I have gotten 4 quotes. The first two told me it would be no problem to pour new concrete on top of our current patio, and then stamp and stain it. The last two quotes told me there would be cracking if we did that and they suggested demo-ing the patio and starting over (of course, this comes with a much higher price tag.)
We plan to be in this house for a long time. We want to "do it once and do it right." However, if we can cut costs and labor by pouring concrete on top of the current patio w/out cracking, we'll do it.
So, WDYT- will the patio crack if we pour new on top of old, or will it be okay? I just don't know who to believe and we're talking about a lot of money here.

One final question- we're looking at about 625 sq feet of concrete. Bc of the way our house sits, the cement truck will have to be on the street. The concrete will either have to be wheelbarrowed back or a pump will have to be used. The two cheaper quotes said wheelbarrowing would be fine. The last 2, more expensive quotes said w/ that much sq ft, a pump would be needed. They said if it was wheelbarrowed back, it would start to set too early and there would be fractures. Any clue??? I just don't know who to trust!

Thank you!!!!!

[K'ledgeBldr]

"do it once and do it right"- You got the right attitude. Now, spend the money for that right attitude.
Pouring over existing can be done. However, you need at least 2" of pour over the existing. How will that be up against the house and maintaining slope? Too close to siding? Too close to the threshold of the doorway? You should maintain at least 6" at the siding and 4" at a threshold. If you can maintain those tolerances, you're probably O.K. (But you could still have cracking that would occur at the outline of the existing)
If not, demo the existing. It's hard to screw-up if you start from scratch.
Another thing to consider/ be aware of, If you do pour over the existing- "dow-in" some rebar along the edges of the pad to tie the two together.

As far as the wheelbarrowing is concerned, 625s/f maybe stretching it on the time line. A line pump (not a boom pump) would make the delivery and the finish go a lot better. And line pumps are not as costly as booms.

[Lauren0319]

Thanks for your thoughts. If we pour 2 inches of concrete we will be covering up the siding on one side of the house. Here's where more confusion sets in- one guy (the cheapest) said no biggie and it doesn't hurt at all to cover up the siding. The last (and most expensive) said that is a big NO and we will be asking for mold and a host of problems if we cover up the siding. He said the house "breathes" through the siding and it shouldn't be covered up. That makes sense to me.

It's becomming very aggravating to get all these mixed messages from different contractors. I'm glad I'm able to do my homework and possibly avoid a disaster. I'm also becoming very glad I didn't go with the cheapest guy... it sounds like I would have gotten what I paid for.

[RoaminRed]

Okay, this may be a stupid question...but here goes! If your existing patio is in good condition, why rip it out or pour over it? Why not just expand the area covered?

[K'ledgeBldr]

Originally Posted by Lauren0319

Thanks for your thoughts. If we pour 2 inches of concrete we will be covering up the siding on one side of the house. Here's where more confusion sets in- one guy (the cheapest) said no biggie and it doesn't hurt at all to cover up the siding. The last (and most expensive) said that is a big NO and we will be asking for mold and a host of problems if we cover up the siding. He said the house "breathes" through the siding and it shouldn't be covered up. That makes sense to me.

I don't know about a mold problem, but, you'd definitely be looking at a rot problem- regardless of the type of siding. Siding only covers the frame portion of the house- if that's covered with concrete, then moisture finds it's way to the framing. After that- the termites find their way.
The cheapest guy was just that- the cheapest! He'll be down the road (and money spent) before anything goes wrong. And your stuck fixin' his @$%&-up!
Stick to my earlier post- you won't go wrong. And don't listen to your thin wallet.

[K'ledgeBldr]

Originally Posted by RoaminRed

Okay, this may be a stupid question...but here goes! If your existing patio is in good condition, why rip it out or pour over it? Why not just expand the area covered?

Read OP post again!
Not only is it bigger, but the surface finish is changing.

[Lauren0319]

Originally Posted by RoaminRed

Okay, this may be a stupid question...but here goes! If your existing patio is in good condition, why rip it out or pour over it? Why not just expand the area covered?

Not stupid..... but this is our "forever" home and I want to do it right (and have it look uber snazzy!!!! ) We spend every evening in our backyard... we are also wanting to install an outdoor fireplace (maybe in a year or two, as the wallet allows.) Adding on just wouldn't give me the LOOK I want.

[tet tea]

Ok, I am most definitely not an expert on this ... but ...wouldn't you need something like an adhesive such as Concrete Glue to bond the new concrete to the old? I'm pretty sure that if you pour the new stuff over the old it will separate and crack in time.

Good luck and enjoy your new and enlarged patio!

[Coldjensens]

First of all, if it does not crack, then it is not concrete. All concrete cracks. However there is a difference between shrinkage cracks and structural cracks. You are more concerned with a break in the bond between the old and new concrete and pieces spalling off of the top layer.

I have seen what you want done, but they used steel mesh and drilled into the old concrete and bolted or pinned the mesh. The pins/bolts stuck up a bit into the new concrete. That was probably overkill , but it worked. This was seven years ago and they still have no problems. However they placed four inches of concrete on top of the existing.

I have seen other people placing concrete on top of old concrete, but I have no idea how it came out.

The old concrete also needs to be cleaned and prepared before placing the new concrete on top of it. There is no glue, but there might be a bonding agent that can be placed on the old concrete. Rebar is the best way to make a good connection.

Hand placing vs. pumping depends on the skill of the concrete crew and the types of admixtures used in the concrete. They can easily control the set time if necessary by changing the mix. We had a concrete deck around our pool that was 1800 s.f. of concrete and they placed it all with wheelbarrows. A year later, there is no significant cracking.

If you use pumping check to see if you have sulfates in your soil/groundwater. If you do, you need to use sulfate resistant concrete. If you pump, they add water to make it pumpable. I think that you can diminish the sulfate resistance by adding too much water.

[Coldjensens]

another issue. If part of you new patio is covering the old concrete and part is on ground (you will put in some gravel and/or sand first), you will get uneven settlement and it will definitely crack at the end of the existing patio. Either put a control joint there, or remove the old patio. If you are on expansive soil, the new portion may lift more than the existing.