New Project

That may depend on what you have, and going to do

1.) the thickness of the orginal concrete

2.) does the orginal have rebar

3.) the thickness of concrete you intend on pouring

4.) plus what type of fill you have underneath the original slab

Concrete over concrete shouldn't be any problem. Think about it, concrete is placed over aggregate all the time, like crushed stone or broken concerete aggregate with no problem. The loading will be spread out evenly over the surface.

Make sure there is no way water can penetrate any possible space between the too. I'd recommend the existing concrete surface be roughened and a bonding agent applied, and any possible source for water penetration be sealed with a good quality (I like Sika) sealant especially if you are in a frost prone area.

Stamped concrete is really pretty. I like the dry-applied coloring, they can make it look like natural stone.

Good luck with your project.

Hmm, You are correct that pouring concrete over a slab on grade should not be a problem if you cover the entire slab (this is basically a composite structure of 2 different concretes, which will behave stronger than each individual layer). However, the rationale about the aggregate base is not exactly correct and misleading. Concrete fails frequently over aggregate, when the aggregate can not adequately bear the load of the concrete, settles locally (differential settlement), or shrink/swells. This failure in the concrete appears as cracks. Similarly pouring concrete (or installing any structure) in a localized area over a slab could cause the additional load to punch through the slab and cause cracking in the slab outside of the new pour. It should be noted though that most exterior concrete slabs are not strucutral and failure is mostly an asthetic issue (though it can lead to accelerated degradation of the slab). Think of it this way, a piece of wet crate paper (the concrete) is bearing on a sponge (subgrade), it is stiffer , but even the concrete flexes under a load, also it moves differentially across joints, which can cause cracks to appear above these joints. The sponge and the paper must bear and distribute a portion of the load. If the load is a distributed load evenly across the paper, then it is an issue of the sponge bearing the load. If it is a point or localized load, if the sponge doesn't support the load adequately, then the paper flexes too much, and you punch a hole through the paper.

Am fully with posts #1 #2

But one Q-how many " do you want to build up?

If say 6" you can put 4" Polystyrene Blocks and pour 2" concrete with steel netmesh

Don't like PS ?

Would you fancy Steel half-round gaps- diameter 8"--i.e.4" high half shells?

If you want Green & cheap-place 4" dia Bamboos with 1" gaps between-and pour

Voila.

"Would you fancy Steel half-round gaps- diameter 8"--i.e.4" high half shells?"

Please explain.

Kind regards

4" high half shells-

These are rollformed 20GaugeSteel sheets shaped like half-tubes or trapezoids used in many countries to enable -- mostly Hollow -- concrete buildup and minimize concrete mass/load

If Diameter 8" - the half circular shape =4" .

Normally available in 6m (20') lengths- but hardware shop will supply cut to length.

Gap left between Half-pipes can be 1". New Concrete reaches old concrete thru' these gaps.

If there is any question at all about what is underneath, piping, gas or if there is a possibility of freezing, then you could consider the new decking systems made out of plastic wood like and put any design you want. You can also add benches, tables, flower pots out of the same stuff.

Go to Home Despot or Lowe's and get a book on the stuff. You can also add a sunroom open in the summer and closed during winter if you have winter. Still no problem with fireplace as there are outside smart designs for them also.

One thing about the new plastic wood-your wife will enjoy not working herself to death cleaning it and you only have to pressure wash it once in awhile.

Cement will have to be taken care of and is still cold

You might also want to check with your local (city or County) Building Department. I assume you will be getting a Building permit. If they are going to inspect it than find out before hand what is acceptable and what is not.

An issue might come into play if the patio doesn't have footers and you are making it load bearing with your enhancements. i.e. the outdoor kitchen, etc. If the old patio doesn't have footers you'll run into to problems of sinking or possible stress cracking.

What they are probably recommending to you is a concrete overlay. We have done a few projects where there were dips, bad grade etc. It is incredibly hard, yet it expands, contracts and even cracks in the same manner as the substrate slab. They trowel in a leveling compound after preparing the surface of the existing concrete. Then another overlay with a bond coat which can be colored, troweled, broomed or stamped just like concrete. What are you building the kitchen / fire place out of? Even if its block you should be ok, as long as the slab thickness is somewhat uniform. As far as pouring standard concrete over concrete- the other contractor was right. There are a myriad of problems that come along with that. But the overlay is amazing stuff, my father and I have been installing it for 3 years all over California and we have had zero problems- not a single customer complaint.

We do it all the time without any problems.

Sounds like the first guy might also own a concrete removal service.

Have us all over for cookout when you are finished.

Sounds like the first guy might also own a concrete removal service.

if you mean me, sorry just related to my experience pouring concrete back when I was on the farm.

But I'm all for the cookout.

phoenix911

Friend,

If you are enlarging the area of the concrete, then look for problems to occur where the edge of the underneath slab is. You can minimize this with proper reinforcement and compaction of the surface before pouring.

If the existing slab is adjacent to the house and sloped toward the house, or a little high at the outer edge, then there probably is the very common settlement of the soil next to the foundation (due to lack of compaction when the initial backfill was done at the time of construction).

If your yard has a lot of hard surface, you may find a permeable surface material to be a good choice, because this would reduce wet weather runoff. This is becoming a requirement in some locations.

Whatever you do, check the references of the contractor and insist on a guarantee. Also, make sure that they specify the slump of the mix they will be using. Many finishers try to add water to make the mix easy to spread and level, but this makes it porous, subject to winter freeze damage, and weak. Even 10% excess water is quite detrimental. (Perhaps you can insist on a maximum 5" slump and have them test it with a slump cone before pouring.)

Stamping and tinting or staining the surface is very attractive. Sealing these types of surfaces is a good idea also.

Regards--JMM