You have to think comprehensively in these situations. Is rainwater seeping under your slab or is this just something you're worrying about?

Granite doesn't decompose. It can be crushed, but I'm betting regular gravel would be more cost effective.

"Decomposed granite" is a thing in my neck of the woods. It is crumbly eroded granite.

You want to remove water from around the foundation. The start is gutters with downspouts that move water far from your foundation. Some people have the downspouts end in a drain that sends tge water in pipes a long way from the house.

If you have areas that collect water, add french drains.

Water is in the ground moving laterally under concrete slabs. Concrete flatwork does not solve any current/future problems with foundation water. Are there problems?

Typically poured foundation stem walls will only have 2 horizontal rebar at bottom and 2 at top. There are many examples of concrete structures without steel reinforcement that have stood the test of time. Are there problems?

Sorry it took a while to respond. Our kitchen was destroyed two years ago (which is related to this discussion) by cast iron pipes that had rusted underneath our concrete foundation. So life here is wackadoo.

So, the reason I became concerned about the foundation is convoluted.

First things first, our house sits on hard clay soil. Because our pipes needed to be placed, our wood flooring had to be pulled up and trail of concrete needed to be jack hammered out from our bathroom to our kitchen. The trail goes through our office, our family room and about four feet into the kitchen. So we can see quite a bit of what the concrete looks like.

In doing this, we found out that our concrete (and apparently most houses built in San Diego at the same time) has no rebar. And we have a large crack that basically breaks our slab in two running right down the middle. The slab is about 1400sf and maybe 4x3 ratio.

A year ago, we got hit with a major rain storm and that's when I noticed the concrete patch (that had been dry for months, look wet. We called the repair guys back and they agreed it was probably moisture from underneath. They weren't sure if we needed to be concerned.

I did notice a large pooling of water about 15 feet from the house just past our back patio which concerned me because I was thinking that maybe that had something to do with that. Or maybe that was a sign that some areas closer to the house might be softer soil and might be allowing too much water under the foundation.

So I was thinking about just pouring concrete in the space between our foundation and the sidewalk (about 1 foot out from the foundation) so that we might be able to put some short planters that with drainage that would force any water (rain or from watering the plants) onto the sidewalk.

So we got quotes from concrete guys and it was really expensive. Then I read about decomposed concrete and thought that if it was less porous than our dirt (obviously it's more porous than concrete), it might be enough of a solution. But I don't know when then planters would be going in. I could be "tomorrow" or two years from now (my family takes a loooong time to make decisions).

So that's where things stand.

I really appreciate everyone's input and guidance. You guys could be saving me a ton of money by keeping me from doing something stupid. :)

Ok, so you have a slab foundation. Usually when speaking of water "compromising" the foundation, it is from freeze/thaw. However, climates with freeze/thaw typically have deep foundations. So you have a slab, probably with thickened edges, that turn down approx 12" deep. Rebar in a slab-on-grade is for two purposes: 1) when a slab cracks, it keeps the pieces from separating (vertically or horizontally); 2) help reinforce the loading capacity of the slab when heavy things are placed on top or in earthquake zones. It is not required for a properly prepared slab to perform (however if built now CA would have rebar).

As far as the wet infill slab associated with the interior work, here is my guess. There is water underneath, period, and that can be ok. Originally, the soil was compacted prior to first building the house. So the soil was consistent in it's water movement under your house. After they dug up the underground pipes and replaced the soil, that disturbed soil is less compacted than the original soil adjacent to it. So, water finds the least resistance, and if there is airspace (at minutae level) water will move to that infill. Therefore you may have a concentrated amount of water where they dug the pipes up, and they also may not have replaced the vapor barrier in the trenches.

To alleviate any water under your slab, you need to allow it to move out from under it and any surface water to drain away. So the soil directly adjacent to the perimeter of the house should be lower (4"-8" below top of slab) and sloped away. Downspouts should have leaders dumping them minimum 10' away. Any sidewalk should be lower than the interior floor slab, and planting spaces between the house and sidewalk should not hold water (so put in drains if the sidewalk acts as a dam).

Adding the decomposed granite as groundcover wouldn't seem to solve the water issues you may have. Exterior pictures and a review of the entire property's ground elevations would need be looked at.