My home was built in 1957. It has a 10x10 3foot high brick patio with a concrete slab on top. We are replacing the deck which is much bigger. The deck on the slab rotted due to water pooling in a small area on the slab. My question is, is that whole patio solid, because we'd like to drill drainage holes to remedy this problem. Can you help?
Drilling through a concrete slab for water drainage , if not done correctly, could lead to bigger headaches. If you need to correct the low area were the water pools it might be better to cut drain kerfs with a circular saw and a masonry blade. This would entail cutting a narrow channel that is pitched slightly to the nearest edge of the slab.
While you don't want water pooling, ideally, the deck shouldn't have been in direct contact with the water in the first place.
ojait's suggestion is a good one (drain kerfs). Another option -- if it's not one monolithic slab is to mud-jack the patio slabs so that there's a proper slope for drainage.
Regardless, the key is to make sure your deck's wood isn't in direct contact with the slab. It needs some form of separation (which could be as simple as some concrete piers).
As other's have stated already, it's not likely solid concrete for 3' and drilling a "drainage hole" is a bad idea.
It's very unlikely to be fully solid to the ground - that would be more than nine yards of (expensive) concrete. It's far more likely to be constructed with brick stemwalls all around, filled with dirt & rocks, and topped with a relatively thin (4" to 6" thick) slab; that's much more economical, since dirt & rocks are far cheaper than concrete.
But... I could be surprised. I actually own a house that has poured-concrete basement walls fully 24" thick. That's an astounding amount of extra concrete, rendering the basement nuke-proof, and it cost somebody tall dollars for no really good reason.