Concrete floor question...
 

This is a subject I know very little about...Concrete

In my basement, I have a 9X12 room. I thought the floor may have been brick with dirt on top, but it's just very hard packed dirt. So hard, that my shovel tip has a hard time getting through.

I can afford only 2 inches of space before I bang my head on the upper floor joists.

Here's my question...Since this floor is so hard packed, and the room seems to be dry, thanks to the work my son did in pouring new sidewalk sections, would I be ok just pouring about a 2" cap of concrete and calling it a day? The room is never cold enough to freeze...it stays a fairly constant temperature down there. The floor is about 4.5 foot below the outside ground, and I'll be adding a furnace register this weekend.

There would be no machinery on the floor, only shelves and a bench, plus a Kennedy rolling toolbox on rubber wheels.

I don't plan on using the room for long, maybe a year or two, depending on the future, before I locate a storefront and move business there.

If its that hard why bother with concrete? I'd prolly not consider less than 3" with some sort of mesh in it....steel. I'd put plastic down first, and bagcrete is prolly not a good idea either.

While I can't speak towards whether it's right or not, that's exactly what my grandfather did in a section in his basement when he replaced the furnace and hot water heater. It's about a 12'x12' pad on the dirt with some storage cabinets. It's held up for the 20+ years since he did it but it sees very little traffic/wear (only about 5' headroom). Even with a firm base, I think dropping a framing hammer would crack 2". That may or may not matter depending on what your going to be doing with it.

If it's hard, flat and level how about whatever laminate "wood" flooring is on closeout special?

2 inches is pretty thin, even for light traffic and weight.

It's not completely smooth...there is a hump in one corner from a no longer used gutter downspout that used to drain into the sewer system, and a 1'X2' section in another corner that is partially buried brick. It it was completely flat, and about an inch or two lower, I'd pour and compact sand, then set concrete patio stones down and dust it with Portland cement instead of sand. I fear digging too deep, because I don't know how far down my foundation goes...it's a 113 year old home with a limestone foundation.

It needs to be bag mix, since ready mix is going to be a PITA to get back there...up a hill and around the house. It would also tip the borough off to work being done without a permit...and I don't want them to know. I may be able to break it up into smaller sections and take two weekends to get it done. I'm not adverse to that at all. According to my calculations, I'd need about 32-80# bags.

What I plan on doing in there is normal gunsmith type work. Mainly a bench, some shelves, a gun safe and my tools. Machinery is in a different section of the basement. Due to the low headroom, and the fact that there is duct work right down the center of the basement, I can't do everything in the one area down there. I'm trying to avoid anymore head trauma...I already have 6 scars on the dome from working down there .

That's what she said....ba dum tsss.

I know it's thin, but like I said, I don't know how deep my foundation is. Building codes weren't really used or enforced when the house was built.

2in should work with reinforcement, push some mesh in and call it a day. You can't have a dirt floor in an area you are gunsmithing.

Exactly...you can't build a business on a dirt floor these days. 150 years ago, maybe...not now.;)

Small excavation to see if limstones are deeper then decide. If the stones are a few inches lower should be safe to drop floor level just a little.

why not drop the floor height a few inches, and pour it back up to where it was?

I wouldn't be comfortable with 2" of concrete. As Tom said, 3" is a better starting point.
No one says the floor has to extend from wall to wall. But digging a couple of inches deeper shouldn't compromise the building integrity. I'd dig a couple of test pits to see what the actual conditions were. Dig next to the walls; not under them! If there is a footing, it should be wider than the wall ( "should" be).
In some of the older sections of Baltimore, I've seen some basements with 5 feet ( or less) of headroom--since the guy was seated at a workbench when he was down there-he had enough room.
I also prefer a drainage layer (gravel, or sand), but if your conditions are historically dry, and its for your temporary use, you might get by OK.

Get, and WEAR a bump cap--not as strong, or heavy, as a OSHA hard hat, but it will offer some protection from banging your head.

Look around some DIY concrete forums for installation tips and specs.

Get your son to pickax out enough to get yourself 4" of concrete.

Undermining the foundation that much will not be an issue unless you are in sand and I believe your description precludes that. Dig next to the stone foundation and after you pour the concrete back in you will be fine.

Spend a little more and do it right. If you are rolling around a heavy wheeled toolbox you don't want to be understrength on the floor.

Usually around here if you have a rough stone foundation there is no footing, they just leveled the ground and started laying stone.

Does sound like your soil is very dense. Not unusual to see no footings even on early concrete walls. A test hole right up against the foundation will answer what is possible.

An electric jackhammer can break the compacted soil. Someone may have dressed that soil many years ago with something if it is hard to dent even with a round nose shovel.

I believe 2 inches of concrete is the least allowed for a top dressing on old concrete. Three inches is an absolute practical minumin on really dense compacted soil like you describe.

Four inch is minumin convention. The problem in shooting for say three inch is getting the base basically perfectly level or thin spots can occur. Depending on the cost of a concrete pumper in your region you could use one of the basically self leveling pours that seem to be catching on.

One problem is that if you get any hydrostatic pressure with no incorporated drainage could be an issue. At least install a six mil plastic vapour barrier under the slab.