Prepping for concrete, what to do?

[sprackydoo]

I'm planning on laying concrete down in a 20 X 40 foot barn. The problem is the barn housed horses for years so the ground is 1/2 dirt and half decomposed hay so the ground is very soft. Can I lay cement over it? What if I use rebar? I don't have much experience with laying cement so any other tips are appreciated

[DynoDave]

I'm sure someone more knowledgeable will post a reply, but if the floor is soft, that would seem to be a recipe for the concrete to crack. I would think about digging out that soft stuff, and replacing it with compacted gravel.

[Ken Greene]

yup it will crack
escavate out all the soft stuff and fill with gravel, compact it with a plate tamper or jumping jack tamper.
then pour away

[GearHead_1]

yup it will crack
escavate out all the soft stuff and fill with gravel, compact it with a plate tamper or jumping jack tamper.
then pour away


This is the correct answer. :thumbup:

[bmwpower]

Technically, you want to compact the new dirt, then put the gravel in (1-2 inches at a time) and compact that. I would put in at least 3-4 inches of stone. Plate compactor seems to work better for this type of work.

Rebar and fiber mesh will help to prevent cracking to some extent, but a solid foundation is the best preventative measure.

If you plan on coating the floor with epoxy, paint, tile, etc throw down a vapor retarder prior to pouring the floor.

[sprackydoo]

Sorry I'm a newb

Don't know anything about a plate tamper or jumping jack tamper. Can I get them in 110V if not do they have gas or pneumatic ones? I'm assuming Home Depot. will rent me out one? Any special type/sive of gravel? Also what is a vapor retarder? How far apart should I lay the rebar? Should I go 4 or 6inches of cement?

[GearHead_1]

Sorry I'm a newb

Don't know anything about a plate tamper or jumping jack tamper. Can I get them in 110V if not do they have gas or pneumatic ones? I'm assuming Home Depot.

These are usually gasoline engines. There are general guidelines for cement thickness, bag mix, diameter and frequency of rebar. These probably vary depending upon location and local code. A good rule of thumb at least within reason is that the thicker the concrete and the more steel you put in it the more stable the slab. A good flat worker can tell you what would be best in your situation. Wire mesh (chicken wire/fencing material) doesn't work as well as rebar regardless of what some may tell you. A good compacted gravel underlayment (sometimes up to 12" thick) will help your slab also. Pea gravel is usually considered 1/2" or less in diameter I believe (someone may correct me on this). Depending upon your location and the humidity a vapor barrier may or may not be a good idea. I recently put down a 10" slab with 1' squares (3/8" diameter) of rebar for a new garage that is to have a lift in it. The lift only required 6" concrete but I decided to go above and beyond. Home Depot or Ace Rents has the plate style tampers.

There is only one sure thing, sooner or later all cement cracks (rebar will stop it from separating). Make sure your strikes or cuts are at the appropriate spacing to minimize these. If you are going to use a creeper on the cement cuts are easier to roll over than strikes.

[bdaz442]

A 20' x 40' foot slab is a big jog even for professional concrete people. I would NOT try this job till I did a lot of research on pouring and finishing concrete.
I've done it and it takes a lot of hard work and even more knowledge. :see:

[sprackydoo]

A 20' x 40' foot slab is a big jog even for professional concrete people. I would NOT try this job till I did a lot of research on pouring and finishing concrete.
I've done it and it takes a lot of hard work and even more knowledge. :see:

I'm gonna be doing it in 10 foot sections by framing it up with 2X6's