questions re concrete foundation for our craigslist shed

[Bob98SR5]

Hey guys,

I picked up a smallish 8'x 3' x 5' (high) shed from a seller on craigslist. perfect for our townhouse backyard. problem though is that the place where we'd like to put it is where the water puddles due to my mom's idiot friend who laid our concrete. the left pic shows a top view and the right side of the pic shows a ground view. the concrete slants towards the middle, so if i put the shed on it as is (can't, but theoretically speaking), there will be a pool of water and the door will be right over it:

http://i176.photobucket.com/albums/w177/bob98sr5/forsale/cheapy-shed-platform.jpg

so i did some searching on google for "laying concrete on concrete" and i got meaningless results . which tells me, this is not "standard industry practice" :angel: so, does anyone have any advice on how to do this? i just want to add that this is not our forever home. i just want a quick dirty solution on how to build a level platform that is a few inches high that the shed will sit on.

thanks,
bob

[tulsa_sr5]

How many inches to you need to raise it? Does the shed have it's own floor?

My first thought would be some pressure treated 4x4's to get it up a few inches, and a cheap ply or pressed wood floor if it doesn't have it's own.

[04 Rocko Taco]

Deck blok. Sold at Lowes. Aisle 20. With the concrete. Its a cinder block that is 'notched' for lack of a better word at the top to support decks, it would also work perfect for a shed floor, and will raise the shed up. Let me know!

[Bob98SR5]

brian,

as far as how high, probably not more than, say 4-5 inches. the shed does not have a floor, but is boxed at the bottom so that a floor could be put on top of it:

http://i176.photobucket.com/albums/w177/bob98sr5/forsale/shed-floor.jpg

chris: thanks for the tips on deck blocks. however, i think it might be too high. not to mention, it would increase the cost of this project

[04 Rocko Taco]

they are fairly cheap, but I think they are gonna raise it between 6 and 8 inches.

[Bob98SR5]

chris,

yeah, i just checked out some pics. they are quite tall

[Erich_870]

There's nothing really wrong with pouring a slab on another slab, especially if it doesn't have to last forever. If I understand your explanation correctly it sounds like your shed would totally cover the existing low spot?

I would personally pour a slab to get the shed above the current runoff (unless you wanted to get into a drainage design, which wisely it doesn't sound like you want to :hillbill:)

If you're able to keep the new slab at least 2" thick in the back and around 5" in the front you should be fine.

I just threw some numbers together, but if you pour a slab that's 8'x3' with a thickness of 5" in the front and 2" in the back, you'd need roughly 12 sacks of ready mix concrete (assuming about .6 cubic feet per sack). Get the "extra strength" sacks with fiberglass fibers and you'll be good to go. I wouldn't try to go any thinner than 2" though, you'll eventually see cracking. Keep your mix on the dry side too. You don't want it to shrink when it cures. Lastly, I'd pressure wash your current slab first, put down a some forms and go to town.

12 sacks is a long day of batching in a wheel barrel, but it's doable. Ask me how I know :flipoff:

Erich

[Bob98SR5]

eric,

cool, thats good information. for the concrete prep, how about muriatic acid? I dont have a pressure washer. and do you think those rebar cage like things are necessary to lay down in the concrete?

[bamachem]

acid will etch the concrete and will suffice if you don't have a pressure washer. make sure to use a broom and scrub it good too.

definitely get the reinforced concrete with the fibers.

no rebar needed.

you'll also need a 2x4 or 1x4 with a good edge on it to rake the concrete in the form to get it nice and level.

[slosurfer]

Bob, you may also want to look into renting a mixer for the day. I think you can buy a yd. of already mixed concrete in a towable container that you would pick up at their yard. The extra cost may be worth it for the time/work saved, not to mention it's hard to do a slab hand mixing because your first load is starting to "go off" long before you are done mixing your last load.

You could see if you have a company called "Hanson", that's who owns the local yards and I think they have yards nationwide.

[Erich_870]

acid will etch the concrete and will suffice if you don't have a pressure washer. make sure to use a broom and scrub it good too.

definitely get the reinforced concrete with the fibers.

no rebar needed.

you'll also need a 2x4 or 1x4 with a good edge on it to rake the concrete in the form to get it nice and level.






Erich
Bob, you may also want to look into renting a mixer for the day. I think you can buy a yd. of already mixed concrete in a towable container that you would pick up at their yard. The extra cost may be worth it for the time/work saved, not to mention it's hard to do a slab hand mixing because your first load is starting to "go off" long before you are done mixing your last load.

You could see if you have a company called "Hanson", that's who owns the local yards and I think they have yards nationwide.



Both good points. Ditto on no rebar, that's what the fibers are there for. Plus, you'd need to be 5" thick for minimum cover on all sides.

Renting a mixer would definitely be easier and since it is a slab, you wouldn't risk problems joining separate batches.

Erich

[Bob98SR5]

Plus, you'd need to be 5" thick for minimum cover on all sides.

Renting a mixer would definitely be easier and since it is a slab, you wouldn't risk problems joining separate batches.

Erich



When you say "5" thick", do you mean the height of the slab? Or the area around the shed?

[Erich_870]

I'm talking about height (or depth) as measured from the top of your existing slab up to the surface of your new slab. This is just a guess based on my understanding of your situation. You need figure out how high above the existing slab you want to be and I wouldn't be any thinner than 2" at your thinnest spot. The closer to 4" avg thickness, the better.

With using rebar in concrete you have to pay attention to the minimum cover of concrete around the rebar. For example, if you were pouring a new slab on the ground and put rebar in it, you need to make sure you have at least 3" of concrete between the bottom edge of the rebar and the dirt. This is to protect the rebar from moister that will cause rust, that will then cause the rebar to expand and pop the concrete loose. Retaining walls are built the same way. The side touching the dirt needs to have at least 3" of concrete and then on top of that, they usually apply some sort of waterproof membrane or coating. The other side of the wall that is exposed to air needs a minimum of 2". If you used rebar, you'd want to stop the bar 2" from the sides of the forms around the out side.

You place rebar in concrete to make up for concretes lack of tensile strength, but you have to protect the rebar because it rusts so easily. Thankfully you can get away from rebar or welded wire mesh by using fiberglass strands. This what we use in all of our curb and sidewalk these days.

That was probably more than you cared to read, but anyway... :hillbill:

Erich

[Bob98SR5]

Erich,

Nah, this is great information, thank you! Yeah, I'll make it at least 4" high and no less than 2". Again, thanks i appreciate the expert advice.

Bob

[Erich_870]

Erich,

Nah, this is great information, thank you! Yeah, I'll make it at least 4" high and no less than 2". Again, thanks i appreciate the expert advice.

Bob



My pleasure, UY is much more than a Toyota Forum to me :love:

Erich :hillbill: