Hello,
I want to knock out the old floor and pour a new one (28'x18' an exesting building). Any recommendations on thickness (I was thinking 4-6 inches). Any recomendations (or tricks) to pouring a level floor?

Thanks

Fordy

 

First trick to pouring a floor is to make sure you DO NOT have it level. you want a little fall towards the door so that any spilled fluids or rain will drain out. You can do this by popping a line along the block wall at the height you want the floor to be. I can't remember how much fall you should have but around 1/2" per 10 feet would probably work. That way you don't end up with puddles when it rains.
Now if you are planning to park a vehicle on the pad you will need to beef up the concrete with some steel (probably not a bad idea anyway). You can use either rebar or steel mesh or both, but either way you will want to ensure that the steel sits up off the ground when you pour the concrete. you can buy "Chairs" for this or you can make something out of bent wire. The purpose is to get the steel in the middle of the pad and not just sitting underneath it.

Finally, if you don't have one buy,or build (i think they have a kit) a bull float. you will use it to finish the surface,basically smoothing it out before it sets up. its not brain surgery but the pivot in the float makes it easier than trying to do something that big with a 2X4.

Good luck
kyle

 

28x18 is a big slab to pour by an amateur and I doubt that you will like the results if you try. I suggest getting a contractor to pour it. Getting the steel set right and keeping it that way is hard to do even with a contractor. Most of them don't have enough people to dedicate one guy to pulling the wire up into the slab. Most of the guys pouring step on the wire/steel driving it to the bottom even if it is set on little supports. You will have to supervise the pour and make sure there is a guy with a long steel hook pulling the wire back up into the slab as it is leveled off. I would suggest a 5-6" slab with 1/2" #4 rebar around the sides and on a 16-24" square grid over the rest of the slab. Unless you get thick wire it won't hold up inside the concrete and it is more difficult to get the wire into the center of the slab. With a 24" grid the guys pouring the slab won't be as apt to stepping on it, they can step inside the squares. 16" is a little harder for those that do not have tiny feet and are not gracefull. I would use 4" square blocks of broken patio paver or concrete bricks to hold the rebar up. They do not drive into the ground like the steel wire supports do when they are stepped on, but they do make for a discontinuity in the slab, a compromise that is acceptable considering the alternative. With #4 bar you will need at least a 1-1/2" covering over the bar and under it making the min slab 4". The 5-6" slab leaves room for a fudge factor since your steel placement will not be exact. If the floor is removed and any grade work done, you can get rebar, wire ties, twist tool, and place the steel yourself. Cutting the #4 bar will be difficult unless you have a torch, hot saw, or a big set of bolt cutters. Use a vapor barier under the slab if you live in a damp climate.

 

There is a type of fibres that you can have added to the concrete that eliminates the need for re-bar.
We had a 30x30 garage built using this material about 15 years ago. It's stood up very well. It has a 6" depth of concrete and is used to store a 26' Sea-Ray on a very heavy trailer every winter.
It's held up very well with negligable cracking even though there is very severe winters here and the building is unheated.

 

I don't know where you live or the weather temperature fluctuation in your locale.

I also don't know how much weight you are planning to put on it.

If it was ME & MY Garage shop.
23 years in the concrete business has taught me to Over spec it.
Doing a slab this size with an experienced helper or two even for me would be stretching it.
I don't know how much experience you have.
Please let me know.

IMHO
I really think you should get a contractor to do this.
The special tools alone will add up.Never mind if you happen to LOSE the slab.

Lumber for forms,Bull Float,Hand Float,Long Handled Steel Trowel,Broom for Apron,Edger,Rake,Shovels,Wheel Barrow,Level Line.

You will also need a power trowel to get the finish you need.
I also don't know what physical shape you're in and what muscles you DON'T normally use BUT,
*This is NOT EASY work*.

What if you hurt yourself during the pour?

Technical stuff:
I would go 5"-6" thick with re-bar 16" squares is good enough > No to the fibre.
Minimum > 25 MPA or 3500 PSI strength concrete poured at no more than a 4" slump.
Make sure you include 4-6% Air-entraining agent(MBVR) for temperature fluctuation.
DON'T EVER Spray Water(This includes a Contractor too)on the laid concrete to help get a smooth Finish.
All you're doing it weakening the strength of the surface and later it will peel off like shale.
Don't pour until the frost is COMPLETELY out of the ground or make sure the concrete is poured 20 days before the first frost.
Concrete takes 28 days to fully cure.

To avoid sinking or having cavities under the concrete > put your road gravel down for as much time as possible before pouring the concrete and drive/park on it to compact it throughly.


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I helped pour a floor last year about the same size as you are talking about. We did an "Alaska slab" 5-6 inches in the center and 12 inches around the apron. With the rebar moving around it was a real pain in the butt like these guys said. We had about 6 guys working and only 2 of them were actually masons by trade. Its was alot of work. If you get a good driver he will know how to pour the concrete moving the shut side to side as he backs up. This saves a ton of work. We had 3 trucks come and only one of them was nice enough to do this. The other 2 just sat back with a ***** eating grin as we worked furiously to move the material around. Then like million says if you going to do this size of a job a power trowel is the way to go. Otherwise you will spend hours with a big float finishing the top on your hands and knees. Been there done that it was not fun. If you do decide to do it yourself better plan all this out and have friends that will actually show up!

 

While I have nowhere near the engineering power you have found above, I spent a year pouring Kalman floors and saw how to do it right.

I cant emphasize enough how important a deep gravel layer and vapor barrier are. My working garage (old and detatched) had been poured directly on top of red clay and the moisture weeping and sweating because of that has rusted tools, mildewed convertible tops and interiors. Adding ridge vents, soffit vents, epoxy painting the floor, and fans have helped, but the problem is forever cast in that damn floor. Looks like a dehumidifier is the only cure ($$$$)

Midnite Cruiser

 

Thanks fellas, I think I will get a contractor to quote on this job as I have limited amounts of experience with concrete work.

Fordy

 

Fordy,

Million has given excellent info. on the tech stuff. It's obvious that he has considerable experience in the concrete biz. This is a job that I wouldn't be afraid of doing myself but then I have laid more mud than I care to admit for my own business. I also have accumulated the tools to do a good job. If you have a bud that has the equipment and the knowledge then maybe he can be coaxed to help. (Might cost a twelve pack tho!!) If not then a contractor might be the best way to go. I'm not sure of your location but out here in rural midwest a general rule of thumb for concrete installation would be about $150 to $200 per cubic yard of mud laid. A floor as yours should probably cost between $1400 and $1900 bucks (six inch pour). Less if the guy is hungry and more if he doesn't need the work. Consider doing your own demolition on the old slab and this will save some bucks. Demo work can be expensive and is something that can be done yourself if your back is strong. A skid loader and jackhammer would probably be easiest unless the old pour is extremely thin. Hammers and industrial compressor will run about $100 to $150 per day and a small skidloader will probably run ya a couple hundy per day. There again a bud with this kind of equipment would by handy and less costly. If you go the contractor route then use Million's specs and you won't go wrong. Don't let the contractor dude convince you of anything less (especially the steel reinforcement). The fiber-mesh system that Frdzilla suggested should not really be used to replace the steel reinforcement. It could be used in conjunction with the steel tho but really isn't necessary with a good reinforcement schedule. It used to be the rage as it was touted to replace the steel and easier to lay mud cause you didn't have to mess with tying rod and tripping over it when you poured. Good concept and some have had success but I have seen some miserable failures with it too. Keep in mind that the fiber is actually glass fibers and until the exposed fiber eventually gets rubbed off you will be running these fibers into your back as you slide under the 'ol Ford to retreive that 9/16 wrench that got away. Some guys will try to convince you of something less and say it's better when in actuallity it is just simpler for then to lay. Good luck!!

Randy

 

Fordy
I recently poured a 30 x 36 slab for my new garage and I can tell you I had 2 friends that where masons with the right tools and There is no way I could have done it without their help. I ended up using 5 1/2" concrete 4000# mix with fibre along with wire and rebar. I also put a 1" saw cut across the slab so if it cracks it will hopefully crack there and not be seen.

 

Welcome to the new millenium - you don't need rebar anymore. You can pour your slab using "fiber" and it's strong.

You might want to just use 2X4s as that is the norm, and then dig footers at whatever depth you'd like, around the edges should you like to put up walls. If you dig footers, make sure to tell the concrete company you want "chairs" these are little wire "chairs" that can hold up some rebar for you to put along the entire length of the footer. Get some wire ties from the concrete company and wire tie all the rebar together with an overlap of at least 1'. In the corners, you should bend a piece of rebar and hook to two striaght pieces (one going each direction) but it's not 100% necessary as you don't know if you will ever want a wall.

One last thing - think ahead. Do you think you might ever want water in the future? Build a little 2X4 box about a foot square, and put that approx a foot from the wall - stake it down from the INSIDE of the box. That way if you ever decide to put water in, you already have a hole in the floor, and you only have to dig in 1' to get to the hole.

Now, to agree with everyone else - you don't have the tools or skills to pull this off. It'll be a mess, and you'll throw away about $80 per yard of concrete. You have to have a power trial and other specialty tools (most mentioned above) to do something this size.

Also, it's starting to get cold out, you'd need a lot of lime in there and if it starts to 'go off' (set up) and you're not ready - bummer.

MP

 

I will quit using rebar when I see bridges, buildings, and roads made without it. The fiber provides a "localized" reinforcement but it does nothing for tensile strength (except in the lab). Fiber also leaves a nasty surface that is hard to finish and bad to crawl around on.

Thanks for using FTE!




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I recently added a 18x24 pole building beside my 30x30 shop I was planning on running PVC water pipe in a reverse spiral thru out the floor area. I found a very informative web site on this type of installation. Using a electric water heater and pump to pump hot liquid thru the floor to provide heat for the addition. Do you concrete experts think I can pour a floor over this pipe with out using re-bar. I have the walls up so it's like doing a basement floor with no side access. I have never used the fibre you guys are talking about. As it is a temporary structure I may have to remove the building at some point of time (at the whim of the city ) Not using re-bar may allow the future removal of the floor easier. I also was wondering if the pipe running thru out the concrete would help keep it all together.

 

You have to use re-bar with piping heated floors.
I put a heated floor in my sister's house when it was built.
There is way too much climate change not to do this.

The fibre was NOT meant for floors because of the finishing aspect.
It was meant more for Sidewalks,Stub Retaining walls,footings.

I never did like using fibre crete.

Just do the re-bar and relax.
The tubing btw will not make it be structurely sound.
The re-bar does that.

Is this being done in a constant weather changing climate?

If so, using M.B.V.R.(air entraining agent) will help with constant temperature changes.

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[updated:LAST EDITED ON 10-Nov-02 AT 03:56 PM (EST)]Ditto on what Mil1ion says. In fact using rebar has an additional advantage in your installation. You can use the rebar to tie your pipes to to insure accuracy of placement in the mix. Also consider using the PEX-AL-PEX pipe which is designed for use for your installation. Is very tough and comes in up to 1000' rolls which will eliminate any joints under the concrete. Cost around 50-60 cents per foot.