Advice for pouring cement

[WMonroe]

I need to know the best way to pour a floor in an existing basement? Heres what we have: an old house that the front half of the basement already has a cement floor, but the back half was just a crawl space. It has had all the dirt dug out so that we can pour the floor even with the front half. How do build forms to skreet off of and still get them out after?



I have never done one quite like this before and am looking for a little advice.



Thanks

Will

 

[DieselMinded]

LOL



you dont use forms you pour wall to wall



DM

 

[DieselMinded]

You snap a chalk line on the walls and use sections of rebar along the interior spaced evenly apart sticking out of the grond the thickness you want to pour then you just skreet to not quite that level. just use them for eyeballing purposes ... . thats how we do it Im sure others have there ways



DM

 

[EBottema]

Deep deep footings. minuimum 8 inches deep for the floor. use rebar forsure... dont skimp or it will end up cracking

 

[DieselMinded]

Out of the 10 houses I have built with my dad (CONTRACTOR) we have never rebar'ed the basement floor. Nor has the 3 diffrenet Sub Contractors we have used when we didnt want to do the Crete work.



Truth be know all concrete is going to crack ... . ALL



thats the reason you Score/ Cut it to give it a weak spot so when it cracks its controled



Atleast thats what they taught us in the Mason Courses



Its when it cracks not if it cracks



they were very clear on that phrase... . LOL

DM

 

[EBottema]

Rebar significantly keeps it from flexing which helps it not crack. The scoring is a good idea too. I would atleast put some rebar in it. I like to overbuild things

 

[DieselMinded]

LOL



You do have those Cali Quakes over there maybe you should rebar



DM

 

[nickleinonen]

I like to overbuild things

then some 1/2" rebar in a 6" grid will do you well :-laf

 

[WMonroe]

Thanks for the advice. We are putting wire grid in it and later going to cut the control lines in so hopefully thats where it will crack.

Will

 

[TWORAMS]

If you really want to screed, I've seen people attach a 2X4 to the existing walls on both sides. Then you attach a stake or something similar to the top edge of your screed board. The stakes hang over the top of the boards on the walls and suspend your screed board so you are dragging the bottom edge of your screed board over the high spots. Hope this makes sense to you but it's a lot better than freehanding it. You might just take your time and of course make sure your screed board is as long as your walls are wide minus the boards you attached to the walls (and as straight as you can get).

Mike

 

[WMonroe]

Thanks Mike, I like the idea of attaching the 2x4's to the walls. I'm putting the gravel in tomorrow and pouring on saturday so theres still some time.

Will

 

[TPCDrafting]

I spec expansion mat'l rather than 2X4's around the perimeter, and around any interior columns. Drill holes at least 8" into the side of the existing slab and use 18" dowels into the new slab, this will keep them flush even if the ground settles/heaves. I also spec fiber mesh rather than steel reinforcement as I have worked with engineers experimenting with WWF and no matter how hard you try, the reinf. NEVER stays in the middle of the slab. We poured several slabs using WWF with steel chairs, using conc. block as chairs, etc, etc. and after the slab cured we cut through and the WWF was never in the middle, always near the bottom where it corrodes and the slab cracked once moisture was in there. I have poured slabs that are over 15 years old with fibermesh and they are not cracking. Be sure the ground is heavily compacted. Thicken the slab around the edges for additional strength and pour concrete rather than cement, it'll make a much nicer floor.

 

[Grizzly]

I need to know the best way to pour a floor in an existing basement? Heres what we have: an old house that the front half of the basement already has a cement floor, but the back half was just a crawl space. It has had all the dirt dug out so that we can pour the floor even with the front half. How do build forms to skreet off of and still get them out after?



I have never done one quite like this before and am looking for a little advice.



Thanks

Will

First of all, you don't pour cement, you place concrete. Cement is a ingredient in the making of concrete. You make the concrete, then you place it. In placing concrete in a basement, I used screed bars, then later pull them as already advised. If you have a well compacted granular base, you won't need rebars. Remember to have a good system of expansion and contraction joints. Grizzly (civil engineer)

 

[bighammer]

If the floor above is level, you can check the height of your new slab with a pole from above.



We put rows of 1x2 stakes down the middle and along the edges. Then with a laser set them to the same depth. Then put nails near the edges. (sorta like rabbit ears) The stakes hold up a steel pipe that lays accross the tops, with the nails keeping it from rolling off the sides. The pipe is then slid along the row as you screed.



Don't let it dry (cure) too fast. Loss of moistue on the surface makes a slab curl. (top shrinks more rapidly)

 

[JPope]

"... Loss of moistue on the surface makes a slab curl. (top shrinks more rapidly)"



Very good point, lots of theories out there about where the vapor barrier should be in relation to the slab, but many concrete installers wet the subbase to minimize slab curling. Curing the slab properly, water, continually wet burlap, plastic, curing compound, is VERY important for a good concrete project!!!!

 

[Byershome]

If you have never poured concrete before you should find someone who has to help. Depending on the size of the pour you could find yourself in over your head real quick... ... ... ... . concrete does not wait for you to finish. You need a plan to get it in and screeded off quickly. Expansion joint around the edges is the best way to go and it will give the slab some room to move. You should also tie into the existing slab with dowels or even just some tapcon screws every foot or so. Plastic on the bottom will help keep moisture out in the future and give you some extra finishing time now. I would use fibre rather than wire too as it simplifies the pour. Depending on the size you may want to use some metal keyway to divide it up into smaller more easily screeded sections. It will also create a straight line for it to crack on and prevent the different sections from moving vertically.



I can't emphasize enough you have a good plan for getting the concrete in and screeded off, as it starts to setup is no time to decide your moving to slow.

 

[WMonroe]

I have poured concrete before just never quite like this one. There are two other guys that will be there to help so we will have enough people. I called and had them add fiber, but I'm still going to use the wire. Can't be too strong right. Thanks for all the suggestions.

Will

 

[GFritsch]

I have placed thousands of yards off concrete and have come to the firm opinion that experienced finishers make all the difference. Your working time and cure time should be a little longer indoors, but knowing when to work the concrete and the right tools etc.



As mentioned before I would use an expansion joint (felt) between the existing walls and the new concrete. The felt also acts as a elevation finish point. I would also reccomend a light broom finish to help the cure process.



Good luck--let us know how it turns out



Greg

 

[WMonroe]

Everything went very well. It turned out to be about 8 yards, estimated about 8. 25. It finished off well from what I could tell yesterday, but I'll know for sure when I go back on Monday. Thanks again for all the suggestions.

Will

 

[Hawkeye 04]

For anyone else referring to this thread when they pour concrete, please do not EVER replace rebar or wire with fiber mesh! Fiber mesh was created to be used as a secondary reinforcement, not as a primary. Every slab of any fair size will crack. We always cut crack-control joints 1/3 of the thickness of the concrete within 6 hours of finishing. If the slab has no other reinforcement besides the fiber, the fibers will be cut and when the slab cracks, the fibers will be separated, therefore the concrete loses all strength to resist heave and yaw. With the wire or rebar, which is supposed to be poured in the bottom 1/3 of the concrete, even when it cracks it still has the support it needs to keep it from separating and dropping or heaving.