# wall to wall basement pour questions



## joecaption (Nov 30, 2011)

Strong suggestion, hire this one out. You say you only want it for storage now but look over the dozens of other post of people trying to deal with poorly laid basement floors.
Far easyer to to have it right the first time.


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## Daniel Holzman (Mar 10, 2009)

My experience with wire mesh has been uniformly bad news. It is very difficult to keep it in position, usually it ends up at the bottom of the slab, where it does nothing but rust. Note that the ACI (American Concrete Institute) does not even recommend use of steel reinforcing for slabs 4 inches thick, due to the fact that you cannot get appropriate cover (2 inches from soil) unless you put the steel in the center, which is the neutral axis of the slab, where it does nothing except provide a little temperature steel to minimize cracking. Crack control can better be accommodated by proper installation of control joints, which you definitely need on a pour this large.

If you are hell bent on having steel in the slab, use number 3 rebar, tied together, supported on chairs.

As for the actual placement, this is about four yards of concrete, which is not a huge pour, but will keep three experienced people very busy for several hours. If you lack experience, this is going to be a very challenging project, make sure your helpers have done this before, once the truck arrives is a poor time for training. Personally I would never tackle a job this big, too much work, too hard to get the floor level, too hard to get a good finish, but maybe you have the skill set to get it done. Best of luck, I admire your fortitude.


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## lee12 (Aug 16, 2009)

Thanks for the input. I was thinking that the wire mesh would be a bit tricky so I'm okay with leaving it out if it's not common practice. 

Regarding tackling this myself, I am confident that it can be done. I have previous professional construction experience and this is the second addition I've put on my home, both of which I've done myself from footer to roof. The inspectors have been pleased with every stage. 

I plan to have 4 people on this, myself included, all of us with construction experience to some degree. What's new about this for me is that it's wall -to-wall and it's larger than the other concrete work I've done. That being said, I am looking for advice from those with more concrete experience regarding:

1) methods for screeding a wall-to-wall pour
2) recommended expansion control for a floor this size

Again, thanks for taking the time to read and help


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## framer52 (Jul 17, 2009)

As you now have it figured out, you can't screed from wall to wall. I divide the pour in half to screed.

as far as expansion joints, why do you think you need them?

By the way, basement pours are not for beginners as you have been told.


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## concretemasonry (Oct 10, 2006)

I assume this is a 4" slab sitting on top of the strip footings to provide the initial bearing against the base of the wall. This is method used commonly here for decades and required in some codes. Compact the soil well, even though the loads are minimal.

Snap chalk lines on the wall to use a guides. If you have a floor drain (good idea), slope the floor slightly for control over where water (if any) has a place to go and not pool elsewhere. You never know when there could be a plumbing or equipment failure. Placement without forms does take more skill and experience than when you can just dump from all side and just drag something around the edges.

You do not use expansion joints in a slab like this. I rarely have seen control joint either formed or sawed in a basement. The shrinkage of the slab will pull it away from the wall slightly since the slab is not connected to the wall.

A basement slab is not prone to shrinkage cracks because of the uniform temperatures, contrary to an exterior slab, so cut/formed joints can become a problem. Use a low slump to maximize the strength and minimize curing shrinkage. Cure slowly and the poly under the slab will maintain much of the moisture to aid in curing. Avoid excessive amounts of artificial heat and mist the floor lightly for the first week or so if it appears to dry out. Avoid the temptation to use a wet mix to make the movement of the concrete around easier and consider another window (if possible) to shorten the length to move it since a truck has wheels for a reason. I have even seen pumps used with super plasticizers used to avoid placement problems and reduce the chance of paying waiting time on the truck.

Mesh or rebar are not common, but can be used if desired.

Dick


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## lee12 (Aug 16, 2009)

Dick - thank you for the input, much appreciated.


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## jomama45 (Nov 13, 2008)

Dick did a good job of clearing most things up, but here's a little more:




lee12 said:


> 1) Do I need expansion joint material at the edges of the floor? Walls are block.
> 
> No, the concrete will shrink away from the walls. If you have a few odd corners close together, like thru a doorway, it doesn't hurt to wrap those corners with expansion material to allow the slab to move freely.
> 
> ...


I would skip any re-enforcement as the floor will likely see no substantial load.


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## lee12 (Aug 16, 2009)

jomama45 - thank you! exactly the type of information I was looking for.

I had also been thinking about driving rebar straight down in a few places toward the center, leaving the top of the rebar at the height of the finished floor. Between this and snapping lines along the edge I figured I'd be able to get the floor level enough. see any problems with that plan?


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## jomama45 (Nov 13, 2008)

lee12 said:


> jomama45 - thank you! exactly the type of information I was looking for.
> 
> I had also been thinking about driving rebar straight down in a few places toward the center, leaving the top of the rebar at the height of the finished floor. Between this and snapping lines along the edge I figured I'd be able to get the floor level enough. see any problems with that plan?


The rebar will work fine, just be careful no one falls on it or tries to drive a wheelbarrow over it........

I would recommend keeping a hammer handy as well to drive the rebar below the surface at least an inch after you hand mag the height around it.


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## lee12 (Aug 16, 2009)

good points - thanks again


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## Gary in WA (Mar 11, 2009)

My 2 cents:http://www.buildingscience.com/documents/digests/bsd-103-understanding-basements?full_view=1

Snap a second line 3-1/2" above the grade chalk line for your screed board when you cover parts of it by accident..... been there, done that, LOL.

Gary


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## cleveman (Dec 17, 2011)

I put a 1x4 on the footing around the perimeter and screed off this. Hopefully, you can pour two pours.


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## concretemasonry (Oct 10, 2006)

cleveman -

If you pouring a slab between walls and on the strip footing, which I assume is also common in your area, how did you remove the 1x4 and fill in the gap between the new concrete and the walls? A 1" gap there is not a good situation. It is best to have floor continuous.

Dick


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## cleveman (Dec 17, 2011)

Dick-I didn't remove the 1x4 and haven't.

I think your concern is justified, that the wall will shift in on top of the footing. Typically, the top of the footing has a bit of a "channel" or "key" tooled into it, plus the rebar every 4' or so.

So it hasn't been a problem, but I get your point.

I have seen a few block basements where the bottom course is held in place by the slab, and the second course is shifted over. These were on foundations with no perimeter drain, bad grading outside, poor soffit coverage (gable end) and obviously no cores filled. So all the planets were in alignment.


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## pls8xx (May 2, 2009)

I'm sure the pros have no trouble working to a chalk line. And the additional chalk line above grade is a good idea. But for an amateur, in the hectic confusion of making the pour, it might be worth all the extra work to establish a screed surface that can be pulled out of the way for finishing. For one such concept see below.


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## cleveman (Dec 17, 2011)

Theoretically, that is a fine idea. I'm sure it will work well. The problem is the cost. If it doesn't matter to you, go ahead and do it.

I think most everyone is using the rod system, where they put some rods on "Y" supports, screed, then pull the rods and the "Y" supports, or drive them down.

I've never used that system because I thought you would need a lot of "Y" supports, and it would be a pain to fill in after the parts have been pulled.

I guess you could just screw on a piece of angle to the wall, screed off it, and remove later.

As far as that goes, you could put a piece of lumber on the wall, put a stick on top of screed board, and go with that.

I just like to have something positive, rather than a chalk line. The chalk line will work fine, until you go laying 18x18 tile on the floor.


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## concretemasonry (Oct 10, 2006)

cleveman -

You are right about a DIYer not having the skill to be accurate enough on a 16x24 addition. Usually, a slab that size is big enough to use ready-mix and have one skilled person on hand that is capable of hitting the chalk line while the others are doing the grunt work. The same thing applies whether the wall is poured or block. One good finisher will not drink any more beer when done than a buddy that does the grunt work. I have seen the same problem for over 35 years.

Sticking a piece of wood between the slab and walls defeats all of the advantages of providing positive lateral support to a wall in the long term in case of floods or poor drainage. If you have any reasonable code, it also defies the code in most areas, plus the wood will eventually be gone and create problems as it deteriorates even if it is PT. - That is almost as bad as the little drainage trench common on some cheap older basements in the east.

The OP has a block wall, so it should be laid in a full mortar bed (first course) and have a minimal amount of vertical reinforcement to satisfy the shear problems on the first couple of courses and to increase the wall structural flexural strength to match or exceed a minimal poured wall of the same thickness. - You may not realize it, but a reinforced block wall can be stronger than reinforced poured wall if someone wants it to be since block can be 8500 psi.

The important thing is the detail of attaching a temporary 1x4 to the wall since the footing may not be as level as you would like it to make it truely level. A chalk line and level gives an accurate positive elevation to work to. One high spot or a few pieces of high aggregate totally defeats the concept of a 1x4 on a footing unless it is just for storage.

Dick


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## cleveman (Dec 17, 2011)

That's a good point about the boards on the footing. I nail them on with concrete nails when the walls are still green.

I had one basement I laid a bunch of tile in and it was fine. 

I guess the same argument could be made about setting form on the center footing.

What about if I use some cement board as a form on the perimeter. Can I get a pass for that?


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## lee12 (Aug 16, 2009)

pls8xx - your idea is interesting. I had seen similar things mentioned other places on the web. Had thought about attaching a board to the wall with the bottom of the board level with what will be the top of the floor, then use a screed board that is notched on the end to allow it to ride on the guide board.










I figure it's probably a good idea to help things move quicker once the concrete is poured.

Another question - how long do I let a floor like this cure before moving things into the room?


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## joed (Mar 13, 2005)

Just use Agilia, self leveling concrete. Google it.


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## concretemasonry (Oct 10, 2006)

No!!!! - Not for a basement slab!!!

Don't over-think a simple project.

Dick


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## lee12 (Aug 16, 2009)

Thanks for the help everyone, concrete was poured 2 weeks ago and went great. Here is a picture of what I ended up doing to be able to screed. Probably overkill for someone who's done this a few times, but it was a big help in my case. We were able to screed quickly and get everything floated with time to spare. Also used an extension ladder with some 2x4s and a roll of metal flashing to made a chute which worked very well. Did not use it quite the way I intended but it still turned out to be very helpful.

Now that it's been 2 weeks - am I good to start moving some things in there (nothing heavy like a car or big equipment)?

Again everyone - thanks for the help!


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