Bricks, Masonry, Asphalt and Concrete - Pouring a large slab

Newbie from Northern MI here.

I gained some experience screeding concrete when I did my 12' X 48' driveway last summer, using a 2X4 across the forms.

This summer, I am going to be building a 30' X 40' detatched garage on a floating slab about 4" thick. How do I go about screeding such a large area?


Thanks!

there are many ways you could do this, if you are installing a floor drain and sloping the crncrete in to the middle of the room then centre your floor drain, conncet a string line from the centre of the floor drain to the top of the form on the outside. this is your slope. put either spikes or cuts of small rebar into the ground to mark these heghts al the way around, stay about a 1/4 inch down from the line so you dont have to pull the spike just pour over it, when you are screeding you use these spikes as guides for your heights. This concept is the same for sloping it the other way from back to front or even just staying level if your forms are level on the outsides then the string stretched accross the forms from one side to the other will give you a guide to install your spikes. your only other options other then this inexpensive method is to rent a laser level on do it that way, probley about 100 bucks to rent for the weekend, also another option is to screw a bunch of long 2x4s together and screed it the way you know how. if your going 20 feet thats not bad just 2 2x4s together and one in the middle to keep it from sagging and just stay with the tops of the forms. hope this helps

It depends on how your floor is going to slope. Will it go toward a central drain, or slope toward the garage door? Let us know to get an answer.

Pecos

Bricklayer and Pecos - Thanks for the help!

The floor will have a slope to the doors, as installing a center drain is not feesible. I plan on setting the rear of the forms slightly higher than the front to achieve this.

I prefer to do what I know best (2x4 method), just had no idea if that was suitable or not, for a 30' span? The wife bought me a laser level for xmas, still in the box - not sure how to use it for concrete work?

Yeah, yeah, I know...Guys with shiny tools. Ha Ha

One other thing that I have been considering is to just pay the extra money to have it done, as I don't think the labor is near as much as the concrete itself.

Thanks again!

UPer (I assume) -

A job that size is quite large for a relative newbie and things can happen - it is not like something 12' wide. If they happen, they can have permanent consequences.

Have you considered hiring a man that knows the business and working with him? You have friends and he had friends. You obviously have some experience and sweat to contribute. Who you hire to help the day of the job will be up to you.

Not the cheapest, but a good way to get it done with some help. - Don't forget the air entrained concrete considering how Michigan is in love with salt so they can build more cars.

Dick

Frame out the area, and install 2 screed boards staked at the proper height in the slab spliting the slab in 3 more manigble sections, directly after screeding pull out the boards the stakes will come along too, walk in the groves and fill in where the screed was with concrete, work it in with the back of the shovel.
A Bull Float would be nice at this point.
Frank

I've never liked running the screed on elevated pipes or boards because of the pain of filling in the voids that they leave. What we do is this:
1) Determine your elevations on the edges of the slab (and chalkline them on the wall, if applicable).
2) Starting in the center of the high end of the slab, tightly stretch a string line across the slab to the center of the low end.
3) Down the center of the slab, next to the string, drive a small length of rebar into the ground and stop when the top of the rebar stake is at the same level as the string line.
4) Move about 8 feet toward the lower end of the slab and repeat this procedure, setting another grade stake.
5) Continue until you've got a line of grade stakes set to elevation all down the center of the slab.
6) When you pour the concrete, pour to the top of these stakes. Use the screed board to screed between these stakes, thus giving you a slick spot (wet streak) to follow. This replaces the pipe or form.
7) As you screed the concrete, have one man hold his screed on the outside slab edge, and the other guy is in the slab riding his end of the screed on top of the wet streak, being careful not to dig in. As you pass each grade stake, tap it down under the concrete surface about 1" and leave it there.
8) After one side is screeded, move to the other side of the wet streak. You will now have the other (screeded) side to rest your screed on, which is easier than just following the wet streak alone. As the man inside the pour is screeding, another man stands behind him and fills in his tracks with fresh concrete, or rakes back concrete that is too high. This is best accomplished with a concrete rake (come-along) or flat shovel.
9) Work your way back and out of the slab, and your floor is at the proper slope with no re-work needed.

This procedure allows you to use a shorter screed that will not deflect. You are also pulling less mud at a time, which is easier on your back. Good luck.

Pecos

(One fellow up'er to another)

I like pouring my garage floors pitched to a drain. If it is going to be a floating slab, then of course the forms have to be level. If one were to start raising one form over another to pitch a floor, won't the building be out of level. I don't mean to cast aspersions on what works bes for others but to each his own.

Who can screed with a 30' screed of screwed together 2 X4's? I would not have much luck as my experience leads me to believe you might have some bowing. And screeds lengthened by doubling up are awful clumsy as they tend to twist . Concrete always screeds best to me when the pulls are kept aas short as practiacal and the 2 X4 screed stays peerfectlly on edge. One of the first things I do after setting forms is take a sack of old mortar or concrete and mix a wheel barrow of mud to set one of those 10 1/2" plastic sumps with a heavy duty lid a car can drive over. I then run a 4" drain pipe outiside the building perimeter and make a dry well type drain or stub it off for other hook ups. At that same time, I see to it I drive a 1 X 4 stake for a pipe (with a pitch to drain sump) into the fresh concrete for pipe screed to rest on.

Everybody has a sysem that works for them. I am not ridiculing those that differ from my method nor has anybody else on this thread. Good luck with your project.

Make sure she's level and square. (grin)

bs5

BS5 is right about the slab needing to be level all around the perimeter. I was thinking more of a regular garage slab where you were pouring inside of concrete block or a poured foundation. In the case of a monolithic slab/footing, a central drain would be best. A pro could do it sloping toward the door while leaving the perimeter level, but it doesn't sound as if you happen to be one.
Dick is also correct in stating that this is a LARGE job for a DIY'er to tackle. You'd be better off in the long run hiring a pro.
Go back through the archives to a fairly recent thread entitled "moving concrete from a chute" or something like that. It may make you think twice about trying it yourself.

Pecos

I found the other thread. It's on page 4. Good luck.

Pecos

Thanks Everyone,

After reading some of the posts, I can see that this is another one of those fine arts in the construction trade. I agree. There are certain things that are best left to Pro's. I sat down and estimated the material, excavation costs, etc... and I am actually saving maybe $500.00 from the first few estimates.

So the real question is: Would I pay $500 to have someone do this for me, and do it right the first time? Yep!

On a side note: I found somebody who knows what they are doing, and will let me put some of my sweat into the job - just need to find out how much??? Again, not sure if it's really worth trying, but the more I think about it, the more I accept that there are some things I just don't know how to do well. This is one of them. Last time, I ended-up tipping the redi-mix driver $50 for helping me move and level the pour with his rake so we could keep up - It seemed like the right thing to do.

Yep, Yooper by osmosis and the salt did me no favors last winter either.

Thanks again!

briguy66