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Allthunbs 06-08-2009 10:38 AM

tips and tricks for laying and removing concrete forms?
I'm about to start laying a floating slab for my workshop and I'm looking for tips and tricks on laying floating slab forms and removing them. How do you drive in the stakes? I'm thinking my brand spanking new pneumatic hammer would come in handy. Do you coat the forms with kerosene or do you have other solutions? Once you have the floor in place, how do you remove the stakes? Any other suggestions? Do you make your own Michigan float or do you feel the store-bought variety is better?

Do you lay the forms then the gravel or the gravel then the forms? Do you back fill to prevent blowouts or do you make sure there is a pair of stakes at any joins?

That's all I can think of for the moment.


Aggie67 06-08-2009 02:32 PM

That's ambitious if you've never done it before. But not totally impossible. Post some more info. Thickness, width, length, reinforcement, etc.

You can buy form release agents at any decent mason's supply store.

jomama45 06-08-2009 10:28 PM


Originally Posted by Aggie67 (Post 284515)
That's ambitious if you've never done it before. But not totally impossible. Post some more info. Thickness, width, length, reinforcement, etc.

You can buy form release agents at any decent mason's supply store.

What he said, & what kind of soil you'll be forming in would be helpful.

Allthunbs 06-09-2009 04:49 AM

Ok, the soil is compacted granular sand 85' thick. It has a compressive strength of 4.5 tons/sq ft undisturbed.

The slab will be 14'x24', 4" thick with mesh reinforcing. The gravel bed will be between 4" and 7", compacted by hand and I'll set level with the gravel. It is a floating slab not a monolithic. My drainage is so fast, there's no need for a footing. 1 bucketful in a hole, drains almost as fast as you can pour.

I was thinking I'll use a water level to set the form height and stake every 2'. That will allow me to use the form sides for screeding the concrete level.

I got some 2 1/2" nails for my nailer so I was figuring they would allow me a good solid predictable form that I can use for screeding without blowing out the other side.

I'm using 1 1/2" square 3' long stakes to support the forms. I'm making about 42 of them. I was going to use a sledge hammer but I had to get a pneumatic hammer for removing mortar on another project so I figured I'd try it for driving the stakes in -- less damage to the stakes I hope.

Dedicated mason's stores don't happen here. I'll have to do some digging. Anybody know who handles masonry supplies in Quebec City?

Thanks for the help.


jomama45 06-09-2009 10:58 AM

If your only setting 2x4's or 2x6's, it's a very easy form job in good soils. No additional bracing needed for 2x4's, other than your stakes. 2x6's may need a few braces, but you'll have an idea how rigid it is once staked. I would personally try driving one of the wood stakes in by hand to see how hard they are to pound. I don't think you'll need anywhere near 3 feet of stake unless the sandy soil is very soft. Cut the rest of when you determine the necessary length. A few more things:
- DON'T use a nail gun, unless you want to spend a lot of extra time stripping.
- I would just use 3" screws in the wood stakes, as they hold great & strip out easy. Important if you want to finish the sides of the slab at all, if you have the time.
- If you do plan on stripping the sides & finishing, I would recommend diesel/kerosene & a new motor oil mixed 50/50. Kerosene on it's own in too thin IMO, & just soaks right in to the boards. Also wait as long as you can before the pour to coat the forms. If your not planning on finishing the sides, you don't need anything for release.
- I would still consider thickening the perimeter edge of the slab, as this is where all the weight (walls, roof, headers on shoulders) of the garage sits permanently. Also consider 1 or 2 rebar around the entire perimeter.

Good luck! :thumbup:

joed 06-09-2009 12:02 PM

I have never used a release on 2x4s used for forms, especially for aone time job. They pop right off when the concrete is hard. It's a different story if you were reusing forms over and over again and needed a clean finish like a basement wall.

2x4 staked and screwed work well. 1x3 works well for stakes as well. Back fill the forms with dirt if you are worried. There will not be a lot of pressure with only 4" of concrete. Make sure to cut the stakes even of below the 2x4s. Makes screeding much simpler.

yesitsconcrete 06-10-2009 06:06 AM

used motor oil, diesel, kero, form release, yada, yada, yada,,, i like wax'd paper - environmentally friendlier, less expensive, no strip just leave in place, & you can line your cookie sheets when its done :laughing:

Willie T 06-10-2009 07:33 AM

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It's not really rocket science. :) Stick the tip of the shovel under a form board (near the end), and push down, prying the board up and out of the ground. The stakes usually come right along with the board.

jogr 06-10-2009 09:20 AM

If you get a little sloppy while pouring/screeding and spill concrete over the edge of the form I've learned is helpful to do a rough clean up of the "spilled over" concrete from the forms the same day - or at latest the next morning. Sometimes that excess concrete can really lock in the forms and make form removal more difficult.

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