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Old 09-17-2006, 11:31 PM
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DDA52 DDA52 is offline
Blood, Sweat & Concrete
Join Date: Jun 2004
Location: Bulverde, Tx.
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The first finish hit.

The water is dried up and all the concrete is crusted over at this point. Now is time to cut it open and let it breathe further. This is called the first hit. You will start using a trowel at this point. If it works up to a soupy mess, get the float back out and use it. All areas will need to be hit again. Edges, perimeter and interior. Run the edges exactly as before, just use the trowel this time. They will start to take shape and begin to look like they should. They will take two more hits and that is all. They will finish first as will all the edge of the slab. This is due to the fact it is done by hand. All hand work will finish faster than machine work. Against the forms will finish faster too. They tend to suck up the water and will speed up the setting process slightly.

Now comes the interior of the slab. As to when this gets done depends greatly on how you will be doing it. By hand, you will need lots of help. It will need to be started as soon as you can get on it with knee boards and not sink. This is due to the fact that it takes much longer to finish by hand and you will need the extra time. The knee boards we use are simple. They are 3/8 plywood, 32" x 24". You need two. One to work on and the other to move to when you are ready. Even if you machine finish the slab, you will need knee boards. They are needed for fixing oopses, and for working around pipes on the inside of the slab. To work the concrete at this point, it is best to use both a float and a trowel. Use the float to cut open the crust and then lay it back down smooth with the trowel. Take out all the marks in front of you and then move onto the next board. Pick up the first board and put it on the slab in the direction of travel behind you. Then repeat the trowel cycle.Do this over the entire area. You may run into wet spots. Just go around them or wait them out and then proceed. Don't get onto it too early or you will spend all your time fixing craters that you make by sinking into the concrete.

Use the float or trowel you are not using at the time to lean on while you are working the surface. Don't use your hands. The concrete is chemically active and can eventually burn you if you don't clean it off of you. It will also suck all the moisture out of your skin and dry it out badly. Cracking will follow. It isn't fun.

Now, if you are using a trowel machine, everything is different. You put it on when you leave a footprint about 1/4" deep. Then you slowly work the surface at a slow speed with the blades almost all the way down. If you hit a dry spot, speed it up, raise the blades slightly and or add a little water. Make passes along the form first and then start working in. Make sure the passes overlap by almost half. This will keep you from floating in a ripple into the surface. You want to fill all holes and craters with the machine or trowel at this point. Never leave anything behind for later...later will be too late. Pay close attention to footy prints too. This is when the most are left in slabs. Once it is all cut open, let it breath and keep an eye on it.
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