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rizzo 04-14-2009 06:30 PM

please help me troubleshoot my poor concrete finishing technique
 
I am placing a replacement section of walkway. The old section (24"x36" by 4" deep) has been removed. I placed re-mesh toward the bottom of the pour, used 2x lumber for the forms, mixed quick-crete and poured to a depth just above the forms. I kept the mix as dry as possible to increase strength, used an air chisel to vibe out the air pockets, lightly compacted the pour, screeeded and then attempted to float the pour with a wooden block by tapping the surface.

The results are ugly with a rough, porous surface showing lots of course aggregate. I was unable to trowel it smooth. This nasty patch now stares back at me and mocks.

Any suggestions on where I went wrong would be appreciated. On a mostly unrelated note, why are concrete floats made of magnesium?

Tscarborough 04-14-2009 06:44 PM

The proper order is: place, screed, vibrate, fill, float, trowel, edge, trowel or broom.

Magnesium is light and stiff.

Phuture 04-14-2009 07:31 PM

your mix was probaly too dry. you want it wet enough so that when you trowel it you get a creamy surface on top. when the wet surface starts to stiffen up you can smooth it some more or "broom" the surface. i hope ths helps you out a little.

rizzo 04-14-2009 08:28 PM

Thanks much. I'll follow the sequence listed and add a bit more water on the next section.

I am not clear, however, on what the "fill" is in the procedure. Is this adding a bit of extra mix to fill in after vibe?

Tscarborough 04-14-2009 08:38 PM

Yes. After you screed and vibrate, you will have to add more concrete in places.

jomama45 04-14-2009 10:32 PM

Quote:

Originally Posted by Tscarborough (Post 259936)
The proper order is: place, screed, vibrate, fill, float, trowel, edge, trowel or broom.

Magnesium is light and stiff.


It's also much harder than wood or aluminum, & concrete doesn't stick to it nearly as well. The only place to use wood (IMO) to float concrete os when excessive bleed water is prevalent on the surface. Normally, wood will "tear" the surface open.

rizzo 04-15-2009 07:54 AM

Wood can "tear" open the surface during float. So true - that's exactly what I found. Can I float with my trowel (steel 5x12), or must I pickup a magnesium float?

Well, at any rate, these small sections are good for trail and error. Mostly error.

joed 04-15-2009 08:32 AM

You usually let it setup for about an hour before doing the finish trowel/broom. If it is too soft you can't get the proper finish. Just do a basic surface smooth and level until it stiffens up.


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