please help me troubleshoot my poor concrete finishing technique

rizzo

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

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

Magnesium is light and stiff.

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Phuture

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

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

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

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jomama45

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

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

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.