When finishing with the corners on slabs, often it appears the sand rises up to give it a rougher finish near the edge, than on the rest of the slab. Is there a technique used that could get more cement up top, that would hopefully prevent this from happening?
Simple method: Slap the wet concrete with a trowel, this compresses the sand and aggregate and the more liquidy cement will float on the top.
Same principle, take your float or edger and kind of…how to describe it. Press down lightly and “wiggle” it. It’ll bring a little of soup up to the top that you can float out.
I just poured a porch a few days ago and was running into the sand roughness, I ended up doing the wiggle thing with my trowel as well as genltly slapping it. Finishing too soon can make it difficult as well. I do the finish and then wait until it starts to set before I do the final finish.
Moral to the story: Wiggling a little bit, along with some gentle slapping, makes it more wet and easier to finish.
Alright guys, got another slab to pour this weekend, will work on your tips some more. Have been slapping it hard with fair results, but I think I waited too long this time.
Sounds like you’re going for a smooth trowel finish, that is harder.
Sometimes it takes a LOT of effort (not to mention technique) to get it right.
like plastering, it’s a matter of timing. Trowelling it up will bring a lot of moisture to the surface, but the wetness will lead to trowel marks. Leave it, trowel again.
A double bullnose trowel is useful, although you’ll need a conventional steel trowel to get in the corners.
I can get it fairly smooth, just not as smooth as I want. I’d like to know how Lowes and Home Depot turn their concrete floors in a very polished like finish. Not sure I would even want something that slick, but still would like to know how it is done. I’ve watched lots of youtube clips, and still can’t find anyone explaining how this is done. I’m not even aware of any classes or vocational schools teaching anything about concrete, at least not in my area, do you know of any?
They polish them. They may have been smoothed initiall by someone very skilled with a float, but if you want a polished glass like finish you go over it with abrasives and then coat it with a sealant.
I don’t have one of those, had to look it up to see what you was talking about. When I had some experienced guys doing some of this for me, they would edge it about 2 or sometimes 3 times, but would use a edge tool like shown here, along with another floating trowel. I noticed on the last pass, they were always putting a lot of their weight on the edge and trowel tools.
I’ve got a 48” magnesium bull float that rotates which is nice along with another 18’ of poles. Also have various other tools, including a 36” trowel machine, vibrator, and a double roller tamp, which sure is nice, not having to get in the slab, and being able to tamp it like that. Definitely one of my favorite tools.
If I’m using the trowel machine, will staying on it too long bring up too much moisture? I always do a few passes, then stop. Wait about 30 minutes, then maybe go again for a second or third time before deciding I better stop now before I really screw things up by trying to get it too good.
Timing seems to be critical alright, especially when doing the trowel machine. Learned the hard way.
Oh, so they actually do polish it. Got a pic of any of the machines they might use to do this?
They also use the propeller floats, they can finish of concrete super smooth.
Here’s one. They aren’t cheap, but you can probably rent one. I doubt it’s useful unless you get a very flat surface to start with.
I imagine so, and that it has to be done soon after troweling for best results while concrete hasn’t completely hardened.
I typed in concrete polishers on e-bay, geeze, some used ones were $18,000.
Fixin’ to ask you what that was, then realized you were talking about the trowel machines, what we also call around here, whirlybirds. 