Friday, January 30, 2015

Float On

So, I pulled the forms from the counter top and was pretty pleased with the way it came out.  As you can see, the concrete has cured to a fairly light color but once I polish it a bit and seal it, it will be a much darker gray.
I set a piece of concrete backsplash up there too and some of the glass tile I will use for the back also, just to kinda see how it will look.  Once the concrete is sealed it will be very close to a grayish slate color and match the glass tile well.

I was fairly pleased also, with the finish I got on this pour, although I think I actually got a smoother finish on the hearth slab.  It's fine though.  I will run over this a bit with 100-200 grit diamond pads and it'll be slicker'n owl shit.  I have no idea where that saying comes from or what it means but I used to hear it all the time on construction sites.  Ha!
It's also quite hard (to me anyway) to get a good slick finish right up to the edge because you can't follow through with your stroke but that is easily smoothed with the diamond pads and I'll round that top corner off just a tad.  The front face of the edge had a few little bug holes in it but I don't really mind that.  It makes it look more like concrete, to me, and I want that to be obvious.  I just really like the look of unstained, natural concrete.

 It's really hard to explain to somebody else how to finish concrete and I looked around for some YouTube videos that might do a good job but didn't really come up with much.  Most of them show how to float concrete, which is good, but none I could find show how to trowel it to a hard finish and that's what takes such finesse.
In the photo above I have the tools most commonly used for concrete finishing and they are not interchangeable.  The one on the left is the float and the one on the right is the trowel.  Since my pour was so small I did not need a screed or straightedge but you need those on a large pour.

The float has a much thicker blade and is longer; some of them are up to 2 feet long or so and this is what you use immediately after placing the concrete.  On really small pours like mine you can use the float sorta as the screed to knock the mud down to the correct elevation.  Then you pass over the concrete in sweeping motions to smooth it down nice.  Now, at first, it's not going to look that smooth and that's okay.  Once you float it off good, with one pass, you just then let the mud sit.  Water will begin to rise to the top and you will see a pool form.  Let this water evaporate!  Do not keep working it back into the mud.  Once the water evaporates you can see the surface begin to "tighten up" as we say.  Make one more pass over the concrete with the float.  Water will rise again.  Let it evaporate.  At this point the mud may have tightened so that you can move to the trowel.  When you go over the mud with the trowel you will begin to get a much smoother finish.  As you can see, the blade on the trowel is much thinner.  And, it's pretty much the same rhythm; trowel it off, let the water rise and evaporate and etc.  Now, at this point, hardly any water will be noticeable on top but you can tell it's happening.  This is the part that is really hard to describe as it's something that a person has to see and do to really "get", but it's much like burnishing clay or similar.  Also, the tighter the concrete gets the harder you have to press down to get a smoother finish.

If you really want to try pouring something like this and have never worked with concrete before I would strongly suggest pouring some little practice slabs first.  Maybe pour some steps or a small patio just to get the hang of floating the mud and those things don't require a really hard finish.  In fact, you don't want to get them too slick or they will be very slippery in wet weather.  Then maybe pour some little stepping stones or maybe a bench seat to practice troweling a smoother finish.  Good concrete work is much harder to do than most people realize but it's not rocket science.  It just takes a little finesse, as I said.  If all else fails, hire a finisher.  And you can polish counter tops once the concrete is cured, to hide a multitude of sins.  I've done all my own concrete work here at my house but I'll say this:  the work I did as a carpenter and welder was pretty hard sometimes, but I always got through it.  I don't think they could have paid me enough money to place and finish concrete however. 

Okay!  I'll be putting this finish on this top before long but we had to order some new diamond pads so it may be a bit before I have another post on this.  And, I have to find a suitable sealer to use on these since they are in the kitchen and would come in contact with food.  But I'll have a complete post on all that when I'm done.  Any questions?


Ed said...

Looking good! That's very descriptive about letting the water come up an evaporate before the next troweling. I never looked at it that way before. I'll have to try that the next time I pour some.

Of all the concrete I've poured, the only finishing I've done is waiting until it sets up enough to run a power trowel across the surface. It is pretty much the same processes but on a bigger scale.

We use the saying of slicker than owl shit up here too. Back in the day, I used to hunt down owl pellets and sell them for extra money in college to classes that dissected them. They were definitely anything BUT slick. Now if the saying were slicker than bat shit, it would make sense to me. I did some spelunking in some caves in the Philippines and in the top section where the bats live, it was like trying to climb through ice covered rocks. I bet if you smeared a thin layer of bat guano across a regulation basketball court and got a run for it, you could slide from one end to the other... easily!

Ed said...

I should also say that letting the water evaporate also solves the problem I worry about and that is getting that soft cream layer on top that can chip and flake so easily. I suppose your sealing process also strengthens the top up too and prevent that.

Do you run your knives across the top when prepping food or do you still use a cutting board?

woodysrockyridge said...

Is there any curing time requirement before using your grinding pads?

edifice rex said...

Hey Ed! I think I've heard the saying with bat shit too but most people around here wouldn't know the difference!
Actually, you want that cream to come to the top because that is what lets you get that hard, slick finish. Floating the concrete is what brings it up. You are basically burnishing that layer when you trowel.. It chips or is soft because the finisher kept working the water back into the mud instead of letting it evaporate. I learned this the hard way!
Yes, using a sealer will help strengthen the finish and there are some sealers and curing compounds made specifically for promoting a super hard surface.
I still use a cutting board because concrete will dull a knife in seconds.

Hey Woody! Generally, I let my slabs cure for 7 days before wrecking the forms or doing any work on them. Especially if you you are wanting a really fine finish. Concrete generally reaches it's maximum strength in 28 days but that only is observed if the slab is going to be moved much. Such as a tilt-up panel etc.

JO said...

Now I will be waiting and chomping at the bit for this next post. Looking good to me.

TexasAnn said...

Ok, I'm impressed. And once again, you make it sound easy, but still nothing I plan to try for myself. Very clear, concise explanation.