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Pressed concrete finishing

58K views 232 replies 24 participants last post by  stonecutter 
#1 ·
I have a neat little fireplace job right now where I have to rip down some horrendous stone veneer and rebuild the raised hearth. I am building the hearth top with a hand pressed concrete top. I am doing this because the immediate area is completely lacking a good stone source. There is a small supply yard that has some stone (I got my veneer stone there)but no large flat stock. The pressed technique is a nice alternative for now...but I was wondering if anyone else crosses over into doing this kind of work. Also, I am going to seal the concrete and was curious what products you use or can recommend that are specific to GFRC concrete.

Of course pics to follow soon...
 
#95 ·
Great work!

Dude, your work is coming out super nice!

I am stunned that you polished/routed/cut your rounded edge!

I have only seen it done within the form!

Friend in Baton Rouge where I lived for 22 years does precast columns and ships and installs the all over the US.

He does tons of same work or repeat stuff.

Told me that the best method was to make up forms with treated plywood and then to fiberglass inside of forms. He would use a release agent sprayed on surface and it would pop out each time with minimal cleanup.

I think this would be a good idea for generic countertop form which could be used over and over again.

Again, great work!

Steve:thumbsup:
 
#97 · (Edited)
I am stunned that you polished/routed/cut your rounded edge!

I have only seen it done within the form!

I think you've just convinced me that I need to get a set of edge profilers.So far all of my edging is done in the form.
I think this really shows my lack of experience. All my fabrication up until now is with natural stone... this is why I choose do the profile with tools and diamond hand pads.

I will say though....the chances are good that I would need to do some touch up and or polishing to the edge no matter what, so this way made sense to me. I'm sure the guys that do this all the time dont need to...just pop the form and thats it. Doing it this way works in my favor to producing the best piece within my ability..while still learning!

Like I mentioned, this concrete has a PSI of 6400 so it shapes out nicely with the profiler bits..and its faster for me than trying to build a form with a profile.:thumbsup:
 
#100 ·
what do the bits for your routing tool cost? A cousin of mine was into granite for a while, did monuments and later installed counters. He said the cost of the routing tool and all the bits he'd need (I think he said about $500 a piece and he'd need about a dozen just to get started but that was about 10years ago) made it more profitable for him to just do install rather than manufacture as well.
 
#106 ·
So what's the process there? What sort of a consistency for the slurry? Is it soupier than drywall mud? What do you use to apply it? I would think a rubber grout float but not sure. How do you get the darker slurry not to stain the already pored concrete, which I guess is pretty porous since it's not vibed.

I know that tha'ts sort odf the point but it looks a lot like stone where there is both mixed and distinct areas of varying coulours.

How many coats would say is typical and is there any treatment between coats?

Thganks again for posting this, it's just great.
 
#107 ·
Here goes...

The slurry is usually made of cement(or similar powdered mix), pigment and acrylic additive.
I used the bag mix for the first slurry...and it sucked because of the sand. I knew it would and did it anyway just so I can see why. It fills the voids ok, it just doesnt do a good job on the pinholes. It created more work doing it this way.

Yes, the slurry should be loose, Buddy Rhodes description is "yogurt like" but it is more like a milkshake..if that makes sense.

Use a taping knife to work the slurry into the slab...I'll document it tomorrow. Wait about 1/2 hr for it to dry(depending on conditions) and do another coat...2-3 coats for first application.

Staining isnt really a concern because you wont have a concentrated amount of pigment in the slurry and polishing removes any surface staining anyway....if you dont want a lot of contrast then use the same or similar color as your slab.
 
#108 ·
heres a picture of the mix that I used for the slurry. It is 1.5 parts Charcoal and 2 parts Pewter so there will be light veining. note the aggregate...

Concrete





My slurry tomorrow will be with grey portland with charcoal liquid color to flush out the voids and create 2 color contrast to the slab.

Dom, the goal is to produce random and natural looking figuring to simulate natural stone...which is how I was drawn to this technique. I guess we all will see tomorrow when I do the first polish.
 
#114 · (Edited)
That's the same rule that I use. I get very black at 10% and cut it back for charcoal. I remember reading though that Cheng has used up to 16% without problem. He's a little ahead of me on the curve though and I wouldn't push it that far myself.

My most sold "color" is the result of the ingredients with out dye. Grey or white portland combined with various bagged sands gives quite a range of colors without messing with the dye.

Good Luck
Dave
 
#115 ·
On a slightly different subject...

I always have to wait a few weeks for the concrete to get hard enough to polish it out right, if I try to hit it too soon, it doesn't polish, it just, bleah...sands away. Might be the mix I use (not a pre-mix). Altho, I've talked to other people who don't seem to have this problem...maybe it's just me. Makita polisher, 300 grit diamond pad.

I'm so glad you're taking the time to upload all the picts, I love it. I'm usually too stressed out to even think about taking pictures....
 
#121 ·
Polished out the first slurry today. I'm happy with the contrast and there was minimal holes even though I used the building mix. I used a screen to get a lot of the sand out of the mix for tonights slurry. I didnt want to use grey portland and color like I had intended..my old sample has some of that and it looks a little muddy. I wanted to keep the color similar, though I did lighten this final mix for a two color effect.


Starting the polish..
Floor Table Countertop Concrete Flooring



action shot..
Angle grinder Machine



result...
Water Floor Concrete Machine Flooring
 
#125 ·
Hey Stoner...lookin' real nice indeed. I like it a lot.

Why ain't you using a pool trowel to burn that slurry - maybe quicker or easier depending.

Regardless, I'd love to see it shine although this is a hearth right? Probably better off matte?

I don't know...what you ask me for :whistling
 
#126 ·
I like the smaller blade of the taping knife works great for the edges.


Yeah this is a hearth..I am starting to think a contrast in finish will be nice. Not a high gloss like when there is water on it, just something above matte. The stone being used is more buff,earthtones with some greys here and there...went for color contrast too.

I'll count that as one vote for shine.:thumbsup:
 
#128 ·
Yeah, I dont want a high shine either...semi is about the max. I'll probably check it after 800 and keep going up until I get what I want.


That was taken just before I reslurried the hearth tonight... so yes, there is still texture. I wont be bothered if there is still some of that after I polish the slab tomorrow..it looks cool and will fit the setting. If it was a counter then that finish wouldnt be good enough.

Yes wet polish...the tool has a water line.
 
#130 ·
matte vs. shine.. IMO shine, I like outlasting fresh looks, it may contrast to the existing but that can help us see what needs an update as well. An example such as stainless steel can be buffed and has many advantages. I'm not a decor expert, I do like things to not be more trouble than they're worth. BTW I'm intrigued by the custom counter-tops, and really like the aesthetic look of the polishing there.
 
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