I am preparing to pour my kitchen countertop. I have one question about the mix:
Are poly reinforcing fibers likely to show through on the top? In Cheng’s book, I believe he said that if any hairs show through, they can be burned away with a torch. Searching around online last night, I found somebody’s recommendation that fibers not be put into the first layer of concrete placed in the bottom of the mold. This guy said that you wanted to keep them away from the countertop surface.
Anyone who’s done this have any ideas?
Thanks.
Outside of a dog, a book is a man’s best friend. Inside of a dog, it’s too dark to read.
-Groucho Marx
-Groucho Marx
Replies
yes abd yes
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two ways to screw up concrete 1) concrete driver 2) concrete finisher
Here's the deal as I see it.
Fibers are not required in a countertop. If you do want to use them, then I'm an advocate of just using them in the bottom 2/3rds of the slab.
I cast inverted, if you're forming in place then don't use fibers unless you're really good with a trowel.
I used them for a set of tops as per Cheng's recommendation. And I wish I hadn't. We could feel them when all finished..... coulfn't see them, even with a 10 power hand lens, but they were there. They finally wore off after three or four months with my wife doing a lot of extra scraping.
I don't think they are necessary..... I'll never use them again.
The torch technique seems like a good way to spall the concrete surface. And if you do, I'll bet Cheng won't even say he's sorry.
I've done three tops according to Chengs book. I used fibers in all of them from top to bottom. The last one I did I wasn't very careful about how I put them in and I got a little bit of clumping. On my countertops I grind up to a 3000 grit disc so having little fuzzies aren't a problem.
If I didn't grind I'd still use fibers. I've never noticed any hairs sticking out on the top surface after pulling the forms off but I do see them sticking out at the edges and corner
i don't think you need fiber... but i have used it... and just burnt it after... a quick sweep of a torch and it's gone... i do use wire and rebar... i cast inverted and inplace... even using the same form/mold i all but never get the same results... defects become "endearing features"...
I can see where fiber might help on sharp edges, points ect... but i think a high portland content is your best friend... i'm sure some of my mixes wind up in the 10,000 psi range...
have fun and post pics...
p
I vote for no fiber just because it's really hard to keep it from clumping in the mix.
If it's really cosolidated and the fibers are individually 'surfacing' it's not a big deal--burn 'em or wet polish with diamond pads
(by the way if you haven't seen how cheap they are on ebay : http://cgi.ebay.com/8-Piece-4-Wet-Diamond-Polishing-Pad-Set-Granite-etc_W0QQitemZ150214890138QQihZ005QQcategoryZ46572QQssPageNameZWDVWQQrdZ1QQcmdZViewItem )
-- and they disappear. If they're clumped, then they definitely don't...
I recently did another countertop and photo'd my whole process with intent to post a thread on it. Once I get some time and figure out how to embed smaller photos, I'll do that! I've got a system down that works.. and a lot of opinions. I don't know if they'll be helpful to anyone or not but I'll give it a go.
"Research is what I'm doing when I don't know what I'm doing..."
I was just checking out the thread with your two posts. You seem to have your system down pretty well - "dirtbag" or not!
I am in the process of making my mold, so your info really comes in handy.
Based on the feedback above, there seems to be more people voting against fibers, so I will probably leave them out. I know the missus wil not appreciate fuzzies, and I don't plan to grind the top, just pop it out of the mold, seal it, and go.
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
"pop it out and go"
That should work fine, as long as there are no large pits or voids in your finished product. Otherwise, you'll have to fill, then grind and polish, however you can.
I've ground and polished the top in my other posts already--I'll photo it and post probably 2x more after I install it.
Cheers,
Pat
"Research is what I'm doing when I don't know what I'm doing..."
I do plan on filling whatever voids come up. Fortunately, the client (my wife) is pefectly happy with a rustic-looking countertop.
I read about using a slurry of pigment and cement, without sand, and to use it like tile grout.
We'll see what is necessary when the time comes.
Facinating posts in your other thread.
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
You have the cheng book then?
Yeah, the cement slurry sucks, IMHO.
Once I get photos together for the next post it will show I use white, unsanded tile grout, pigmented with whatever color I want, to fill anything.
In your case you can just 'grout' any voids, sponge 'em off just like tiling.
In my case, I fill thickly, then grind and polish again.
Cheers,
Pat"Research is what I'm doing when I don't know what I'm doing..."
You have the cheng book then?
Uhh, no... I just spent a couple of evenings studying it at Barnes and Noble. (My own version of 'dirtbag' - I'm too cheap to buy the darn book.)
Yeah, the cement slurry sucks, IMHO. Why is unsanded grout better?
Thanks again.
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
unsanded is smooth--like you want the counter to be. If you used sanded grout you'd have spots of gritty grout like between smooth tiles. so to speak."Research is what I'm doing when I don't know what I'm doing..."
For what it's worth, I line my forms with glossy formica. I buy the cracked and busted sheets at the box store for $10-$15 a sheet. I can reuse them several times.
When the form is removed from the slab, the surface of the slab has a mirror-like finish. No grinding or polishing required. Quite often I have to give them a once-over with a diamond pad or ROS them to take the gloss down to a matte-like finish.
Mongo
Ok, so I just posted what I know about what you're about to undertake. I hope it's not all review!
See "dirtbag backyard concrete counters"
"Research is what I'm doing when I don't know what I'm doing..."
Review? Not at all. The sides are not attached to the mold yet. That will happen after coffee tomorrow morning.
Outside of a dog, a book is a man's best friend. Inside of a dog, it's too dark to read.
-Groucho Marx
It depends on what kind of fibers you add. I think the most offensive fibers would be polypropylene and he least offensive nylon.
Call these guys http://www.nycon.com for the best fiber to use for your application. Nice guys, and very knowledgeable. Ask for Bob. He's got the technical stuff down.