concrete countertop sanity check

[n8huntsman]

I'm about to pour the entry to my oven. It's 5.5" thick with rebar and only a small cantilever, maybe 5" or so. The countertops to the bar will be about 25 linear feet. It will have a center support and be cantilevered on both sides; one side for the bar stools and on the other side for the bar equipment, kegerator, etc. It will be a full 3.5" thick.

I'd like to use Portland and sand with no aggregate. Add my color to the mix and hard trowel. If that doesn't come out well I can grind and polish if need be.

I'm thinking of using a 2:1 mix of sand and Portland and adding the color to the mix. Will this work? Should I add acrylic fortifier/bonding agent? I can't find plasticizer locally, should I add a little dish soap to the mix?

Thanks

[dakzaag]

Re: concrete countertop sanity check

Standard cement mix is 3:2:1 sand,aggregate,cement. I would think that a bit of pea gravel in the mix would help unless you just can't get it.
Your mix is pretty rich, even for a counter top. Maybe bring the sand up a bit if you can't get the pea gravel.

It's your top, so you do what you want, I would take some time and get the best materials available. A flow agent or water reducer improves workability without sacrificing strength. There are literally hundreds of supply stores in California, perhaps asking around will help find the material you want.

I don't see the benefit of a bonding agent. At 3.5" thick, you have a lot of weight to be balancing on a ??? wall? with an overhang on both sides? (For example, if your bar is 3' wide by 25' long you will need .8 yards of concrete which will weigh about 3200 pounds.) If it ever starts moving, it will come down hard.

I'm not saying your insane, but the fact that you asked suggests that you have doubts about how this will turn out. My eyebrows are above my forehead...

[Gulf]

Re: concrete countertop sanity check

Dakzaag,
I think that the formula for standard concrete is 3 (gravel) 2 (sand) 1 (portland). I used a 3 to 1 (sand to portland) mix for my landing. But, a 2 to 2.5 sand and 1 portland is what is mostly recommended for a "sand only" countertop. Here is the discussion during my build.

I used the acrylic fortifier in the mix to help guard against water (freeze damage). It also helps to guard against stains from soaking in to the finished countertop.

[n8huntsman]

Re: concrete countertop sanity check

The cantilevers will probably end up being more like 9" not 12". I was being conservative in my estimate. The counter will be sitting on a steel frame with supports for the cantilever to prevent it from tipping. Weight may be an issue, I'll have to do some calcs when I get closer to that stage. For now it's just a concept, nothing has been built. I called the local ready-mix companies and when I said plasticizers you could tell they didn't have a clue what that was. Throughout this project I am continually amazed at the lack of knowledge of some of the so called experts around town.

I decided to give the Maximizer Countertop mix a try because it was in stock locally and it's lightweight. The local shop that sells it said they had grey or white and I chose grey since I will be aiming for a dark finished color. When I went to pick it up the grey was just the standard 5500 Maximizer, and the white specifically says countertop mix. He said they are the same thing except you pay twice the price for it to be white. Is that correct? I'm a little doubtful.

I was also able to find packets of Concrete Pharmacy Flow Control at home depot. Is this a plasticizer or simply a water reducer?

Now I don't know what to do and getting more frustrated by the minute... I wanted to get this done today on my day off and now it's too late anyway so I can take my time and make the right decision I guess. Here are my thoughts on how to proceed...
a.) Return the grey 5500 maximizer and get the white countertop mix
b.) return it and just mix my own with sand and Portland
c.) return it and order the quikrete countertop mix
c.) Keep it and use as is
d.) Keep it and add a couple packs of flow control

[dakzaag]

Re: concrete countertop sanity check

If the supplier carries the product, they probably know a little bit about it. White seems to always be more expensive, don't know why other than it is white. The purpose of the additive is make the mix more soupy without adding more water. This is easier to work with and prevents honeycomb but doesn't reduce the strength of the final product.

I am still a bit sceptical about your proposed mix. 2:1 sand to cement should crack like an egg on a gravel road, but if that is what everyone is saying then I will be quiet.

Not trying to scare you on the bar weight, but just do the math and make sure you have your strength in the right places. A yard of concrete weighs 2 ton more or less.

[Tscarborough]

Re: concrete countertop sanity check

White cement is expensive because after it is kilned, it can not touch metal, all the grinding and piping is done with ceramic lined materials and piping. And as an aside, buff Portland cement is produced by injecting diesel in the kilning process of otherwise white cement.

2-1 is junk, don't even consider it for anything more than a 1/4" parge coat.

The Maximizer is a good product, but the countertop mix is not the same as the regular mix to my knowledge (although it is bagged locally and may well be in your area). For a colored countertop over 2" thick, use regular gray with a bonding agent. White cement will not give you expected colors with ferrous oxide dyes.

Maximizer contains expanded shale, so it is a little different than mixing regular pre-mixed concrete. I would not recommend either water reducers or plasticizers, just use a latex or acrylic bonding agent, and you will get over 6000 PSI compressive, and a very good flexural strength.

Expanded shale is extremely dry and will suck up all of the mix water leading to a flash set unless you mix it correctly and carefully, preferably in a mechanical mixer.

Put in 60-70% of the recommended water per bag, then 50 percent of the bag. Let that mix to slush then add the rest of the bag, and add water until it is no longer dry appearing, but before it get slushy. Give it time, let it mix for at least 5-10 minutes before adding excess water, at about the 6 minute mark it will get loose as the shale becomes saturated, but will still have the appearance of chocolate coated nuts, not soup, stew, or even chunky peanut butter.

If using color you will have to measure the amount of water used, the exact amount of color and the mixing time. 25 feet times 3.5" is going to take multiple batches, so you need to be ready and have lots of help.

Just a note about Gulf's link. It is for a different method of counter tops, i.e. dry pack, and if that is what you plan to do is excellent. If you are doing a wet pour, then be cautious.

[rodeair]

Re: concrete countertop sanity check

I'm trying to plan ahead for a counter pour of 80 sf total. Of all the different methods I found, Z liqui-crete looks pretty good. Has anyone heard of it or used it? It's not the cheapest way to go, but for a layman like myself, it looks alot easier with a very fluid pour. If all goes well, I'll use it for my entryway also. Good luck whichever way you go.
Leigh

[jeeppiper]

Re: concrete countertop sanity check

I would be careful with large unsupported overhangs.

If it is color you are looking for, there is a lot you can do with concrete acid stains, dyes, and sealers. I did a concrete countertop for an open grill..

http://www.fornobravo.com/forum/f38/...ill-20448.html

I used plain old 5000 psi Quikrete mix and then played around with different stains and sealers. The only problem I had was when I polished the surface with a wet grinder, the aggregate became visible, which I didnt really want to see (the aggregate doesnt take to stains/dyes.

[n8huntsman]

Re: concrete countertop sanity check

I'm still trying to wrap my head around the overhang. I know it can be done, just not sure how yet. I want this to look like a real commercial bar. If you look at those, you'll see they have an overhang on both sides. The inside slightly overhangs the bar equipment, ice bin, speed rail, beer cooler, etc. The outside hangs over so you can get all the way up to the bar with ample knee clearance. I can't add too many steel support arms because they will interfere with the bar equipment or people will bang their knees on it. If I go thinner on the concrete, maybe 2.5" rather than 3.5" I'll have more room for the steel, but then I'll be sacrificing concrete strength I think. Still thinking about this obviously...

I like the idea of the maximizer because it's lightweight but I'm not sure I can get it troweled as smooth as ordinary concrete. I'd like to put the color in it, trowel it and be done with no sanding and polishing. If it was as smooth as my oven hearth, I'd be pleased. Just not sure I can achieve that with maximizer? Here's my hearth pour with standard concrete:
http://www.fornobravo.com/forum/8/na...tml#post183335

Most of the maximizer pours I've seen have a flagstone like finish instead of a smooth garage-floor-like finish. I'm not sure if this is by design, or if it's just the way the maximizer is.

[rodeair]

Re: concrete countertop sanity check

I used Maximizer for my bar pours. Although I plan to cover with some kind of material, (granite if I can afford), I was pleased with how the Maximizer worked. It's like any other concrete as far as finishing. I was able to get a nice finish even though I wasn't trying since they'll be covered. Like anything, if the basic structure and foundation is strong, it'll work fine.
Good luck

[Greenman]

Re: concrete countertop sanity check

Not sure what happened with the pics but I could not open them. Still interested though.

[n8huntsman]

Re: concrete countertop sanity check

Not sure what happened with the pics but I could not open them. Still interested though.

Same here. I was able to find the original post thought: http://www.fornobravo.com/forum/8/pe...tml#post184873

[n8huntsman]

Re: concrete countertop sanity check

Anybody know if this stuff will work as a fortifier? SikaLatex 1-Gal. Concrete Bonding Adhesive and Acrylic Fortifier-187782 - The Home Depot
I've heard to use about 8:1 water/fortifier but the instructions on this stuff say to use it instead of water. That will get pricey.

[Gulf]

Re: concrete countertop sanity check

Yes, it is exactly the product that I used as the acrylic fortifier for my small pour. I actually, went with 1/1 water/fortifier. Some have even used it as a total water replacement for decorative concrete counters. That would really make it too expensive for you purpose. But, there is not as much water added to the concrete mix as some would think. That is, if it is mixed correctly. As Tom pointed out, the method that I used is not really applicable to a fixed full thick pour as you are doing. The thickness, weight, cantilever, and open span of what you are proposing needs structural concrete with plenty of tensil strength.

I don't really think that you would have to use the fortifier for the majority of the pour, though. The fortified concrete only needs to be near the exposed surface. You could pour the center core with standard concrete and then immediately finish with a fortified concrete. By that, I mean that the concrete core is placed to thickness of just under the the top of the form. (Maybe, about 3/8th to 1/2"). The outside forms would have to be protected from getting dirty also. That could possibly be done with a 3/4" removable band inside the form. Of course, the temporary band would have to be removed immediately after the core is poured. There would no worry of the core concrete running back against the form bands if the slump (consistency) is correct. No concrete needs to be soup. The fortified concrete would then be mixed to finish out to the bands and the top of the form. The fortified concrete would need to be done immediately after the core is poured to eliminate a real cold joint.

You can just seal the finished concrete after it is either finshed or polished. Sika also makes a natural look and high gloss sealers.

[rodeair]

Re: concrete countertop sanity check

I'm going to have a 7 inch gap to my oven landing. What I plan to do is cut some block to within 2 inches of the oven landing, bond them to the existing landing and then bond concrete board to the block, then use countertop pour for the last two inches. The Z liqui-crete is the added blend you need for a bag of sand mix to get a nice counter. I think I'll use that for all of my counters. Might check "Z Counterform Liqui-Crete", seems to be some cool stuff.