Concrete countertops from scratch?

[couchpotatoe]

I have some questions for the any of you masons out there who have made concrete countertops. I have to put a new surface on an old, outdoor counter that is 15 feet long and has a large sink at one end. It is currently covered with large, ugly porcelain tiles and leaks like a sieve. Since it's builder failed to slant the top at all, water pools on it and soaks through the grout into the cabinet below. I want to tear all that off and replace it with a homemade concrete countertop with a slight slope to get the water to flow off. I should mention that I am in Mesa, Arizona and this counter is on the south side of the house and gets a LOT of sun, so it will get pretty hot in the summertime.

Can I pour one, very long countertop or must it be divided into segments? It will be cast in place and have plenty of rebar. I'm wondering just how much movement will take place from heat. Any movement around the sink could be a problem.

What would be a good underlayment to keep any water out of the cabinet? Would roofing paper or composition roofing work?

Rather than buying the rather expensive countertop mix from Sakrete, I am wonder it I could use regular concrete made with small aggregate but with the addition of some "Rapid Set, Concrete Pharmacy Flow Control Additive" which is supposed to "increase strength and fluidity and reduce shrinkage." I have poured many slabs over the years and they are always very strong with virtually no cracks, so if I use the additive, minimal water and pack the material tightly, would that be good enough? I will probably also add a bit of colorant to tint the material. I'm going for a 2" thickness.

If this one works out, I plan to put concrete countertops on several more cabinets that I am going to build for my outdoor kitchen.

Thanks to all for your input.

Russ

[Tscarborough]

Re: Concrete countertops from scratch?

I would not have a lot of confidence in a 15' single piece slab. Add fibers, get rid of the rebar (use horizontal reinforcing wire made for CMU, rebar, even 3/8", is too big for a 2" slab), an use a latex additive/water reducer and cross your fingers. Better to incorporate a joint into the decorative design.

[deejayoh]

Re: Concrete countertops from scratch?

I'd use the alkaline-free fiber mesh instead of steel mesh. And do some research on distance between control joints - but you will definitely need some in a counter that long. I think the rule of thumb is 4 feet or something like that. I think you can fill them later with grout to hide them.

[UtahBeehiver]

Re: Concrete countertops from scratch?

CP,

I linked a number of concrete counter threads, one being Tscar and the other DJ, there are others so maybe it will help.

http://www.fornobravo.com/forum/f8/c...ers-18388.html

[couchpotatoe]

Re: Concrete countertops from scratch?

Hey guys, many thanks for your help! I will continue to do some research but your comments help a lot. This is truly a great forum.

The base is made from stacked and filled concrete block (wonder where that idea came from??) and is very strong. There are cross members of 2x4s and that was overlaid with plywood and then concrete panels under the existing tile. I will get rid of the adhesive and then make forms. Hadn't thought of usine horizontal reinforcing wire. Is it really better than rebar? Thanks again.

Russ

[couchpotatoe]

Re: Concrete countertops from scratch?

The 2x4s form a grid that is about 12" apart. There is exterior plywood of unknown thickness (probably 5/8 or 3/4) on top of that and there are 1/2" cement panels on top of that which I can see from one end where I removed some trim. Then the mastic and finally the tiles. It leaks because there was no slope to the surface. The tiles are 20"x20" so it looks like whoever built it did make an effort to make it plenty strong. With it's concrete block supports that divide it into three sections, it should be fine for a base for as much as 3" or 4" of concrete - but that would make the counter too high. I think my wife (who uses it for her papermaking endeavors) could deal with about 2" and no more, so that's the plan.

I think I will probably cast three panels, each about 5' long, in place with a 2" thick drop extending down about 4" or 5" molded in around the front and sides. It should be a lot easier to form up with welded wire than rebar.

As far as isolation, I was thinking of laying down either roofing paper, composition roofing, or something similar on which to pour the concrete countertop. Is that reasonable? What do the "pros" use?

I've been reading several of the threads that were compiled by UtahBeehiver and they have been pretty helpful. Lots of great ideas and nice builds.

Thanks again for your advice.

Russ

[texman]

Re: Concrete countertops from scratch?

CP

I poured my own with a lot of help from TScar. I used maximizer concrete, fiber, bonding agent in mix and pencil rod for a 16 foot radius bar top with overhang. I did not take the advice to cut a joint and so far no cracks.

are you planning on an overhang at all or just a lip?

My thickness is 2" and supported by concrete board. If you pour the the whole thing in one pour, get some help. Especially with the maximizer. IT is different stuff, but strong. I would start early in the day. Decide what finish you want now. either troweled, polished, etc. Also, decide on what edge you want-bullnose, radius top, coped, crown, etc.

Good luck! It is some work, but i am very happy with mine. Especially the cost!

tracy

[stonecutter]

Re: Concrete countertops from scratch?

I built my own and used a mix recipe from Fishstone supply. Fishstone - Fishstone - Concrete Countertop Supplies
I think it ends up being much cheaper than anything you can buy.
They were great to work with. You can call them and they will tell you everything you need to know.
Everything worked out pretty good. (had a slight math error on my first pour so ended up short on mix)
The counter is extremely strong and has no cracks after three years.
I can stand on the very edge of the overhang without a problem.
I used rebar, glass mesh and fiber.
Toughest part was trying to keep things even when polishing.

That's quite a set-up...looks great.


The bagged mixes are never cheaper than making your own, but it makes pouring your own concrete much more user friendly, with a high quality product.

[deejayoh]

Re: Concrete countertops from scratch?

They aren't that much of your cost for the project - but it depends on which one you buy - QC countertop mix is about $12 a bag. Buddy Rhodes is about $60!

[old_spaghetti]

Re: Concrete countertops from scratch?

I live in NE Washington where it can snow 6 feet in three days, rain for weeks, get below zero in the winter and run 100 for a month in the summer. I've got two winters and summers on my counter-top with zero issues.

I used 2 layers of Durock NextGen board, attached tile with Mega Flex, and grouted with pre-mixed, ready-to-use QuartzLock 2? urethane grout. Mega Flex was recommended for outdoor used and applied with a 3/8 x 3/8 trowel and back buttered the tiles before adhering. The tile is colored throughout and has not cracked and can be polished on the end if desired. The grout has not chipped or cracked will not stain and I think waterproof. I'v never had water inside the cabinets. I used this system to house the oven and cover counter tops.