To anyone with any thoughts, ideas, etc.:
I read last issues article on concrete countertops and just had to make one for my new kitchen island. My second attempt (don’t ask about the first) was a success; the countertop looks beautiful! Just one question: what do I finish it with? The top is dark grey (nearly black) and I’d like a finish that will give a wet, glossy look. Will polyurethanes work? If so, what are the preparation concernes? What about food contact? Mineral oil? Wax? HELP!
Replies
I also have been experimenting with concrete since thte article. I plan on using to in my kitchen someday. My plan was to use mineral oil. Its non toxic and if you keep applying it over a long period of time it will saturate the concete( like they do soapstone). It would give it a wet look and kind of pre-stain it so that the occasional greese, oil or what ever spills wont penetrate.
Two choices...a penetrating finish of a film finish.
Film finishes present problems of adherance to the concrete. Some require acid-etching of the surface for better tooth, followed by neutralizing and a rinse. If you screw it up...you're screwed. Your film finish will start peeling after a while, leaving you with a nasty looking slab.
Also, film finishes, while bulletproof in terms of "sealing" the slab, are sometimes not able to handle severe and sudden differences in temperature. Meaning, you may not be able to take pots out of the oven or off the cooktop and slide them directly on to your supposedly bulletproof countertop. The film finish can discolor, blister, or detach from the slab. Again, a nasty result.
For the DIYer, and for someone who actually uses their concrete slab as a working countertop instead of treating it like a dainty piece of balsa wood, I advise a penetrating, food-safe sealer.
My favorite? Sealer's Choice, by Aquamix. It takes about a half-hour, maybe 45 minutes, to do the first three coats. It's food safe. It doesn't discolor from hot oven or cold freezer items being placed upon it. It'll never peel, as it's not a film.A quart jug will last you ten years.
On the downside, it's not permanent. It does need to be renewed, and renewal depends upon how much you abuse your slab. I recommend the initial 3-coat application of Sealer's Choice, followed by a protective coating of paste wax. Renew the paste wax every 4-6 weeks or so. Takes 5 minutes. Renew the Sealer's choice every 3-5 years, or as required.
I cast all my slabs inverted, they come out of the mold with a glass-smooth, usually too glossy surface. Virtually a mirror finish. Even with the SC and the wax, they still shine, too much for me. Most of the time I first scuff sand the slab down to get a gloss level similar to honed stone, then seal.
Mongo
Edit: Oops! I came in under my wife's registration...this is from "Mongo."
Edited 4/27/2002 9:53:19 AM ET by Rebecca
Thanks for your advice! I also cast my slab inverted, but will probably keep the glossy surface. Your info on film finshes has converted me to mineral oil, as this island top will be heavily used.
Thanks again,
Jeff
Have not done this yet....but I was in the home of an architect who had concrete in his entire kitchen. Down two years. Not a mark on them.
Asked what he'd used for sealer. Didn't tell me the brand....but said that he'd used a marine epoxy, thin coats, 15 coats, sanded w 220 between each coat.
Beautiful satin finish. No rings, no stains. Had never resealed or waxed.
Shelley
We are planning to try out the concrete c'top concept. The owners want stone in all kitchens and baths, but will allow us to do the concrete in the laundry room. We've a 60" run of straight 24" depth counter, with one sink cutout for a topmount. We are planning the inverted cast method, using melamine board to cast against, cured silicone in the corners of form bottom and edges to achieve an eased-over edge for the slab. We have powdered dye and have cast some 12"x12" samples to make sure we are going to be happy with the color (a mocha brown). As for the surface, we are going with a moisture cure urethane, three or four coats, wet sand in between. These types of urethanes are supposedly very durable. Tell us what to look out for when doing this. It sounds like your first attempt was a learning experience. We have learned from doing the group of small samples that a lot of tapping and vibrating is required to get the mix to flow out completely and get no voids or bubbles on the surface. What else?
Gene,
It sounds like a well thought-out plan. The film finish will work well in a laundry room, and many thin coats are preferable to a single thick coat.
A plasticizer added to your mix will reduce the amount of water you need to add to your mix, while at the same time improving the flow characteristics of your concrete. Less water means a stronger slab, improved flow means less bubbles in the mix.
Instead of the silicon to "ease the edges", consider adding pieces of molding to the inside edges of the mold to create decorative edges. Realize that you're casting, so the molding you use will give you a negative, or mirror image, on the slab. Example, a cove molding will give you a roundover edge on your slab. You can take it further by using full depth crown-type (or some other) moldings to really set the edge off. A silly reminder...but only use the molding on your "show" edges of the slab. For example, if your 60" by 24" laundry slab is to be installed between three walls (back and two side walls), then only use the decorative molding on the front, or face edge of the slab. Leave the other three sides with either a straight, flush edge, or slightly back-beveled edge (sometimes back-beveling makes it easier to slide the slab between walls) so you don't end up with an eased-over or rounded-over slab edge butted against a wall.
Vibrating the form will eliminate bubbles from the slab. Hammering it or running a sawzall against the form are both techniques used successfully. I use an electric motor with an eccentric weight mounted on the axle so it "wobbles" the table that the form is on. Works like a champ.
I have been thinking about trying concrete tops too. Have lots of requests for them in my cabinet shop. How thick do you guys make these and if they are long runs, are they difficult to move/install. What about an intigrated sink bowl ( seems difficult ).
For you professionals how much do you charge per foot?
Mike
Mikey,
If you have "lots of demand" I highly encourage you to satisfy that demand. Material costs are minimal, the labor involved is not extraordinary, though moving them can sometimes be a literal pain, depending on size. I have moved and installed 550-600 pound slabs solo.
There is a learning curve to concrete...for me, at least. Make many samples, save those samples, and document the batch recipe used in those samples. I have hundreds of samples to display slab coloration, various decorative edging, surface detailing, various types of drainboards, and even variations in slab thickness.
Typical thicknesses are 1.5-2 inches.
I charge more than I should, and people still pay. The majority come in at about $130-ish a square foot. Done some freebies, as well as some over $300 a foot.
I've done integrated bowls, and they are a pain to fabricate. Did some out of curiousity, but only a couple for money...usually small bowls for a bathroom to top a piece of furniture. I prefer to not do them. I wouldn't think of doing an integral kitchen sink.
hi mongo...
you have posted a lot of your cctop knowlege on the board over the years, i was wondering what you thought of the new book (if you have had a chance to look at it)
oak
Greetings Oak,
No, I haven't checked out the book. It did initially pique my curiousity, but after reading the segment in the last issue of FHB my enthusiasm waned.
I decided that I'd like to check it out hands-on before purchasing. Personally, I'd want to give it a once-over in a brick and mortar bookstore to see what tidbits it offers instead of buying it blind over the internet.
Mongo,
For those prices it would be stupid not to satisfy some of this demand. I don't know of anyone here in town that does concrete tops.
I still have some questions that might help me through that learning curve. First, how do you move a 500 lb slab solo? Second, and more importantly, what do you do about out of square or irregular walls? Seems like it would be difficult to scribe a concrete top to the contour of the wall (he he). Backsplash material would hide some irregularities.
Would you build your form out of square to match the walls?
Do you ever have seams? ( Install a large L-shape in two pieces)
Ever need extra support for a large top? ( some "nice" factory cabs have half inch sides with flimsy joinery)
Any extra advice would be greatly appreciated.
Mike
First, how do you move a 500 lb slab solo? Carefully.<g> I have a rig that holds the slab on edge. It has dolly wheels so I can then wheel it through the house right up to the cabinets. Lean it against the cabinets, dissemble the frame, and flip it up on top of the cabinets.
If I formed the slab on-site, in the garage, for instance, I'd just screw dolly wheels to the long edge of the frame of the mold. Flip the whole thing on edge and wheel it over to the cabinets. Lean it, unscrew/disassemble the frame, then pop it into place.
...what do you do about out of square or irregular walls? Seems like it would be difficult to scribe a concrete top to the contour of the wall (he he). Backsplash material would hide some irregularities. If the wall can't be floated square (with drywall mud, for instance) then it depends. Irregularities can be hidden by a backsplash to some degree. If the fit needs to be perfect, then I scribe a filler piece to match the contours of the wall. The scribed filler piece, which is a "duplicate" of the wavy back wall, is then inserted into the mold.
Would you build your form out of square to match the walls? Yes. For a "captured slab", one that is to fit against two or more walls, It's almost a requirement to make a template on-site and build the form to "capture" the template. It's really not a tough as it sounds.
Do you ever have seams? Yes. I prefer to not have seams, and will go to extraordinary lengths to avoid them. There are some cases, though, where a two-piece slab is unavoidable either due to size or shape.
Ever need extra support for a large top? Some cabinetry does need to be beefed up. Normally, something as simple as a top of 3/4" ply screwed to the tops of the cabinets is enough to provide additional weight transfer and slab support.
Some links on concrete countertops:
http://www.decorative-concrete.net/
http://www.pcinews.com/concrete/condesin.htm
http://www.concrete.com/forum/Forum.htm
http://www.worldofconcrete.com/content/splash_woc.htm
Ted