I know this is not a wood question, but if any of you have poured your own counter tops, and have any advice, I would like to hear it.
I am getting ready to build a bar that is 12″ long by about 28″ in the middle. The front will arc down to about 18″ on the ends and be about 3 -4″ thick. I am planning to pore it upside-down.
I will be using melamine for the mold, with some changing levels on the top.
Tonight I was making the form for an elliptical pilaster for the lower middle bar-front. The trunk is about 24″ wide, by about 6″ deep with a 7″ base. Both of these are bending ply with plastic laminate faces and about that much for the crown which will be made from stacked particle board which will be shaped and filled with epoxy and filler then faired. I don’t have any mold release on hand, and was wondering if there is any kind of product that I could find in an auto parts store or hardware store. I want to pore this part Saturday, and don’t want to have to wait for mail-order.
I don’t want to use oil or anything that might contaminate the surface for later finishing steps if I have to go back and fill any air holes etc.
This will all be dyed black, by the way.
Replies
I know this is only half a reply, but I recall seeing in Fine Homebuilding about 2-3 years ago a pretty extensive article on making concrete countertops. Try asking at Breaktime or check their index of topics.
DR
rootburl, see http://www.taunton.com/store/pages/nmbh027.asp. Ruth DobsevageTaunton New Media
Ruth, Thanks for the link. I have seen the countertop book, and read most of it, but I have not seen the new book yet. I need to get them both for my office library.
As far as a release agent, A good coat of mineral spirits works fine. Another thing, if you have a palm sander, run it against the edges of your forms to release the air from your concrete otherwise you will have a lot of pitting on the sides. use the edge of the sander pad against the form not the pad flat against the form. You will see the air come to the top of the form. Also make sure that you know your pigment mix as you will need to make a slurry for filling the pits that may occur in the top after it has dried. Use some form of wire mesh to help stabilize the material also, hog wire works well for this. You can polish it some using wet and dry sandpaper if you do this soon after the final drying of the top slurry. Then a good coat of wax and buffing will bring out the sheen. Concrete counter tops are one of kind and they will have flaws, That's what makes them neat. but they do require maintenance on a periodic basis and they do scratch from knives.
Hope this helps,
Mike
I have used regular paste wax as a release with success. There may be some small transfer to the concrete but it will be surficial. Let the wax dry well and it probably won't transfer. However, melamine really doesn't need a release agent. Your epoxy mix may, but I'm guessing it won't. You can tape the flared sections with vinyl or packing tape which doesn't bond to the concrete. (Actually, not much will bond to the concrete.) The tape seams will leave lines on the concrete surface but are easily removed with grinding/polishing.
I just installed new concrete countertops into my kitchen and bath. They look great.
Jeff
Thanks Jeff, and Mike, You have helped confirm some of what was already thinking. I just have never done concrete other than making a sample where I would be using the mold side before, and I am hoping that I haven't overlooked something that may cause me to have problems getting it out of the mold, because I would like to be able to re-use it for making a separate art pedestal after this if all goes well.
Rootburl,
I have poured several countertops, and 5 bar tops(one was 95 feet long). Typing is slow, but you can email me or call @ 570.419.1963 with questions. I'm happy to talk with you about this, I think that it's one of the neatest styles going. Let me know.
Regards,
Nate
Wow Nate, 95'. You must have poured that one in place. I have done that type before, but this will be my first that I will pore into a mold and have to turn over.
I will be poring the half elliptical column that will go under and support the top within the hour, so I will get a little test run with this.
Thanks for your offer, Keith
rootburl
Woodworking is my passion, but I've been a concrete contractor for over 20 years, with daily experience in release agents, coloring, dying, stamping, etc... If you have not proceeded as of yet, let me know. I'll tell you EXACTLY what to do, and where to get the release agent for the best results. Release agents come pre colored, and you can achieve a multicolored texture if you wish.
Jeff
Jeff,So concrete is your profession and woodworking is a passion. My profession (for the most part) is woodworking but I get most passionate about concrete and metal. And we share the same name ....... go figure.I've never heard of a colored release agent. Can you point me in the right direction? Also, my casts usually have a number of pin-hole and larger air pockets. I've been filling them with cement, latex additive, and dye to match the integrally colored mix. But getting the color to match really well is trying to say the least. Do you have any tricks that you can share? Thanks......Jeff
Facinating thread Jeffs. Never even heard of concrete counter tops until you posted. Any recomendations on where I can learn more?Thanks,
Mark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
Jeff
Find out who your local concrete contractor supplier is. They will sell integral colorant and release agent for stamping concrete. Increte is a top manufacturer who makes both. You can get a powder release the same exact color as the integral color, so you don't have problems with two tone unless that's what you want. If you want to texture the surface, they'll have a stamp for that as well.
As far as air pockets go, we use vibrators. But, if you form the countertop upside down, you're asking for trouble. All the aggregate will surely show up on the bottom. I'd suggest finishing the top surface exposed, and have that be your top surface. Then, you know what you have by troweling it.
Make sure to reinforce the countertop with rebar running in both directions.
Voilla, there you have it. Regarding finishing, practice makes perfect. Get some sand mix from the local home center, and practice till you've got it. At $3 a bag, it is the cheaper alternative to wrecking your countertop without practicing first.
Anything else, just ask.
Jeff
Jeff -I used to do a lot of contract detailing work for a major precaster in the area. All their work was cast finish face down in molds. To achieve a pinhole/bunghole free surface, they would apply the specified finish mix, aggregate+ color + whatever as a thin coating in the form first. Which was then vibrated sparingly to consolidate the matrix. Then after a short set time, they'd back that up with a normal, less expensive concrete "core" mix if you will. Not much if any of their work consisted of a, shall we say, polished surface the kind one would want to achieve for a counter top. But I'm wondering if casting face down in a mold this way, using a rather rich fine silica sand mix as a finish layer perhaps 1/2" thick that was then backed up with another inch or so of regular concrete mix would achieve a smooth finish?? One would have to expect one time use out of forms no doubt. I'm asking these questions since I, too, am considering making a sink counter for a garden work area outdoors. Concrete is the obvious countertop material for such a location. I'd anticipate doing a little (perhaps more) sacking and finishing of the form finish once done I suppose.In your experience, is it possible to achieve a form finish that's anywhere near as densified as a well troweled surface that's finished face up? Would a special 1:1 cement sand mix for the form finish make for a good outdoor working surface?I get too impatient with my concrete to wait until it's adequately set to get a decent finish is why I'm so enthralled with casting face down (grin)...........
From Beautiful Skagit Co. Wa.
Dennis
Dennis
O.K. First of all, you cannot rush the finishing process on concrete. If you trowel it too soon, you're just asking for trouble. The water has to come out somewhere, and with a form, it comes out the top. So, if you trowel and leave it too soon, the water stains come to the top surface, and look like crap, at least to a pro.
Countertops aren't that thick. To try to save money with a 2 part mix of finer and heavier course aggregate is a recipe for a cracking disaster, especially in an outdoor environment. Plus, if you DO get a chip, or a crack, and the inside is not the same color, it will stick out like a spot on Fido's behind.
When we install stamped and colored stairs, we have to take the forms off to trowel the face of each step by hand, to get a smooth finish. If you do it too soon, everything collapses. If you wait too long, or forget about it, it will look like crap.
Same thing with molds. The only way to get a consistent (I mean every stinking time) finish with concrete is to trowel it smooth, to take the air bubbles and imperfections out. Otherwise, on the bottom of the mold, there will always be something, however slight, to repair. All repairs in concrete are tough to match both in color and texture.
That's it in a nutshell.
Jeff
P.S. Someone here is bound to tell you that it's not necessary. I tell you that for the prices that my company charges, perfection is expected. So, I'll only tell you how to get those results guaranteed every time. The last thing you want with a countertop experiment is to take the mold/boards off, only to find aggregate and airholes showing. Now, you've got to do it all again. Time is money.
Edited 5/1/2005 1:55 am ET by JHeath
Jeff,
Just curious, why does the two part mixture invite cracking? My bathroom is in the middle of a remodel, so I don't have time to experiment but this does sound interesting.
Jeff
Jeff
Concrete is a very rigid, very brittle hard surface. An 8 foot sidewalk, poured 42 inches wide, lifted up in the air and supported on the ends only will crack from it's own weight (gravity). Without getting into statistics ( which I guess I just did) it's not a very strong substance. When subjected to movement, it cracks easily. I have 3 crews raising (called mudjacking) concrete every day, all day long, so I know.
Epoxy is the only product that when adhered to concrete, has a stronger bond than the concrete itself. All other mixtures create a cold joint, even if poured together before curing. The joint between the 'topping' and the main body of concrete is weaker than the concrete itself.
Does your house settle, creak, or move a little. Almost all do. I have poured stamped concrete floors 5 inches thick, reinforced with #10 remesh (10 guage wire sheets) inside multimillion dollar homes as floors, foyers, etc... with control joints cut in every 8 feet (exactly what is required), and they STILL crack from slight movement.
There are guys in my business who only color the top of the concrete, instead of mixing it in the truck so that the color is even throughout the concrete. They broadcast a powder dye, and color the top 1/2 inch. When it cracks, or a "rock popper" occurs (spauling) you can see the difference in color immediately. Those jobs end up looking like you know what in 5 years.
What type of finish do you want to achieve on your countertop? Smooth or textured?
If you don't mind imperfections, than go for it. I'm just trying to tell you the correct way, without cutting corners.
I'm the same guy who will not deliver a custom woodworking job to a customer with a flaw in it. I'll remake the piece, instead of trying to hide it. It's just the way I am.
The way I see it ( here comes the self horn tooting!!) at over a million $$'s a year in business for 20 years straight, I must be doing something right. LOL
Jeff
Jeff, have you ever tried the "fiber" concrete reinforcement (instead of rebar)?I wanted to build a sub-woofer cabinet of concrete but didn't want all that rebar so I looked into this fiber that you add to the mix - supposed to add quite a bit of strength...Mark
Measure it with a micrometer, mark it with chalk, cut it with an ax.
Mark
Yes. Many guys use it in curbs and steps to set it up quick, so you can take the forms off fast. The problem with it is finishing. Unless you're a pro who finishes all the time, the little fibre hoops always show like fish eyes in the finish. Quite frankly, I wouldn't use it in a project where finish is critical. Imagine 50,000 little fibres, all linked together, surfacing up all over the concrete. I've seen garage floors that looked absolutely hilarious. They look "furry".
Adding rebar is tried and true, inexpensive, and you can get it cut and bent to size at the local contractor's supply.
Jeff
Mark -Look into a technique called "FerroCement". This is basically a form built of hardware cloth, 1/4" mesh screen, one or several layers thick. The mud is then plastered over the mesh by hand rather than poured in a mold. Plaster one side being careful to not push too much through the mesh, then once it's set, work on the other side then finish the first side.There's a competition back east at some engineering school where students have to build a concrete canoe then they have a race in the end products. Large boats to the size of yachts have been built using this technique. It's amazing how thin you can make a ferrocement section and the strength it has. Of course in the case of marine applications we're talking about compound curves rather than flat panels, the former providing a lot of geometric strength in themselves. ...........
From Beautiful Skagit Co. Wa.
Dennis
Continuing the debate.....I'm not a professional concrete guy.....not in the least. But I have done a fair amount of concrete work, both cast in place and in forms. For me, the advantages of form work are the same for casting anything....you can cast other than flat surfaces. I've made a fireplace surround using narrow boards on the form surface to give the concrete a horizontal multi-plane surface. On another fireplace, I cast 1" x 1" square steel mesh just below the surface then chipped the cured concrete away to reveal parts of the internal steel. On concrete countertops, like my own, I cast an integral drainboard next to the sink opening. I also cast an upturned back-splash to eliminate the always nasty to keep clean joint at the back edge of the countertop. All of these projects couldn't be done via a surface trowled method by other than a very practiced professional.I recommend for reading: Concrete Countertops by Fu Tung Cheng. This book is a Taunton publication.
Jeff
Mind sharing how you formed the radius of the integral back splash?Jeff
This is how I did it. This creates a low shelf for the backsplash. The actual splash will be concrete tiles. Jeff
Thanks. Great idea.
Interesting post!
As far as the chopped fiber for concrete reinforcement: DON'T.
Recently had a home in central Tennessee with all outside concrete containing this material, and not a piece of steel. I had specified 6 x 6, 10 ga welded wire mesh, and inabsentia, the highly respected & experienced builder (45 years) claims he upgraded the installation using the fiber. They had no knowledge of tamping the base under the concrete, preferring to pour over crushed rock: loosely packed 1/2" aggregate or smaller. Everything in town was cracking and heaving, or drooping where the rock shifted. My elevated & crowned patio, 16' x 38', eventually settled until the center was 1" below the brick border .... and it's likely still settling.
Consider for a moment, the rebar has ridges, the welded wire has the next strand .... all to provide a place for the concrete to grip the steel and prevent movement. Consider also prestressed concrete, where the reinforcing is held under tension while the beam is poured and cured. Tremendous strength. However, with the fibers there is nothing to grip, just slick glass fibers. And they make finishing a nightmare ... that's why you see all those coarse finished sidewalks and driveways .... it's not to increase traction when they're wet, it's to mask the protruding fibers .... they can't finish it slick, it's way too fuzzy!
As for strength, the coloring usually adds significantly to the final tensile strength of concrete, and the finish troweling increases the surface strength and wearability as well.
Just my 2 cents!
John, back in Texas now!
TailsOrPins -I will definitely second your opinion and comment regarding glass fiber reinforcing in concrete. It adds little to the bending resistance to a slab the way conventional reinforcement does.We installed in floor radiant heating during our remodeling project. Hired a contractor to pour regular weight concrete (not lightweight concrete or, heaven forbid, gypcrete). He used a high range water reducer along with a heavy dose of retarding agent to achieve a very flowable mix with a low water/cement ratio. I should have persisted in my preference to install a light weight mesh rather than relying on his use of glass fiber reinforcement alone.The slab, 1 1/2" thick to cover the tubing only, is not structural, of course, and will be covered with a finish floor of limestone tile. I was anticipating shrinkage cracks but certainly not to the extent they've appeared. Mesh would not have eliminated the shrinkage, of course, but there are smaller sections that now sound "hollow" over the wood framed structure that have me somewhat concerned about installing the tile, fracture isolation membrane not withstanding.Glass fiber has its place but not as a structural enhancement. The countertop I'm planning for the outdoor garden center cleanup area will be an experiment with ferro-cement. Several layers of 1/4" hardware cloth with a rich plastic cement/sand "plaster" troweled on in multiple coats. As I said, it is an experiment. ...........
From Beautiful Skagit Co. Wa.
Dennis
JeffThanks for your generous explanation. You saved me the inevitable frustration that would've resulted from ####two-part pour.Jeff
Jeff
No problem. You'll be happy you did it the right way, believe me. For one coutertop, who cares about saving 50 bucks on the dye. Do it right.
Jeff
Jeff -With regard to the two-pour method of casting a slab in a form, I wasn't that clear about how the precaster went about it. The initial high-cost finish mix was poured (or sometimes shot when in the case of GFRC) and let to take the initial set. Once this finish had set enough to inhibit migration between the next lift and the surface, the backing coat was poured and the two vibrated together to provide a bond sufficent to withstand stresses of handling and erection. I don't think they ever experienced a case of a panel cracking as a result of this, shall we say, laminating technique.This is NOT to argue with your advice against casting countertop slabs finish face up. I totally agree with you. I don't think anyone could expect to achieve the kind of finish necessary for an interior countertop by using a form finished surface unless he/she was willing to do an emmense amount of had grinding and polishing after the fact. And then as you point out, surface repairs are next to impossible to disquise let alone hide............
From Beautiful Skagit Co. Wa.
Dennis
Jeff -You pretty much confirmed what I had anticipated - that a form finish for a concrete working surface like a countertop wouldn't be satisfactory at all. I was just hoping you had some trick up your sleeve that would alleviate the inevitable pour & wait routine involved with a troweled finish. I've done a moderate amount of concrete finishing myself, not nearly as much as you and defer to your expertise, of course. Plus, by finishing the surface face up, I have the option of including some "features" that I've been troweling into various little concrete projects around our place. Splash basins for the gutter rain chains, for instance, have pressed fern frond and maple leaf imprints. I wouldn't suggest these would be appropriate for a kitchen counter top, no, but for a utility surface out by the garden I think they'd be kiinda ..... well, cute (grin)Thanks for the excellent advice, Jeff.I'll try to be more patient in the future (haha)...........
From Beautiful Skagit Co. Wa.
Dennis
I like the sound of applying the finish mix in the form first. I had been thinking of trying that, but was wondering if I might lead to problems. Would the sand mix be as tough as the finish worked up from the soup of the regular aggregate mix?
Root -I trust you read Jeff's reply to me. Given the thickness, or thinness if you will of a countertop in comparison to the precast building panels I used to detail, the process wouldn't be appropriate to a countertop. I should have given it more thought before I even posed the idea. Building panels (not counting certain types of metal frame composite panels) are from 3" thick and up. Not your average countertop.Aside from that, again after I reflected on the process, a good hard troweled surface on concrete provides a much denser and uniform end product that a form finish does. Unless you've had a great deal more experience dealing with precast concrete than either of us has. Add to that the fact that building panels are generally finished with a sandblasted finish as opposed to an extremely smooth dense surface, the two are worlds apart.Go with the pro's Root - cast it face up. Pour the mud, go have a cup o' java and be sure to let the bleed water evaporate. Timing, as Jeff says, is everything.Also, perhaps Jeff will add something to this, but as I understand the chemistry of concrete, use the driest mix you can while still getting good consolidation along the edges of the form. Excess water = more shrinkage + potential for shrinkage cracks. Question for Jeff along these lines -Do you use any kind of water reducing/plasticizing agents in your work? What about retarders or accellerators? Would you be willing to share your design mix?...........
From Beautiful Skagit Co. Wa.
Dennis
I've obtained helpful information in the past from these two forums that have a section on concrete countertops: decorative-concrete.com & acid-stain.com. Also, on jeffbridges a post details their pouring concrete counter tops.
I'll be buying Buddy Rhodes mix for my countertops and his slurry to fill the holes. For the minimal amount I have to pour, this will save me the time of making samples to get the right color.
Jeff
I helped my son redo his kitchen almost two years ago and he wanted concrete counter tops. Black. Here's how we did them.
We used melamine for the forms and poured the countertops upside down. We used no release. We used a very little bit of clear caulk in the corners where the melamine pieces mated. Be absolutely sure that you get all extra caulk out of the form or you will leave an impression that will be a lasting reminder ...
We used the concrete chicken wire in the forms but made the mistake of not using something to keep it from settling. If you use rebar or wire in the form, for strength, make sure you use string or something else so that it won't drop and be visible (or weaken the top because it is too close to the surface.
We used palm sanders to vibrate the mold and went over every inch of edging several times, spending a fair amount of time.
The melamine comes off fairly easily. After you take the form off, you will need to polish the concrete and then use wax. We got some polishing paper and used a grinder with the polishing paper to get a nice smooth finish. The more you grind/polish the more aggregate/sand you expose, and this changes the texture.
I'd recommend building a small setup that you use for a test. We did that and it worked well. Note that you may also need to make a slurry of colored concrete to fill in any gaps (from air and such) that are in the countertop.
If you have further specific questions feel free to send me an e-mail.
John
I JUST LOVED THIS POST
I {WAS} going to make a concrete counter top..
I know better now.. Thank you for the info...
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