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Erik and I are planning to make our own concrete counter tops for the kitchen. We got the Fu-Teng Cheng books and will watch his instructional video for family movie night this weekend.

My favorite fount of information so far has been this wonderful Instructable. It has a few hundred comments which are full of extra tips and information. While I was reading all of this, I cut and pasted some notes. I figure that it might help someone else if I posted this condensed, organized group of comments. There is surely stuff that I missed, though, and new comments get added all the time, so be sure to read through them all as well.

CONCRETE

A cubic yard of concrete weighs 2 ton.

I would calculate a 2 inch thick countertop being about 22 lbs. per square foot.

Mixes

There is a bagged mix from ZipMixx (GFRC concrete, this is amazing stuff.

Quikrete Countertop Mix--I have used it several times with great results.

There's a guy on the web that sells a great manual on how to make a concrete countertop, he gives you the right mix to buy and he talks about what to do if you are out of the U.S. and can't find the cheaper supplies they have here. his name is Pete Hawes and his website is doyourownconcrete.com

I came up with my own concrete recipe that seems to have turned out well. Here's my recipe;

In 5 Gallon Bucket:
1 1/2 Bags Quikrete 5000 Commercial, Measured by Weight (Don't forget to weigh bucket first and subtract from total weight to equal 1/2 bag weight.)

In a Separate 1 Liter Container:
1 Liter Water
2 T. Enflow High Range Water Reducer for Concrete Countertops ($4)

Another Liter of Water

1/10 Bag of Enforce Heavy Duty Fiber ($10?) (I divided the bag of fibers in half and then "eyeballed" 5 equal piles and put them in baggies for later use.)

Put premeasured Quikrete in a wheelbarrow. Add Water Reducer solution a small amount at a time and mix thoroughly. Add more water, a little at a time, until the mixture looks like thick oatmeal. Add fibers a little at a time. Mix thoroughly. Let mix "rest" for 10 minutes. Add a LITTLE (a spray bottle works well) more water and mix to return to the thick oatmeal consistency. You are now ready to pour!

FYI, this makes one square yard of concrete. You can find all of the enCounter products online (http://www.encountertop.com). If you choose to use and different brand of water reducer and fibers, just convert the measurements on the bottle to those for 1 square yard and substitute in place of mine above. This can be a little tricky but I was able to do so using the product websites.

as long as it's 5000 psi, it should be fine and the fast setting is what I used as well.

REINFORCEMENT

Fiber are used by most professionals, some of us use PVA , nylon or glass as in GFRC (glass fiber reinforced concrete).

I always pour a 1/2" of mix in the mold then put the remainder back in the mixer and add the fibers. By adding the fibers last you eliminate them from poking their little heads out of the finished surface. You can torch them...

Not all reinforcement is the same. Most WWM is already rusting, and rust expands and cracks the Concrete in time. Some are plastic or epoxy coated to help with this issue. My favorite is an additive called PVA fibers (PolyVinyl Alcohol). They form a molecular bond to the calcium, and keep non fatal cracks almost invisible.

Some sort of reinforcement is needed and one of the best is remesh. You can get it at HomeDuh Poe. To suspend in a 2" thick piece, cut some foam or wood blocks 2" or so. Cut the grid about 1.5" short all around the mold. Lay the wire grid on the blocks that you have spread out in the mold. Now use drywall screws about 1.5" in length and screw them on the outside of the mold by the side pieces. I angle the screws out and leave about 3/4" sticking out. Then take some tie wire and wrap around the wire remesh, then over the side to the screw, wrap firm not tight. I usually do one on each side then I can pull enough to just suspend the remesh. I will usually tie the grid up about 18"-20" apart. After it is tied up and tight, then remove blocks It will stay in about the middle or higher. Ideally you want the reinforcement in the bottom 1/3 of the finished slab (right side up). I do not use rebar but instead I use allthread or threaded rod.

Chicken wire is good, but a fiberglass screed might be better for structural integrity. The weave is tighter and less deformable than metal in the tensile department. But of course chicken wire is probably cheaper and more readily available.

INSETS

Use spray adhesive to attcach things you wish to inset to the mold before pouring.

I would advise (well, actually, the concrete professional I've been working with advises) not to use aluminum with concrete, they're not very compatible both chemically and due to thermal expansion differential issues.Stainless steel is the way to go for an insert, it's coefficient of expansion is closer to concrete and it's chemically non-reactive for the most part with concrete.

DO Not Use aluminum because it will eventually react with the cement in the concrete. A better choice would be stainless steel, brass, or copper.
the lye in concrete will eventually eat away the aluminum insert you put in the sink piece, stainless steel or brass are recommended. Both can be picked up at metal supply stores.

The glass is an awesome affect, if you're not gluing it down first I recommend adding like 50% more to make up for migration. For my next project I want to swirl 2 colors of concrete together.

THE MOLD

The biggest thing is patience and prep work. Molds are THE most important part.

I spent a week just getting the forms made and caulked

Mold materials

Plexiglass

If you build your mold out of a shiny material, like plexiglass, you do not have to grind the countertop. It will come out of the mold as shiny as the plastic. It is amazing how precisely the concrete will pick up every detail in the mold. It will even pick up a fingerprint if you get one on the plastic mold material.

Melemine

One disadvantage of using Plexiglas is that it scratches.  For a DIYer Melamine is still the best bet. As a professional I use several different pour surfaces yet  Melamine is still at the top of my list.

I'm testing melamine, acetate, and something called tile board (looks and feels exactly like a white dry erase board). ended up using melamine.
all "melamine" is not the same, the original company stopped making it (that's what I heard) and some finishes will peel off when you flip your mold. Look at the edge and if it feels like paper then I'd go somewhere else. I reuse my mold since I build on top of a full sheet then flip it over. After that if it's in good shape I rip it into strips for sides. There is also a heavy weight plastic sheet that you pour, I haven't tried it yet.

Formica

Medium density overlay

MDO (Medium Dentisty Overlay). It has a smooth paper covering. We reuse these sheets. That was used as a stable, flat base. Over that we used a thin plastic sheet that comes in rolls. For the sides we used MDO with a thick tape over it for a smooth finish.

The thin plastic sheet is PETG but any smooth sheet will work. You have to experiment because thin flat sheets will expand and contract with the room temperature.

Building the mold

We screwed the sides in then made it watertight with black latex calk. The reason we used black is so you can see it well in the mold and can make sure you have very clean lines.

The rounded corners were done with pvc The PVC is 2" if i remember correctly, A wanted a certain radius on his corners and I think I had that pipe sitting in my shop. We sanded the edges to make them thin again to reduce sanding. I imagine if you wanted greater or lesser radius any diameter within reason would work. Keeping the PVC in place was a little tricky. We taped and backfilled the spaces to support the corners and keep them as straight as possible.

We used Irwin Bar Clamps to hold everything in place.

You pre-drill the holes and I would follow with a countersink bit. We would then carefully place the screws in with a battery drill set on low torque. The tough part was not drilling to deep into the side of the Melamine which may crack or distort it.

I took the workshop through Cheng Concrete Exchange, and I learned a lot. The things that we did that weren't in the book or DVD were that we spread our black caulk in the corners of the mold with a beveled plexiglas rod, then cleaned up the excess with a straight edge razor blade. I don't know if this saved anytime. The blue tape is time consuming, but so is the razor blade cleaning method. Cheng liked the plexiglas rod at the time I took the workshop. We also used metal angle brackets to brace the outside of the mold to the table. For final vibration, we were told that at home, we could use a Saw-Zall without its blade placed againts the sides of the mold. We had 2 of them going, and they worked well.

There was no glue used. We screwed the sides in then made it watertight with black latex calk. The reason we used black is so you can see it well in the mold and can make sure you have very clean lines. White blends in so well that you wouldn't be able to see how clean a job you did.

Do you think it would be possible to incorporate a backsplash in the concrete mold or would it need to be a separate piece of material, cast independently?
Absolutely, it just has to be integrated into the mold. Cheng's Book goes into detail on this, as well as many other options you might not think of - like integrating a removable cutting board into the counter or adding a piece of rough cut marble into it for the perfect area to roll out dough and pastry.

Thickness

They don't recommend making them any thinner than 1.5", mainly because you could get a "ghosting" effect from the wire mesh you need to put in it for support.

Vibrating the mold

When I worked for a concrete solutions outfit we added 'sulfur fume' to each batch for a creamier, more even result with less pitting/bubbles at the initial pour. We also used industrial vibrators and shake tables to eliminate 99% of air bubbles (although many people prefer to leave the pitts and air for a more industrial look). Also something to consider is using an even bead of caulk inside the mold to give the piece a rounded edge when stripped.

Lubricating the mold

Use vegetable spray (pam) or form release.

After cleaning your molds and preping to pour, use a cooking oil or spray butter on the inside of the molds, this helps to release them after the pour.

When I first started I sprayed the molds with Pam. Worked great, now I use a form release.

PUORING

You never push the concrete around in the mold.  You put in clumps (piles) and vibrate the mold to make it flow.  You can pound the bottom of the mold with rubber hammers or use a commercial vibration table.

Pour in Place?

Here is a link to how we poured our countertops in place using the 'bullnose' edge forms: mydiyhome.wordpress.com/concrete-countertops/ We did not polish ours since I didn't want to make a complete mess of the house

Pour in place (in the trade it's called CIP, cast in place)is not necessarily without it's own difficulties. Tom Ralston has DVDs and books on CIP. www.tomralstonconcrete.com

I have only seen it poured IN PLACE..... In other words, supported and framed on top of the counters, then poured and finished. Cuts out all the backbreaking moving of the slabs (and the dropping of said slabs). Really, it's the only way that makes sense to me.....but that's just me.

Have you taken into consideration the gallons and gallons of spraying water that comes from wet grinding and polishing the counter? If you want a rough or very matte finish (and also very porous - more stains), then maybe poured in place makes sense, but if you want a very polished appearance, you will have major water issues. Moving the counters only happens within minutes. Wet grinding with spraying gallons of water lasts upwards of 20 hours. To each his own...

COLORING

I want to dye two different batches and pour them into the counter mold from opposite ends so they meet in the middle and blend together naturally.

2 shades that were placed in the mold and then vibrated together giving a marbled look.

CURING

About the curing concrete, the best way is to pour some water on top (slowly) and cover the concrete with plastic and if the water evaporates put add more water. As mentioned before, might sound crazy but you can even cure concrete underwater with great results.

Portland cement is not like Elmer's glue, which becomes liquid by dissolving in water, and solidifies as it dries.

Rather, it's like epoxy; it undergoes a chemical reaction as it cures. The hardener, in this case, happens to be water. That's why I said "to hydrate" earlier: the *anhydrous* form of the chemicals in cement are a loose powder, but the *hydrated* form is a solid block of stone.

This is why high heat destroys concrete: it drives out the water, and returns it to a powdery, anhydrous state.

The cracking you mentioned doesn't come from too-rapid drying; rather, it comes from incomplete hydration, similar to epoxy with too little hardener mixed in. You can dry concrete in the sun if you keep sprinklers on it. Similarly, you can cast concrete underwater without any problem.

UNMOLDING

Your tops should release easily, if not just pull up with steady pressure and use compressed air between the melli and the countertop. How long were they in the mold? 3 days is more then enough, with the mix design I use I flip in 12 hours.

FILLING

I filled the holes on the surface with a sparkly epoxy.

POLISHING

Protecting yourself is never overkill!

Wear not just a mask, aka a cheapo white one, wear a respirator type mask - or a particulate mask. I teach sculpture - this is not something you want to inhale in any amount and the cheap masks don't protect you.

3m makes a line of disposable masks rated for all sorts of things that are regarded as "respirator-only" territory. They aren't the same thing as what you are referring to as the "cheapo white ones" but they are a heck of a lot less expensive at 3-4 bucks each than a good respirator at $50+, so technically they are pretty cheap and most of the particulate masks are white or gray. (Some of the vapor masks are different colors though) Also if you do jump for a respirator get one that has the standard-size screw-in cans and replaceable one-way valves. These are generally a bit more expensive but a lot of cheaper respirators use proprietary filter cartridges that either become impossible to find after a while, lock you into a single source for replacements, or don't give you the selection of filters you might need in the future.

Make sure your grinder is a variable speed. The discs are expensive and you will benefit from the slower speeds. definitely under 4k rpm and right about 2500 is what I am discovering.

To polish start with 400 but don't polish past 800 if you applying a topical sealer it need to be able to grip or biet on to the surface.

A 400 grit is the last pad that is considered a grinding pad, so I would say start polishing with an 800.

I got a tip from one of the commenters here that I could do some light grinding with my wet sander without making a mess in my kitchen. Basically, you take 2" painter's tape and wrap the edges so you have a protective "lip" to hold water in. Then you use a spray bottle to control the amount of water instead of hooking the grinder to a hose.

The more you grind down, the more aggregate is exposed, so since I spent a good amount of time grinding, alot of the smaller aggregate was exposed.

You have to be careful grinding ovals like that because you can cause gashes with the lower grit pads. I suggest just using a light touch and also remember that you may not get the exact same shine off of the inside, but as long as the top of the countertop is done right, you won't notice the insides if they have a bit more of a matte finish.

If you don't want to go with a true wet grinder/polisher, I'd suggest an air sander. Of course, you'll need a big air compressor to run it, but at least you won't have to worry about using water with electricity of a standard grinder.

You know there is no law of air compressors that says you have to get all of your output from a single monster tank/compressor. Getting to 9scfm@90psi is not that hard given two or three of the little guys.

Well I am by no means an expert, but without getting into the nitty gritty it's really fairly simple. The first thing to remember is that the ratings on compressors are (generally) sustained SCFM -- ie how much air the compressor itself can deliver. When you add a tank to a compressor you get two benefits: 1) The assembly can deliver a higher SCFM than the sustained rating for "burst" work (this is why your pancake compressor can drive a roofing nailer) and 2) The compressor doesn't have to run constantly. So, if you were only going to use a tool that requires 9scfm for a few seconds every minute you wouldn't need a 9scfm compressor to use it. Unfortunately for a grinder you need the sustained duty, so tank size is actually quite unimportant. I guess I should have included an example for plumbing compressors together -- I can't find much about it online (there is not a step-by-step or anything) but people frequently do this and it is very simple. You basically just put a tee fitting between each tank and its regulator and plumb them together with a high pressure hose. This gives you increased total tank volume (burst scfm) and the advantage of having two compressors that can keep it full (sustained scfm). You can use a high pressure valve on each fitting so you can disconnect them when necessary. There is flex hose that is rated for pressures high enough to use without being regulated down to 90psi or less but be sure yo do not use a 90psi rated hose on this 120+psi air! You also want to make sure your compressors have similarly rated pressure tanks. Do not plumb a compressor that shuts of at 150 psi into a tank that is designed for one that shuts down at 120psi unless you can adjust the 150psi compressor to limit at 120psi. Hope that makes sense.

WAXING AND SEALING OR PATINA

Concrete is VERY sensitive to citrus.  Citrus etches the concrete and requires repolishing and waxing. A regular coat of wax will help, but it is more sensitive than granite.

There are many new concrete countertop sealers that are not for the novice. Some involve a mix design that requires additives that are very expensive, others a $3000 UV light to cure them. As concrete becomes more popular we see more user friendly sealers that will help us all.

Hi all. I am a professional countertop restoration specialist and I reccomend using stonetec waterbased dealer (I am NOT an employee of them or affiliated with them) I use the whole line of their products on a day to day basis. Insofar as wax is concerned I use Cheng's wax availabe at his website concretexchange.com.

For a wax finish contact buddyrhodes.com and use his wax. Or go to a True Value Hardware Store and get some Trewax it is a furniture wax with carnauba in it.

Waxing just makes the countertop more resistant to stains, although even with wax applied, things such as citrus, wine, etc. will still stain if left on the countertop for more than 15 to 30 minutes. Over time, however, the stains form a patina on the countertop which makes concrete very unique and desirable. I've read where some people say that their countertops look better after several years of forming a patina than they did when they were brand new. Wax also adds a sheen to your countertops which will wear away if not applied every 30 days.

It has been well over a year and I haven't been good at all about waxing it every month. At first I was freaked out, mainly by citrus stains, because they actually etch into the concrete. But over time it really has formed a patina that is looking much better.

Water glass (Sodium silicate) painted onto the surface, will help quite a bit. I'm not sure it will make the concrete completely impervious, but it's permanent until the surface of the concrete wears away.

There are polyurethane finishes that you can use on concrete that produce an ultra-high sheen, however they will burn if hot pans are put on them. They also wear off and every few years you have to strip them and re-apply. After taking this into consideration, I chose to rub wax on mine once a month.

Ever thought of a resin overlay? Clear polyester or epoxy? there are many resins approved by the FDA for use on food surfaces...laid over an unfinished piece and then polished smooth could provide some dramatic looks.. most resins are self-leveling and very easy to apply. They require almost no prep as the stick to almost everything (too well sometimes) and you can usually just pour a batch onto your project and lightly brush around to coat it nice and thick. A couple of applications while its still wet isn't bad. just let it flow over the sides and drip.. essentialy drench the piece, obviously cover the floor well wih plastic. When it gels up and the drips turn into stalactites, you can use a sharp blade to run under the edges and cut them off. Applying it wet like this makes it look like water and ultra clear. Just a tip.

There are also some densifiers (penetrating sealers) that are pretty killer for sealing/strengthening concrete. Check out ConcreteNetwork.com for ideas!

INSTALLATION

Most all modern cabinets can support concrete countertops without a sub-top to distribute the weight. I always install directly on the cabinet bases. If you want to put a sub-top on then trim the raw edge with a strip of wood molding stained to match the cabinets. With the overhang of the top any slight miss match in color won't be noticed.

Since the counter weighed in at 200+ lbs., I wanted to reinforce my cabinetry. So what I did was create a frame around the inside perimeter of the cabinet with 1x5's, then cut the melamine board I used for the form to fit recessed inside and flush with the top of the cabinet. I then mounted the melamine to the 1x5's, layed the counter on top and traced my sink holes and faucet holes. I then cut the melamine with a jigsaw to fit the sinks and have cutouts for the faucets. Then I treated the sink as a drop in on the melamine, securing it with caulk, and installed the counter on top to create the undermount.

I did add some support to the ikea cabinets where needed. The center island does have a 1/2 plywood support running down the center to increase the support. 2A in fact bought a floor jack and placed it in the basement under the center aisle to help support the floor. You'll realize just how heavy concrete is when you go to put it in place. Support will save you grief in the long run.

You could use the Ikea legs for the initial setup but then use 1/2in. and or 3/4in. plywood to support the load. Now would be the time to level your floor with self leveling cement. Ask a tile setter what he uses. I have been doing concrete countertops for about five years and only install on good custom bases or build my own metal stands

I'm wondering about clipping the wires that support the internal mesh. I don't recall you mentioning this step, I did mine after the final pour and a little action with the rubber mallet. I couldn't figure how to screed with the wires in the way so I hope it didn't sink to the bottom ("top").

You did right by cutting the wires before you screed. The cage will stay in place once you surround it with concrete.

COST AND TIME

All of the countertops that I poured (one countertop isn't pictured) came up to about 36 square feet @ 2" thickness, which came to 6 cubic feet of concrete. This is alot of countertop space, so you're countertop could cost less depending on the size of your kitchen. This is a fairly comprehensive list and I didn't include the cost of the grinder in my estimate of less than $800. If you add up everything except the grinder, it comes to $792. Depending on how you finish the countertop and whether you need to support your cabinets and floors, you can include the grinder in the estimate and still come in less than $900. Cheng Kits, Slurry, Glass + Sealer - $230 Melamine - $100 9 Bags Quickrete 5000 - $72 Cement Mixer Rental - $50 Aluminum and Galvanized steel - $60 3/4" Plywood for adding support to the cabinets and tops - $90 Steel Supports for the basement- $60 Screws, Caulk, Epoxy, Wire Mesh, PVC, Styrofoam, other misc. - $60 Hellcat Grinder - $270 Diamond Pads - $70 As you can see, the Cheng supplies were one of the biggest expenses. If you'd like to experiment, you could really get the cost down. I knew that I couldn't afford the time or money to redo the countertops, so I spent the extra cash....let's just call it "insurance".

If I were to do the countertops again, I would estimate that it would take me a day to build the molds, a day and a half for mold preparation and pouring, two days for grinding, slurry, and polishing, and a half day for installation, sealing, waxing. I'd guess about 48 hours of work spread over a 2 to 3 week time period.

UNDERMOUNTED SINK

To attach an undermount, depends on the style of hardware with the sink. most of the time you use the hardware that is supplied, most are designed to mount to granite and if properly mixed and cured, those pieces will work. if unsure of how strong your mix is, good old epoxy. when mounting the sink, just epoxy the underside of the counter, and position sink, then use scrap wood to prop the sink up between the base of cabinet and top.

6 Comments:

  1. Rick Buckman said...
    Thanks for your great instructions and step by step instructions. I just flipped the countertops and removed the molds. They look great so far. My wife would like me to sand them so you see more of a rough look before I buff and polish them. My question is this; when I start with my diamond pads what will happen to my pieces of glass I have in the concrete.
    Dan Gaskin said...
    Wow! A lot of information. I wish I would have read all about your tips a year ago. I have been experimenting with concrete countertops for awhile and finally have enough confidence to provide a customer with a decent product. I have been using cheng sealer, wax, and polish and the sealer is a penetrating. I was thinking of using a different sealer that is more affective towards preventing etching from citrus foods and liquids. Gonna be delivering my first set of countertops to my first customer for install. Wasn't sure on how to charge, but came up with a $55.00 square foot rate since this is my first. I have been told not to charge less than $65.00. What are your thoughts?
    Darpan Ahuja said...
    Excellent post on Curing Film. Concrete mixes usually have more than enough water initially. However, that water evaporates quickly unless you take proper measures/precautions. The process by which concrete hardens is called hydration. The longer the hydration process continues the stronger and denser the cement paste becomes
    Bruce Ray said...
    I am planning a concrete countertop for my bath vanity. I'd like to try the glossy look without polishing, using acetate inside the mold. (I happen to have a roll of it lying around.) Does it need to be sprayed with Pam, or will it just peel off the concrete? Thanks for the very informative post!
    Clemens said...
    orm a molecular bond to the calcium, and keep non fatal cracks almost ... concretemoldsforms.blogspot.com
    forexbureau0 said...
    There are various online sources to provide you informative details on this topic,
    but this is one is very helpful.
    plastic forms for concrete

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