Concrete Countertop - advice needed


After much research I have decided I would like to build my own concrete countertops. I like the whole modern look so I am going for a simple 1.5 inch cement gray counter. Rather than casting and trowleing them in place I plan on casting 2 x 4 pieces upside down in a melamine mold and then piecing them together on my cabinets. My understanding is that makes for much easier process and smoother top since the bottom of the melamine is nice and smooth to begin with. The few grout lines I have are not a big deal. After doing a lot of research on the web I still have a few questions I need some help on:
1) Quikrete has a product called Non Shrink Precision Grout. Their website recommends this for counters since it will dry to 3000PSI in 2 days and 8000PSI in 28 days. A few questions: 1) They recommend to blend this to a syrupy consistency - this makes it easy to pour and reduces makes a smoother finish - any experience with this? 2) They say to use this without rebar or reinforcement except for around the sink, is that correct? 3) I have seen a few negative comments on this particular product. Any experience out there in using this product for counters?
2) If I use the grout mentioned above (or other concrete mix) and want to use reinforcement, can I use simple chicken wire I can buy at Lowes for this? Or do I have to use the real rebar stuff?
3) I want to use the non shrink grout because it sounds like it makes a smooth finish, especially since I am casting them upside down in a mold. If I do need to sand can I just use regular sandpaper and an orbital sander while the concrete is still 24 -30 hours fresh? I am not looking for a glass finish, just smooth enough
4) Any recommendations for a sealer.
thanks John
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john wrote:

Ther curse of any casting process is bubbles..bubbles...bubbles. That's why concrete is treated with vibrators after dumping nto a foundation form, for example. If you could fasten your orbital sander to the bottom of the mold it could eliminate the bubble problem in just a few minutes. Your other problem will be getting a good release from your mold. Do some experiments with different release agents, like waxes, Pam, silicone sprays, whatever. You might even visit a place that casts concrete garden statuary and ask for some tips or advice. For advice on finishing a flawed surface, a terrazo expert would be the person to ask. Sounds like a challenging project...let us know how it turns out.
Joe
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Rebar is there to give it strength against flexing. Concrete is only strong in compression. However there is very little flex on a worktop except over regions where there are massive holes for the plumbing.
Do you really think that chicken wire is going to be of any use there?

Drumming the mould after the pour will also do that job. Be careful not to vibrate the pour too much as it can adversely affect the mix, vibration is responsible for the stratification of layers in the planet, see how it will affect a sample mix of assorted sizes of particles in a concrete mix.

The main problem is flaking at the corners. Smear or bead internal angles with oil based moulding clays, wax and spray with a PVE/meths mixture.
Do not over vibrate. Major problems with commercial production, is turnover, weather and quality control vss expenses. A DIYer can afford to take his time, use a large variety of releases agent together, watch the weather and use a stronger mix than required.
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Fine Homebuilding had a step by step article in its May 2002 issue on this
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I do concrete casting as a craft. I'm not going to give you any advice other than this. You can create your own great recipe (better than commercial) but as a Newbie you are better to use a commercial redi mix designed for countertops. Just finding all the additives for your own recipe can be a huge problem because many are not sold to the general public.
As to the casting itself, PRACTICE first, follow all curing advice to the letter, and then after 2 weeks if you think your first attempt is good then cast another.
Odds are your first attempt is going to be sub par.
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buy a "FireSlate" top http://www.fireslate.com/pages/counter.cfm or maybe get some helpful tips from them
| After much research I have decided I would like to build my own concrete | countertops. I like the whole modern look so I am going for a simple 1.5 | inch cement gray counter. Rather than | casting and trowleing them in place I plan on casting 2 x 4 pieces upside | down in a melamine mold and then piecing them together on my cabinets. My | understanding is that makes for much easier process and smoother | top since the bottom of the melamine is nice and smooth to begin with. The | few grout lines I have are not a big deal. After doing a lot of research on | the web I still have a few questions I need some help on: | | 1) Quikrete has a product called Non Shrink Precision Grout. Their website | recommends this for counters since it will dry | to 3000PSI in 2 days and 8000PSI in 28 days. A few questions: | 1) They recommend to blend this to a syrupy consistency - this makes | it easy to pour and reduces makes a smoother finish - any experience with | this? | 2) They say to use this without rebar or reinforcement except for | around the sink, is that correct? | 3) I have seen a few negative comments on this particular product. | Any experience out there in using this product for counters? | | 2) If I use the grout mentioned above (or other concrete mix) and want to | use reinforcement, can I use simple chicken wire I can buy at Lowes for | this? Or do | I have to use the real rebar stuff? | | 3) I want to use the non shrink grout because it sounds like it makes a | smooth finish, especially since I am casting them upside down in a mold. If | I do need to sand | can I just use regular sandpaper and an orbital sander while the concrete is | still 24 -30 hours fresh? I am not looking for a glass finish, just smooth | enough | | 4) Any recommendations for a sealer. | | | thanks | John | |
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