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Concrete Countertop - advice needed john 02-13-2007
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Posted by john on February 13, 2007, 5:34 pm


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



Posted by Joe on February 14, 2007, 12:13 am



john wrote:
> 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

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


Posted by Weatherlawyer on February 14, 2007, 8:39 am


> john wrote:
> > I would like to build my own concrete countertops
> > Rather than casting and towelling 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.
>
> > 2) If I want to use reinforcement, can I use simple chicken wire or do
> > I have to use the real rebar stuff?

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?

> The curse of any casting process is bubbles.
> That's why concrete is treated with vibrators after dumping into 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.

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.

> 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.

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.


Posted by steve on February 14, 2007, 6:08 pm



Fine Homebuilding had a step by step article in its May 2002 issue on
this


Posted by David on February 14, 2007, 6:34 pm



>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.
>
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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