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Concrete countertop advice


kcd2015's Avatar
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Join Date: Nov 2015
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12-07-17, 08:19 AM   #1 (permalink)  
Concrete countertop advice

I'm building a grill table for my ceramic grill with a steel frame, wood paneling, and a concrete countertop.

The countertop will be roughly 61" x 28" x 1 1/2", it will have a 22" (or 21") circle formed out of the middle of the slab where the grill will sit. This will leave 3" of concrete on either side of the circle connected the parts of the slab. This will be a precast slab formed with melamine and foam.

I've got a basic good idea on what to do based on the million how-to articles out there but I've never worked with concrete before.

1) What kind of reinforcing should I use for the whole countertop, and should I have extra reinforcing in the narrow 3" wide parts?

2) I planned on having a 1" overhang all the way around the table, will that be fine or should I go smaller?

3) I plan to embed a decorative steel plate on the top side of the countertop, how should I fix this plate to the bottom of my form so it doesn't move when pouring/vibrating?

4) Would it be necessary to weld some tabs to act as sort of nelson studs to the plate to keep it secure?

5) All the internet how-tos show pilot hole and screwing the forms together. Then I watched the guys on "This Old House" build a concrete countertop and simply hot glue the forms together, no screws at all. Thoughts?

Here's my sketch of the slab:


(zoom)

Here is an example of a project very similar to what I'm building (not mine and not concrete):
Source: My XL Table Build - Final Reveal ? Big Green Egg - EGGhead Forum - The Ultimate Cooking Experience...

 
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Pilot Dane's Avatar
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12-07-17, 08:58 AM   #2 (permalink)  
1. Like you've found there are numerous "how to's" out there. For a counter your size I would embed welded steel mesh then I would lay at least one stick of 3/8"(#3) or 1/2" (#4) down most of the length and through the narrow strips on either side of the hole.

2. I" overhang should be fine.

3. You can use hot glue to stick your decorations down to the bottom of the form so they will end up on the top side of your counter. Some liquid from the concrete will seep under and get onto the face of the decorations but it can be washed or polished off after the counter is flipped. A medium to mild solution of muriatic acid and water can also be used to clean off any concrete juice that gets on them but be careful to not get the acid onto the rest of the concrete.

4. I've only done metal decorative inserts out of brass and copper. I've done some by leaving long tabs at the edge of the decoration and bend them down to embed and anchor in the concrete but there is always a slight radius visible where the tabs are. Soldering or welding on a few bolts or metal tabs to the bottom can also be done. If doing steel use metal thick enough to not distort from the heat of welding. Soldering copper or brass usually isn't hot enough to cause a problem with distortion.

5. Wood forms are stronger and can be screwed together. They are also strong enough to withstand hammering and vigorous tapping to remove air bubbles. Foam forms must be glued together and are more fragile. So you can't hammer on it and the foam insulates the concrete from some of the vibrations so you have to be more vigorous but gentle with the vibrating. Many use a palm sander without sandpaper held to the side and bottom of the form but if the foam is blocking too much of the vibration you can wrap the palm sander or vibrator in a plastic bag and place/hold it right on top of the concrete. You need to hold it so it doesn't sink but just touch it enough to transmit the vibrations.

 
kcd2015's Avatar
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12-07-17, 10:57 AM   #3 (permalink)  
Regarding #5: What I mean to say is that on This Old House the guy hot glued his melamine forms together! No screws.

I will only be using foam for the circle.

It did occur to me that welding on the relatively thin decorative plate could warp it, I suppose I could attach anchors with jbweld. Thoughts ?

 
Pilot Dane's Avatar
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12-07-17, 11:46 AM   #4 (permalink)  
Melamine is too thin to screw into the end so glue is about the only option other than using blocks of wood at the corners so there is something to screw into. Then you have to be careful and plan so you can remove the form because you may have screws running from the inside out where you won't be able to get to the heads after the concrete is in.

 
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