How do I build a form and pour a concrete pad?

Question

I have a new safe that I want to put out in the garage. I'd like for it to be in a specific corner, but that corner has a few quirks.

First, the slab is pretensioned. No cutting, drilling, coring, etc. All around the garage the concrete comes up about 6 inches, and drywall starts above that. In this particular corner the concrete juts out, making a sort of "L" shaped curb that sticks out about 4 inches. Here's a super-crude ascii-art isomorphic picture of what I mean. Yeah, it's a weird angle, but I can't describe it any better.

             |
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             /\
            /  \
           /    \
          /  /\  \
         /_ //\\  \
        |__|/  \\  \
        /       \\  \
       /         \\  \
      /           \\  \

What I was thinking of doing is pouring more concrete with a form to make an 18" x 24" x 6" pad that my safe can go on, but I know nothing about pouring concrete. Anything I need to know?

Answer 1

This was a project I did earlier in 2012. We wanted to install central air conditioning for our new furnace and there was no better place to put the outside unit than on this side of the house. Unfortunately, the pad there was a wedge shape. So I made a form and turned it into a rectangle. Couple hours of work including a trip to Home Depot for concrete.

Determine the depth of your pad - For mine, I used 2x6's to build my form. You should use a material that will determine your depth, ie: a 2x4 for a depth of 3.5 inches

Use screws to connect the wood together - this will make disassembly of the form easier when you're finished.

Mix the concrete per the recommendations on the bag.

If you're concerned about strength, you can use rebar rods or wire mesh inside the pour. Pour half the depth, lay the mesh or rebar, pour the rest.

Make sure the concrete is level or sloped if need be. A 2x4 can be used to do this or a wooden level. Make sure to wash the level when you're done.

Make sure to tamp the concrete down into the corners of the form and into the field of the form. You don't want any air pockets. Use a trowel to help move the concrete around. Use the edge of the trowel to help remove air pockets.

You want a nice flat surface. Use the level or 2x4 that spans from edge to edge to "screed" the surface flat. Use a flat trowel to raise a bit of water to the surface to make it nice and clean.

Let the concrete set per the instructions on the bag - if the weather is colder, give it another day or 2.

Once everything is dry, remove the forms.