Concrete Work

To put it simply, wood forms are templates, usually built from 2×4 lumber, that contain and shape poured concrete.  They serve to establish not only the shape of your design, but also the depth, which will determine in great part the strength and soundness of the structure. 

Your first tool to build a wood form is going to be a readily available spool of mason’s string.  It will serve as a three dimensional reference guide as you excavate and lay your boards in place.  Using some wooden stakes, layout your project with a number of points and tie the string tight to give you a representation of the design.

With any outdoor concrete work, a slight slope is required to prevent water from pooling.  A safe slope for this purpose is usually 1/8” per foot, which can easily be arrived at by taking the distance between both ends of your slab and multiplying by 1/8”.  For example, if the stakes are 10 feet apart , the result would be 1 1/4” and you will move the strings down 1 1/4” down on the stakes at the low ends.

In some cases, plywood will work better as a concrete form, especially on tall projects such as steps.  Thin sheets of plywood, such as 1/8” can be bent and formed into curves that will give you even greater latitude with your design.  Pre-formed tubes of strong cardboard are readily available also to use as forms for footings that must go deep into the ground.  One of the simplest, and most common forms however is the earth itself, but for any project that requires the footing to be visible standard wood forms are preferable.

In addition to forms, some projects will require per code to be reinforced with either metal mesh or rebar.  Strong and durable, #3 rebar is usually a perfect choice and can be cut right on site with a metal cutting blade attached to a circular saw.  These elements added to the structure create a very strong core that can support large and broad surfaces.  When installing the reinforcement, be sure to give proper clearance between the form,  the mesh or rebar, and the subbase.  Small chunks of concrete can be used to raise the mesh up off the subbase, as it has to float at least 2” off of the top of your form.  You will also need to overlap the pieces of mesh by at least 12” and bind them together with heavy gauge tie wire.

And here is the step by step on how to build wood frames for concrete.  You can see the basic before and after in these pictures from an outdoor remodel in Santa Monica, where we built a wood fired pizza oven for a client.

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1. Excavate the project area for depth and establish your slope of 1/8” per foot using the method outlined above.  Work the subbase until your soil is evenly sloped away from major structures.

2. Cut your lumber to create a frame with inside dimensions equal to the size of the project, then position your boards so that the inside edges are directly below the mason’s strings that outline the project.

3. Using iron or scrap pieces of 2×4 (cut to form a point) drive in stakes at 3’ intervals at the outside edges of the form boards.

4. Drive screws through the form boards into the stakes to create the form.

5. Using a level that spans your form, adjust stakes on opposite sides so that they correspond evenly.

6.  Coat the inside of the forms with vegetable oil or release agent to ensure the concrete does not adhere.

7, Mark spots for control joints at intervals that equal 1.5x the width of the slab. For example, with a slab that is 3’ wide you would set control joints every 4.5’.

8. Install your metal reinforcement with concrete chunk bolsters and tie everything together with heavy gauge tie wire.

Jannone Construction and Development
502 San Vicente #105 Santa MonicaCA90402 USA 
 • 310-989-3499

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