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   Articles | How-Tos | Ask the Expert   

How to Mix,Pour and Place Concrete

Recommended tools:
—4-ft. level
—Bull float
—Concrete mixer
—Concrete rake
—Concrete tamper
—Duplex nails
—Dust mask
—Framing square
—Garden hose
—Hand tamper
—Line level
—Lumberv —Masons line
—Plumb bob
—Pointing trowel
—Posthole digger
—Safety goggles
—Steel trowel
—Tape measure
—Wood float
—Work gloves

There are many different types of concrete you can use. Some choices are: —Pre-mixed concrete which only requires the addition of water
—Transit-mix concrete is delivered on-site in revolving barrel trucks. This is best for use on larger projects.
—Dry ingredients—Portland cement; fine sand; crushed rock or gravel and water—and mix them yourself.

Concrete recipe

A basic concrete recipe is 1 part Portland cement, 2½ parts sand, 2½ parts gravel and ½ parts water. The amount of water may vary, but it's important to add a little at a time.

Special concrete mixtures

There are many specialized concretes available: vinyl, quick-setting, fiber-reinforced, sand-mix and anchoring concretes.

Vinyl concrete (or patching concrete) is mainly used for repairs. You can make your own by adding a bonding agent to the dry ingredients.

Quick-setting concrete uses Type III Portland cement and is faster-drying than regular concrete. It is not as readily available and is more expensive.

Fiber-reinforced concrete is expensive and is not normally used by the do-it-yourselfer.

Sand-mix concrete has no gravel. It is useful as a grout but shrinks more than regular concrete since it has no gravel.

Anchoring concrete contains an epoxy cement that allows it to adhere to regular concrete. It is also 2½ more times stronger than regular concrete.

Mixing concrete

For large projects, you'll probably want to use transit-mix concrete. For small projects, a wheelbarrow is a good mixing tool. Fill the wheelbarrow no more than 3/4 full with the dry ingredients (or premixed concrete). Make a mound of the ingredients, punching a hole in the center. Start adding water a little at a time, mixing well to test the consistency. The concrete should cling to the side of the mixing tool.

If you rent a concrete mixer, fill no more than half full of dry ingredients. Add the water and let mix for about five minutes then test the consistency.

A good test for the consistency of your concrete is to make a slice through the center of the concrete. If it is too wet the edges will fall and you'll need to add more dry ingredients. If is it too dry, the edges will crumble and you'll need to add more water.

Building the forms and pouring the concrete

Almost all concrete jobs require some type of form. Some are built above ground, others require digging.

For a slab, dig down to the desired level and build forms to the shape and size needed. Use temporary posts to establish the proper grade or slope of the concrete. Use a level to ensure that you have the proper grade or slope of the concrete form.

Pouring concrete

After the forms are set, spray the entire area lightly with a garden hose then pour in concrete.

Tamp the freshly poured concrete to compact it. Use a tamper or rent a roller tamper.

After the concrete in the form has been tamped, use a straightedged 2x4 as a screed for leveling the concrete. Work back and forth in a sawing fashion to level the concrete.

When the concrete has set sufficiently to support a 2x8 plank, use the plank as a straightedge to guide a groover to cut contraction joints. Contraction joints are necessary to allow hardened concrete to expand and contract in extreme temperatures.

On sidewalks or other narrow concrete areas, contraction joints should be cut every 4-6'.

On patios or other large concrete areas, expansion joints should be cut in each direction every 4-6'. Use two lengths of beveled clapboard placed in the position shown in Fig. 7 to cut these joints.

Drive a nail into the top of one board and paint both boards with motor oil. The boards should then be embedded in the concrete.

After the concrete begins to set, the board with the nail in the top can be removed, leaving the second board hidden. This provides an adequate contraction joint for a large expanse of concrete.

Reinforcing Concrete

In some cases, concrete needs reinforcement with steel mesh. You can use regular fencing material with 2x4 or 2x6 mesh.

If the pressure on the concrete is to come from the top of the slab, the reinforcement should be laid deep near the bottom of the slab.

If the strong point of the slab is at the center and the pressure will come on either end, the reinforcement should be laid as close to the top of the slab as possible.

Different ways to finish concrete

For a smooth finish, you can use a trowel and float.

You can create a light, swirled pattern by holding a steel trowel flat against the surface of the slab and moving it around in a swirling motion. Do this the last time you trowel the concrete.

For a heavier swirling imprint, use a wood float instead of a trowel and do the swirling while the concrete is still fairly wet.

Create a soft pattern of parallel lines by dragging a soft brush straight across a moderately wet surface.

For heavy lines, use a soft brush while the cement is still wet.

For light-texture parallel lines, trowel the concrete and allow it to dry slightly before dragging the brush across.

Letting the concrete cure

Concrete must be given time to cure. During this period, the concrete surface should be kept wet by repeated hosing with a fine mist. This hosing process should be done at least twice during any 24-hour period for about three days after the concrete is poured.

Concrete poured indoors can be left exposed, but you should place a guard rail around the area to keep any child or animal from walking on the surface until it is dry.

Concrete laid in the open air or in direct sunlight should be covered with burlap, roofing felt or building paper during the curing period. Remove this protective covering before wetting the concrete.

Never attempt a big concrete job on an extremely hot day. Concrete sets extremely fast in direct sunshine. It's better to wait until mid-afternoon-even if this means you must work late into the evening.

Pouring a concrete pier

Determine placement of posthole and using a posthole digger, dig a hole one-half the exposed height of the post. Add 4" of gravel to the bottom of the hole for drainage.

Put the post in the hole and brace.

Add 6"-8" of concrete in the hole and tamp with a 2x4. Continue shoveling until the hole is filled. Give a final tamping. Add more concrete to the top so water will drain away from the post.

Pouring a fiber tube form

Place fiber form in hole, supporting a few inches above ground by nailing with 2x4s. Make sure it's level.

Insert the post and brace, making sure it is level.

Fill the form with concrete, make sure any trapped air is removed and crown the top so water will flow away from the post.

Let cure at least two days and backfill around the form. Cut off the exposed form with a utility knife.


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