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Do-It-Yourself Weekend Project #102
"How to Work with Concrete"

Tool and Material Checklist

Concrete mix, Garden hose, Level, Float, Hatchet, Tiling spade, Groover, Long 2x4's for screed, Line, Brush or broom, Concrete hoe, Pail, 2x4's and other material for forms, Edger, Rubber boots, Line level, Reinforcing mesh, Trowel

1. Determining How to Secure your Concrete

Concrete can be secured in many forms. Ready mix concrete, which requires only the addition of water, is the simplest to use. It is ideal for small jobs but becomes quite expensive when big projects are undertaken. Transit-mix concrete is delivered to you in revolving barrel trucks. This is the simplest and easiest way to buy concrete for large projects. However, you obviously have to pay for the delivery of the concrete and the convenience of premixing. Check local sources for prices on concrete of this type.

You-Haul concrete can be purchased in some areas. In this case you buy the concrete and rent a You-Haul trailer mixer for taking the concrete to the job behind your car. Again, you have to pay for the premixing and the rental of the trailer. Check locally for prices on concrete of this type.

No doubt the cheapest way to secure concrete for large projects is buying the dry ingredients and mixing them yourself. Of course, this requires a lot of work and the rental or purchase of the necessary mixers and other equipment. Figure the amount of concrete needed and make local comparisons of prices to determine which approach to purchasing concrete is best for you.

2. Making your Own Concrete

There are four basic elements in any concrete. These are Portland cement, fine aggregate such as sand, coarse aggregate such as crushed rock or gravel and water. The aggregates (sand and gravel) usually makeup fro 2/3 to 3/4 of the volume of any finished concrete. All aggregates used should be clean and free of organic matter. Water used for making concrete should be clean, free of acids, alkalis, oils and sulfates.

Although the ingredients in concrete are always the same, the results depend largely on the proper mix of these four elements. The intended use of the concrete you are pouring will determine the amount of water and other ingredients used in each mix.

For foundations or retaining walls, about 6-1/4 gallons of water will be used for each sack of cement if the sand is damp. However, if the sand is wet, 5-1/2 gallons of water will easily do the job. Concrete mixed for pouring sidewalks, stepping stones, slabs, etc. will require about 5-3/4 gallons of water per sack of cement if the sand is damp; approximately 5 gallons of water if the sand is wet.

If you are pouring heavy footings for walls where waterproofing is not a factor, you mix can consist of 1 part cement, 3 parts sand and 4 parts gravel. If you are pouring sidewalks, steps, driveways, etc. use 1 part Portland cement to 2 parts sand and 3 parts gravel.

You can measure the ingredients on small jobs by using an ordinary galvanized or plastic pail. A wooden box measuring 12 in. x 12 in. x 12 in. can be made to give you an accurate measurement for 1 cubic foot of sand or concrete.

A 3/8 in. half round can be nailed on one side of the box at carefully measured points. This will enable you to measure 1/4, 1/2 or 3/4 of a cubic foot. Always follow the mixing instructions on the bag when mixing any concrete.

3. Estimated Materials Needed

The following is a table giving the number of cubic yards of concrete required to pour slabs of different size and thickness. To use this table, multiply the length by the width of the area you plan to concrete. This will give you the square footage in the area.

Thickness in Inches
area in sq. ft. 4 5 6 8 12
50 0.62 0.77 0.93 1.2 1.9
100 1.2 1.5 1.9 2.5 3.7
200 2.5 3.1 3.7 4.9 7.4
300 3.7 4.7 5.6 7.4 11.1
400 4.9 6.2 7.4 9.8 14.8
500 6.2 7.2 9.3 12.4 18.6

Cubic yards of concrete in slabs of various thickness

Cubic yards of concrete in slabs of various thickness

Now, refer to the number of square feet and the thickness in inches of the slab you plan to pour. The figures on the appropriate line will show the number of cubic yards of concrete required to do the job.

For example, suppose you are planning to pour a patio 10 in. x 14 in.. This is a total of 140 square feet. Suppose you plan to pour the slab 5 in. thick. by using the table you find that 100 square feet of a slab this thick would require 1.5 cubic yards and an additional 50 square feet would require .77 cubic yards. Adding these two together you would find you will need 2.27 cubic yards of concrete to do the job.

4. Building the Forms for Pouring Concrete

Almost any concrete job will require some type of form. In some cases, forms are built above ground. In other cases, digging is required. Dig down to the desired level and build the forms to the necessary shape and size for the concrete job you are starting.

Use a few temporary posts to establish the proper grade or slope of the concrete to be poured. Nail the stakes lightly to the forms used or the forms can be temporarily clamped to the stakes with a C-clamp. Use a level to get the proper grade or slope of the concrete form. After the proper grade has been set, permanent stakes can be driven and the form nailed to them.

5. Pouring Concrete

After the forms are set, spray the entire area within the form lightly with a garden hose and pour in the concrete. After the form is filled, tamp the freshly poured concrete to compact it. This can be done either with a tamper or by putting on rubber boots and walking around the poured concrete area to make sure it is compacted around the edges.

Small concrete areas can be compacted with a 2x4. For larger areas, roller tampers can be rented. After the concrete in the form has been thoroughly tamped, use a straight edged 2x4 (used as a screed) for leveling the concrete. Work the 2x3 back and forth, saw fashion, to level the concrete at all points. A magnesium concrete rake with an extension handle can be purchased to reach concrete in hard to get at places.

When the concrete has set up sufficiently to support a 2x8 plank, use the plank as a straight edge to guide a

groover to cut contraction joints. Contraction joints are necessary to allow the hardened concrete to expand and contract in extreme temperatures. On sidewalks or other narrow concrete areas, such contraction joints should be cut every 4 ft.. to 6 ft.

On patios or other large concrete areas, expansion joints should be cut in each direction about every 4 ft. to 6 ft.. This can be done by using two lengths of beveled clapboard.A nail should be driven into the top of one board and both boards painted with motor oil They 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. The removal of the first board provides an adequate contraction joint for a large expanse of concrete.

6. Reinforcing Concrete

In some cases, concrete needs reinforcing with steel mesh. Regular fencing material with 2x4 or 2x6 mesh can be used. If the pressure on the concrete is to come from the top of the slab, the reinforcing should be laid deep near the bottom of the slab. If the strong point in the slab is at the center and the pressure will come one either end, the reinforcing should be laid as near the top of the slab as possible.

7. Different Ways to Finish Concrete

Concrete can be given a smooth finish with a trowel and a float. The float is used to smooth out the concrete on the first rubbing. A trowel is used to five the concrete a finishing touch. A light, swirled pattern can be created by holding a steel trowel flat against the surface of the slab and moving it around in a swirling motion, on the last troweling of the concrete.

For a heavier swirling imprint, use a wood float instead of a trowel and do the swirling while the concrete is till fairly wet. A soft pattern of parallel lines can be created by dragging a soft brush straight across a moderately wet surface. To achieve heavy lines, drag the soft brush across while the surface is still wet.

To achieve light texture lines of the same pattern, trowel the concrete and allow it to dry slightly before dragging the brush across. A very attractive and practical pattern can be placed in concrete by using an ordinary broom as a brush. Such brushing provides a rough finish that makes the surface of the concrete much safer when wet.

All brush strokes can be made in the same direction or each block between contraction joints can be brushed in opposite directions for a very desirable effect. An ordinary garage floor brush can be used to create extremely attractive wavy patterns, in newly laid concrete. The wavy patterns add to the appearance and make the surface sager when wet.

A flagstone pattern can be created by tolling the concrete after it has been leveled off with a float. A tool for creating the flagstone pattern can be made by cutting an 18 in. length of 1/2 in. or 3/4 in. copper pipe and bending it slightly.

The surface of the concrete should be troweled lightly and brushed after the flagstone pattern has been

placed in the wet concrete. Fossil like effects can be created along the edge of newly laid concrete by first troweling the surface and then pressing leaves into the freshly troweled surface along the edge.

Completely embed the leaves but do not cover them. Remove the leaves when the concrete is stiff. Brush away bits of concrete as the leaves are removed. Attractive ring patterns can be created by pressing tin cans or glasses of different sizes into the freshly laid surface.

The pattern can be created at random or specific designs can be followed. Keep rim of can or glass wet as designs are pressed into the freshly poured concrete.

8. Letting the Concrete Cure

All concrete must be given time to cure. During this curing period, the concrete surface should be kept wet down by repeated hosing with a fine mist. Such a hosing down process should be done at least twice during any 24 hour period for about three days. Concrete poured in a basement, garage or other under-cover area can be left exposed. However, a guard rail should be placed around it to keep any child or animal from walking on the surface until it is dry.

Concrete laid in the open air or direct sun should be covered with burlap, roofing felt or building paper during the curing period. This protective covering should be removed before the concrete is wet down. Never attempt a big concrete job on an extremely hot day. Concrete will set up extremely fast in direct sunshine. It is always better to wait until mid-afternoon even if this means working late in the evening.