Step-By-Step Instructions For Concrete

 Many times, the average person uses the terms "cement" and "concrete" interchangeably without realizing that there is a difference. Even when the handyman refers to "cement," there is often a question as to exactly what he means. Before going into the details on mixing and various projects, here is a definition of terms:

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1. Portland cement is a manufactured product purchased in sacks that usually contain 1 cubic foot.

2. Cement is a mixture of Portland cement, sand and water.

3. Concrete is a mixture of Portland cement and sand with gravel added to give it strength and bulk, plus water.

4. Mortar is a mixture of Portland cement, sand and water with about 10% hydrated lime added.

5. Grout is a flowing mass of cement or concrete.

How Much of Each?

For most cement jobs - to set flagstones or patch a house foundation, you need 1 part of Portland cement to 2½'' parts of clean, fine sand.

For concrete jobs, the proportion varies depending upon the use to which the concrete is put.

For mortar mixes - for playing brick or concrete block or repointing brick - use 1 part mortar cement or 1 part Portland cement with 10% lime added to 2½^'' parts fine, clean sand plus water.

Basic Tools for Concrete Work

Here are several of the basic tools you need when doing cement or concrete work about the house:

1. General-purpose trowel - for placing cement or concrete when doing any concrete work.

2. Pointing trowel - for smaller repair and patching jobs and also finishing details, especially the joint between rows of brick.

3. Wood float - for finishing the surface, making it smooth but with a gritty texture.

4. Steel float - for finishing the surface, making it smooth, slick and hard.

5. Edger - for finishing sidewalks and large surfaces where rounded corners are desired.

6. Strike board - for striking off the excess of the concrete; it leaves the surface level.

7. Tamper - for removing air inclusions in thick sections of freshly poured concrete.

8. Broom - for finishing surface of concrete jobs with a rough, non-slip surface.

Making a Measuring Box

When doing any extensive mixing of your own cement or concrete, a measuring box is exceedingly helpful, especially when using large quantities. You can make this bottomless measuring box in just a few minutes and avoid counting the ingredients by the shovels-full.

Use ¾'' plywood or 1" thick lumber to make a box with four sides - a cubic foot - 12" high, 12" wide and 12" deep. Secure the sides with screws set about 2" apart. Two short lengths of 2x2 attached on the sides make it easy to move the measuring box about.

How to Mix

All the ingredients must be thoroughly mixed to do the job. If you have failed to mix the Portland cement with the other materials, you undoubtedly will encounter difficulty later; the job just won't turn out right. If you follow several basic rules, you will be able to handle cement and concrete like an expert.

1. Mix the cement or concrete near the place where it is to be used.

2. Mix the cement or concrete just before you are ready to use it. Once mixed, the cement or concrete begins to set.

3. You can mix cement or concrete in a wheelbarrow, on any concrete surface or on a sheet of ply-wood. However, once you have finished pouring the mix, wash the surface off completely so that no cement or concrete hardens and sticks.

4. It is best for the homeowner doing a job to mix about a half a bag of Portland cement with the needed amounts of sand and gravel (when making concrete). This is about the most convenient amount for a handyman to handle at one time.

5. Mix the Portland cement and sand thoroughly when dry. After these two are fully mixed you can add gravel when making concrete.

6. Only after the gravel is thoroughly blended in with the Portland cement and sand should you add the water.

7. Always measure the ingredients - don't just guess. As a guide, if you don't have a "measuring box," use a shovel to measure. Remember that 1 shovel of Portland cement is equal to 1 shovel of damp sand or 2 shovels of dry sand or 2 shovels of gravel.

8. Follow the formula necessary for the mix you are preparing. Cement and concrete used for different purposes contain different proportions of Portland cement, sand and gravel.

9. When mixing concrete, the size of the gravel you use depends upon the thickness of the concrete you are pouring. The gravel should be not less than one-fourth nor more than one-third the thickness of the concrete mass. For example, when pouring a 4" thick layer of concrete, use clean, hard gravel in sizes from ¼'' up to about 1" or 1½''.

READY-MIXED CONCRETE - Relatively new is the availability of already mixed concrete from local companies. The concrete is delivered in a special truck and is ready for pouring in place.

The handyman can also use another form of ready-mixed concrete; this is sold already mixed in bags. All he has to do is add the water. This ready-mixed concrete and cement is prepared at the factory. Here is all you have to do:

1. Empty the bag of ready-mixed cement, and mix it once more by hand while still dry.

2. Add water as specified on the bag. A good proportion is one gallon of water to 90 pounds of the concrete mixture.

3. Mix thoroughly using a hoe, shovel or trowel.

4. Use the mix immediately; in no case should wet mixture stand for more than 45 minutes.

Concrete Forms

Many home improvement projects you will undertake involve the making of a wooden form. These forms should be made of sound lumber, free of knots and decay. The lumber should be dressed or smoothed on at least one side because it is easier to remove and leaves a better finish. This is particularly important if the surface is to be painted afterwards.

If the cement of concrete will not be painted afterwards, you may use oil, shellac or varnish over the wood to make them easier to remove.

If the form is set in the ground, as for sidewalks, stake the outside of the form. But if the object you make is separate, as a stone for a walk, you can set the form on a sheet of tarpaper or roofing paper.

Always align the form to see that the tops are level. Also make certain that the concrete fills in all the form and that there are no "holes" in the mass.

The Curing Process

When a high degree of water-tightness, durability and strength is desired, the cement or concrete should be cured. Curing is a process that delays the evaporation of the water in the mix. It lengthens and intensifies the hardening process, which is simply a chemical reaction between the Portland cement and the water.

The curing process continues as long as water is present to hydrate the cement. If concrete is not moist-cured, the surface dries first, often just after finishing, and before hardening of the mass below. Thus floors, sidewalks and all surfaces subject to wear will last longer if they are moist-cured for several days. Moist-curing of all patch work is essential.

The curing process itself is very simple. The cement must be covered and kept moist. The covering material can be wet burlap, canvas or straw. It should be kept wet by periodic sprinkling for at least five days. The covering should be placed on as soon as it can be done without marring the surface.