Mixing Concrete

by Sr. Mixalot

Mixing concrete details, You have several types of mix to choose from: you may buy the cement, sand, and gravel and blend them yourself by hand or by machine; you may get the sand and gravel already mixed. Requiring only the addition of cement: or you may buy all three ingredients premixed delivered to your doorstep ready to pour in place.

Hand Mixing Concrete: You can produce first-class concrete by mixing it yourself on a platform by hand. It is slow, hard work, though, and best suited to small jobs or piecemeal laying of a large area. You will need a pail marked off to show gallons and quarts: two shovels, one for mixing dry materials, the other for blending wet and a large flat surface to use as a mixing platform. Build a makeshift platform 6 or 7 feet square of old lumber. Don't use lumber that is badly warped or full of knots, for it will let cement and water trickle through and weaken the concrete. An old square of plywood makes a good mixing surface: some home masons mix right on their driveways. Heap the mixings on the board, one shovelful at a time, keeping the proportions in line with the formula and blend the ingredients together. For each shovel of cement, figure about 3 quarts of water (based on an average of 6 to 7 shovelfuls of cement per sack).

To save effort, learn to use the shovel with a rolling motion, turning the ingredients under with the blade. You will find this less tiring than the scoop-lift-dump method. After you have thoroughly blended the dry aggregate and cement, scoop out a hollow in the center of the heap, and fill it partly full of water. Mix in the water by working your way around the edge of the puddle with the shovel, rolling the dry mix into the water with the blade. Be careful not to break the dam, for if much cement and water escapes, the batch will be weakened.

If you are stocking with the separate ingredients, first make a trial batch to test the workability of the formula. The mounds of sand and gravel that you bought are certain to contain enough moisture to require you to vary the formula slightly. To make the test batch, spread 2 1/4 shovelfuls of sand on the mixing board and add 1 shovelful of cement. Blend together until no gray or brown streaks remain. Then spread 3 shovelfuls of gravel over the cement-sand mixture, and blend until the gravel is evenly distributed. Scoop out the center, pour in 3 quarts of water, and mix it in. If the trial batch is too soupy, add a small amount of sand or gravel. If it is too stiff, cut down the quantity of sand or gravel in the next batch and proceed with the jolt, mixing hence-forth to the -adjusted formula worked out in this batch.

Machine-Mixing Concrete: old timers will tell you that there is a limit to the amount of concrete that you can comfortably mix at one time on a board. They recommend that you rent or borrow a portable mixer and a large wheelbarrow. Most efficient mixer for a one-or two-man job is the half-bag machine. These are resolved by gasoline or electric motors or by hand. If you have the choice stay assay from the latter—they're not much fun, although turning the crank is easier than shovel-mixing.

Toss into the revolving drum 1 cubic foot of sand and ½ sack of cement. Allow them to mix until the blend is free from streaks of brown or gray. Add 1 1/2 cultic feet of gravel and continue mixing until the pebbles are uniformly coated. Then, empty 2 1/2 gallons of water and allow the wet mixture to tumble for 2 or 3 minutes. Finally, pour into a wheelbarrow and dump into the forms. This load should cover about 8 square feet of 3-inch paving, 6 square feet of 4-inch, 4 of 6-inch.

Ready Mix Concrete: If you have a vast amount of concrete to pour, you can pass along the labor of mixing to the concrete dealer by ordering "ready-mix" or "transit-mix" delivered to your backyard. Ready-mix is prepared in a giant truck with a revolving drum that mixes it while rho truck is on its way to your home. Surprisingly, concrete in this form usually costs about the same as the home-made variety; There is a "catch," though. Transit-mix companies will not usually deliver less than a cubic yard (enough for about 100 square feet of 3-inch paving) and they charge penalty rates if the truck is not emptied within a short time. There is also a limit to the distance that the companies will carry the wet concrete (usually 114 to 2 hours' drive from plant).

There are further considerations to be weighed before inviting the truck into your garden. For one thing, the truck carries more concrete than one person can lay. It can spend a half hour in your yard and remorselessly empty enough plastic concrete to keep you and several willing neighbors hopping for the rest of the day. If your patio is inaccessible from the street—uphill or down too steep a slope—you must forget the idea. If your lot is laid out so the truck can back its stern close to your patio, you had better find out if your driveway can support the heavy load. Planking the driveway with 2x12's should prevent its cracking under the weight. Planks can also be used to form a roadway across a lawn—but a dry lawn, by all means

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