Foundation Design: Pouring Concrete

STEP 1: First you must figure how much concrete you need in your foundation design. Most house slabs are 4” thick, or 1/3 cubic foot per square foot of area. The better you placed your fill sand, the closer your estimate will be to correct. If you are uncertain, it is a good idea to have the concrete company representative assist you. They are glad to help because they don’t want a disaster, either.

STEP 2: Multiply your area width by length to find the total square footage. If your house is 40 x 60, your square footage will be 2,400.

STEP 3: Then divide the square footage by the average depth of the concrete (4 inches in most cases). This would give you 800 cubic feet in your foundation design.

STEP 4: Then divide the cubic footage by 27. (There are 27 cubic feet in a cubic yard.) This would give you 29.63 cubic yards.

When you order the concrete you will tell them your expected total pour, when you want the first load, how much time between trucks, and what amount to pause at and wait for a final call back. If you are using a pumper you will tell them how you want the mix – what slump – and any additives required. The pump operator will help you with this, and the concrete companies are accustomed to working with them.

Word to the Wise: When pouring concrete you simply cannot have too much help. At a minimum, you will need one man on the boom or chute, three men helping place the concrete, and two men pulling the screed. With enough people, placing concrete is not hard, just heavy. Without enough people, you may expect disaster. Remember, concrete is a ticking time bomb and must be placed within a few hours, rain or shine, day or night. You will need shovels, concrete rakes, hand trowels, a four foot magnesium float, extension handles, water bucket, rags, trowel machine, gasoline, pick, 10 inch long anchor bolts – sometimes called ”J” bolts, and rubber boots.

Concrete is worked in steps in good foundation design – place the concrete, screed the concrete, float the concrete & finish the concrete. Each step must be accomplished within a time window.

Word to the Wise: Put less concrete than it looks like you need. Screed the section off and see how you did. If you need more, just place a little more. If you put too much there is only one way to make it less and shoveling concrete will exhaust a strong man fast!

STEP 5: Pull the concrete truck up to the edge of the forms, but not too close so as to influence them.

STEP 6: Discharge a very small amount of concrete to check the slump. Adjust if needed.

STEP 7: Chute the concrete out and pull it to the middle of the run.

STEP 8: Select a straight 2x4 for a screed board. With one person on each end of the board, with the board across the section, begin at the start of the section. Drag the screed board on top of the 1x4s to pull any excess concrete out of the way. If there are voids or low areas, add concrete as you need it. Use a concrete rake to push or pull the concrete in the foundation design. Use the hook on the rake to pull the reinforcing wire up into the concrete. Patting the board on the concrete and/or sliding the board back and forth will help level the concrete and bring the slurry to the top. The goal is to quickly level the concrete out and ensure that the correct amount of concrete has been placed for the foundation design.

STEP 9: Continue until you work out to the edge of the section.

STEP 10: Relocate the truck to the other side of the house and finish pouring the first section, working out from the middle to the edge of the foundation design.

STEP 11: Screed the second half off and then put one man to floating the first section, while the other folks start the pour on the second section.

STEP 12: Pour the second section, dragging the concrete to the middle.

STEP 13: As you finish screeding the first joint of the second section (the first ten feet or first length of 1x4) you will need to remove the1x4 screed board that is between the first and second sections before you move on. Using a claw hammer, pull the end near you up and tap the board to remove excess concrete from it. Then push or pull the board as needed to loosen the stake on the far end. Lift the board clear and throw it outside the slab area. At this point, don't worry that the 1x4 leaves a little dip.

Important: In the event that you can't get a stake out no matter what you do, you will need to drive it under the concrete. Use a 2x4 a couple of feet long set on top of the stake to hammer the stake down.

STEP 14: As you are screeding the concrete, keep a hand float with you or close to hand. When you encounter plumbing or other obstructions, use the hand float to work the concrete into place and smooth it out in the foundation design.

STEP 15: Continue this process until the slab area is full.

STEP 16: When you finish the pour you need to place the anchor bolts on all exterior walls, spaced four feet apart. Set the bolts about an inch and a half in from the form board and keep about 2 and a half inches sticking up out of the concrete. Wiggle the bolt once you have it placed to work the cement back around it tightly. Be careful not to allow any “pucker” of concrete around the bolt sticking up above level. If necessary, work it a little with a hand float.

STEP 17: Float the concrete using a four foot wide magnesium float. The float is used to work the slurry around and average the concrete level out. You will need several extension handles to reach all areas of the slab.

WARNING: The extension handles are aluminum, for strength and light weight, and you may well have a 20’ length assembled. Watch out for power lines!

As you work the float you can begin to smooth out the surface of the concrete. You may float the concrete two or three times in your foundation design while waiting for it to begin to set.

STEP 18: The final step is to finish the concrete in the foundation design. Finishing requires working the cement with a steel blade as it cures to produce a smooth, slick surface. A trowel machine is a gas powered machine that spins a set of blades to permit finishing larger areas. They come in several sizes but unless you are experienced using them, I suggest you use a 36” diameter machine.

When the concrete is hard enough, set the machine on the slab, beginning at the area that was poured first. Crank the machine and start it to spinning. If the blades are kicking up a lot of gravel and cement, it is too wet. The blades should generate a little slurry, but not cut into the surface of the concrete. You will continue running the trowel machine until all the concrete is hard and smooth.

Word to the Wise: If you have never worked concrete I strongly recommend that you hire a crew to pour and finish your slab. At the very least, if you and friends can place the concrete, hire a finisher to run the trowel. It will be money well spent. The expression “set in concrete” should give you all the warning you need. If you don’t get a smooth, level finish, it will give you major problems laying wood or tile floors.

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