What Are the Correct Proportions for Cement Mix?

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Concrete is typically made of four components mixed together and poured or placed in a stiff, slurry form. This material goes through the chemical process of hydration, which hardens the concrete into a rock-like material. The proper proportions of the four components of the concrete mix are important in producing a workable material that is durable and looks good. The common proportions are one part cement to two parts sand and two parts gravel, based on volume.

Cement

Cement is a calcium product processed through a kiln in to a fine powder. Cement makes up the smallest part — 12 percent — of a standard concrete mix. The cement is the active ingredient that generates the chemical process that causes the hardening of the concrete.

Sand

Sand is fine particle inorganic material. For masonry mortar it is the principle fill material; gravel is omitted due to the size of the organics. Sand can be screened to remove larger stones or aggregate pieces. The sand should not include any organic materials. The sand component of the concrete mix is commonly about 34 percent.

Gravel

Gravel, also inorganic, is larger pieces of material. Think of it as small stones or crushed pieces of rock. The gravel increases the volume of the cement and provides strength. Gravel or crushed rock is sold in various sizes of stone separated by a screening process. Masonry mortar contains smaller pieces of gravel, if any, while cement for walkways or driveways could include stones up to 3/4 inch.

Water

Water reacts with the cement to cause the hydration or hardening process. Water makes up about 6 percent of the weight of the concrete although the amount is more commonly determined by slump tests rather than measurements. Cut out the end of a Styrofoam cup and fill with the concrete mix. Place the cup upside down on a dry surface and remove the cup. The concrete should “slump” to about half the height of the cup if it has the proper water quantity. If it slumps more than half it is too wet. If it doesn’t slump it has too little water.