How to Mix Bags of Portland Cement

Decide on the proportion of concrete, sand and gravel you will use in your project. For a typical driveway or sidewalk, you can use one part cement, two parts sand, and three parts gravel or crushed rock. For a smoother surface, you can add less gravel, although your concrete will tend to shrink more. The gravel acts as a filler and has little affect on the strength of the concrete. If you don't mind a rougher surface, you can even double the amount of gravel as a way to save on costs.

Get a concrete mixer if you are doing a large job. You can buy one for about $400, or you can rent one for less. A concrete mixer will save a lot of heavy labor and ensure a more even mix of your concrete, which will make it stronger. Get a wheelbarrow for small jobs that you plan to mix by hand. The wheelbarrow will allow you to move and pour the concrete more easily.

Read the instructions on the cement bag to determine to correct amount of water to use in the mix. As a general rule, never use more than six gallons of water for every 80-pound bag of Portland cement you add to the mix. Always use clean water, such as drinking water. You also must keep in mind that the sand and gravel may be wet and contain a significant amount of water, and you will need to add less water to compensate. Even dry-looking sand may contain some water.

Find out how much concrete your mixer or wheelbarrow will hold. If it will not hold the entire batch at once, you will have to prepare it in separate batches and figure out how much of each ingredient to add to each batch.

Pour about 75 percent of the water you plan to use for a batch into the mixer or wheelbarrow.

Add about half the sand and gravel you plan to add to the concrete, and mix it with the water.

Add all the concrete you plan to add to the batch, and mix it thoroughly.

Add the rest of the sand and gravel, and mix it until the cement is distributed evenly throughout the mix.

Add the rest of the water, a little bit at a time, until the concrete reaches the proper thickness. You should be able to slide a shovel or trowel through the top of the concrete and create a groove with a smooth surface that does not slide or cave in. If the surface of the groove is not well-defined, add more water. If the concrete is too mushy, add more dry ingredients. You may have some water left over at the end, if you used wet sand or gravel.

Mix the concrete for an extra two or three minutes before pouring so that it will begin to set immediately after you put it onto the mold.