2torial #0675:
Learn2 Mix Cement

Get in the mix

From setting fence posts to pouring footings to repairing old mortar--a little cement can go a long way. But first you have to know how to mix it. Before you call the professionals, read on. We'll take you through the tools and techniques of this procedure.

This 2torial details the steps for mixing cement by hand, which is a strenuous procedure. First off, the bags of mix are heavy--70 to 90 pounds (32 to 41 kilos). Add the muscle power needed to mix the material (and possibly the sand or aggregate) with water, and you have a pretty serious workout on your hands. For this reason, use these steps only if your project requires less than 10 cubic feet (3 cubic meters) of mixed material. Anything more and you should probably either rent a cement mixer (available at most building supply stores), or hire professional pourers with a mixing truck.

Given the physical requirements, be aware of safety. Don't overextend yourself when lifting, mixing, or pouring. Wear heavy-duty work gloves and boots. Also, cement mix contains somewhat hazardous ingredients, such as lime, so work in a well-ventilated area (preferably outdoors) and avoid touching the dry mix or the wet cement for any extended period of time. The chemicals can irritate or even burn your skin.

Understand the basics

Wondering what the difference between concrete and cement is, and where mortar falls into the equation? Mystery solved:

Cement is actually an ingredient, although most people interchange the word with concrete or mortar. It's the bonding agent that, when combined with water, sand, and aggregate (crushed, washed stone), creates concrete or mortar.

Concrete is usually a 3:2:1 mix of aggregate, sand, and cement, plus water. It's used for a variety of jobs, from house foundations to footings to driveways and sidewalks. This is what's being made in those giant mixing trucks. It's also poured into forms to create blocks that are used as building material.

Mortar is used as a kind of glue, for bonding brick or stone together, patching old, cracked mortar, or for plastering walls. It doesn't contain aggregate, so it's not as strong as concrete, but it does contain more lime than the concrete mix, which gives it a sticky elasticity.

Know your materials

Here are your choices for cement products and materials:

Pre-mixed concrete and mortar. You'll probably want to go with these, since the bags already contain all the necessary ingredients except water, so all you have to do is mix the two together. Be sure you buy the right material for the project, though--concrete mix doesn't work as mortar, and vice versa.

Note: If you're buying mortar mix specifically for brick, the bags typically come in different strengths, labeled as Type F (the strongest), M, or N. Ask the retailer what he or she would recommend for your particular project.

Portland cement. This is the straight cement ingredient, used if you want to make your own concrete or mortar from scratch. It's cheaper than the pre-mixed packages, and it creates more material in the end, but you have to add in the extra expense and work of buying the necessary sand and aggregate and mixing it in. But if your project is somewhat large (and you still want to mix it by hand) you'll definitely save on costs.

Masonry sand and aggregate. You'll need these materials only if you're mixing your own mortar (for which you'll just need sand) or concrete with Portland cement. Most building or garden supply stores will deliver them for you. Both are usually sold by the cubic yard (or cubic meter). Be sure you buy aggregate that's no larger than 1/2- to 3/4-inch in diameter (1 to 2 centimeters) so you can shovel and mix it easily.

Lime. This is the ingredient that gives mortar its extra holding ability. Portland cement and mortar mix already have lime in them, but if you need your mortar to be particularly sticky (such as for plastering walls or attaching the backs of stone to a vertical surface) you might want an extra bag of lime. It should be available at a building supply store. Check to see if the retailer recommends extra lime for your project, and follow the measurement directions carefully for adding it to your mix.

Set up your work area

Given the effort it takes just to mix cement, you'll want to cut down on any excess labor before you start the procedure, plus take a few safety precautions:

Make preparations. Have all the prep work done before you start mixing. This includes any digging or building of forms (the mold, usually made out of wood or heavy-duty cardboard, into which the concrete is poured to set).

Use a level surface. Avoid setting up your work area on an incline or an unstable surface. You'll be mixing in a wheelbarrow, which can tip easily, and you don't want to accidentally spill a mixed batch. (If you do have a spill, shovel as much as you can back in. If the spill is on dirt or grass, wait for the remains to dry, then rake them up. If the spill is on a paved or stone surface, hose the remains off while they're still wet.)

Keep materials close. Make sure your materials, as well as a water supply, are located as close as possible to your work project. You don't want to be lugging sand or cement bags across the yard each time you mix a new batch. Remember that most building supply stores will deliver your materials, usually if they meet a minimum weight requirement. If you decide to do this, be specific about where you want them put.

Keep materials dry before use. Keep cement bags--pre-mixed or Portland--away from all moisture until you're ready to use them. If you have to leave them out overnight, make sure they're resting on a platform (like a wooden pallet) off the ground, and are completely covered by a waterproof tarp.

Mix pre-mixed cement

Just add water, right? Actually, the process is a bit more complicated. Here's how it's done:

Add the mix. If you have a normal-sized wheelbarrow (2 by 3 feet, .6 by .9 meters) you can probably mix two bags at a time without too much trouble. Otherwise, just mix one bag at a time. To avoid a big cloud of cement dust when you open and pour the bags, place a bag so it's standing up like a cereal box on the flat bed of the wheelbarrow.

Next, rip open the top (there should be a marked tab to help with this), then gently push the bag on its side, so the open end points toward either the back handles or the front nose. Pull the bag away by its bottom. The mix should slide out without too much trouble. Repeat with the next bag, if possible.

Once you have the desired amount of mix, spread it out over the wheelbarrow's bed with your hoe and make a recess in the center down to the bed's surface.

Add the water. To avoid adding too much, use your 5-gallon (23-liter) bucket as a measurement gauge. One pre-mixed bag typically takes about 1.25 gallons (5 liters), so if you fill your bucket halfway, that should be enough water for two bags. Pour half of this amount into the recessed area of the mix. Note: The amount of water you use can depend on the weather. Heat, cold, humidity, and dryness can affect the ratio slightly, so go by consistency rather than exact measurements.

Mix to the desired consistency. Using your hoe, rake through the watered mix, back and forth across the wheelbarrow's bed. The mix is heavy, and it gets heavier with water, so you'll have to work hard to combine it smoothly. Dry mix can also get trapped under wet mix, so be sure you dig deep with your hoe to stir everything up. Chop up any clumps. Add the rest of your water gradually and be aware of the consistency you want for your particular project.

For concrete, you'll want a thick, slushy feel. The wet mix should slide off the hoe's blade when you pull it out. However, don't make it too soupy. If you've mixed all the material and water is still pooling on the surface, then it's probably a little too wet (add a bit more dry mix to fix the problem). Too much water won't weaken the concrete, but it will add to the time it takes to set.

For mortar, you'll want a stiffer, more granular consistency. The wet mix should stick to the hoe a few moments before it slides off. If it's too wet, the mortar won't hold its shape. It can dribble over and stain the brick or stone you're trying to set, or slough off the surface of what you're trying to plaster.

Apply. Whatever your project, be wary of dumping directly from the wheelbarrow, which can be hard to manage with all that weight. For concrete, you're usually better off shoveling the mix from the wheelbarrow to the spot. For mortar, use a trowel and a small board (called a mortarboard) to carry a lump of mix. Note: If the mix stays in the wheelbarrow for more than 10 minutes, you'll need to remix it and possibly add more water.

Mix Portland cement

The process of mixing Portland cement differs from pre-mixed mainly in the setup (since you have to add sand and aggregate). Keep these guidelines in mind as you start your work:

• For mortar, the ratio of sand to cement to lime (if necessary) is 3 to 1 to 1/2. Usually this works out to be about 12 heaping shovelfuls of sand, half a bag of Portland cement, and a quarter bag of lime.

• For concrete, the ratio of aggregate to sand to cement is 3 to 2 to 1. About 13 shovelfuls of aggregate, 8 of sand, and half a bag of cement should do it.

• Mix the dry materials thoroughly in the wheelbarrow before adding water. Use your hoe to do this.

• Add water to the mix, using the same techniques detailed in Step 4. Start with the same amount of water (about half a bucket), adding it slowly, and add more until you reach your desired consistency.

Whether you use pre-mixed or your own blend, knowing how to make concrete and mortar can pave the way for a host of home improvement projects. So get ready, get mixing, and watch it set.

-end-