Working with Concrete
Concrete is one of the most versatile building materials. It can be used for anything from entire buildings to portions of buildings, sidewalks, patios, post holes, steps and even decorative projects. Concrete work is also easy to learn, although it can be back-breaking.
The tools needed for concrete work include woodworking tools for building forms, a hammer, hand cross-cut saw, portable circular saw, measuring tape, square, level and string level, along with a small sledge and a maul. A pry bar is needed for disassembling the forms when the concrete dries. A builder’s transit or a laser level can make it easy to level or place a form to grade.
Concrete preparation tools are also required. The tools needed depend on the jobs you will be doing. Shovels and hoes are required for moving the liquid concrete around. Rubber hip boots are needed for wading in the wet concrete. For small jobs a wheelbarrow or mixing box are required for mixing the materials. A mortar hoe with holes in it makes it easier to mix the materials. A power mixer can also be mighty handy for small- to medium-sized jobs.
Concrete finishing tools include: a screeding board that is longer than the pour to pull the concrete off and level it with the form edges. A tamper can also be helpful in settling concrete in the forms. Other essential finishing tools include: an edger, groover, magnesium or wooden float, finishing trowel, pointing trowel, cement broom and a water hose. For larger projects such as floors or slabs, you’ll need a bull float with a bracket.
The Marshalltown Trowel Company models include an Auto-Just or RotaLeveler.
Marshalltown also makes it easy for the beginner with a Concrete Apprentice Tool Kit. It includes: finishing trowel and magnesium float (both with DuraSoft handle), wood float, groover, curved-end edger, margin trowel and a Marshalltown “Tips” book, all packed in a sturdy canvas tool bag. Suggested retail price is $138. For large projects, you may wish to rent a power trowel. The materials in concrete can irritate the skin so wear long-sleeved shirts, pants and gloves.
Concrete. A mixture of sand, gravel and Portland cement (this is not a brand name, but a type). Cement is available in five types, but Type I, which is carried by most building supply dealers, is the most commonly used type for homeowner projects. The materials must be mixed with enough water to form a semi-fluid state, which is then poured into a form. Concrete is heavy, and the single key to safe and effective pours of concrete is building sturdy forms. Concrete is available in three ways: individual bags of cement, normally packaged in one-cubic foot bags of 94 pounds that is mixed with separate gravel and sand aggregates; Quikrete, which comes in a bag, prepackaged with the required aggregates; and ready-mix, delivered by a truck to the site.
Quikrete. The most convenient for small projects, such as anchoring posts. Simply mix with water according to the package information and pour in place. Mixing your own with cement and aggregates is more economical, but you must have the separate materials on hand and measure them properly. This is also a good choice for small- to medium-size projects. Mixing with a powered cement mixer should be considered for medium-size projects. With this method you can, for instance, pour a wide walk in sections, forming one section, pouring it, allowing it to cure and then pouring another. For strength and performance, concrete pours should all be done at one time, unless they’re fairly large, in which case they’re poured in sections.
The cement, sand, coarse aggregate and water must be mixed in the correct proportions to create a durable, long-lasting job. There should be enough large aggregates (gravel) to make the mix economical. Yet there should be enough small aggregates to fill in the spaces around the larger aggregates. There should be enough cement to hold all the materials together, and there should be the right proportion of water to mix the materials and bind them together. The amount of water needed varies with the dampness of the sand. The less water used, the stronger the concrete, but there should be enough water to make the material workable. A fairly common mixture for foundations and footings is one part cement, three parts small aggregates and four parts large aggregates. Driveways, garage floors, walks and steps should be mixed one part cement, two parts small aggregates and three parts large aggregate. I like to mix with a square cement shovel. Just count the shovels full of materials, or you can use a bucket as a measuring device. The amount of water for average work, with slightly damp sand, is about 6 gallons of water per bag of cement. Finer pours, for basement walls, walks, garage floors and driveways with the same moderately damp sand would require about 5 1/2 to 5 3/4 gallons of water. Regardless, thoroughly mix the dry materials together first, then slowly add the water, thoroughly mixing as you go. You may find you don’t need quite as much water, or you may need more.
If building a floor, slab or foundation, the best choice is ready-mixed delivery. To order the correct amount of concrete, tell the supplier the width, length and thickness of the slab or foundation you intend to pour. They’ll help you calculate the quantity needed. On smaller jobs you can figure your own. The following chart from Marshalltown provides the basic information on cubic yards required:
Area in Square feet
(width x length): 10 25 50 100 200 300
4″ thick 0.12 0.31 0.62 1.23 2.47 3.7
5″ thick 0.15 0.39 0.77 1.54 3.08 4.63
6″ thick 0.19 0.46 0.93 1.85 3.7 5.56
When forming a sidewalk or slab, the first step is to dig up the area and remove all sod and debris. The area should also be recessed to the desired depth. For instance a 4-inch pour might be recessed so the top is slightly above ground level. The entire area should be well compacted and of a uniform depth. Also, keep the ground slightly moist, as well. The form is then constructed using 2-by-6’s. Drive stakes into the ground on the back side of the forms about every 3 to 4 feet apart. Drive or cut off the stakes flush with the tops of the form boards. Fasten the stakes to the form boards using duplex nails, or those with double heads so they can be pulled out after the concrete sets up. Curved areas can be formed with one-quarter-inch plywood or hardboard. Make sure the forms are level or of the grade desired. A carpenter’s level can be used for small projects, a string level can be used for long runs, but a builder’s transit is best for larger pours. Then establish a uniform grade using sand or fine gravel 1- or 1 1/2-inches deep.
First step is to build a form to hold the semi-liquid concrete material until it sets up. Good, solid forms are a must because concrete is extremely heavy. Shown are batter boards used with string to lay out a slab for a garage floor.
Duplex nails are used to fasten form boards together. Their double heads allow for easy dismantling of the form once the pour has been made and the concrete has set up.
A concrete walk is one of the simplest projects and a good “beginning” project. Shown is a typical form before the gravel or sand base.
A driveway or patio may have a “stiffener” edge to add strength. Note the use of gravel and steel reinforcing materials.
Concrete steps are another common concrete project.
If the slab is large, you will need to divide it into smaller, easily workable sections. Driveways and garage floors will need to be reinforced with steel rods or wire mesh.
This is a completed form for a garage floor. Note, the pour is on a slope, and the inerior has been filled with a rock/dirt fill. A layer of gravel will then be installed and steel reinforcing added before the pour.
Footings and foundations should also be reinforced according to local code regulations. Driveways and garage floors are usually poured 4 to 6 inches thick. Sidewalks and other works are usually poured 3 to 4 inches thick. Foundations and footings are poured to code.
Concrete footings and the foundations of buildings are a fairly complicated chore, both in building the forms and making the pour. Footings must follow regional guidelines concerning frost depth.
House foundations and basement walls require expertise and specialized equipment. The inexperienced should leave these jobs to the pros.
Making the Pour
Concrete should not be poured on extremely hot, dry days as the concrete will dry out before it can cure properly. Concrete should also not be overworked. For this reason the concrete should be spread evenly and quickly once the pour begins. Make sure to overfill the forms slightly. If the pour is overworked, too much water will be floated to the surface, which can cause scaling after the concrete dries.
Once the concrete is spread well over the area and into all corners and crevices, use a screed board to drag off the excess. This is a two-man operation and at best is hard work, especially on larger pours. The screed board should extend past the form edges at least 3 inches on either side. Beginning on one end of the form, place the screed board over the form boards and then, using a side-to-side motion and at the same time pulling the board, inch it across the form boards to the opposite end. Screeding levels the concrete with the tops of the form boards, pulling excess concrete off. Any low spots will be visible and should be immediately filled and the area rescreeded.
The next step is to float the surface. Small projects can be floated with a wooden or magnesium float. This helps fill any small voids and works the aggregate slightly below the surface. On larger pours a bull float is used. Push the float away from you across the surface with the front edge slightly raised to prevent the blade from digging in. Then pull the float back at an almost flat angle.
Use a wooden or magnesium float to smooth up the concrete and work the aggregate down. A bull float is used on larger pours.
The Marshalltown Rota-Leveler bull float bracket allows for easy changing of the float level on the push and pull strokes. Floating smoothes the surface and works some water to the surface.
Concrete finishing consists of several steps. Some steps should be done regardless of the desired roughness of the surface. Some concrete finishing results in either a roughened or a smooth surface. Regardless, the first step is to use a pointing or margin trowel to separate the edge of the concrete from the form.
Use a pointing trowel to “cut” the concrete edge from the form board.
Then use an edger around the top edge of the form. This creates a rounded edge that won’t chip off when the form is removed. The edger should be held fairly flat, but keep the front tilted up slightly when moving forward and the rear tilted up slightly when moving backward.
Use an edger to slightly round the edge of the concrete.
Jointing is the next step on projects such as sidewalks and driveways. This prevents cracking the slabs. Control joints are normally spaced at intervals equal to the width of the pour. It is recommended, however, not to exceed 10 feet in any direction without a joint. The joint should be cut at least one-fourth the depth of the slab. A jointer tool is used for this step. Place a straight-edge across the surface and run the jointer along the straight edge to create a nice straight line. As with the edger, hold the front up slightly when pushing forward. Control joints in large slabs can also be cut after the concrete cures, using a masonry blade in a circular saw or concrete saw.
Expansion joints must be cut in large slabs. A jointer held against a straight edge produces a nice, straight-line groove.
Next, use a float to smooth and level the surface. This will also help remove any marks left by the edger or jointer. For rough or textured surfaces, use a wooden float. For projects requiring a smoother finish, use a magnesium or aluminum float. Hold the float flat on the surface and move it in an arc, overlapping the arcs as you proceed. Don’t overwork the surface.
The final finishing step is troweling. Small projects can be hand-troweled. Marshalltown recommends a 14-by-4 or 16-by-4 trowel for most finishing jobs. The first troweling should be done with the blade held flat down on the surface. Again use the trowel in an arc, overlapping each previous arc by about 1/2 inch. The surface should be well troweled several times to produce a hard, durable surface. Allow the concrete to set up slightly for the additional trowelings. The proper time is when the sheen of water disappears and a footprint leaves less than 1/4 inch of an indentation. These trowelings should be done fairly vigorously and with the trowel tilted up slightly, pressing down on the “rear” edge.
The final step is to smooth the surface using a trowel.
A power trowel is the best choice for large slabs. These units can be rented at tool-rental outlets. Troweling will provide a smooth, hard and slick surface. These surfaces are easy to clean, but can be slippery when wet. Lightly brooming the surface with a shop broom after troweling can provide a rougher, more non-slip surface.
Keep the concrete damp for five to seven days after pouring. Do not allow it to dry out. Cover it with plastic sheeting and dampen the surface down every day or so.
Creating a “Brick” or “Country Stone” Project
One fun and unusual project is using concrete in special forms to create walks, patios and courtyards. The Quikrete WalkMaker form is available in brick or stone patterns and they also have cement color in brown, buff, red and charcoal to make the projects look more natural.
Place the WalkMaker level on the ground. (You may prefer to remove the turf first.) Mix the color with the water and then add it to Quikrete fiber-reinforced concrete according to the instructions on the package. Do this in a mixing tub or wheelbarrow. Fill the mold cavities with concrete. Smooth the surface on all edges with a pointing trowel until even.
Immediately remove the mold and move it adjacent to the section just completed. Repeat the process until the project is completed. Keep the surface damp for about seven days to allow the concrete to cure properly. After the entire project has cured for one week, sweep Quikrete mortar or sand mix between the bricks or stones. Make sure the materials are well packed down in the crevices, and then hose the excess off.
One very interesting project is texturing concrete to resemble any number of “masonry” materials using BonWay Tool texture mats. A plain-Jane concrete patio immediately takes on the appearance of anything from ashlar cut stone to London cobblestone or old Mexico tiles. The steps are simple. Finish the concrete in the conventional method. Add Bon True Color Hardener or Bon Ironex Integral Colors to the concrete (adding the latter directly to the concrete during mixing). Then apply Bon True Color Release Agent. Before the concrete sets up, tamp the texture mats in place. Wash off excess release agent with a pressure washer. Finally, apply Bon BossGloss or Boss Matte Clear Enhancer. “Voila” — an exciting new patio or walk.
Texture mat in use.
Additionally, companies such as Increte and Excellent Coatings manufacture cementious overlays that offer further color and texture options for concrete surfaces.
Contraction and expansion due to ice, frost, and hot and cold temperature variations can damage concrete, creating cracks and breaks. These days concrete repair is fairly simple due to a number of modern adhesive compounds. The most common is latex cement. Two agents are blended together to create a quick-hardening solution. Vinyl patch repair requires only to be mixed with water. Epoxy concrete repair comes in a kit with an emulsion, hardener and cement. When all three are mixed according to the instructions, the material is virtually impregnable and will bond to just about anything, including steel.
Regardless of the material used, it’s extremely important to clean all dust, dirt and loose materials from the area. Driving a few masonry nails into the area can provide “anchors” to help hold the material in place. Then mix the materials according to the package instructions. Apply and trowel smooth.
Concrete materials are heavy. Prevent back injuries when lifting bags by squatting and using your legs — not your back. Wear goggles to prevent eye injuries from splashing materials. Use a dust mask to filter out concrete dust. Wear waterproof shoes to protect your feet if standing in concrete. Wear rubber gloves to avoid skin irritation. Wear knee pads when floating or troweling.