Concrete Form Walls
Today with escalating construction costs it is getting more and more expensive to have concrete walls done by a contractor but don’t dive up hope. For simple walls, the process can be done fairly easily if you follow a few simple rules.
The availability of commercial concrete form rentals and inexpensive concrete ready-mix delivery to most areas has made it much easier for the typical homeowner to pour their own concrete walls. Good instruction is the only thing that is needed. The learning process begins with an understanding of the forming and pouring process.
All concrete walls are supported on a poured footing. This is a concrete beam that is pour on solid ground. Start by determining the size of footing you will need. Footings are usually eight to twelve inches deep and twelve to eighteen inches wide depending on the size of the wall and how many stories it needs to support. Check with your local building code official to determine the appropriate size.
Begin the forming process by laying out the dimensions of your footing with a string line and then excavating a level place on the undisturbed ground to pour. Make sure, if you have any corners, that everything is square and true. Then form your footing using the dimensional lumber closest to the depth of the footing. For example, if you want to pour an eight-inch deep footing it is usually ok to use a 2 x 8 piece of lumber.
This lumber can be secured with metal or wood stakes every couple of feet on the outside of the form and should have a 1 x 2 nailer across the top about every three to four feet to prevent the form lumber from spreading during pouring. Concrete weighs about three thousand pounds per yard and if the footing lumber is not secured properly the forms can blow out. This can create a real mess.
Most building codes require some reinforcing steel in the footing. This is most commonly two runs of steel reinforcing bar (rebar). Check your building codes for the local requirement. These rebars sticks can be laid into the concrete during the pour or elevated one halfway up inside the form on pieces of concrete block or stones.
Most supply centers that sell rebar also have special rebar chairs that will elevate the bar but these can be very expensive. Next, you must have vertical bars usually about every two feet to keep the concrete wall from sliding off the footing. These can be set in after the pour when the mud is starting to get hard and will keep them vertical. Another code requirement you may encounter is something called a keyway.
This is usually a two-inch by two-inch groove in the top of the footing that keeps the wall from slipping off. Keyways are not always required but they are easily created by supporting a well-oiled 2×2 in the center of the top of the form hanging from your 1 x 2 braces.
After you have set up your form and checked their integrity, it is time to calculate and order the concrete. Be sure and figure an extra 10 % concrete as there is always some wastage and you don’t want to run out at the end of the pour. When the ready-mix truck comes you can place the mud with the shoot from the truck or from a wheelbarrow.
After the mud is placed, level it by tapping with a heavy hammer on the outside of the form lumber and then screed or push the excess concrete off the top of the form with a 2×4 running perpendicular to the top of your form lumber. Scrape and shake this board across the form until the concrete is fairly flat and level. Then let your footing set at least several days before you pour a wall on top of it.
The Concrete Wall
After you have removed the form lumber from the outside of the footing, you are ready to set up the wall forms. If your footings are square and level this should be easy. For wall forms, you can build custom panels from plywood or rent out reusable forms. If you have never poured a wall before or are a beginner, I would recommend renting forms. The newer forms are fairly easy to set up and you can ask for detailed instructions.
These forms are usually well constructed and if properly assembled should never blow out or fall over. When a form wall blows out, you have to pull the forms and remove the heavy concrete, reset the forms and pour again. If you are not able to pour at the same time you will develop a cold joint. This is where dried concrete meets wet concrete and it will make your wall look bad.
Rental forms usually come in two-foot increments so if you are pouring a three-foot wall you will need to get a four-foot form and mark it with a nail or chalk to pour only halfway up. Set up your forms per the rental instructions and remember to check them again for integrity before you pour.
The next step is to oil the forms to assure the concrete does not stick to them. The form rental companies usually sell form release oil that works well. Additionally, you may also need to place a reinforcement bar in the wall forms but the rental instructions should tell you how to do this. Calculate the concrete you will need and again be sure and over order by at least 10% so that you don’t run out during the pour.
When you pour your wall the concrete can be placed by truck shoot or you can rent a concrete pumping machine for difficult access areas. It is usually best to place the concrete in the form in less than two-foot lifts. That means don’t try and pour one side of a foundation but work your way equally around the wall as you pour. The concrete can be consolidated in the form by tapping with a heavy hammer, using a wetter mix, or with the aid of a vibrating device called a concrete stinger.
Stingers are electrically operated vibrators that can be rented at most rental outfits. The vibrating head can be lower down the form and used to vibrate the mud causing air bubbles to come the surface. The stinger also creates a smoother finish against the forms but be careful not to over vibrate. Two or three passes every couple feet is usually good. If you over vibrate the concrete will start to segregate and you will lose strength.
When you reach the elevation at the top of the wall screed the concrete of the forms just like you did with the footings. If you are pouring a foundation wall you may also need to set J bolts in the concrete every four feet to hold down your treated floor plate. These can be handset when the mud starts to get a little harder and will support them vertically. Let the foundation forms cure at least a few days and then carefully strip them.
Sometimes the stripping process involves breaking form ties and scraping and cleaning the bleed lines on the forms. This is best done while the concrete is still soft. With the removal of the forms, you will also be able now to see any bubbles or flaws in your wall. If looks are important, these can be patched with a non-shrinking grout. If waterproofing is important research the best method of waterproofing your wall carefully and do not backfill until the wall has gained sufficient strength or you will crack it.
Pouring concrete form walls is a fairly simple process if you follow a few simple rules. Make sure everything you form is level and square and that the forms are strong enough to prevent blow out. Check local code ordinances for sizes of footing, the thickness of wall, and reinforcement required by code.
Use the best form system you can rent and be sure you understand how the forms go together, how they are oiled, and everything there is to know about the form removal process. Use the proper tools like pumping machines and concrete stingers when necessary. Remember what you create will be set in concrete.