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Home > Services > Forming > Walls

Wall Forms:
Wall forms are made up of five basic parts. They are as follows: (1) sheathing, to shape and retain the concrete until it sets; (2) studs, to form a framework and support the sheathing; (3) wales, to keep the form aligned and support the studs; (4) braces, to hold the forms erect under lateral pressure; and (5) ties and spreaders or tie-spreader units, to hold the sides of the forms at the correct spacing (fig. 7-29).

Wall forms may be built in place or pre-fabricated, depending on the shape and the desirability for reuse.

Wall forms are usually reinforced against displacement by the use of TIES.

Figure 7-29. - Parts of a typical wall form



Figure 7-30. - Wire ties for wall


Figure 7-31. - Snap tie forms

Two types of simple wire ties, used with wood SPREADERS, are shown in figure 7-30. The wire is passed around the studs and wales and through small holes bored in the sheathing. The spreader is placed as close as possible to the studs, and the tie is set taut by the wedge shown in the upper view or by twisting with a small toggle, as shown in the lower view. When the concrete reaches the level of the spreader, the spreader is knocked out and removed. The parts of the wire that are inside the forms remain in the concrete; the outside surplus is cut off after the forms are removed.

Wire ties and wooden spreaders have been largely replaced by various manufactured devices that combine the functions of the tie and spreader. Figure 7-31 shows one of these, called a SNAP TIE. These ties are made in various sizes to fit various wall thickness. The tie holders can be removed from the tie rod. The rod goes through small holes bored in the sheathing and also through the wales, which are usually doubled for that purpose. Tapping the tie holders down on the ends of the rod brings the sheathing to bear solidly against the spreader washers. After the concrete has hardened, the tie holders can be detached to strip the forms. After the forms are stripped, a special wrench is used to break off the outer sections of rod; they break off at the breaking points, located about 1 in. inside the surface of the concrete. Small surface holes remain, which can be plugged with grout, if necessary.

Another type of wall form tie is the TIE ROD, as shown in figure 7-32. The rod in this type consists of three sections: an inner section, which is threaded on both ends, and two threaded outer sections. The inner section, with the cones set to the thickness of the wall, is placed between the forms, and the outer sections are passed through the wales and sheathing and threaded into the cone nuts. The clamps are then threaded up on the outer sections to bring the forms to bear against the cone nuts. After the concrete hardens, the clamps are loosened, and the outer sections of rod are removed by threading them out of the cone nuts.

Figure 7-32. - Tie rod



Figure 7-33. - Method of joining wall form panels at a corner


After the forms are stripped, the cone nuts are removed from the concrete by threading them off the inner sections of rod with a special wrench leaving the cone-shaped surface holes. The outer sections and the cone nuts may be reused indefinitely.

The use of prefabricated panels for form work has recently been on the increase. These panels can be reused many times, thus reducing the time and labor required for erecting forms on the site.


Foundation Walls: A very good rule to fix the thickness of rubble-stone foundation walls is, that they shall be at least 8 inches thicker than the wall next above them, for a depth of 12 feet below grade or curb level; and they should be increased 4 inches in thickness below that point, for every additional 10 feet or less in depth. Thus, if the first story walls are 12 inches thick, the stone foundation walls would have to be 20 inches thick for 12 feet in depth, and 24 inches thick below that point for 10 feet or less. Rubble-stone foundations walls are seldom made less than 18 inches in thickness. A wall 18 inches thick is not always needed to carry the superimposed weight, but smaller walls are more expensive to build consequently are seldom constructed.

The thickness of foundation walls in all the large cities is controlled by the building laws. Where there are no existing laws, Table 1 will serve as a guide.

Stone Walls: The laws regarding the thickness of stone walls differ in the various cities, and no uniform rules can be given. For ashlar work, the New york law states that "where walls or piers are built of coursed stones, with dressed level beds and vertical joints the Department of Buildings shall have the right to allow such walls or piers to be built of less thickness than specified for brickwork, but in no case shall said walls or piers be less than three-quarters of the thickness provided fro brickwork."

The following regulations apply to the District of Columbia for rubble work: "Walls laid with rubble work shall be one fourth thicker than required for brick walls, but never less than 18 inches thick; they must be constructed with flat stone, sound and durable, laid on their natural beds, and brought to a level every 3 feet in height. They must be built between two lines, shall have bond stone or headers extending through the thickness of the walls at intervals not exceeding 3 feet, and shall be laid in cement mortar composed of 2 parts sand and 1 part of cement. No rubble wall shall be located as a party wall unless the written consent of the adjoining owner shall first be filed in the office of the Inspector of Buildings. The restriction as to location of the party wall above mentioned shall not apply to stone foundation walls which support brick walls."

For ashlar facing, the requirements for the District of Columbia are as follows: " Thin ashlar facing shall not be counted ted in determining the thickness of walls. If stone facing is used with bond courses alternately, not less than 8 inches thick, on the beds, the n such facing shall be counted as forming part of the wall, and the total thickness of the wall and facing shall not be required to be more than that herein specified for walls (meaning brick) but never less than 13 inches thick." that way. Nail your 2x6 down all the way around, along the chalk line. You are now ready to start the forming of the wall itself.

Form work for your forms should be 3/4" plywood. This will come in 4'x8' sheets with no holes for ties. You will need to drill holes in all the sheets for the ties to go through. The ties will hold both sides of the form work together at a set dimension while you pour the concrete. Typically, I will drill holes at 16" on center and start 8" in from each side. After drilling you will begin at a corner and nail the bottom of the plywood to the 2x6 "sill plate" with 8d box nails or roofing nails. Do the two pieces on each side of the corner first and nail the tops together, which will insure it doesn't fall over while you are putting up the next piece.

After you get the outside of the form up you will start installing your vertical and horizontal rebar. Start with your 3'-9" vertical #4's by tying them to the stubs we talked about in the Concrete Footing article. After this is complete install the horizontal #4's. On a typical 4' tall wall you should have 3-4 rows, of which the first will be about 3-6 inches from the top and the bottom one about 10-12 inches from the footing. Make sure to wrap the corners and not just dead end it, and also to overlap each new piece at least 12 times the diameter of the bar.

Before you start on the inside form you will need to "Stuff Ties" on the outside form. For this operation you will need to purchase ties that will hold the inside and outside form at the correct distance apart. These ties will need to be placed in the holes talked about earlier and 2 - 2x4s (whaler) placed on the outside with a locking cam to hold it in place (you will probably need to rent the cams or borrow from someone). Now that you have all the ties stuffed you can begin to hang your inside form. You will probably need to rip 8" off the inside corner form to line up with the outside form tie holes. As before, start at a corner and work around the foundation. After the inside form is set go back again and install your whalers and cams.

NOTE: What is described above is a typical method of forming a stem wall. Make sure to pre-plan everything. Did you make the wall a length that is divisible by 4? If not, where are you going to put the filler, and will the tie holes line up? How much do you need to rip off the ends to start a corner?

Pre-made forms come in a dozen different varieties and each has it's own benefits and problems. When selecting forms talk to your local concrete rental store to see what would be best for you.
Pre built forms are fairly easy to set. The same principles apply as the plywood forms, except that you will probably have fillers for most typical widths and pre made corners. Your concrete rental store should have installation directions and can answer questions. I would go into more detail but there are so many different systems that it wouldn't be very beneficial. Just remember - PREPLAN.

The last thing to do for your form work is plumb it and square the top. Again start at a corner and plumb the corner with a 4' level. Have some 2x4's and form stakes nearby. When you determine where the wall needs to go place your 2x4 bracing accordingly. Nail it to the top whaler and place a form stake a distance away that will allow you to nail the stake to the 2x4 bracing. Push and pull the wall until it is plumb and square.You are now ready to install your screed strip. A screed strip is a reference line that you can't miss when pouring concrete made of 1/4" x 3/4" pine or something similar. Use a builders level or a laser level to put a line around the entire inside form at finished concrete height. Nail the top of the screed strip at this line. I suggest putting it to the inside form so that it won't show after stripping and backfilling. Now when you pour the concrete you will have a good reference of exactly where to finish to.

Pour the concrete and finish the top level with the screed strip. After finishing the top of the wall place your anchor bolts 6" from each corner and 3' on center around the wall. Some say that 4' is good enough and it probably is, but I usually go with 3' or sometimes less. The anchor bolts will be used later to hole your sill plate down.

Stripping your forms is a simple task that involves popping the cams off and stripping the whalers off. Then strip the plywood or pre built forms off and break your ties off. If the wall will be exposed you can patch the tie holes back in later. Now strip your footing form work
The last thing you will need to do is waterproof the wall. This can be a pain, but is a necessary step. There are many different types of waterproofing materials; ask your local home building center what they recommend.

 

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