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Concrete Footing and Pier Forms

Alternatives to conventional forming methods for concrete footings and piers

Tube formed concrete footing.

There are new alternatives to conventional forming methods for concrete footings and piers that are quicker and less expensive. For point footings, there are two approaches: rigid plastic footing forms, and a fabric "bag" footing form. For continuous strip footings there is a specialized fabric form held in place by a temporary structural system.

Typically a standard construction tube provides the form for a concrete pier. However, a special fabric alternative can also provide a suitable pier form when properly installed and braced.

Plastic rigid footing forms differ mostly in their shape, though there are variable sizes available, as well. Some are similar to the conventional block shape, while others are bell shaped with a round base. They have a circular opening on top to accept the concrete as well as to connect to the construction tubes above. Rigid footing forms have ribs to provide extra strength, and some have small holes to release air during the pour. Fabric "bag" footing forms are exactly what their name implies. They are flexible fabric sacks with a circular hole on top into which concrete is placed. The shape of the fabric form approximates a standard rectangular footing, but all edges are rounded with bowed sides, and the form may be installed on and conform to uneven ground. For footings that require rebar reinforcing, there is a form sack which has a zipper to open the top of the "bag" enough to get the reinforcing rods inside the fabric form before placing the concrete. Also, there is a foundation pier product developed specifically for manufactured housing that uses footing form bags as a key part of its design.

Fabric strip footing forms can be used for level and step footings, as well as for deep footings, and, they can be installed over uneven ground or rock, if structurally acceptable to do so. A temporary simple form must be built to which the fabric attaches to hold its shape while the concrete cures. This is made with a board for each side that defines the top edge of the form to which the fabric attaches, held at the required height and width by a special "yoke" support system. Long boards that hold the fabric in place must be stabilized laterally. This is achieved by regularly spaced metal stakes pounded into the ground along either side of the form. Once the concrete sets, the rigid formwork may be removed and reused, while the fabric form remains in place.

There is a proprietary foundation pier product called the 'Buttress' which combines the the fabric bag with a steel pier, and which has been developed specifically for HUD-code housing market.

For large pier pads, a system similar to the fabric forms for strip footings can be used. This system consists essentially of a sufficient area of fabric laid out over the ground with its side walls held in place by a temporary form system of "top-edge boards" and metal stakes, similar to the form described below for the strip footing system.

The fabric strip footing forms can be used for level and step footings, as well as for deep footings. And, they can be installed over uneven ground or rock, if structurally acceptable to do so. A temporary simple form must be built to which the fabric attaches to hold its shape while the concrete cures. This is made with a board for each side that defines the top edge of the form to which the fabric attaches, held at the required height and width by a special "yoke" support system. The major lengths of boards that hold the fabric in place must be stabilized laterally. This is achieved by regularly spaced metal stakes pounded into the ground along either side of the form. Once the concrete sets, the rigid formwork may be removed and reused, while the fabric form remains in place.

Fabric pier form material comes in 120' lengths, with diameters of 8" or larger. They are the shape of a tube with an attachment tab running down their length. Because they are made of a flexible fabric, the forms are flat before filled with concrete. The fabric is easily cut to length.


Affordability

The plastic footing forms offer the advantages over conventional wood forms of fewer materials and tools required, ease of installation, and significant reduction in labor time and skill.


Easy

The installation for the rigid plastic footing forms is similar to that for conventionally formed footings, but with fewer steps and without the labor and resources necessary to construct wooden form.


The plastic footing forms offer the advantages over conventional wood forms of fewer materials and tools required, ease of installation, and significant reduction in labor time and skill.


Not Applicable


Some plastic footing form products have had code compliance reviews by the ICC Evaluation Service Inc., and many comply with the Uniform Building Code (UBC), International Residential Code (IRC), and International Building Code (IBC). Code questions should be addressed on a case-by-case basis by the local building code authority.

The fabric form bag systems meet the performance requirements set forth in the Uniform Building Code (UBC), as well as standards set forth by American Concrete Institute (ACI). Fabric form systems for strip footings and extra large footing pads must be designed and approved by a qualified engineer. Any regulatory questions should be directed to the manufacturer and local code official on a project-by-project basis.

Codes should not be an issue for the fabric form because this is a temporary form system.


Not Applicable


Installation of rigid plastic footing forms is similar to that for conventional wood-formed footings, but with fewer steps, and without the labor and resources necessary to construct wood forms. Typically, modifications to the form itself are made first, such as adjusting the top opening size to match the diameter of the construction tube for the connected pier, and then attaching the construction tube to the footing form with screws or in some cases duct tape.

Excavate to the code frost depth, and prepare the area for the footing which must be placed on level, undisturbed soil or on 4" to 6" of compacted crushed stone or gravel. Follow by placing and leveling the footing form in the excavation. The usual procedure to backfill (without mechanical compaction / tamping) is completed before the concrete is placed. Another plastic footing form when inverted can function as a funnel for placing the concrete. Once the concrete is placed and the funnel removed, all potential settling and air pockets are removed by tamping or vibration and additional concrete, as necessary. Place three to four #4 or #5 rebar in the construction tube extending approx 6 in. below the bottom ring of the footing form.  The top surface may be trowel finished. If an anchor bolt is required, it is inserted at this last stage of installation, before the concrete has cured. Ridged plastic forms used below grade stay in place.

The fabric bag footing form is first spread out on the desired location, after suitable grade/base preparation. Then a small stake is driven through the center to act as a screed stake. If reinforcing is required, the zippered bag is used. The bag is unzipped, and reinforcement is placed within it before zipping-up the bag again. Next, the bag is filled with concrete. Stripping of the form is not necessary. Just like any concrete placement, timing must be properly coordinated with any connecting systems, such as a foundation piers that will be supported by the footing.

Fabric forms for large pier pads as well as for strip footings are installed similarly. First, stakes are driven into the ground at the outside edge of the footing location. Pairs of 1x4s or 2x4s are then attached to the stakes with screws or ring nails (the "yoke" support system is used where necessary to hold the wood form members). Next, the form fabric is laid out appropriately and stapled to the temporary wood form. Lastly, the concrete is placed, just as for any conventionally formed large pier pad or strip footing.

For the fabric form, first the tube is cut to the appropriate length. Then, the attachment tab on the form is stapled to a 2x4, cut to the height of the desired pier/column. Another 2x4 of the same length is then nailed to the first, locking the tab in place between them. Next, the 2x4s are braced into position (typically using other 2x4s in a "lean-to" configuration). Lastly, the fabric tube form is filled with concrete. After the concrete sets, the fabric is stripped away using a utility knife.


Varies with manufacturer.


The plastic footing forms offer the advantages over conventional wood forms of fewer materials and tools required, ease of installation, and significant reduction in labor time and skill. Some of the systems can be installed on a slightly pitched base and even allow some distortion in or cutting of the shape to accommodate protruding ledge or other obstructions. There is a wide range of prices for the various plastic footing forms, depending on the product, the size of the form, the source, and the number purchased. Prices can be reduced significantly if there are no shipping costs, if purchase is made in bulk or purchased through a national distributor.

The fabric bag form systems are easily transported as they are light weight, can fold flat, and can even fit in a large pocket. Because they are flexible, they can adapt to uneven ground. No wood, stakes or other tools are required, and the manufacturer claims that installation is simple and fast, not requiring skilled labor to complete. Finally, the bags prevent concrete leakage and allow above grade placement.

The manufacturer of the fabric strip footings claims a fast and easy installation ("unroll, staple, pour"), and that the fabric itself reduces dampness by providing a capillary break between the ground and the concrete. The amount of wood required for the form is drastically reduced, and what is used can be reused for a different application, as it does not actually contact the concrete. Fabric offers the benefit of flexibility to adapt to uneven ground, rocks or other obstructions. According to the manufacturer, the fabric form system is convenient to transport and work with given its light weight (120' of 10" tube weighs less than 15 lbs.), compactness (the 120' pack is the size of a box of nails), flexibility and ease of cutting to size and stripping away after the concrete sets. The manufacturer also states that the fabric tube may be braced easily and installed quickly, from start to finish.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.