THE RETAINING WALL FOUNDATION SYSTEM This recipe is based on using 1 1/8 plywood forms ripped from 4x8 sheets into halves. It incorporates Rapid Form brand clips and anchor bolt holders. It is based on my successful formula. It can be adjusted to suit with other systems and materials. FORMING THE RETAINING WALL FOUNDATION OUTER WALL Install string lines to the inner batter board screws. Strings for the foundation walls are placed on the inner screws at ¼ inside the home footprint, allowing boards to be installed at 1/8 to ¼ clearance to the strings. Ideally the concrete ends up inside the home footprint by at least 1/8. Layout the form boards and support stakes around the foundation as you proceed. It is helpful to lay a form board across the perimeter footings to aid in walking in and out without breaking the sides of the trenches. Leaving boards on the ground in the sun for an extended time in the sun will cause the boards to warp. A carpenter s level will not be very accurate so set up a laser or water level. You should already have the foundation elevation established and batter boards set at that elevation so set the level to that elevation. Lay out the first form board at a string line intersection or home corner. Drive form stakes about 18 from each end of the form board and one in the center at 1 1/4 outside the string line. To install the stakes plumb, hang them from your fingertips and install them level. Drive the stakes deep enough to support the form boards and steel, but not so deep they cannot be easily removed after pouring the wall. With help from an assistant, hang the first board inside the stakes, outside the string and support at roughly the string level. Starting at the stake closest the string line intersection; set the board at wall grade using the level. Install one screw at the top of the stake. Now level the board at the other end and fasten that stake. Now rack the board forward or back until the board is just inside the string line intersection and fasten the stakes at the bottom on the first board at corners only to isolate movement. Install kicker stakes on the outside adjacent each support stake, hold the form board clear of the string and then adjust to 1/8 to ¼ clearance. Push or pull the support stakes as needed and fasten kicker with a screw at the top of the form board. If the board bows in too much, kick the inside temporarily out as needed to keep the string clear. Install a splice to the end of the form board needed to couple the next board. Lay out the next form board precisely as needed to aid in correct placement of the support stakes. Install stakes, and hang the next board. While holding the board roughly level, fasten the next board starting at the splice, butting square and tight. Next level the board at the far end stake and fasten the stakes and splice. Beyond the corner board, install only the top screws in the form boards for now, allowing flexibility at the bottom for rapid form clips that will be installed later. Install kickers as before and continue the process as needed. At the end of the wall, allow the form board to run past the string line intersection as convenient to avoid cutting a board. Continue around the perimeter securing the corners with kickers outside and inside if needed. To square offset wall sections, measure all wall insets at each end from the end strings adding string inset as needed. Fasten corners with screws on the outside intersections.
Upon completing the outside forms, remove the inner and center batter board screws, leaving the outer screw for plate installation. Check the footing for proper clearance set up the laser level Hang strings plumb 1 ¼ outside the string set the fist form board at a string intersection Level the board at each end stake set the kicker stakes clearing the string
Install a splice for the next board join the next board INSTALLING THE REINFORCING STEEL Install 5 lengths of tie wire to the inside of the wall tying the wire to the top of each support stake with a single twist. Allow the wires to hang free inside for tying and supporting steel. Layout 3 lengths of steel or per plan, starting at a corner and lower it into the footing starting 3 from wall corner. Lift the top piece of steel and support with a tie wire 5 in from each end and adjust it to 3 below the top of the form board. The tie wire should go behind and under the steel, up the outside, over the top, around the back of the wire, back out the front and down to the next piece. Adjust the steel ensuring the 3 clearance from the wall corner. Finish tying the top bar and lift out and support away from the wall with 1x3 form stakes on edge. Next hang the center bar the same way at midpoint of the concrete but no more than 18 from any other bar. Adjust the bar to 3 clearance from the corner like above and finish tying. Hang bottom bar 3 to 4 from the bottom of the footing. Wire should go under the bar, up the other side, wrap tightly 4 or 5 wraps, use up extra wire wrapping around the bar or cut off as needed. The next set of bars can be started allowing 24 minimum overlap or 30 for worry free inspections. Hang the bars as before, adjusting the overlap as needed. At the corners, either cut the bars to size or place corner bends as needed. It can be easier to start new stock at the corner and use a 5 piece of bar bent 90degrees at the center for a corner joint and splice. Tie splices and bar overlaps and is tied with doubled wire at each end. Speed ties are good for this, but standard tie wire can be used doubled for strength. The vertical steel reinforcing bars can be added next. Typically, reinforcing steel is placed at 32 or 48 on center but check the plan. Mark the forms for correct steel placement. Cut steel to length from top to bottom rebar with an extra inch for securing. Some plans require 90degree bends on the bottom end. Tie the steel starting at ½ above the top bar. Tie steel to each bar, keeping bar plumb. After all the reinforcing steel are tied and in place supported away from the wall with wood stakes; the footings must be cleaned again. Ensure that 3 minimum clearance exists from any steel to soil. It may help to dig under vertical
reinforcing steel if extra clearance is needed there and the horizontal steel has good clearance. Remember to remove the wood stakes supporting the steel away from the wall prior to pouring. \
After the inner forms are placed and rapid form clips used, the tie wire is moved to the rapid form clips and adjusted for height. THE UFFER GROUND INSTALLING The UFFER ground is a length of re bar or copper wire in the foundation footing that works in place of the grounding rod to ground the electrical service entrance panel and home. Typically, a length of grounding rebar or copper is placed in the footing with 20 minimum in the trench and supported separately from the reinforcing steel. If using copper, I suggest #4 solid bare copper wire, which is good for up to 200amp service, in a 30 length allowing 20 in the footing, 2.5 to the top of the wall and 7.5 outside the top of the wall to tie into the house panel unbroken. It is crucial to know where the panel will be on the house and allow extra wire as needed. Support the copper wire on concrete dobie blocks to keep it off the ground and keep it clear of the other reinforcing steel. Rebar can be used for a UFFER. Use 2 lengths of 20 bar. Place a 90degree bend at one end each allowing a tail long enough to go from near the bottom of the footing to above the wall high enough to tie on with a copper lead to the service panel. The 2 lengths are placed with tails back to back and rods running in opposite directions. Using 2 bars allows the minimum of 20 in the footing as required.
INSTALLING THE INNER FORM BOARDS Start with cleaning the footings again. Most walls are formed at 6 wide. I like the rapid form clips to properly space the forms for correct width walls. Start at an inside corner, 6 from the inside of the corner. Layout stakes, boards and form clips. Using a form clip for a guide to install form stakes, drive stakes plumb at the outside of the form clip. Stakes go at 18 from each board end and one in the middle. Use a torpedo level to level across from the outside form board at each end stake and fasten the stake to the board with a screw at the top of each stake. Rack the first board into final position and add the bottom screws to the stakes on the first board only. Install rapid form clips to the tops adjacent each outer stake with a screw each side. Add a splice board and start the next board leveling by lining up at the splice and then the outer stake. Fasten the forms to the top of the form stakes and continue the process until finished. At the corners, add brackets or blocking to prevent the forms from blowing out at the corners. Upon finishing, install kicker stakes and fasten with a screw on top at the form board. Where footings interfere with kicker layout, install kickers angled as needed to solid ground beside the footings. Move the reinforcing steel support wires from the support stakes one at a time to the rapid form clips, which will provide the support and center the steel. The wire should go through the hole in the center, over the top adjusting the steel to 3 clearance, wrap around itself 4-5 times and use extra wire around re bar. PLACING THE ANCHOR BOLTS Consult the plans for correct bolt spacing. Often the bolts are spaced at 2 to 4 on center on the short transverse walls. Usually they are placed at 4 to 6 on center on the long or longitudinal walls. Bolts must be placed with the length of plate to be used in mind. Bolts must also start at 4-12 from the end of each plate board. Each piece must have a minimum of 2 bolts each with spacing as required by the plans. I like to use 16 plate stock and 6 wide on retaining wall foundations is common. Start by marking the wall in 16 intervals. Next mark each 16 interval into proper bolt spacing. For instance if 6
maximum spacing is required, place bolts at 6, 5 6, 10 6. 15 6, then from the next interval start over and complete the process around the foundation. Don t forget short offset walls and other places plate is needed. End one corner and start the next, starting back the width of the plate, such as 5 1/2 for 2x6 plate. I like to use commercial bolt holders such as monkey paws, or other holders that fasten to the wall. Install the bolts allowing proper clearance from the forms, usually 2 minimum. Bolts should be installed to a proper depth of 7 embedment, and enough bolt exposed to fasten the plate with a load bearing washer and a nut leaving 3 threads minimum exposed. Basically the bolt is set with the threads starting at the top of the concrete wall. Check the bolts for correct spacing at transverse and longitudinal walls. Ensure that each piece of plate will have a bolt at 4-12 from each end. When finished, clean the footings. A bolt had to be added where the anchor bolt did not have 4 minimum from the plate end. From the plate end, 4 to 12 is allowed for bolt placement. I use 10 in from each corner so that with either plate running to the corner, I am still within tolerance. Typically a 7 embedment will have the threads of a 10 bolt start at the top of the wall height.
Note the bolts at 4 minimum from the plate ends at this crawl space opening. The plate will stop at each side of the opening. The finished foundation ready for inspection should be clean, organized and look professional. Drain pipe for sewer A sewer drain pipe must be installed in a logical position determined by the drain layout on the house and the sewer hook up outside the home. The trench should start about 2 inside the forms and end about 3 outside the forms. Cut the trench across the perimeter footing so the sewer pipe will be at least 12 below finish grade. Level the trench to fall a quarter inch per foot. The pipe should be 3 ABS with a sleeve of 4 styrene pipe or foam pipe wrap to protect it from the concrete. On the inside the pipe should have a long sweep
elbow and a riser pipe for hook up later. Outside the wall the pipe will eventually have a 2 way clean out installed with a riser pipe high enough to cut back to finish grade later. After finish grading is completed cut the pipe below grade and install a clean out cap. The Foundation drain pipe If the foundation is the be back filled for a low finish floor height; grading the interior of the pad for drainage and installing a drain pipe to low ground is helpful to carry away unwanted water. At times a French drain is necessary or required to be installed outside the retaining wall. For the foundation drainpipe, install a length of styrene pipe through foundation wall at an elevation that will work with the grading to carry water out. Continue the pipe with at least 1% fall to low ground. If there is no low ground to drain the pad, a sump pump can be used. Sandy soil drains well and may not need any drainage considerations. Clay soils drain poorly and should have a drainage system. Inspection Install string lines for each row of footings and inspect the location or each footing. Inspect the form boards for proper bracing at joints, fastening at support and kicker stakes, clearance for the rebar, UFFER, footings clean and proper depth, ridge beam supports correct size and location. When the foundation has been fully inspected and passed by you, call in the inspection as directed by the permit. Stand inspection and have inspector sign off on the foundation, UFFER, setbacks, and any underground utilities that are ready. THE POUR Estimate your concrete volume using common geometry. A 12 deep x12 wide footing equals 1 cubic foot. Multiply the perimeter length by the footing value of 1 cubic foot 180 perimeter is 180 cubic feet. By using a 3 ½ slump mix, you can use up to a third less concrete on a perimeter footing. Next add the wall at 6 x24 equals 1 cubic foot multiplied by the perimeter length at 180 equals 180 cubic feet for the wall. Next add up the interior drilled pier footings and multiply x 3.14square feet for 24 diameter footings (Pie x radius square or 1 x1 =1 x3.14=3.14 square feet). For instance 60 footings at 3.14square feet equal 188.4 cubic feet. Add these valued for a total of 548.4 cubic feet. Divide by 27 cubic feet per yard to equal 20.3 cubic yards. Next determine a multiplier for waste based on footing condition and depth. Usually 10% to 20% is common. At 15% over the total is 23.3 cubic yards. Determine the size of the concrete trucks; 9 yards is common. Order 18 yards and a clean up truck (balance of the yardage needed as determined during the pour). Order a concrete pump and coordinate the rock and slump with the redimix supplier. Rock comes as pea gravel commonly used in a grout mix, a blend mix of pea gravel and ¾ rock and ¾ rock is standard. I prefer to use a ¾ blend mix which can be pumped through a 2 ½ minimum pump hose. The blend mix uses 5 ½ sacks of concrete per cubic yard. A grout mix can be pumped through a 2 pump hose and the ¾ mix requires a 3 hose which gets very heave and difficult to move. Slump is
a measure of the thickness. Picture filling a tube with concrete and removing the tube; how many inches the column slumps is the way slump is measured. Slump is critical. I order a 3 slump for the first truck which will be pumped into the perimeter footing to seal the base of the forms. The 3 slump is difficult to pump but reduces the yardage used by up to 1/3 in a perimeter wall since it stacks up nicely and seals the forms. Pour the perimeter footing just enough to seal the form boards at the bottom. I prefer a 4 slump mix for the balance of the interior piers and the wall portion of the pour. The 4 mix pumps reasonably well and makes a good finish product. More water nets a higher slump such as 5, 6 slump etc., which pumps and finishes nicely, however, it may crack excessively from evaporation and cause a homeowner concern. Next pour the wall just above the form boards and mechanically vibrate to blend the fresh concrete with the footing concrete. If no vibrator is available, tap each side with a hammer to settle the concrete. Use caution to not over stress the forms with the vibrator; make fast stabs in and out of the concrete since too much time with the vibrator may cause the concrete pressure to blow the forms. Have an assistant hand consolidate the wall with clean concrete as needed to top it off and fill voids on top. Screed the form boards at the top. Pour the interior footings with the remaining concrete and estimate shortage at between 4 and 8 footings per cubic yard depending on the overall size. 36 footings will require about 6 yards. Level the interior footings using a jitterbug tamper. Finish the foundation wall and clean around foundation bolts and rapid form clips. Using shovel, pull concrete away from the form boards to facilitate stripping the forms. Finish interior footings true and level using a swimming pool trowel if possible. Remove form support stakes as quickly as possible. Leave the forms in place for a few days. Poor a stiff mix to the bottom of the form boards with the first pass. I order the first truck with a 3 slump mix for the footing since it is thick enough to stack up and seal the footing yet can still be pumped. The mix in the photo is about 4 ½ slump and is flooding out from the bottom of the form boards. This costs a lot in lost concrete and labor.
The second pass fills the forms to the top. A 4 slump works well for the forms. One worker should quickly hand consolidate the top of the wall, filling voids by hand staying within reach of the pump hose. If necessary, an electric vibrator is used to consolidate and settle the concrete. Make quick stabs every couple feet. If you spend too much time, the concrete can blow the forms apart. In lieu of a mechanical vibrator, a hammer can be used to tap the forms for settlement with pretty good results.
A worker must quickly follow with a wood trowel to screed or strike of the concrete to grade while staying within reach of the worker consolidating or vibrating. A worker must quickly follow up with a finish pass using a steel trowel and staying within reach of the worker who is screeding. This worker should clean around the anchor bolts as he goes. After the wall is poured, the interior piers are filled and jitterbugged into rough level and then troweled smooth and level.
The excess concrete must be pulled away from the forms unless you would like to jack hammer it out later. Go fully around both sides and make sure the forms are scraped to the bottom. This work can be nearly eliminated by using a stiff slump such as 3 or 3 ½ slump for the perimeter footing. When using a 4 slump or higher for the perimeter footing, the concrete flows up and around the form boards. The vertical stakes must be removed now before they are stuck for good. Remove the screws and pull the stakes. Stakes can usually be pulled by hand or with a stake puller if necessary. Wipe them off and bundle them up for storage. FOUNDATION FORM STRIP & PLATE Listed below are items needed before completing a Foundation Form Strip & plate. Form Stripping Items Drills & Batteries (with Phillips bits) Flat Shovels (for scraping form boards) Mortar Patch Mortar Pan Mortar Trowel Duct Tape (to wrap stakes) Claw Hammer
Cement Finishing Block Jack Hammer Platting Items Pressure treated Plate (2x4 or 2x6) (verify quantities) 5/8 Nuts (verify quantities) Baring Plates (verify quantities) Sledge Hammer Corded drill Paddle Bits (11/16) Impact Wrench & 7/8 Socket Generator Extension Cords Skill Saw Builders Square & Pencil Chop Saw String Line STRIPPING THE FORMS When the concrete has set enough to remove forms (about 1day in hot weather, and 3 days in damp weather) you may begin stripping forms. First remove any remaining kicker stakes, fully removing the screws as you go and lean the stakes against the wall for easy pick up. Bundle the kicker stakes and put away. Remove the screws from all rapid form clips top and bottom. The rebar support wire must be snipped on the top rapid form clips. Remove all the rapid form clips from the top of the wall. Start pulling forms from the inside of the wall testing the concrete for surface strength. If it is not ready stop and resume later. If it is ready, proceed from the inside removing form boards, then the outside. The form boards must now be scraped clean of concrete both sides and edges. Spray diesel fuel or another form release agent on the boards as you put them away. The concrete surface should be inspected for rock pockets and damage. Proceed now with mixing mortar. Patch any significant rock pockets and holes in the wall. The mortar patch should be done within 8 days of placing the concrete in order to adhere to the curing concrete. Blade off the excess mortar as it sets. Next brush the surface with a burlap sac. This will help to blend the color in with the wall.
INSTALLING THE SIL PLATE The plate can be fit to the wall after stripping; however, the bolts should not be tightened more than snug until the concrete has set for 8 days or more. Tightening the bolts prematurely may cause failure of the concrete. Put the strings up on the outer batter board screws. Lay the plate out with concern for the corners and bolt layout pattern. Keep in mind the plate must have a bolt at 4-12 from each end. With a helper, hold the plate in position on top of the anchor bolts, leaving 1/4 clearance to the string line. While holding the plate firmly and precisely, strike the plate with a hammer to cause indenting by the anchor bolts. Repeat this process at each bolt checking the string line clearance at each bolt. Turn the plate over and drill the plate at no more than 1/8 diameter greater than the bolt diameter. Be careful and accurate to avoid having to open the hole excessively. Fit the plate section and fasten with a proper load bearing washer and nut. Tighten only to snug until the concrete has set 8 days or more. Proceed around the wall, keeping layout in mind. Check the plate for square, width and length in various locations. Ensure the plate matches the footprint of the home and the additional width gained at the marriage seams. With the plate on and fastened, double check all dimensions and make corrections as needed. Now the batter boards may be removed and put away.