How to Build a Club-Foot Concrete FoundationFitness Gear & Equipment
So you need a new garage or utility outbuilding? In your city or jurisdiction, you may be required to obtain a building permit and submit your building plan for approval, but after that, the first step must be to build a solid foundation for the new building.
It's time to think about footings. What do footings do? Well-built footings carry the weight of the structure and provide stability for the building walls. Properly built footings will ensure the structural integrity of your new building.
Many garages are built as slab-to-grade on standardized footings , perhaps 24" wide, 6 or 8" thick, and are usually reinforced with two rows of steel reinforcing bar ( steel “rebar” ) for strength. The building can then be built directly upon the footing, and a concrete floor is poured inside the building after it is constructed to the completed roofing stage. If no concrete floor is desired , the floor area may also be filled to the required grade with gravel and packed .
If your project involves a finished slab-to- grade, ( a slab built on grade or close to ground level) and want a superior result, however, the most efficient, strongest, and most convenient way to do the job is to build a one-piece "Club-Foot" foundation or pad.
The construction of a club-foot foundation involves forming the footing and the floor simultaneously as one unit, which is then subsequently cast in concrete.
Ordinarily, concrete forms for footings are built separately using two 2x10" planks, or form boards carefully set to width, grade and level. A clubfoot foundation is different. It is formed with one row of wooden planking or concrete forms set accurately, but around the outside perimeter only.
Here is how to build a clubfoot foundation.
1. Establish the location of the building, and set up " batter boards" at the side to establish the exact grade (height) of the finished concrete floor. Normally a garage slab on grade might be established 6" to 12" or even higher above the original grade, depending upon ground conditions. A planned increase in elevation may be required to ensure correct drainage around the pad.
2. Install pickets to delineate the approximate location of the corners.
3. Excavate all topsoil and soft organic soils from the enclosed area down to undisturbed mineral soils. Stockpile the topsoil so you can use it for subsequent landscaping as required.
4. Import granular "A" or a similar grade of granular gravel that will pack properly.
In your jurisdiction, your building code may specify the installation of crushed rock or other materials to a specific thickness. Use what is required, but in no instance use less than 8" of granular or gravel when packed with a plate packer unless you are building upon solid bedrock. Using an adequately packed gravel pad will reduce the likelihood of the concrete floor cracking at some time in the future.
5. Remember you are preparing for a combination footing and floor, so it is necessary to
" sculpt" the granular material to reflect the thickness of the footings, for instance, a 24" wide footing will be the same depth all the way around, and 24" wide, then starting from the INSIDE edges of the footing cavity, bevel the granular shallower toward the centre, packing the gravel to the correct elevation, which will be at the underside of the concrete floor, for example, 4" below the desired, finished concrete surface.
If your proposed footings are 8" thick, and your concrete floor is 4" thick, the final result along the outside edge of your concrete "club foot" should be 12" deep, with 8" or more of packed granular or gravel underneath it.
6. Set up the concrete forms. Using 2x6 pickets driven into the ground on the outside of the form, set the first plank level and nail it into place. Elevate or dig down the first corner as necessary to optimize and set the top of the form accurately to the correct grade.
Square the corner using the magic geometric measurements 3'-4'-5'.
Measure 3' along one side from the exact corner, make a mark on the footing board, and from the same corner, measure the second side off at 4'. When the corner is set perfectly square, the marks you have made will be exactly 5' diagonally from one mark to the other.
Use a carpenter's line to ensure the inside surface of the forms are perfectly straight, and the form planks or boards must be perfectly plumb, or vertical.
Using adequate 2x6 pickets and planking, set all subsequent forming in place. For a superior job, do not overlap the form planks, but rather butt the planks end to end, and scab the joints at a picket location with another plank on the outside of the joint. Alternatively, you may drive extra wide pickets carefully to support the joint locations, but using a support “scab” ensures the joint will remain straight.
Check the levels, preferably using a transit level. Careful use of a laser level or skillful use of a 4' carpenter's level can do a perfect job. You can use a garden hose full of water as a very accurate leveling device if you ensure there are no air bubbles in the hose.
Square the footing by measuring in "X" fashion diagonally across the corners. Both measurements should be precise and identical but reasonable error may allow 1/8" difference. Adjust the forms as necessary, and place them as accurately as humanly possible.
7. Brace the footing planking in place on the pickets by nailing it from the INSIDE of the planking to the pickets and shoveling dirt behind the planks on the outside.
8. Verify your forms are square, and always double check your grade level and position.
Correct as necessary adding extra gravel if required to ensure the bevel from the footing inward is uniform as called for in the plan. The bevel width should be uniform all around the footing. Raise the concrete form up, or dig it down as necessary, maintaining the required elevation and removing any extra granular as required.
9. DO provide a pathway for any electrical cable entrance necessary under the footing at this time if you plan to install an underground cable to the electrical panel inside the building instead of coming through the wall later. Put the cable in place, allowing adequate length to reach the electrical panel, or alternatively, correctly position a suitable conduit under the footing to allow the cable to be pulled in later.
Similarly, if any plumbing is desired, place the pipes to grade and under the footing, and install any drain pipes necessary. For a garage, be sure to check to see if floor drains are allowed in your jurisdiction !
9. Water the gravel heavily and pack it using a tamper or a motorized plate packer so the surface is smooth, uniform, firmly compacted, and sculpted to profile. Do not hurry this process; the better the granular is packed at this point, the less likely your concrete floor is to crack or fail at some point in the future.
10. Install 6 mil polyethylene on top of the gravel. Avoid the temptation to economize and eliminate this inexpensive step. Polyethylene sheeting installed under the concrete will keep the concrete floor dry. It will prevent water from soaking up through the concrete floor from the soil below.
11. Install 6" x6" steel mesh as required on top of the poly, or place steel reinforcing rod (rebar) on 12" or 16" centres as required by your design and plan, or as specified by code.
Wire- tie the rebar as recommended by your steel supplier. Install steel "beams", in the footing around the edges and tie in place appropriately with steel wire. The "steel beams" are usually specially formed short pieces of steel that are assembled using longer pieces of rebar to form an open skeleton or “rebar beam" that will sit in the footing cavity and be flooded with concrete.
12. Verify all measurements and adjust the rebar for elevation as necessary, ensuring that it is not laying on the polyethylene. Steel reinforcing may be lifted and blocked up using small pieces of concrete, brick or stone.
13. Identify the locations of all doors by marking on the concrete forms. Do not forget to install anchor bolts at 4' centres around the perimeter as necessary, and plan on beveling the concrete floor at vehicle entrance points, about 1' wide and the full width of any roll-up garage doors . Doing so will allow water to drain away from the garage door seal quickly, preventing the door seal from being frozen in ice and tearing off the door seal. Do not bevel the concrete at standard “man-door” openings.
14. Get the building inspector to to approve your work prior to pouring cement if required in your jurisdiction and make changes necessary.
15.. Before the concrete arrives, do have a rented "power trowel" on hand, and other tools such as a long-handled bull float, shovels, wheeled barrows, hammers, hand trowels and rakes necessary. Ensure that adequate help is available. Pouring concrete is heavy, tiring work. Work carefully.
Start in one corner, and as you pour the concrete, level it to grade (the top of the form planking) and tap the outside forms hard with a hammer to ensure the concrete settles smoothly against the forms to avoid "honeycomb" or holes in the finished concrete.
Ensure that no steel rebar is set too high, but take care to raise the steel rebar assembly up if necessary so that it is in the middle of the concrete pour.
"Screed" the rough cement surface to the desired rough level as you go using a handled screed, a suitably long 2x4, or equivalent dimensioned lumber. Add more concrete in spots if necessary.
16. Use the wide "bull-float " a long-handled metal or wooden float to rough-finish the surface to grade, and allow the concrete to "set up" for a while so that it will support the weight of the power trowel and operator. Power trowel the surface to finish, applying extra water if necessary.
Install 1/2" x 8" "J" steel anchor bolts on 4' centers around the perimeter where required.
17. Polish the concrete with the power trowel to acceptable finished condition. A top quality finish should show no “ trowel marks” or defects.
18 . Cover the new concrete pad with polyethylene to prevent the concrete surface from drying too quickly. Work carefully to avoid damaging the troweled surface.
*Note that after the first day, if the concrete looks dry, remove the poly, soak the concrete thoroughly with water, and reinstall the plastic cover. Leave it covered for a minimum of 7 days if possible to ensure the strongest possible concrete. Although you can begin construction on it much sooner, concrete reaches it's maximum strength after about 28 days and continues to get harder.
19. Pry off the forms carefully to avoid breaking the corners of the concrete pad. Fill any honeycomb holes with cement mortar and smooth. Consider pargetting (applying a thin layer of mortar to the visible surface) to correct any defects and improve the appearance if required.
20 Apply waterproofing and weeping tile around the bottom of the footing if required .
21. Get the final inspection if required, and fill around the pad with gravel as required.
Now you know how to build a clubfoot foundation! Admire your handiwork and don't forget to thank your helpers!
The next step is to proceed to lay concrete blocks around the perimeter for the base of your walls to the height desired, or get out the hammer, and start framing the walls!