© 2008 by Raymond Alexander Kukkee
Garage, Utility, or Workshop -Here’s how to build A Concrete Clubfoot Foundation
Do you need a new garage or utility building? You must obtain a building permit and get your building plan approved, if applicable, —but after that, the first priority must be to build a solid foundation for the new building. It is superior economic planning to build your project properly. Your garage floor will be much more attractive ten years from now if it is not riddled with huge cracks.
It’s time to think seriously about footings . Well built footings will ensure the integrity of your new building. Properly built footings and foundation work can easily last for a century or more. Why not do it right?
Many garages and utility buildings are built as slab-to-grade on “standard footings” that might be 24″ to 36″ wide, and from 10 to or 12″ thick, depending upon the size of the building, use, and design. Concrete footings are usually reinforced with a minimum of two rows of steel reinforcing bar (rebar) for strength. The building can then be built directly upon the footing with a concrete floor poured inside after the building is constructed and the excavation filled as necessary with gravel to the required grade.
There’s a better way.
When your intention is to have a finished slab-to-grade, (slab on grade or at ground level) and you want a superior result, the most efficient, strongest, and convenient way to do the job is to build a one-piece “Club-Foot” foundation.
A club-foot foundation involves forming the footing and the floor together, which is then subsequently all “poured” or “cast” in concrete simultaneously.
Ordinary footings are built separately using two sets of parallel planks, or forms set to width, grade and level. A clubfoot foundation is different. It is formed with a single set of planking or concrete forms set around the outside 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 of the finished concrete floor. Normally a garage slab on grade may be anywhere from might be 6″ to 18″ above the surrounding grade to ensure drainage.
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 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.
5. Remember you are building a combination footing, so it is necessary to ” sculpt” and pack the granular fill material to reflect the transition from the thickness of the footings to the underside of the pad. For instance, a 24″ wide footing will be the same depth all the way around, and 24″ wide, and the transition area would be 18-20″ wide beveled up to 4″ below the finished surface. Starting from the INSIDE edges of the footing cavity, bevel the granular fill up toward the centre over a width of 18″, packing the gravel to the correct elevation, which will be just under the established thickness of the concrete floor, for example, 4″ below the desired, finished grade of the concrete surface.
If your ” 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.
Building the Forms
6. Set up the concrete forms. Using 2×6 pickets driven into the ground on the OUTSIDE of the form, set the first plank and nail it into place. Elevate or dig down the first corner as necessary to optimize and set the top of the form to the right 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 plumb. (vertical)
Using adequate 2×6 pickets and planking, set all subsequent forming in place. For a superior job, butt the planks end to end, and scab the joints at a picket location with another plank on the outside of the joint. Alternatively drive extra wide pickets to support the joint locations.
Check the levels, preferably using a transit level. Careful use of a laser level or even skillful use of a 4′ carpenter’s level can do a perfect job. You can even 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 identical; realistically, they may be within 1/8″ difference. Adjust as necessary, as accurately as possible.
7. Brace the footing planking in place by nailing it from the INSIDE of the planking to the pickets and shoveling dirt behind the planks on the outside for additional support.
8. Verify your forms are square, and always double check your grade level and position.
Correct as necessary with extra gravel, 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 necessary under the footing at this time if you want to install an underground vertical cable to the electrical panel inside the building instead of coming through the wall later. Install the end of the cable, or alternatively, position a suitable conduit under the footing to allow installation of the cable later.
Similarly, if any plumbing is desired, place the pipes to grade and under the footing, and install any drain pipes necessary IF allowed to do so by the building code.
9. Water the gravel heavily and pack the granular using a “whacker” or plate packer so that it is smooth, uniform and sculpted to profile. Do not hurry this process; the better the granular is packed at this point, the less likely your garage floor is to crack or fail at some point in the future.
10. DO install 6 mil polyethylene on top of the granular prior to installing steel mesh or reinforcing bar. Do NOT be tempted to eliminate this inexpensive step. Polyethylene sheeting will keep the floor dry by preventing water from soaking up into the concrete floor from the soil below.
11. Install 6×6 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. Wire tie the rebar as recommended by your steel supplier. Assemble and install steel “beams”, in the footing around the edges and tie appropriately with steel wire. (The “steel beams” are usually specially formed short pieces of steel that you assemble using longer pieces of rebar to form a “box beam” that will sit in the footing cavity.
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. Mark where the doors are to be installed. Do NOT forget to install anchor bolts at 4′ centres around the perimeter as necessary, and DO plan on beveling the concrete at vehicle entrance points, ( i.e. 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 for ordinary 3′ entrance doorways.
14. Get the building inspector to to approve your project if required in your jurisdiction and make any changes necessary.
15.. Before the concrete truck arrives, DO have a “power trowel” on hand, and other tools such as shovels, wheeled barrows, hammers, trowels and rakes necessary, and ensure that adequate help is available. Pouring concrete is very 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 concrete.
Ensure that no section of rebar is “too high” or two low. Dig it down, or lift it up as necessary so that it is positioned in the bottom two-thirds or middle of the concrete pour.
“Screed” the cement surface to the desired rough level as you go using a handled screed, a suitably long 2×4, or equivalent dimensioned lumber. Add more concrete or remove extra in spots if necessary.
16. Use a 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 only if necessary. On humid days, the concrete will will take longer to ‘set up’ on the surface to a point where it can be finished properly.
17. Polish the concrete with the power trowel to finished condition. Hand trowel around anchor bolts and remove any excess concrete or lumps that will impede installation of wall plates or other wall-building processes.
18 . Cover the new concrete pad with polyethylene carefully to prevent it from drying too quickly.
*Note that after the first day, if the concrete looks dry, DO remove the poly, spray 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 build 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.
20 . Apply waterproofing and weeping tile around the bottom of the footing if required .
21. Get your final inspection and fill around the pad with gravel as required.
. Admire your handiwork and don’t forget to thank your helpers! Have a party.
There you have it. Now you can set up and proceed to lay concrete blocks around the perimeter for the base of your walls, or get out the hammer and start framing the walls! Don’t forget the gasket underneath the wall plates, and always use treated dimensioned lumber for bottom wall plates!
Now YOU know how to build a concrete clubfoot foundation for that garage, workshop, or utility building!
Is that Incoming I hear?