Welcome back! If you missed part one we covered how to size and form a foundation along with starting basics. Let’s keep moving!
Rebar reinforcement. Standard is two 1/2″ rebar laid horizontally in the footing and one every 18″ in the stem wall. Rebar ends are joined by overlapping 40 times the width of the rebar, or 20″ for 1/2″. These are tied together at two or three points with tie wire. Local codes and specific structural conditions may require a different program, such as adding vertical pieces with an “L” bottom in the footing placed every two feet. Rebar can be bent for corners by doing it over your knee (not always fun), using the ball hitch on the back of your truck or SUV, or ideally with a cutter/bender. You will usually want to lay the footing rebar in the trench before form ties cut off access, meaning before the opposing form is set.- Bracing and squaring. To check square you can use the aforementioned 3:4:5 method, but also want to compare the diagonals of any square section. If your addition is 20′ out and 16′wide, you would place a mark back 16′ on each side. Then compare the diagonal measurement of the created square. Ideally they are within an 1/8 or 1/4″. If it is too late to make an adjustment a larger descrepancy could be tolerated. If you are using form ties to hold the stem wall forming together, you only need to run a stake to the form top on each side to stabalize your formwork. Without ties lower sections of the forming must also be supported by stakes.
- Pour day. We carefully measure and calculate the amount of concrete to order. Usually you will order a 5 sack mix with 3/4″ aggragate or what is equaivalent for your area. The dispatcher will ask you what slump you want, but you will confess what you don’t know and they will be happy to help you select. You need a plan for how you are getting the concrete to the forms. Can the truck drive right up? Will you carry it in wheelbarrows? Are you forced to bring it in 5 gallon buckets? You will want extra hands to help get your concrete placed quickly. Usually you will make one pass filling the footing and up into the stem wall to “seal it off.” A second pass will top off the forms. Sometimes you will add a little water to the mix (the driver will have water on the truck to mix in) for the walls after using a stiffer mix in the footing. To assure that the concrete mix is settling, you will work a stick up and down or rent an electric vibrator. You will want to tap the outside of the forms with a hammer to smooth out the concrete there. Don’t forget to put in your anchor bolts, closer together than code, for a good job.
- After pour. When the concrete is in place and you are congratulating yourself, go around and look for any place concrete has fallen against forms and remove it. It is amazing how little amounts of concrete once hardened can make form removal difficult. If your pour was early enough, you might be able to remove form stakes after a couple hours, saving a harder job later. This depends on all the factors, such as air temperature and amount of moisture in concrete, that determine how much your concrete has set up. In any case this is just removing the vertical form stakes which now penetrate the footing, while leaving the forms in place.
- Stripping forms. The next day, remove all form stakes and bracing and all wall tie wedges first. Remove top cleats and any attachment of form to forms. Use a tool to “cut an edge” where form top meets concrete to make sure removal of forms doesn’t take some of your soft concrete with it. You will continue to gently break the suction grip the concrete has on the forms. You want to be very careful in any prying not to mar the soft concrete where you are leveraging. As the formwork is removed, you will want to clean it up before stacking.
- Finishing. Look for places where concrete has built up too high such as around anchor bolts and remove with a concrete chisel. If there are any voids in the stemwall, where concrete didn’t fill in, fill these with redimix concrete if large (which would mean you didn’t tamp or vibrate well), or mortar mix if small. Clean everyything from inside the new structure. Backfill against stem walls and grade entire inside surface to a racked smooth level. You will also backfill against the outside forms and may want to do some grading for drainage now. If you are beginning construction immediately be careful, such as when tightening anchor bolt nuts and certainly when straightening an anchor bolt. Your concrete will be relatively soft for days.
If all of this overwhelms you, you may want to hire a recommended remodeling contractor or recommended professional concrete specialist for all or part of this vital process. Wasn’t this fun?
JR Mathwig Builders on HelpHive
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