Planning on doing some pouring, but don’t know much about building forms? Or maybe you just want to know more about the subject?
Concrete forms are the most important thing doing pours, you’re left with a lump of nothing without them. The formwork is the mold for concrete and creates the shape of the concrete using a series of wood, composites, or steel forms.
Formwork not only holds the shape of the concrete as it dries; it also bears the weight of the pressing concrete. That’s why it must be built strong to resist the weight with supporting structures. The weak form will result in tears and curses so it better be done well.
The basics of formwork begin with the blueprints. A simple sidewalk requires the least of drawings and thus the least of formwork and materials. A complex two-story stem wall requires multiple pours and deep footers. That’s why it requires a complex blueprint and a complex set of forms, with multiple materials.
Know your limits when doing and concrete work basics. Remember, you can only pour concrete once as it has its own working time. Once it starts the curing process and hardens, it will be really hard to remake it.
With that disclaimer in mind, basic footings that adjoin the house are best left to the professionals. Any slab that bears weight or is on sloping land is going to have a footer.
How to build wood concrete forms
Slabs like a detached or abutting patio, sidewalks, and driveways all need no footer and can be done by the average homeowner. Simple sidewalks and driveways need no excavation (except for grass and surface roots). Learning how to build wood concrete forms will help you in many different home projects as well like building concrete countertops.
Concrete forming supplies
Forms made from pressure treated 1×4’s, or plywood, are placed on the surface of the ground and held in place with stakes. Making your own stakes is easy and can be done by ripping a 2×4 precut stud in half with a circular saw.
Using a miter saw, cut four 45 (or 52 if your saw has it) degree angles one end of each half of the ripped boards. Then cut the other end square to length as needed into thirds or halves.
Long runs of 1×4 stock are easy to bend and curve to the landscape as needed for driveways and sidewalks. while using 2×4’s work best for rigid straight lines on rectangular and square slabs. Tighter curves require different materials. 1×4 pieces of a hardy plank or other cementitious siding boards flex quite a bit when bent at radiuses and arcs. Scoring the back of the form with vertical lines will help increase the bend into an even tighter radius.
Estimating concrete amount needed
Concrete work from a hobbyist perspective can be a difficult process, even if it’s just a small amount to pour. That’s why it’s important for the average homeowner to learn the basics of each particular process of concrete from beginning to end. This will ensure that everything comes out right the first time. You don’t want to end up short of concrete on your big day.
The first step is to use the blueprint or drawing of the actual dimensions of the slab. These dimensions are length, width, and height or thickness of the slab (add ¼” for waste). Now multiply these dimensions and you get the square footage amounts. To get the concrete yardage, simply divide the answer by 27 and you get the correct amount of concrete needed for your slab.
Odd shapes can sometimes throw a loop into the mix when estimating concrete. Where diagonal lines meet perpendicular lines, confusion can ensue. A driveway apron where it meets the road is a prime example. Calculate the average distance between the largest and smallest measurement of the diagonal area.
For example, if a driveway measured 20 feet wide at the road and 16 feet the rest of the way up the driveway, the mean measurement would be 18 feet wide for the diagonal section that abutted the roadway and 16 feet for the remaining driveway.
Breaking concrete slabs into a square and rectangular sections work best when estimating complex-shaped slabs. This is especially true for footers. Footers will also need to have rebar calculated into the picture.
Simply add the width and length of the slab to find the area and multiply it times two. The sum is the number of square feet you need for rebar. It must be divided by 20 since rebar comes in 20 foot long sections.
Depending upon the size of your concrete pour, you may want to use bags or ready-mix delivery service. The basic rule of thumb is a ready-mix will only bring out a truck if the delivery size is at least within 50 miles of their yard. Also, it needs to be more than three yards and adequate access is available for the truck to deliver the mix. A concrete pump can be rented for hard to access areas.
If you have less than three yards of concrete getting bags is going to be your best bet. When your pour is close to three yards, you may want to rent a concrete mixer to mix all the bags. It will help in completing the pour in a fluid motion. Bag amounts come in 40, 60, and 80-pound sizes.
The best way to work with the mixer is to have a dedicated mixing spot with the mixer, water, and bags available. That way you can leave the mixer rolling with water and ready to mix concrete in it while you empty your bucket/wheelbarrow in the forms.
As always, knowing your concrete forming basics will help you to achieve better results. Wood forms for concrete are quite easy to build on a small scale, the bigger it gets the more math is involved.
If you’re interested in alternatives, there is an article here about Insulated Concrete Forms, where insulation is used to make the forms and these are not removed. It’s more costly, but it provides some benefits with heating for example.
This guide can be taken as a general direction on how to go about it, being a basic guide. It’s good for building small concrete slabs.