What to Know About Concrete Forming and Forms

Planning a new concrete project for your property? Concrete’s durable nature makes it a frequent pick for a new patio, a raised flower bed, a foundation for a greenhouse, and plenty of other projects. However, concrete needs a firm hand, and that’s where concrete forming proves useful. Forming is a reliable way to create a framework to contain concrete as it cures, keeping it level, stable, and crack-free. Read on to learn the secrets of concrete forming and what your project may need.

What Is Concrete Forming and When Is It Used?

Concrete forming is the process of creating strong frames to hold the concrete in place as it sets after being poured. They also hold reinforcements like rebar in place to add strength to the concrete once it cures. Most concrete projects require forms before you even order or mix the concrete. Otherwise, the concrete alone can’t hold a form and will collapse into a blob before it begins to cure.

Forms for concrete don’t need to be pretty, but they do need to be tough. A single square foot slab of concrete typically weighs around 150 pounds. That’s a lot of pressure pushing against the framework, so forms need extra strength to hold the concrete in place.

While you can buy prefabricated concrete forms, these are typically reserved for commercial users. Home-based projects use timber to create on-demand concrete forms that make disassembling easy when the job is done—often around two days after you pour the concrete. Concrete forming helps create things like:

• Patios

• Driveways

• Terraces

• Garden or berm borders

• Pathways

• Retaining walls

• Slab foundations for new buildings

• Concrete countertops or workbenches

Different Types of Concrete Forms

There are a few different types of concrete forms you can use, and the finished product and your long-term goals will help you decide which type of concrete form is right for you.

Wood Forms

Almost all home-oriented forms are made from timber and screws, affordable materials you can find in any home improvement store. However, concrete will stick to normal timber as it dries, so forms need either a special application of a “release agent” to make them nonsticky or a pretreatment on one side with a resin that does the same thing.

Wood forms are not only affordable and easy to construct, but they’re also easily customizable, and you can reuse them a few times if needed. These are popular options if you’re building concrete steps, patios, walkways, sidewalks, or small retaining walls.

Insulated Concrete Forms

Insulated concrete forms (ICF) are made from styrofoam or similar material, and they “click” into place like building blocks. ICFs are gaining popularity as a means of building concrete walls for home foundations, especially because the insulative foam blocks can remain in place after the concrete cures. The blocks on either side of the foundation wall increase the efficiency of the basement or crawl space.

Insulated concrete forms are most common when building home foundations, although you could use them for retaining walls and other vertical sections of concrete.

Foam Concrete Forms

Foam concrete forms are made from melamine or another slick, perfectly flat material and usually appear as a box without a top. After you pour the concrete and disassemble the form, you flip the concrete upside down, and the side that cured perfectly flat against the form serves as the surface on display.

Foam concrete forms are most common for building concrete tabletops and countertops.

Concrete Wall Forms

Concrete wall forms are prefabricated wood or steel forms designed to hold concrete vertically as it cures into a wall. The forms hold rebar or other reinforcements in place while the concrete sets to add strength and durability.

You can get custom-made concrete wall forms, buy prefabricated forms with dedicated sizes, or build them yourself.

Steel Forms

Steel forms are just like wood forms, but, as the name suggests, they’re made out of steel. Much like wood forms, the builder will spray the inside with a release agent or oil to prevent sticking. Steel forms are harder to construct and more expensive, but they can last indefinitely and are ideal for concrete companies that will use them over and over again on different projects.

Decorative Forms

Finally, decorative forms take more of an artistic approach to concrete work. They usually consist of fiberglass, acrylic, or moldable material, and the builder will use negative space to create a finished concrete form. As you can imagine, decorative forms range wildly in size and design, so they’re often custom-made and come with high price tags.

Concrete Forming Process: What to Expect

Concrete forming can be a pretty involved process—you also have some preparation work to do before you set the form in place. Below is a quick look at the process from start to finish. This is the process for wood concrete forms, as this is what most homeowners will use when DIYing concrete projects:

• Digging out sod, soil, and clay and leveling the ground

• Setting a perimeter with string

• Measuring and leveling wooden forms

• Precise cutting with a circular saw or similar tool

• Connecting the sides of the form using a drill and wood screws

• Measuring and hammering in bracing stakes to keep the form in place while the concrete cures

• Placing fill materials like gravel or sand at the bottom of the form and tamping them down, often with a compactor

Other types of concrete forms may require extra details as your project progresses.

Concrete Forming Tips

Concrete forming might seem simple. And while getting the basics down is fairly straightforward, some projects have a lot of nuances that make concrete forming a challenge. Below are some tips to help you get your concrete project started in the right direction:

• Develop a plan before you start: One of the most important things to do before any concrete project is to come up with a solid plan. This is especially important when making a form for a foundation, as you might need to set in anchor bolts or holes for drainage before you pour.

• Prepare for preparation: A lot of the concrete forming process is preparation, like checking that your form is square, level, and plumb before pouring. Triple-check your measurements and make adjustments before you pour.

• Not all concrete slabs should be level: Foundations should always be level to provide the best stability, but something like a concrete patio should have a slight slope for drainage. Consider this while you make your concrete form.

• Use caulk for smaller projects: If you’re using a foam form for a concrete countertop or tabletop, use caulk to seal around the edges to prevent leakage after you pour.

• Check building codes first: Many concrete projects will be governed by building codes, so check with your local building department before proceeding. Making concrete forms for outdoor structures like fence posts, retaining walls, and shed foundations are all concrete projects that need permits and inspection to ensure they follow local codes.

• Get the concrete mixture right: Adding too much water to your concrete mixture can lead to the segregation of concrete and a loss of strength, while not adding enough can cause crumbling and collapse of the finished product. Your form could go to waste if you don’t get the mixture right.

• Think about agitation: When you’re building your concrete forms, consider how and where you’ll agitate the poured concrete to remove air pockets. Planning ahead could make your job easier when it’s time to find a portion of the mold to vibrate.

For example, if you’re working on a large patio, you would need to measure a 1/4-inch slope to help with rain drainage. If you’re building concrete countertops, you’d use melamine instead of wood and seal the corners with caulk to prevent leakage.

DIY vs. Hiring a Pro

For smaller projects like small walkways and countertops, you can DIY if you feel comfortable and have the concrete tools to get the job done. Just remember to take your time during the planning stage, double- and triple-check your measurements, and make sure your form is level, square, and plumb before you pour your concrete. Additionally, always wear protective gear like safety goggles, gloves, a respirator, and skin protection to avoid chemical burns and irritation from concrete dust.

For larger forms and anything structural—like a foundation for a house or outbuilding or a driveway that will need to support heavy vehicles—we strongly recommend hiring a concrete company near you. Experts will be able to get the job done quickly and avoid mistakes with mixing ratios, get enough agitation to remove air pockets but not too much to cause concrete segregation and abide by building codes.

Tyler Lacoma contributed to this piece.