What is “Form Lumber?”

Construction and masonry professionals rely heavily on form lumber as a support for concrete projects for residential and commercial buildings. Wood used in form lumber is expected to support the weight of wet concrete until it hardens.

Form lumber is made from rigid wood that can withstand 150 pounds per square foot of wet cement. The amount of concrete to be poured into the form lumber is known as “pour size.”

“Pour size” refers to the amount of concrete form lumber needs to retain and also the pressure or weight of concrete pushing against the wood form.

Form lumber is the choice for flat work construction projects for residential and commercial patios, driveways, roads and industrial building walls and foundations.

Why Form Lumber is the Choice for Construction Projects

Flatwork construction projects require form lumber that typically ranges from 3 to 12 inches in height. Most of the weight of concrete in flatwork construction projects is spread over a prepared sub-base. This alleviates much of the pressure of concrete weight pushing against form lumber.

The sub-base or sub-grade, as it is sometimes referred to, is an important factor in the stability and durability of the concrete and the form lumber that creates the shape or “form” to be constructed. Sub-base or sub-grade is soil based beneath the concrete to be poured into the form.

How is Form Lumber Used in Construction Projects

The usual steps to using form lumber as a support for a concrete pour is first to evaluate the stability of the soil sub-base. This is may be done by structural or geotechnical engineers.

Thus, an engineering determination is made as to viability of the soil to adequately hold the weight of the proposed concrete flooring or slab.

Geotechnical engineers will also check that the water table within soil structure for the proposed construction project will not result in problems affecting the soil or concrete and wood form.

If the soil is determined to be unstable, these engineering professionals may suggest a “compactable-fill” sub-base to ensure the weight of concrete and form lumber will be stable.

Most Basic Form Lumber Uses

Form lumber is used in most basic concrete slabs. Concrete poured into wood forms should not exceed 6 inches in height. Form lumber boards are screwed or nailed into wood or metal stakes and stakes are driven into the prepared sub-base.

Using a leveling device, contractors set form lumber boards according to the proper slope or sub-base level. Leveling devices used for this include laser levels, string lines or hand levels. With the use of leveling devices, contractors can accurately set lumber form to proper sub-base level or slope.

How to Measure Form Boards

Each measurement for form boards such as thickness, width and length are calculated in inches and divided by 144. If you measure just the length in feet, divide by 12 to arrive at the same measurement result. A standard board foot is also a standard industry measure of wood measured at 12”x 12” by 1” thickness.

Additional form lumber boards are used to secure areas where a single board butts against another board.

When free form designs, turnings or rounded edges are part of the construction project design, thinner, cross-section lumber boards may also be used.

In order to keep concrete from adhering to the wooden lumber forms, they are coated with a special form releasing agent or a low-grade oil. This process keeps lumber forms clean and allows them to be reused effectively multiple times before they are discarded.

Weight Determines Form Design

Construction of new homes are likely to require several lumber forms for sidewalks, carports and garage floors and patios. All of these residential forms can create decorative designs. For example, construction projects like circular driveways and bases for above ground pools require sound structural bases of concrete slabs.

Construction of a circular driveway requires professional design and impeccable configuration to ensure the end result is durable and attractive.

The form is created after the sub-base is inspected and determined to be sound. The form is built to blueprint design specifications for location, width and length. Stakes are attached and driven into the wood and when the lumber form is completed, cement can be poured directly into the form evenly to create slabs.

Bases for above ground pools must be strong enough to withstand the pressure of the gallons of water the pool will contain. These wooden forms may be rectangular or circular according to pool design.

In this type of residential project, debris in the soil like pebbles and stones are removed and then the soil is leveled. The wood form is created to match the configuration of the pool design. Once the form is set in place, concrete is poured over the soil within the wooden lumber form.

Cement weight determines the configuration of the wood form to be used. This is one reason commercial and industrial building projects require the services of trained professionals who can calculate the specifications needed when form lumber is part of a project design.

The Value of Using Wood vs. Steel

One of the reasons there has been a resurgence of the use of lumber for forms as opposed to steel is cost. Project managers with proposed projects that include cement slabs find it more cost-effective to use wood forms.

Wood offers superior performance and also environmental credentials compared to steel. Today’s project managers endeavor to ensure materials they use for residential, commercial and industrial structures will be compliant with state and federal regulations.

Project managers find wood forms have an added feature of capturing carbon that wood fibers absorb during growth stages even when heat treated. Thus, a wooden form will help control heat absorption of cement in higher temperatures as well as in colder temperatures.

Wood forms also reduce levels of adsorption of external ions, molecules and atoms in cement that adhere to the wood surface. All of these factors are benefits of using wood forms for proposed projects.

If your company is looking for construction materials and building material supply in Tulsa, contact Security Building Services and Building Supply of Tulsa today! Call us at (918) 663-6272 to speak to a qualified lumber expert.

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Further reading:

Most Common Uses for Lumber in Construction Projects – Building Supply of Tulsa

There are many different types of building materials involved in constructing a house or building. Learn more about Most Common Uses for Lumber in Construction Projects with Security Building Service and Supply of Tulsa.