Get the Most Out of Formwork

By Claude Goguen, P.E., LEED AP

The precast concrete industry produces a vast array of products. From small, decorative architectural features to massive bridge beams, precast products may differ in materials and manufacturing processes, but they share one common thing: all are manufactured using formwork.

These molds are carefully designed and assembled in order to house concrete’s metamorphosis from fresh to hardened state, and they are critical to every structure’s function and quality.

Form technology continuously evolves to keep up with precast concrete manufacturing practices and uses. They can be some of the costliest pieces of equipment on the plant floor and for good reason.

That is why it is vital to properly take care of this essential set of equipment to minimize wear and extend use.

USING FORMS PROPERLY

Formwork used in precast concrete manufacturing can be divided into two major categories:

• Modular forming systems. These systems come with panels and hardware and are assembled to pour custom structures. These panels can be aluminum- or steel-framed with structural plywood facing.
• Permanent formwork. These forming systems are designed and manufactured to pour a specific type of structure such as manholes, tanks, traffic barriers and beams.

These systems also include tables that are used to pour wall panels and slabs.

Forms used in precast manufacturing can range from complex systems with many moving parts to relatively simple ones. In either case, always thoroughly review supplier instructions to implement them properly.

With new forms, invite supplier representatives to demonstrate proper employee usage and record the process to serve as training videos. When lifting, handling, assembling, stripping, cleaning and maintaining forms, employees must be aware of approved processes, materials and tools.

The absence of appropriate guidance and training could result in improper handling, such as an employee grinding or sandblasting a casting surface to the point of significant damage. Worse yet, an individual could lift these heavy pieces without using designated lift points and risk a serious workplace accident.

“If you have a question or issue with your formwork, you need to resolve it the right way,” said Derek Von Cannon, Afinitas vice president of sales. “Talk to the manufacturer. They made it and will know the right way to fix it. Good manufacturers will help you.”

Whether placing a new form or returning an old form to service, they first need to be properly leveled. A form even slightly off level can result in product quality issues and damage to the formwork itself when it becomes difficult to open or close assemblies. Even minute variations can cause issues.

For example, one-sixteenth of an inch does not sound like much. However, on an 8-foot-tall form, that translates to a quarter-inch out of level and would be out of tolerance in most cases. Smaller forms can be verified with a 4-foot level, and larger ones may require a laser.

PROPER TOOLS AND SAFETY

Forms are designed with a maximum lateral pressure due to hydrostatic forces exerted by fresh concrete. That pressure depends on the concrete’s density, the height of concrete placed and the concrete’s properties.

Form manufacturers usually add additional load capacity as a safety measure. However, if a precaster makes drastic changes to concrete mix properties, it may prove a challenge, especially for older forms. Check with the form supplier or add additional bracing when a concrete mixture is significantly modified, such as going from conventional to SCC. Restrict concrete placement speed to minimize formwork pressure and avoid potential hardened concrete issues.

When using external form vibrators, consult with the form and vibrator suppliers on correct placement. Form vibrators attached directly to a form skin not only can diminish the vibratory efficiency but can lead to fatigue stresses in the area near the vibrator mount. Attach form vibrators to a structural stiffener in locations recommended by the suppliers.

Handling formwork pieces can be challenging. Some components have a center of gravity that is offset because of the form’s shape and may swing once lifted. It is important to use the specially designed lift points for this reason. Also, the lift points are reinforced to withstand the stresses of handling.

Train employees on how to properly align, assemble and close the formwork. Forcing clasps shut over time can bend form surfaces. Bob Mills, director of sales and marketing with Hamilton Form noted: “If a form is hard to close or set up, there is a reason. Do not force it. Stop and see what is causing the issue. A simple repair or process change will save a major issue in the future.”

Employees also must use proper tools when stripping formwork. Nothing sends a shudder up a plant manager’s spine like the sound of a hammer hitting formwork. When dynamic forces are required to strip concrete from a form, use manufacturer-designated tools for that task. It is best to use stripping tools provided by the form supplier when available. In the absence of those, employees must know exactly what tools are approved for use.

Never climb formwork using horizontal framing, bracing or latches. It is a safety risk and can damage those components.

MAINTAINING AND PROTECTING FORMS

Maintenance, like safety and quality, is everyone’s responsibility. An employee who works around formwork should understand the basics of form maintenance.

This includes how to inspect formwork, how to perform daily maintenance and how to assess potential issues.

Formwork Inspection

Similar to most other equipment in a precast plant, forms should be inspected on a regular basis as defined by the plant-specific quality control manual. Daily checks are performed based on this list.

Relegating form inspections to maintenance staff only can delay attention to issues that intensify with time. Also, training everyone on basic maintenance has the benefit of cross-training, meaning employees add to their skills so they can fill in important duties when needed.

Forms should be inspected daily for surface condition and cleanliness. Any leftover concrete, especially on casting surfaces, needs to be removed. Check the formwork assembly for stability. If it rocks like a table with an uneven leg, the footing needs to be adjusted or shimmed. Check moving parts for any concrete, other debris or damage.

Examples of Formwork Inspections

• Daily Formwork Inspections
• Surface inspection
  • Inspect casting surfaces for cleanliness and defects (blemishes in the skin, pitting and rust).
  • Inspect welds for separation, cracking and bending.
  • Loose or missing nuts and bolts.
• Latches, hinges and other moving parts
  • Confirm proper operation and range of motion.
• Form stability
  • Ensure formwork is stable and level.
• Form dimension
  • Check dimensions of forms.
• Electrical and hydraulic connections and hoses
  • Check hoses and cords for leaks or wear.

Weekly or Monthly Formwork Inspections

• Weld inspection
  • Check all weld points for separation, cracking and bending. Tip: Shine a light inside a closed section of formwork and look for escaping light on other side.
  • Check chamfers for positioning and damage.
  • Check all other form components (hinge plates and clamped connections).
  • Check any bolts, nuts for tightness.
  • Check connection of reinforcing structure to form skin.
• Levelness and Dimensions of Formwork
  • Check with level or laser.
  • Verify inner dimensions of formwork.
• Under formwork assemblies
  • Inspect anchors and shims under formwork.
  • Look for any signs of rust.
• Moving parts
  • Thoroughly check all moving parts.
  • Check tightness of all bolts and other hardware.
  • Check tolerances.
  • Hydraulic hoses and electrical connections. Thoroughly check for leaks or wear.

Formwork Cleaning

In the hustle and bustle of precast operations, cleaning equipment at a shift’s end sometimes lacks due process. Stress that cleaning all equipment, including forms, is part of the production process.

Proper attention to cleaning can be the single best means of prolonging the precast formwork’s life. All form components require thorough cleaning, including form surfaces, locks, pins, hinges, latches, clasps, collapsing devices, pallets and headers. Special attention is needed for joint corners, jacket and core seams.

“We recommend starting the cleaning process during your pour,” Von Cannon said. “If you are careful, there’s way less cleanup work on the backend.”

Preferred cleaning tools include soft brushes, mops, wire brushes, brass wool or other minimally abrasive materials. They also include scrapers (putty knife), air hoses (when applicable) and grease.

Avoid grinding, sand blasting and hammer impacts when cleaning forms unless approved by the form supplier.

“Damage from hammer blows is one of the leading contributors to decreased aluminum panel performance, and even increased labor costs. Even what appears as minor damage can lead to major problems in a short amount of time,” said Jim Aylward, precast director with Western Forms.

There are products available to help clean stubborn concrete buildup. Make sure any tool or material is approved for use on aluminum or plywood surfaces. With wood forms, it is recommended to use a hardwood wedge and a stiff fiber brush for cleaning. Avoid using metal brushes.

Formwork Maintenance

Suppliers should have lists of scheduled maintenance to be performed on formwork systems. Obviously, this will differ if you are maintaining a self-stressing bed versus a modular panel, but the importance of scheduled maintenance is the same.

Apply grease to all hinges, gears and other designated areas. When adjusting locks and collapsing devices, be careful not to overadjust as this could cause the form to distort and can cause permanent damage. Overadjusting also can break or bend of the working parts of the locks and collapsers.

Welding on formwork should be kept to a minimum, and when it is required, follow supplier instructions. Welding can distort the metal, cause deformations and remove protective oils.

Using magnetic chamfer strips at formed corners can alleviate slight leaking issues and permit easier form removal.

PREPARING NEW FORMS

When forms or form accessories arrive at a plant, they typically are coated in some protective material to prevent rust and other damage during transit. The formwork supplier should provide detailed instructions on how to transform this product from transit/storage mode to production mode.

Many times, the protective coating needs to be washed off the form surfaces using brushes, solvents or other means. Some companies do sell products that are specifically designed for cleaning of forms and can effectively remove these corrosion inhibiting coatings.

Once the protective coating is removed, the form may need to be seasoned. This is a process commonly used when using cast-iron and carbon steel cookware. Without proper seasoning, food sticks to a skillet, and it can rust quickly. When it comes to precast formwork, lack of seasoning can result in frustrating issues with stripping and concrete quality as well as potentially damaging the form surfaces.

Steel, aluminum and wood form surfaces have an open grain, and seasoning allows a form release agent or seasoning agent to penetrate the surface and fill the grain. The seasoning needs time for full penetration, and once the excess material is removed, the forms are ready for use. Seasoning oxidizes the surface of aluminum forms to help prevent concrete from adhering to the form surface on initial pours. It also helps to reduce the break-in period of new or recently cleaned aluminum forms.

Producers may encounter mill scale, which is a grey flaky surface found on hot rolled steel consisting of mainly iron oxides. This is a byproduct of the hot-rolling process during the manufacture of sheet plate. The presence of mill scale can be detrimental to new molds, causing many problems such as severe sticking and pitting of the surface. It can be difficult to remove using abrasives because of its hardness, and scouring can be detrimental to forms as this can cause accelerated corrosion.

The proper way to remove mill scale is with a diluted acid such as muriatic acid that dissolves mill scale, similar to how vinegar dissolves lime scale in a kettle. The acid remains on the form for a period of time to react with the mill scale and then washes away, leaving a smooth, scale free surface. Once removed, the form can be seasoned normally.

EXISTING FORMS BROUGHT IN FROM LONG-TERM STORAGE

It is quite common for precast manufacturers to have formwork stored for a few weeks to more than a year until there is a need for that specific product. Getting that form back to casting condition requires a process similar to the one mentioned for new forms.

The biggest difference is the potential for finding rust and having to remove it. This must be done carefully. Trying to remove rust from casting surfaces with grinders can damage the surface and cause long-term issues when stripping.

Never sandblast or grind the casting surfaces to remove rust. Signs of rust on non-contact surfaces can be removed by sanding, grinding or sandblasting. Always use a NIOSH-approved respirator when sandblasting.

Be sure to protect all surfaces as rust forms rapidly on unprotected steel surfaces. All moving parts need to be greased.

The next step is to perform a thorough inspection, including measuring the form dimensions to ensure that there was no excessive bowing or bending. Check all the clasps, hinges, locks and levers to make sure they work properly.

STORING FORMWORK

The big project has wrapped up, and it’s time to move the formwork to a storage area. This is a crucial part of form maintenance that can extend the equipment’s life.

Start with a thorough inspection of the form. Surfaces where paint is peeling or flaking off should be recoated. Remove any remaining concrete on the form, especially the casting surfaces.

If the formwork is stored for a short amount of time, coating the surfaces with a form release agent may be sufficient. Liberally apply a good quality VOC compliant petroleum solvent-based form release.

If the forms are being stored for a longer period, coat the form with a weatherproof rust inhibitor. Coat parts and moving components with suitable grease or rust inhibitor.

If the formwork has hydraulic cylinders, cap ports and fully retract cylinders while in storage.

Choosing an appropriate storage area is important. Pick a location that is the most protected from traffic and elements. Do not store forms or components directly on dirt.

Store them on durable dunnage following supplier recommendations. Dunnage should be placed to avoid warping or bending of the forms that can become permanent.

Store forms flat on a level surface and in a way that prevents standing water from collecting on them. Use covers or tarps for moisture and dust protection when possible.

Make sure that maintenance schedules and logs include checking on these stored forms from time to time. Some rust inhibitors must be reapplied periodically and that will depend on local conditions. Signs of rust should be addressed immediately.

THE ESSENTIAL FUNCTION OF FORMWORK

Formwork quality often reflects on the finished product quality. Avoid having employees dedicating hours every day to fixing form blemishes on finished products by taking better care of the formwork up front.

The most effective way to convey a positive equipment care culture and proper maintenance is training. Every plant should have training devoted to the topic of handling, cleaning, operating, storing and maintaining formwork. Checklists on the plant floor also are helpful.

Forms can be considered as cocoons for the amazing precast structures that will emerge. No other equipment on the precast plant floor shapes and holds structures while they go through the process of setting, gaining strength and reaching those important hardened properties.

Treat forms with the respect and care they deserve to preserve their efficiency and extend their useful lives. PI

Claude Goguen, P.E., LEED AP, is the director of outreach and technical education at NPCA.