There is more to form release agents than many realize. Understanding the types, considerations for selection, potential unintended reactions and proper application techniques is key to taking full advantage of one of the unsung heroes of precast concrete manufacturing.
By Claude Goguen, P.E., LEED AP
Form release agents are an important component of precast concrete manufacturing. They influence the finished product’s quality, forming equipment’s longevity and production efficiency. Precast concrete form release products have evolved considerably since they were introduced. Today’s products are easier to use and more effective than ever. Still, proper application procedures are key to their efficacy.
Form release agents’ purpose
Release agents are everywhere. For example, cooking sprays that facilitate the removal of prepared food from ooking or baking surfaces can be found in nearly every kitchen.
In precast manufacturing, release agents facilitate the separation of concrete from the forming surface. However, form release agents in the precast industry serve a variety of additional purposes. They are also used for cleaning and protecting formwork and producing a quality concrete surface. However, their ability to fulfill these functions depends on the type used.
Form release agent types
Form release agents can be categorized as follows:
- Barrier: Provides a physical barrier between the form and the concrete.
- Reactive: Contains compounds that react with agents in fresh concrete to produce an interface material.
The earliest barrier form release agents were unmodified animal-, fish- or vegetable-based oils. Petroleum products such as diesel fuel or heating oil were used extensively. This approach evolved into using oils mixed with surfactants such as a wetting agent or emulsifier. These products were functional but were primarily intended for wood forms.
The next form release agents included waxes, silicones, synthetic resins, soaps and other materials to facilitate use with other form types, including steel. These agents are commonly used today.
The one constant has been using petroleum- or vegetable-based oil, which is why form release agents are commonly referred to as “form oils.” The other ingredients in the release agents help evenly distribute the oil, carry it to the forming surface and prevent it from staining the concrete’s surface. Waxes can also be used as form release agents and initially were applied by hand. The advent of emulsified waxes has enabled rolling or spraying application.
Reactive form releases contain ingredients that chemically combine with the lime in cement. Fatty acids in a reactive form release agent produce a metallic soap after reacting with the lime. This soap is water-insoluble and prevents the concrete from sticking to the form surface. The soap also facilitates air bubble passage, which reduces bugholes on vertical surfaces. Just like the barrier type, reactive form release agents have varying compositions depending on the manufacturer.
Which type of form release should I use?
Many factors come into play when selecting a form release agent, and precasters are advised to work with their supplier to answer these questions.
1. Is it safe to use?
Be aware of any safety risks associated with the form release, including exposure to skin and eyes and potential inhalation. Also ensure that the product meets any applicable OSHA standards.
2. Is it compliant with applicable environmental regulations?
Some products will be exposed to the environment when sprayed, resulting in residue that can be washed away or create particles in the atmosphere. Your state may have specific regulations regarding runoff water quality and amount the of volatile organic compounds (VOC) contained in the product. A 1999 federal regulation set the maximum allowable VOC level in concrete form release agents at 3.80 pounds per gallon (450 grams per liter).1 Your state may have adopted this regulation or have more stringent rules. For example, some areas in California require a maximum of 250 g/L. Also, if your products will handle potable water, the form release agent may have to meet specific requirements such as NSF/ANSI 61.
3. Is it compatible with the concrete?
Find out if the ingredients in the form release agent adversely react with any other mix constituents, including admixtures, cementitious materials or fiber reinforcing. The form release agent should not soften the concrete surface or create excessive dusting that may affect the surface’s durability.
4. Is it compatible with anticipated concrete surface treatments?
The precast structure’s surface may receive additional treatments after stripping such as water/steam curing or curing compounds, sealers or coatings. This must be considered when choosing a form release agent to avoid negative interactions. There also may be further architectural surface treatments including painting, plastering or other finish processes applied at the precast plant or on-site that may adversely react with the form release residue on the concrete’s surface. It’s best to consult with the manufacturer of the coating or surface treatment.
5. Is it compatible with the forming materials?
What works with steel forms may not work with formliners, blockouts or wood siderails. Some form surfaces may require specific release agents.
6. Will it impact appearance?
A form release agent may inadvertently affect the surface appearance of concrete. Tests should be conducted before committing to a product. Precasters should consider the potential for staining or discoloration, which becomes critical when dealing with architectural elements.
7. How easy is it to use?
Some form releases may be more labor-intensive to apply, so this factor must be part of the selection process. In storage, the product may or may not stay in suspension and may require periodic mixing as it’s used. If the product requires some time to dry, it’s important to know this so you can plan your operations from application to casting. If your operations are delayed for any reason, you should know how long an application can remain on the form before reapplication is necessary.
8. Is it compatible with plant conditions?
Every plant is unique. The product must be effectively used in your plant environment. Consider the highest and lowest casting ambient temperatures and whether the form release agent can be applied within that range. Some agents can thicken in colder temperatures and solidify inside the spraying equipment.
9. Is it cost-effective and readily available?
Once you determine the product cost, the equipment needed to apply it and the associated labor required, then assess whether the product is cost-effective. Some release agents can also protect formwork and other form accessories, which can extend the forming equipment’s lifespan. Is your ideal form release agent readily available in your area?
10. Does it work?
This may seem obvious, but it’s important to try products to measure their performance. Over time, the forms may stick to the precast products or leave excessive residue on the form surfaces that must be cleaned. It is always best to establish a relationship with your supplier so that you can address such issues should they arise in the future.
Best practices for form release application are determined by technique, which includes the following: spraying, wiping and dipping.
Spraying is the most common application method. Spraying can be performed with a hand-operated spray canister, electric portable sprayers or with a centralized compressed air system. A fine mist of small droplets applied to the forming surface may be optimal while a heavier application may be necessary with barrier type agents.
Two important factors influence the spray’s quality: spray tip and pressure. The sprayer tip controls the application. Broader spray nozzles that produce a fan of fine droplets work best. Cone-shaped nozzles work well, but they may produce larger droplets and a higher application rate.
Higher pressures may produce smaller droplets but may also lead to more volume flowing through the tip and more loss of release agent in the environment. It’s important to consult with the sprayer manufacturer to determine the optimal pressures. Typically, form release manufacturers state that you need at least 30 psi of pressure to apply form release properly. Some say that a pressure between 30 and 60 psi is sufficient.
When using centralized compressed air systems, it is recommended to use air pressure exceeding 100 psi. Some systems may have just one main air pressure regulator and some have regulators at multiple spraying stations throughout the plant.
When using a reactive release agent containing fatty acids, it’s important to know that fatty acids may react with bronze; aluminum; gray, ductile and malleable iron; and mild steel. Brass and bronze spray tips are susceptible to plugging when used at low pressures and to orifice enlargement when used at high pressures. Using plastic or stainless-steel nozzles can help prevent these issues.
Swabbing, painting or wiping by hand is a method of form release agent application that eliminates the majority of airborne particulates. This is also a preferred method for specific products including burial vault and architectural products due to the surface finish requirements. However, applying form release by wiping can result in a heavier application that what is needed. Swabbing may result in excess release agent which generally ends up dripping onto the floor or the ground. Wiping the release agent on the form is more labor-intensive, but can result in an optimum coating thickness and coverage.
Dipping is a process where the formwork is lowered into a form release holding tank. It’s automatic, fast, labor-efficient and helps ensure complete coverage. It’s used predominantly in the dry-cast pipe industry. The important thing to consider when using this method is to keep the forms clean prior to dipping and monitor and maintain the dip tank contents for form release quality. The reason for this is concrete residue from forms that may not have been thoroughly cleaned can accumulate in the form release and start to negatively affect its reactive properties.
An unsung hero
Form release agents are often undervalued. Some tend to think of them as just an aid in the stripping process, but they also can protect and extend the life expectancy of forms and enhance stripped concrete surface quality.
For these reasons, it’s important to periodically train employees on proper form release application. To assist in this process, NPCA has developed a video on form release application as part of the NPCA Learning Lab available at precast.org/learning-lab. Any costs accrued ensuring the use of the proper form release agent and equipment and mastering the practice of application will pay off in production efficiency, formwork maintenance and overall product quality.
Claude Goguen, P.E., LEED AP, is NPCA’s director of technical education and outreach.
1 Federal Register, Vol. 63, No. 176, Friday, Sept. 11, 1998, under 40 CFR-59, , RIN 2060- AE55, National Volatile Organic Compound Emission Standards for Architectural Coatings