Form Release Agents
Defining, selecting and applying concrete
form release agents.
By Robert F. Waterloo
Robert F. Waterloo is the
technical sales manager, concrete release agents,
for The Hill and Griffith Co., Greenwood, Ind.
There are more than 400 different
concrete form release agents offered in today's market.
Some come from major suppliers to the concrete industry
and are distributed nationally, while others are produced
by local oil companies and distributed within their
own local areas. Until recently, technology and regulations
have been somewhat limited and products such as straight
kerosene with used french fry oil have been used as
concrete form release agents. Some have had limited
success but have cost, environmental, employee safety
or handling problems.
With proper information on concrete
form release agents, the precaster can improve production
and quality while reducing costs. The precaster should
also know the definition and types of release agents,
application methods, form care and environmental concerns.
Definition
and types of release agents
Hardened concrete will bond with any form surface,
whether it is made of iron, steel, wood or other.
Release agents, applied to the forms, are materials
that permit, enhance or aid in the clean release of
the partially hardened concrete from the casting form.
The release agent is also expected to protect the
form and contribute to the quality of the casting.
In today's market, the release agent must also be
acceptable to the environment and to employee safety.
Some block-outs, depending on their
composition, will react with some release agents.
Before introducing any new block-out material, or
using a new release agent with an existing block-out
material, an immersion or reactivity test should be
performed in order to assure compatibility.
Release agents fall into two primary
categories: barrier and reactive. Barrier release
agents actually create a physical barrier between
the form and the concrete, while reactive release
agents go one step further. In addition to forming
a barrier, reactive release agents typically contain
normally proprietary materials that react with the
free lime on the surface of the concrete, forming
a chemically inert metallic soap that enhances the
separation of the concrete from the mold surface.
The intent is to minimize the damage to the product,
minimize sticking, help keep the form clean and extend
the life of the mold.
Barrier release agents fall into
six primary categories:
Plain
petroleum oils. These are normally light bodied,
low-viscosity petroleum oils that often contain paraffin.
Straight diesel, fuel oil and kerosene fall into this
category. Plain petroleum release agents are becoming
less prevalent in the concrete industry because they
require heavier application and often raise environmental
and employee safety concerns. Straight petroleum oils
will encapsulate air on the vertical sidewalls of
the mold, causing voids, or bug holes. Staining is
also a common problem.
Water
emulsions. Water emulsions are typically petroleum-based
materials dispersed in water with the aid of polymers,
or surfactants, to form emulsions. Water-based emulsions
can also fall in the "reactive" category
if they contain some type of reactive material such
as fatty acid or tall oil. While they are a step in
the right direction of a biodegradable release agent,
they are still petroleum-based and subject to local,
state and federal disposal regulations and to the
recent VOC (Volatile Organic Compound) regulations
published by the U. S. Environmental Protection Agency.
Further, as emulsions contain water,
they may cause rust. These materials must also be
kept from freezing, as separation will normally occur.
Another category for emulsions contains
caustic materials and forms a barrier on the form,
requiring special protection for employees. Emulsion
release agent typically build up on the form surface,
requiring regular cleaning.
Nonreactive
coatings with volatile solvents. These release
agents are also typically petroleum-based. They contain
waxes, rosins, silicones, soaps or synthetic resins,
which act as a barrier between the form and the casting.
After application to the form, the solvent evaporates,
leaving a barrier and/or a reactive surface. The surface
film normally transfers onto the concrete, which must
be cleaned before applying paint, sealant or other
coatings.
Waxes.
Waxes include paraffin-based materials and
even car-waxing compounds. They are difficult and
labor-intensive to apply and will generally build
up on forms in a short period of time. Waxes are nonreactive
and more inclined to cause surface voids, or bugholes.
The residue transferred to the concrete should be
cleaned before applying paint or other coatings.
Soaps.
Soaps are surfactants. Application is relatively simple,
but they are typically alkaline and often require
special handling precautions. Soaps may also build
up on the forms.
Biodegradable.
The term "biodegradable" is used to describe
a material that is environmentally friendly due to
its limited impact on the environment, and will return
to its natural state within specified time limits.
"Biodegradable" does not necessarily mean
that it is harmless for employees to handle.
Reactive release agents typically
contain weak acids derived from vegetable oils and/or
animal fats, and all fall into the category of "fatty
acids." Also included in this category are byproducts
from paper manufacturers, such as lignosulfonates
and tall oils. The most common reactive materials
are fatty acids. A large number of fatty acid blends
is available, so finding the one that works most effectively
with concrete is often the most difficult part.
The key to "reactive"
release agents is the reaction of the fatty acid with
the free lime on the surface of the concrete. This
reaction causes the formation of metallic soaps, which
are water insoluble and chemically inert. This metallic
soap is what allows for the easy release of the product
from the form and also allows the entrapped air on
the vertical walls of the form to rise more easily
to the fresh concrete surface during casting. Good
vibratory practice is essential for reducing surface
defects such as bugholes.
Reactive form release agents fall
into two primary categories:
Vegetable
oils. Vegetable oil-based release agents are
typically more environmentally friendly, biodegradable,
non-photochemically reactive and renewable. Only recently
have they gained the required performance characteristics
and lack of buildup on forms.
Petroleum-based
reactive release agents. The majority of reactive
release agents in use today have petroleum-based carrying
agents. Since only a small percentage of the right
fatty acid is needed to get the job done, the majority
of the release agent will be the petroleum-based carrying
agent. An excessive amount of fatty acid in the release
agent can actually result in the fatty acid migrating
into the concrete, acting as a retarder and causing
soft crumbly surfaces. However, high concentrations
of fatty acids can be used for conditioning and/or
seasoning of forms (see seasoning).
Application
methods
A number of options are available to apply form release
to your forms. Spraying is the most common method,
but swabbing, fogging, wiping and dipping are also
acceptable methods. In all cases, a thin coat of form
release is all that is needed and will help to minimize
staining and surface defects. Coat all form areas
before placing reinforcement in the forms so the reinforcement
can bond properly to the concrete.
Spraying.
Spraying is by far the most common and labor-efficient
method. The idea is to get a thin layer of release
agent on the form with as little airborne particulate
as possible. Tip size, or orifice opening, spray pattern
and pressure should be your primary concerns. Most
form release agents will have viscosity variations
during colder or warmer weather, so it is not unusual
to have different nozzles and variable air pressure
for different weather conditions.
Pressure and nozzle orifice size
are most important with automated spray equipment,
as the application generally is not watched on a continuous
basis. Viscosity, nozzle size and air pressure can
be controlled more consistently than by hand operation.
Temperature changes, which result
in viscosity variations of most form release agents,
require flexibility in order to achieve a thin application
of the form release. Petroleum and vegetable oil-based
release agents will have the greatest increase in
viscosity as the temperature drops and, to a certain
extent, will become thinner as ambient temperatures
increase.
Spray application pressures should
normally not exceed 40 PSI, while nozzle orifice sizes
can be varied from 0.05 gallons per minute to 0.5
GPM. Pressures higher than 40 PSI will generally result
in unwanted airborne particulate, which can create
an uncomfortable and unfriendly employee environment.
With constant pressure, colder weather requires increased
GPM rates, while warmer weather requires smaller GPM
rates.
Generally speaking, broad nozzles
with flat spray patterns are preferred for speed and
thin applications. A fan spray tip is preferred over
the conical spray tip, and fan nozzles should be typically
between 40 degrees and 80 degrees. Excess application
should be wiped, blotted or drained off.
When using a reactive form release
agent containing fatty acid, it is important to know
that fatty acids will react with brass, bronze, aluminum,
gray, ductile and malleable iron and mild steel. The
use of lined spray or holding tanks, non-reactive
transport lines and non-reactive wands and spray tips
is always best.
Swabbing.
Swabbing or painting the form release by hand is an
acceptable method of application as it eliminates
the majority of airborne particulate. On the negative
side, application tends to be heavier than needed.
Also, the excess form release often ends up on the
ground.
Fogging.
Fogging is an acceptable method of application,
but requires experienced personnel to achieve thorough
coverage and to minimize the airborne particulate
while assuring complete coverage on the form.
Wiping.
Wiping the release agent on the form with a sponge
or soaked rag will normally give the thinnest application,
but it is very labor intensive. It is not unusual
to see burial vault and architectural precast manufacturers
use this method because they offer the best surface
finish after pouring and stripping.
Dipping.
Dipping is automatic, fast, labor-efficient
and assures complete coverage. The excess material,
however, must drip freely from the forms/pallets/head
rings. Under normal circumstances, the thicker application
from a dip tank is not detrimental to the product,
but it may use slightly more material compared with
other methods. Dipping reduces waste by allowing excess
material to drip back into the holding tank.
Form care
On new metal forms, once the protective coating is
removed from the form, raw metal is exposed. Fatty
acids in reactive form release agents have an affinity
for raw metals, and will react with the raw metal
and form a metallic oleate, or a protective coating.
Metal forms should be sufficiently seasoned, forming
a protective coating on the metal surface that will
not react with the fatty acid in the release agent
when it is time to pour concrete.
To season forms, apply high-concentration
reactive material, typically fatty acid, liberally
on the forms and allow them to set for 24 hours. Wipe
the forms down and repeat the process. Then they will
be ready for regular production. You can accomplish
the same thing with normal reactive release agents,
but it will take longer since there is less reactive
material available to season the metal.
Heavy cleaning of forms should be
done as necessary, but minimize it whenever you can.
Ideally, you would not have to clean your forms after
stripping. If heavy cleaning is necessary, severe
abrasive cleaning with metal brushes will wear off
the metallic oleate protective coating and expose
raw metal. If raw metal is exposed, the fatty acid
in the form release agent will start to react with
it immediately in order to form a new barrier, reducing
or negating the available fatty acid to react with
the free lime on the surface of the concrete.
Coatings are often put on new forms
to prevent them from rusting during storage and transit.
The protective coating usually consists of resin,
petroleum-based gels or acrylic sealers. In all cases,
remove the protective coating and season the form
before using the form to cast product.
Rusty forms, used as is, will promote
sticking and staining. Rust should be removed, normally
by steel brush grinders, and the forms seasoned before
returning to production. Rust is oxidized metal, and
the fatty acid in your release agent will attack it
immediately. Coat your forms with a rust inhibitor
before storing them to eliminate or reduce the amount
of rust. Even better, use a rust inhibitor that is
compatible with your release agent so no cleaning
is necessary.
Environmental
concerns
VOCs are compounds that create ozone at ground level
and contribute to air pollution. Since September 1999,
the U.S. EPA has required that VOC emissions be reduced
by 113,000 tons per year in the United States. These
regulations affect 62 product categories used by the
concrete industry. However, the new limitations on
VOCs can be met with existing technology and with
reasonable additional costs.
Stormwater runoff is another concern
because most concrete producers are subject to contamination
regulations. The concern is not only with stormwater
discharges, but also with seepage into the aquifer.
Be aware of your own local and state regulations to
avoid serious problems. Also, keep in mind that some
states have more stringent rules on VOC and stormwater
regulations than does the U.S. EPA.
If your castings are to be used
with potable water, such as cisterns or aqueducts,
you may want to check if your release agent has been
approved by the National Sanitation Foundation (NSF
International).
References
Avoiding a Caustic Handshake;
Yelton, Rick, The Concrete Producer, May 1999, pp.
21-23.
Guide to Occupational Exposure Values
- 1997; Compiled by the America Conference of Government
Industrial Hygienists.
Federal Register; Vol. 63, No. 176,
Friday, September 11, 1998/Rules and Regulations,
pp. 48848-48887.
NSF Listings, Drinking Water Treatment
Chemicals and System Components-Health Effects; August
13, 1999.
Federal Register, Title 16 - Commercial
Practices, Chapter I - Federal Trade Commission, Subchapter
B - Guides and Trade Practice Rules, Part 260 - Guides
for the use of environmental marketing claims (16
CFR 260.7)
Physical and Chemical Properties
of Mineral Oils That Affect Lubrication; Godfrey,
Douglas and Herguth, William, Herguth Laboratories
Inc.
The Application of Renewable Resources
in the Foundry Industry; LaFay, Victor
University of Kentucky Research
Report, 2001
