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
