Contact US

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Form Release Agent on Steel Reinforcing

Form Release Agent on Steel Reinforcing

Form Release Agent on Steel Reinforcing

So, today I was asked to review a report, observations, and photographs regarding a site visit to determine if a retaining wall, being constructed on a residential site, was being constructed according to the plans and current adopted building code. The engineering for the retaining wall was performed by a PE in our office who is no longer employed with our company.

As I am scrolling through the photos, I came across one where a worker was standing atop the formwork with a sprayer wand and a cloud of whatever he was spraying coming up out of the formwork. So, I called the inspector and asked just what was being sprayed. Form release agent is what I'm told. So I ask was the reinforcing already set and of course the answer was yes. Further questioning revealed that, at least for this particular wall contractor, it was common for the form release agent to be sprayed into the formwork after all the reinforcement set. This particular wall was only 10" thick so I can imagine ALL of the rebar was well coated.

What research I have been able to sift through has revealed that ACI 301 says form release agent should not be applied on to the reinforcement. Most manufacturers of form release agent, whose application instructions I have read, specifically warn against getting the product on the reinforcement and advise to coat the forms prior to installation. As I generally do not review residential retaining wall construction observations, I do not know how long this has been going on nor just how many retaining walls, and foundation walls for that matter, out there have been constructed in this manner.

I am trying to do as much research as I can before I stir the pot but, from what I have found so far, this is potentially a huge problem and a wide spread (locally anyway) issue.

Has anyone else run across this before? Are there any papers, publications, specs, etc, on this that I could read before I kick start this sh&$ storm?

RE: Form Release Agent on Steel Reinforcing

Explicitly designed to prevent concrete sticking to forms, including steel forms...definitely does not seem like a good idea to touch any reo with it at first glance

That being said, below seems to suggest otherwise:


Not particularly relevant but at least one study found engine oils specifically do have a detrimental effect on the bond


Most useful source I could find was from here: https://www.sria.com.au/pdfs/tn-1.pdf

"Surface Contamination Of Reinforcement

A common issue is cement-paste splatter on the surface of reinforcing bars from previously placed concrete. This should not be regarded as a problem provided the mortar is adhering
firmly to the bars. If the cement-paste splatter cannot be removed, it should be left. Another common issue that is the subject of much debate is the presence of surface
contaminants such as form release agents or bond breakers and oils on the surface of reinforcing bars. Suprenant and Malisch11 report on a limited test program that the
Aberdeen Group undertook to determine the influence that these contaminants have on the bond strength. A number of Grade 420 (minimum yield stress of 420 MPa), 12 mm
diameter bars had 100% of the surface coated with form release and curing compound/bond breaker, with others having the entire length coated with motor oil with a rag. The ends of
the bars were cast into 300 mm deep by 150 mm diameter cylinders and subjected to pull out testing and comparison to uncontaminated bars. The results showed that the ultimate
stress achieved by the bars was not affected by any of the contaminants. In terms of slip, this was greater for bars with contaminants due to the early loss of adhesion along the smooth
part of the bars between the deformations or ribs. However, after the initial slip, the load was resisted by bearing of the deformations on the concrete and the shear strength of the
concrete between the deformations or ribs. In summary, it was concluded that based on this limited test program involving 27 tests of 12 mm diameter bars with nine different surface
conditions, the contaminants did not adversely affect bond, at least for the one bar grade, size and concrete strength tested.

The Concrete Reinforcing Steel Institute (CRSI)7 list another more recent study conducted at the University of Missouri-Rolla12 that provided similar results. These two studies have
formed the basis for the American Society of Concrete Contractors (ASCC) releasing Position Statement #313 which states that, “The test results of both studies indicate that form-release
agents (3 different types including water- and petroleum-based products), bond breakers (3 different types including water- and solvent-based products), and cement splatter (same
mix proportions as the concrete) did not affect the bond for concrete strengths of 4000 and 5000 psi (28 and 34 MPa). Based on these test results, and the statements in ACI 31814
and ACI 30115, removing these materials from reinforcing bars isn’t required because the materials don’t decrease bond.” They add that, “ASCC concrete contractors believe that the
removal of form-release agents, bond breakers and cement splatter, provides no structural performance benefit to the owner.” While contaminants such as dirt and mud should always
be removed from reinforcement, based on the available research, Engineers and Certifiers should not be too concerned about some localised areas of surface contamination of the
reinforcement from products such as form release agents, bond breakers and oils. The final decision as to what is acceptable regarding surface corrosion/rust and surface
contamination is usually left up to the experience of the Engineer or Certifier, however, the information provided in this Technical Note is intended to provide guidance as to what
should be considered as acceptable."

Seems to me the takeaway is that initial slippage occurs sooner but ultimate strength is left unaffected...whether that has significant implications for serviceability is a mystery to me


Why yes, I do in fact have no idea what I'm talking about

RE: Form Release Agent on Steel Reinforcing

Do you have the manufacturer of the agent used? Do their instructions prohibit coating bars? That's it. I wouldn't pass it.

I'm in my phone and it's almost midnight, so this googling is the best I can do for you:


RE: Form Release Agent on Steel Reinforcing

Is the bond between the steel and concrete mechanical or by adhesion.

RE: Form Release Agent on Steel Reinforcing

There's a big difference between 'splatter' and rust, and form oil. A light area of rust actually improves bond. It's not good. For normal flexure it is not likely an issue because the bonding forces are small and the deformations accommodate that. I would be concerned about high bond areas, where the shear stresses are often high, such as the ends of beams or the ends of wall supports. If there are issues with the bonding, other than an extraordinary event, any harm (cracking) will likely occur at an early age.

I'm not a big guy for 'tearing things out', and try to work around that... maybe with an extended warranty if necessary... there is an element of risk.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates


RE: Form Release Agent on Steel Reinforcing

Here's a link to the study referenced by the SRIA in Just By Nerd's post (EDIT - Also linked by wrantler in first post). While it is probably not ideal, form release oil is commonly applied AFTER the rebar are in-place (thus coating them all) since it can be dangerous to place rebar while walking on a surface coated with form oil (very slippery). If you can coat the form far enough in advance such that the oil will soak in a bit, there is less of a health and safety concern. But time constraints sometimes dictate such a quick schedule that people arn't waiting around for days while the oil sinks in, and thus is applied after bar is in-place. While adhesion to the bars is reduced the bearing of the ribs is enough to ensure the usual behavior we rely on in most circumstances. This is obviously the position of the ASCC.

Here's how it generally goes. If it's just splatter on bars (read: not fully coated and generally applied before bars are in-place) combined with a mix in the typical range then you shouldn't be telling the contractor to do anything. If they did spray the entire matt then it probably wont be a problem, but you do have the ability to do something since ACI provides wording that allows you to do so. In which case you should evaluate how critical the area is that you're looking at, and if you need to teach the contractor a lesson.

IMHO in your specific case, with it being a retaining wall and not much H&S risk, I wouldn't be adverse to siding with these guys need to be taught a lesson.

RE: Form Release Agent on Steel Reinforcing

if this is governed by ACI 301 it is prohibited:

ACI 301-10 "...Do not allow formwork release agent to contact reinforcement or hardened concrete against whic fresh concrete is to be placed"

The residential concrete code ACI 332 says differently:

ACI 332-10

4.2.4 "Surface conditions of reinforcement—At the time concrete is placed, deformed bar and welded wire reinforcement shall be free of materials deleterious to development of bond strength between the reinforcement and the concrete."

R4.2.4 "Common surface contaminants such as concrete splatter, rust, form oil, or other release agents have been found not to be deleterious to bond."

RE: Form Release Agent on Steel Reinforcing

Quote (and if you need to teach the contractor a lesson)

in over 50 years, I've never taken that approach... it's just wrong!

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates


RE: Form Release Agent on Steel Reinforcing

Quote (dik)

it's just wrong!

The world's not black and white like that. If a contractor makes an honest mistake, I'm all for finding the most economical way of safely correcting the situation. But every now and then (especially in residential construction) you'll get a contractor who considers the code and an engineer's drawings to be suggestions at best. Why? Because they know better than some college kid. Or because their grand-daddy knew better. Besides - their engineer will sign off on it for them. I've seen guys like that create some dangerous situations. So I don't tolerate them. As soon as I get the sense that I'm dealing with one, I hold firm to the drawings, specs, letter of the code, etc. If they have to rip it out, that's their problem. Will they learn? More than likely they'll just learn to avoid me. But that's okay, too.

RE: Form Release Agent on Steel Reinforcing

All good reading. A lot of that which was posted I had found in my initial research. Some I hadn't. I was sort of dismayed at ACI's stance on this matter.

My first order of business is to place this issue exactly where it belongs. I have advised the contractor that this report will not be reviewed further, much less approved, until I am provided with a) the manufacturer of the form release agent, b) the specification data from the manufacturer, and c) a letter from the manufacturer, on the manufacturer's letterhead, stating that their product will have no negative effect on the bond strength of the concrete and the reinforcing steel and that even with the product fully coating the rebar, which it is, that the performance of the wall will not be affected. Additionally, I will be re-reviewing any previous reports and photos that may have gone through the system already.

My second order of business is to call ACI on Monday and find out why its ok for rebar to have form release agent on it in residential construction but not in commercial or industrial construction. Do the concrete and steel know whether or not they are at a residence or a factory?

RE: Form Release Agent on Steel Reinforcing

You will not get c), even if it had no adverse effects. Can the contractor get a letter from a consultant saying there will be no adverse effect?

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates


RE: Form Release Agent on Steel Reinforcing

dik, absolutely. And that's part of the problem. A bunch of idiots with seals running around saying anything for a couple hundred bucks. Just because it's on sealed letterhead doesn't mean it's legitimate. I've had contractors try to pull that on me before. My response was this: if your consultant is willing to assume the roll of EOR for this project and accept all design liability, I will step aside and allow them to approve whatever they want. If not, then you do it my way. (Also, no refunds.)

I wouldn't be worried about that letter unless the installation instructions tell you not to get it on rebar.

RE: Form Release Agent on Steel Reinforcing

I likely will never see a letter of any kind but I have put the burden of this issue where it belongs. Its not up to me to prove or disprove that everything is ok or not. I wasn't the one with the spray wand in my hands. Let them do whatever research and contacting and phone calling and letter writing that may be necessary.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close