bond-breaker vs tilt-wall rebar ?? 7

[boffintech]

Am an inspector (not EOR) on some work on a tilt-wall project. I have not asked the EOR about this yet but will if needed. No tilt panels have been poured yet. Thirty to 40 are under construction. The contractor is using Maxi-Tilt as the bond-breaker between SOG and tilt-panels. It says right in the Dayton instructions "Do not spray on reinforcing steel." But regardless I'm apparently the only one on the project that thinks it a bad idea to spray the reinforcing steel with the bond-breaker. Do I have it all wrong?

 

[msquared48]

Definetly not. Call the EOR.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[TXStructural]

ACI 301-10 3.3.1.1 "When concrete is placed, reinforcement shall be free of materials deleterious to bond. ..."

Bond breaker, by definition, interferes with bond, and should be avoided.

Some overspray of things like form oil is inevitable. Very thin mists of oils have not been shown to be deleterious to bond, but the line between acceptable and problematic is not well defined.

 

[frv]

No, you don't have it wrong.. but why would the reinforcing steel be sprayed with bond breaker? The slab should be prepared prior to constructing the panels.

 

[boffintech]

"why would the reinforcing steel be sprayed with bond breaker? The slab should be prepared prior to constructing the panels. "

1. slab sprayed
2. slab sprayed
3. rebar placed
4. rain
5. rain again

They all think I'm crazy and that some how tilt-wall panels are exempt from this ACI rule.

 

[frv]

boffintech..

Any bond breaker will have the exact same warning. How do you propose that they form the panels?

You have to trust that the subcontractor knows what he's doing. If you are going to micromanage every aspect of a project based on potential problems, it will not come close to being done on time or under budget. That's not to say you shouldn't be vigilant or speak up when it comes to pointing out errors or shortcuts, but the sub who does the tilt wall panels will be experienced with potential issues.

 

[TXStructural]

If they can demonstrate that the bond breaker will not be deleterious to bond between bar and concrete...

http://www.concreteconstruction.net/concrete-construction/how-clean-must-rebar-be.aspx

AND can show that the bond breaker will not increase corrosion in the bars.

Depending on the type of material applied, one or both could be an issue. Bar development is primarily a function of deformations wedging against the surrounding (well-consolidated) concrete, so a very thin film of material may be OK. A film-forming, membrane-type bond breaker may well significantly interfere with bond, while a waterborne material may form a reactive salt or soap layer which could lead to increased corrosion. Some bond breakers would do neither, and may be perfectly acceptable.

Remember that the EOR can waive provisions of ACI 301 when they have compelling reasons to do so. (Or no reason at all, if they really want to, and have the insurance to back it up.)

There are instances where our business is excessively conservative, but I don't think particular prohibition this is one of those.

 

[boffintech]

From the article:
" "When concrete is placed, all reinforcement shall be free of materials deleterious to bond." Inspectors often cite this sentence when requiring contractors to remove form-release or bond-breaker overspray and cement splatter from contaminated rebar. But is this work really necessary?"

Well over-spray is one thing and re-spraying an entire panel area with the rebar already in place in my estimation is something else altogether. I mean if rebar has been placed is a panel and the panel area next to that panel is being sprayed with bond-breaker and some "over-spray" drifts over in a breeze well OK, but if the rebar is already in the panel and the panel area is re-sprayed holding the wand 1' above two-mats of rebar so that all the rebar get thoroughly coated well that's just bad practice.

When any engineer says: "a little over-spray is OK" you have to try imagining that run through contractor DNA which is hardwired at birth to actually hear/interpret that as "100% coated with bond-breaker OK".

 

[spats]

"You have to trust that the subcontractor knows what he's doing"... good lord! I'm dumbfounded to find a polite way to respond to that statement. The reinforcing mats should be removed before respraying. Too bad it rained. Is that a good excuse for taking shortcuts that jeapardize the integrity of the panels? I've seen a lot of tilt-up in the field, and subs don't think it's even necessary to remove standing water in the forms. Would standing water be OK with you because the sub said it was OK?

 

[frv]

spats..

Read the OP's original post. He simply asked whether the bond breaker could be used. I took his scenario about raining as a hypothetical situation against which he was guarding by prohibiting the use of this bond breaker. It never occurred to me that anyone on this thread could seriously consider that a subcontractor would respray without removing the steel. Again, if the subcontractor knows what he is doing he absolutely knows that this is simply not OK.

But as to you being dumbfounded at my suggestion that at some point you have to trust that your subs know what they are doing.. why is this such an outlandish suggestion? Do you seriously micromanage every decision made by subs? That is precisely why you specify what inspections are required and you require an independent inspector. The subs are free to use means and methods they see fit and which, in theory at least, have worked successfully in the past. Provided they pass the inspections and your requirements, why would you micromanage. I'm assuming, of course, that part of your requirement is that all rebar be free of materials deleterious to bond.. or other such verbiage. If you have this in your inspection requirements, as most engineers do, then how do you think they will be able to justify spraying with the cage in place?

We work with a lot of tilt wall. I've never once had a contractor request spraying after the cage is in place. That's not to suggest it can't happen, but in the many tilt wall jobs I've worked on, it hasn't happened once.

I'd appreciate it if you were be a bit more judicious when throwing around words like "shortcuts". I explicitly stated that an inspector should be vigilant about compliance and spotting shortcuts. How do you take what I wrote and then literally suggest I'm advocating the contrary?

 

[BAretired]

I have not been involved in tilt-up wall construction, so I may not be understanding correctly, but there seems to be something wrong with the following:

1. slab sprayed
2. slab sprayed
3. rebar placed
4. rain
5. rain again

Shouldn't that read:
1. slab sprayed
2. rebar placed
3. rain
4. slab sprayed through rebar
5. rain again
6. slab sprayed through rebar again???


BA

 

[TXStructural]

It is common practice to spray in one direction, then spray in the orthogonal direction. THEN place the bar.

 

[Ron]

I'm with spats on this. My first thought after ready frv's post was "Are you nuts?" No disrespect intended, but I deal in the failure world daily and I can make this generalization with confidence and observations to back it up.....Most subcontractors know little enough about what they do (they often know one or two techniques to implement) and NOTHING about the repercussion of what they do. The GC's who supervise them usually know even less, but that's another soapbox that I won't climb on this time.

This has nothing to do with micro-managing and everything to do with the poor state of construction education, training, certification and licensing in the US (I am only referring to US construction as I know that boffintech is in the US). boffintech is exactly right to call them on this and exactly right to do his research and show them the error of their ways. He is being diligent and protective of the necessary process. The SEOR will hopefully laud his attention to detail and diligence. He should.

It never occurred to me that anyone on this thread could seriously consider that a subcontractor would respray without removing the steel.

Removing the steel takes time and effort. The spraying is probably being done by a subcontractor that has nothing to do with the steel placement, perhaps even the GC is doing that. Again...the guy probably knows how to spray bond breaker, but doesn't know the repercussion on other systems. If such a condition has not occurred on any of your jobs, you are dealing with a much better than average group of contractors. Congratulations. I know quite a few, but they are not the norm.

The subs are free to use means and methods they see fit and which, in theory at least, have worked successfully in the past.

Herein lies one of the problems. Design professionals usually refrain from dictating means and methods for liability purposes and under the sometimes false assumption that the contractor knows better ways to accomplish the end game. The difference is that the "end game" has to be performance of the system over its expected useful life. The "end game" to a subcontractor is often the lesser of either "when I get paid" or "when my warranty is up". That leads to the commonly used statement "I have over 20 years of experience doing this and I've never seen a problem"....well the problem is that they probably have 1 year of experience, 20 times over, having never seen the failed result of their work because either no one pursued it or no one could find them when a problem occurred. They usually don't know if their techniques have worked well in the past, they just know that no one has called them on it. Big difference. It is similar to the false assumption that is made about structural performance of buildings....they haven't failed in the past so they are not likely to fail in the future! Not true either. They probably have never been close to the design conditions.

Keep it up boffintech.

 

[Ron]

...sorry, "ready" should be "reading". I should proofread better or at the least, sooner!

 

[sandman21]

Ron is exactly right. The EOR should have some very kind words for the GC regarding this issue.

 

[boffintech]

sandman21 wrote: "The EOR should have some very kind words for the GC regarding this issue."

And he did: OK as-placed - spraying rebar with bond breaker not as issue.

 

[hawkaz]

CYA Time- Get a sealed letter in writing from the EOR, and include this letter with your inspection report

 

[BAretired]

That was a curious comment from the EOR. Perhaps he felt he had excess development length in the bars so that he could rely on mechanical bond of the deformations against the concrete...similar to epoxy covered reinforcement.

BA

 

[spats]

Nice rationalization BA... but I'm not buying it. Sounds to me like he caved, so as not to make waves and maybe jeopardize his relationship with the contractor or owner. Hope he sleeps well at night!

 

[BAretired]

You may be right, spats...I don't really know. I would have guessed that bond-breakers should not be applied to reinforcement, but the attached article seems to suggest that some bond-breakers do not affect bond between the bar and the concrete. I would have to study the issue a little more before drawing any definite conclusions, however.

BA