Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
(OP)
I am curious if anyone has any experience or knowledge regarding the effect that construction marking paint applied to non-epoxy coated rebar might have on bond strength (i.e., development length). Specifically, we are constructing large, circular foundations that require personnel to walk on top of the top mat of rebar. In order to "improve safety", it has been decided that they will spray paint a 4' wide "walk-way" all the way up the foundation. This results in a 4' wide by 30' long strip of rebar that is covered in paint (at least on the top half of the bars).
My concern is that this might act to debond the rebar from the concrete which would result in an increase in development length (similar to classifying these bars as epoxy coated rebar). However, I think that this case might even be worse than epoxy bars because the epoxy is fused to the bars whereas this spray paint is simply applied to the surface of the bar.
Any thoughts or concerns on this practice?
Thank you!
My concern is that this might act to debond the rebar from the concrete which would result in an increase in development length (similar to classifying these bars as epoxy coated rebar). However, I think that this case might even be worse than epoxy bars because the epoxy is fused to the bars whereas this spray paint is simply applied to the surface of the bar.
Any thoughts or concerns on this practice?
Thank you!






RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
https://www.facebook.com/AmericanConcrete/
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
Dik
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
1) I've seen a little research indicating that it's not big deal.
2) The mechanical action of the knurls is still in play and counts for a lot.
3) You're only painting one side of the bars.
4) In one direction, it's just some bars of many.
5) In the other directions, it's just a part of the span in the field.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
Dik
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
Here is an article from the American Society of Concrete Contractors:
https://www.ascconline.org/Portals/0/docs/POSITION...
Linked here is one of the studies they reference (click download to see the pdf):
http://www.concreteconstruction.net/how-to/materia...
Linked here is the other paper they reference:
https://www.concrete.org/publications/internationa...
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
MightyEngineer - I am not sure if the bars work as epoxy coated. We are not the engineer of record.
KootK - I agree with your points. All of these concepts "help us out" in this situation.
DETstru - Interesting articles. I am very surprised that bond breakers do not affect bond as is stated in the ascconlne.org article..
I've attached a photo showing the current practice.
On a similar note, if none of these substances (e.g., form release agents, bond breakers, cement splatter, and potentially spray paint) effect bond, why does epoxy coating effect bond? Is it more related to the thickness of the epoxy coating that reduces the effectiveness of the knurls?
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
On a side note, if such a footing had any problem due to this spray painting, the problem wouldn't be the spray painting...
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
I am curious, what does your statement about the footing having problems that are not due to the spray painting imply?
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
My statement was just a smart ass comment. Sorry for not being clearer. What I meant was that the impact of the painting on a foundation of that size was certainly negligible and that if it had any problems it wouldn't be because of the reduced bond on such a reduced length.
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
RE: Does spray painting rebar with Construction Marking Paint effect bond between rebar and concrete?
DETstru - Yes it is an interesting foundation! It is a wind turbine foundation. See the attachment for a photo of a different foundation.