Does anyone know if intumescent can be applied over existing fireproofing in a remodel project?
I don’t know for sure, but this sounds like a problem in the making. When the intumescent foams in a fire, wouldn’t it physically pull off the “regular” fireproofing? That is, if it even could be applied to such a porous surface. Why not just repair the existing fireproofing?
I believe most manufacturers have standard details and caveats to transition between the two. As I recall the preference is typically to apply the intu over the spray-applied fireproofing as activation will protect the sprayed fireproofing.
Like John my first reaction would be to repair the existing fireproofing. Has the existing product been tested for asbestos?
Ask the AHJ. I suspect the answer will be, show me the test report or approval, which no manufacturer is likely to have paid for. (Unless both products are by the same mfr.)
Just a guess.
I almost agree with John Bunzick here, except I think a 1/4" thick coating of intumescent mastic would fall off a friable surface like fiber or cementitious fireproofing all by itself.
What is the purpose of this “execise”? If the purpose is to increase the fire resistance of the structural members, then the best solution is to use additional thickness of the same type material.
I found an very informative article by the CSI Worcester chapter that address this very issue.
http://csiworcester.com/existing-buildings-fireproofing-to-patch-or-not-to-patch/
Dave, thanks for posting the article from CSI Worcester. We had a similar question come up on a project lately. Long story short: no one wanted to do what needed to be done (analyze a sample) to determine the exact makeup of the existing SFRM. I hope that eventually happened.
On a side note, I shared the article with the project architects for whose projects I usually prepare specifications. So far I’ve had no response - not even a thank you for sending. Perhaps the article was too long. After all, it took me two whole minutes to read the article and highlight the important points. [despair]
James, maybe you can make it into an in-house education program for them. You know, read it to them. Think audio book vs. reading.
Ken, you always have the best ideas. Actually, we do lead off every Friday morning practice meeting with a “quality moment” and this would be an ideal subject. The last quality moment I presented was on the evils of writing “Match Existing” in the specifications and drawing notes.
The real problem is there is so much to know and no one can really know what he or she doesn’t know. 
Good morning James,
I am guilty of using the “Match Existing” phrase.
Will you share your “quality moment”? If yes,
please email me wayne.yancey@crtkl.com.
Thanks,
Wayne
Wayne, I sent an e-mail to you from my gmail account. In a nutshell we should not write “match existing” unless we actually know what it is that is existing.
Another problem with “match existing”: Are you matching what “was” when the product/material was installed or what it “is” now? After being exposed for however many years, colors (among other aspects and characteristics) change. And of course, the eye of the beholder may also have an impact on “match”. The phrase leaves too much to chance and discrepancies.