Code and/or allowable +/- thickness allowance over specifed Paint thickness

I would be Inclined to ask the client for a tolerance! or even give him some test samples with different thicknesses of paint that he can see and say "no less than this" and "no more than that"

Till now, I didn't seen such code that stated the acceptance of criteria for percentage of total dry film thickness, DFT. But a lot of companies state their own standards which define the tolerance and their acceptance of criteria. It is recommended and necessary for the QC to measure the wet film thickness, WFT to adapt the actual thickness required.

For me, I recommend a ±10% as a tolerance and an acceptance criteria for DFT.

Painting a truly UNIFORM thickness (on a large structure) is next-to-impossible. The SSPC (formerly known as Steel Structures Painting Council, but now known as the Society for Protective Coatings) and NACE (National Association of Corrosion Engineers International) both have extremely good training programs for paint & coatings inspectors ... (it would boggle your mind, all of the tools, instruments, and surface contaminent test kits available, and what it takes to use them all properly!).

Paint & Coating SPECIFIERS ought to be required to attend such courses. Most paint manufacturers train their representatives accordingly, so they can help the end users obtain the degrees of performance that are capable of today's High-Tech coatings.

You did NOT state what TYPE of coating was applied, or whether a primer was involved, or for that matter, what the surface profile was (was it blasted; if so, with what type & grade of media, and what were the peak-to-valley measurements?).

The specifier should have specified ALL of these things (and more, including an acceptable RANGE of thickness; e.g., 275-400 microns). On your carbon steel shell, a magnetic-type coating gauge (in the right hands) might give you better data, depending on the profile (and of course, a proper calibration which takes the profile into account!).

Your 200 micron measurements are probably a bit on the light side, regardless of the type of coating. The 650+ readings might or might not be detrimental to the coatings longevity, depending on the type of coating and its exposure (environment).

Take a little more data straight to the coating manufacturer themselves, and they should give you a straightforward reply.

Best Regards . . .

Dear all,

Painting Specifications are as follows:

Surface preparation: SSPC-SP2/SP3

Prime Coat : APCS 26A Epoxy Mastic DFT = 125 Microns min

Intermediate Coat = APCS 26A Epoxy Mastic DFT=125

Finish Coat = APCS 25 Polyurethane DFT = 50 Microns

Finish Color (Indicative) = Light Green Munsell 5G-8/2

The Contractor is explaining that as while coating, at few of the places, the old coating was intact and good and as they didn't wanted to remove hence they have done coating over it, and this is the reason of the increased thickness indications and hence we should accept it. Now the contractor have also submitted a document from the Paint manufacturer's officials telling that there should be no problem for its increased Paint thickness and that the increased thickness can go upto a maximum of 900 Microns.

However what ever is his (Contractor) justification, The problem is that how we should accept it and on what code/Justification/Technical support Information etc.

Please Guide

Dear sirs,

I am the client, and the Paint manufacturer's officials have given a statement telling that the thickness can go upto 900 Microns. So I wanted some code/guidance/Technical support for you all Guru's, so that either I should accept Paint Thickness upto 900 Microns inspite of being specified 300 Micron in the submitted scope of work to the contractor, or to outrightly reject it, or accept it with a pinch of salt, as now after painting it for more than the required thickness now he can not go back and grind it/rub it so as to reduce it to 300 Microns, come what may.

Looking for a support statement.

Thanks and regards.

In the US, our Code of Federal Regulation mandates that protection be applied for atmospheric exposures (plus CP if buried or submerged, referring to gas, oil, and hazardous materials vessels and pipelines), but the *Codes* do not apply to water containing vessels and pipes, nor do the Codes get into the arena of "Specifications". That is up to the team of engineers, including whoever is chosen to write the Paint Specification. This has long been an often overlooked or understated aspect of MANY jobs ... tanks, bridges, ships, etc. Both NACE and SSPC (mentioned earlier) are doing what they can to change this...!

The SP2 Standard relates to hand tool cleaning... the SP3 Standard relates to power tool cleaning. Thus, the *Spec*, stated above, is INCOMPLETE. Purchase a copy of the Visual Reference Standards, and you will see the wide acceptance range afforded by such a broad statement (in the spec).

Nowadays, SSPC and NACE have teamed-up to author "Joint" Standards. It behooves anyone with a large paint/coating/lining job to hire a Certified Coating Inspector to oversee everything from the surface prep thru mixing thru application and curing of todays high-tech polymer coatings. Especially given the tendency of contractors to cut corners wherever possible, and the need to adhere to proper environmental conditions (per manufacturer) during application.

Go to www.nace.org , sign-up (free!) for the Network (List Servers) in the "Coatings Forum", and you can pose such questions to the experts WORLDWIDE. What you will probably be told is "Hindsight is always 20/20"... One of our esteemed colleagues lectures: "You don't always get what you pay for, you get what you INSPECT!" which means, inspecting all-along-the-way, from start to finish. What degree of surface contaminents were permitted by the Specification (meaning soluble salts, ferrous salts, sulfates etc)? At this point, if the manufacturer themselves are saying that the high dft's are acceptable, it's going to be a case of c'est la vie. Lesson learned. Next time, know exactly how and what to specify, and then make sure a qualified inspector is there to enforce the specification.

Best of luck to you...

Dear Sir,

I am thankful for the detailed answer.

However for Paint rehabilitation work at some locations due to Operation restrain we can not use power tools thats why generally we specify both, SP2 & SP3 as if in case Power Tool use is not allowed than he can apply SP2 type of cleaning, and the surface roughnes could be checked by visual Inspection.

Now if I understand what you telling and please correct me if I am wrong is that as for now I should accept the paint, there is no +ve tolerance allowance for paint thickness, and in future we have to depute a full time Inspector.

If that is the case, then I can do nothing but to accept the Paint.

However if other Guru's are having a different opinion or view about the whole activity, than they are more than welcome and are humbly requested to do so.

Thanks and regards.

VKJ

Although there is no official Code jurisdiction in your case... for future reference, you will want to arm yourself with the knowledge to know HOW and WHAT to specify. (You write the spec that the contractor must adhere to, so you must be detailed, with NO ambiguities.) The American Water Works Association writes Standards which may be referenced by any end user who might benefit. Some of these are authored jointly with ANSI. Check out the steel water storage tanks document at their site:

http://www.awwa.org/bookstore/product.cfm?id=30042

God bless your future endeavors.