SSPC question

By swnorris (****)

Date 06-28-2007 16:29

I think that you'd measure a number of uncoated spots to obtain a representative average value, and then measure a number of spots in accordance with Section 3 of SSPC-PA 2. You'd then subtract those readings from each other to obtain the DFT, which you'd then compare to your 3 mils DFT requirement. It should all be addressed in SSPC-PA 2.

By jwright650 (*****)

Date 06-28-2007 16:47

Which type DFT gage are you trying to use?

By hogan

Date 06-28-2007 17:35

it's electronic
the issue is i have a dot inspector that is trying to tell me that i need to subtract the profile reading (replica tape) from my 1st coat. i have never seen this requirement. i've asked for a code reference, and have not received one yet.

By jwright650 (*****)

Date 06-28-2007 18:20 Edited 06-28-2007 18:23

He's thinking of a Type I gage(banana gage). You establish the BMR and then subtract the BMR from any DFT readings taken after you have painted it (for each coat).

For your Type II gage, you use a selected shim on the bare blasted surface and make the gage say what thickness shim you used. This type II gage already takes into account the BMR so all of your subsequent readings are correct as read on the gage.

By Joseph P. Kane (****)

Date 06-28-2007 21:01

Hogan

Regardless of the type of instrument you are using here, Type 1 or Type 2, or even UT, you have to be very cautious here. If the Product data sheet from the paint supplier calls for 2 to 3 Mils surface roughness profile, and your contract specification calls for say 3 to 5 Mils DFT, and you have a 3.5 Mil profile, you may have to put down 6.5 Mils to be sure that you cover all the peaks.

The relationship between 2 to 3 Mils Surface Roughness Profile and a 3.2 Mil or a 3.5 Mil profle is not arithmetic. I won't say that it is Log - Log or Geometric progression, but it is definitely not just add .5 Mils to the 3 Mils and add a .5 to the thickness.

I might be able to explain this concept better over the phone.

Joe Kane

By hogan

Date 06-28-2007 21:20

joe
do you know of any sspc code reference, or commentary. something that says to add the profile, or not to? i can appreciate the reasoning either way. i would like to see it in writing.

By Joseph P. Kane (****)

Date 06-28-2007 23:18

Hogan

There is an explanation of how to use the type 1 and type 2 instruments In SSPC PA-2. However, since I do not have more details about your painting requirement, the contract requirements, and the type instrument you are using, I couldn't give you anything definitive.

I am influenced by a problem that is rather timely with your question. I am inspecting the painting on some of the he World Trade Center Transportation hub steel. The Painting Contractor had to place a 2 to 3 mil blast profile and then coat 3 to 5 mils of Carboline 859. When I checked his blast profile, I noted that he had 5.6 Mils when merasured with an Elcometer 224 Electronic Profile Meter. The contractor was using the Testex X-Coarse Tape and showed 3,6 Mils. So, the Client / Owner agreed to use the Testex Tape profile readings. The contractor called Carboline Technical, and was told that he had to add three mils over whatever readings he had above 3.0 Mils. Thus, the painting contractor had to place 6.6 Mills of paint to get the minimum 3 Mils of coverage.

Now. this contractor can achieve a 2 to 3 Mil profile, he just has to use lighter shot/grit combination. He dosen't want to do that, because it would double or tripple the time it took him to blast the beams. What he didn't know, was the effect that going over the maximum recommented blast Milage would have on the paint thickness requirements.

Both the contractor and I (as the third party inspector),have Type 2 DFT gages. With the Positector 6000, I zero it on the bare blasted substrate, then adjust it on a 6 Mill plastic shim. I also have an Elcometer 345, ( 9 button) Type 2 DFT gage. With that instrument, I use a 5 Mil shim on the blasted substrate and then a 10 Mil shim. This assures accurracy within a certain range.

If you go on the www.ktagage.com web site and look in their catalog, there is a book about using paint testing gages. It costs about 80 dollars. The SSPC- PA2 costs about $20.00.

If you want to Send a private message, and give me your phoine number. I can call you tonight.

Joe Kane

By Greg G. (**)

Date 07-16-2007 17:05

Look at your spec. It will tell you the coating system that needs to go onto the part. Or if there is no spec then look at the top coat that will be used. Look at the suppliers book and it will give you what the top coat should be primed with and it will give the DFT for each coat. International Paint will have all that information.