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May 31 - June 22, 2010

If I apply a zinc-rich epoxy primer at 3 mils’ dry film thickness in the shop with air temperature of 90 F, what checks can I make to determine when it is safe to handle and stack the primed steel components?


Selected Answers

From Adam Backhaut of Diamond Vogel Paints on June 9, 2010:
All technical data sheets will outline dry times, flash times, mix ratios, surface prep requirements, and other information. I would revisit the data sheet since every coating is formulated with different resins and solvents, which will change dry times. I would check the dust free, dry to touch, and dry to handle times to verify the proper use of the material.

From TOLGA DIRAZ of PPG Industries - Bursa Plant on June 7, 2010:
I assume that the key word here is the "dry-to-handle time," which is theoretical information available on the paint product datasheet with respect to a certain temperature and and relative humidity. This parameter can be also be measured at the shop by Pencil Hardness Test (ASTM D 3363) if the specific pencil hardness,i.e., 6H-6B at the dry to handle stage of the paint is obtained from the paint manufacturer's datasheet.

From VCBud Jenkins of CSCS on June 6, 2010:
Take a rag dipped in lacquer thinner or MEK and do 50 double rubs. If there is no mark left on the coating or no color transferred to the rag, the coating is probably fully cured and should not block. Also, you can coat two panels at the same time you are coating the parts and put them in a vise face to face for an hour or two. If they come out of the vise without blocking, it is another good indicator that the parts will not block.

From VCBud Jenkins of CSCS on June 6, 2010:
Take a rag dipped in lacquer thinner or MEK and do 50 double rubs. If there is no mark left on the coating or no color transferred to the rag, the coating is probably fully cured and should not block. Also, you can coat two panels at the same time you are coating the parts and put them in a vise face to face for an hour or two. If they come out of the vise without blocking, it is another good indicator that the parts will not block.

From Barry Barman of Barry Barman & Associates on June 1, 2010:
Typical zinc-rich epoxy primers (SSPC Paint System 20 - TypeIIB) applied at 3 mil DFT and held at 90 F will be sufficiently dry to handle in as little as 2 hours - after the solvents have evaporated and the cross-linking is substantially complete. The dried coating may be tested for degree of cure in accordance with ASTM D5402 - 06, Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs. If there is little softening or color transfer using MEK solvent, the coated parts should be relatively safe to handle and stack. Of course, care must be taken to prevent mechanical damage, especially along edges from slings when loading. The coating may require as much as 7 days to fully cure, dependent on humidity and temperatutre.

From Trevor Neale of Blastech Corporation on June 1, 2010:
ASTM D 3003 is a test method to evaluate the blocking resistance of organic coatings on metal substrates and consists of pressure, time and temperature measurements. Since not all zinc rich epoxies are created equal, the answer to the question is best generated by a practical test with the selected product in the shop which will reproduce the condition of the weight/pressure on the coated parts for a time span necessary to meet the job requirements. Alternatively, the coating supplier may have the necessary test equipment to generate the information for the selected product.

From Ron Lanter of Protec on June 1, 2010:
I would check the paint manufacturer's product data sheet. It should tell you when you will be able to handle the material due to temperature and paint thickness when it was applied. After the specified time has passed and dft was taken I would use something like a quarter and perform a scratch test, visually confirming that it is dry enough to handle.

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Tagged categories: Coating / Film thickness; Zinc-rich (organic)


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