Issue link: http://www.e-digitaleditions.com/i/799392
28 POWDER COATING, March 2017 Adding something that ultimately raises the final TDS of water will have a detrimental effect on ASTM B-117 salt-spray or humidity results. In addi- tion, if you don't batch your rework for the end of a particular shift, you'll deter results on virgin work, so this must be tested to really know if you're solving one issue, but creating another. When batching and adding a wetting agent, you should dump and recharge that stage with freshwater after run- ning the rework. As far as what the best TDS is, DI or RO is preferred. If you don't have a high-quality water option, then take your virgin well water and best possible TDS water to test on parts to see if you telegraph or deter coating specs. This could also be done with panels in each chemical vestibule entry; for example, near the pump and the screen (tank lid). To directly answer your question, I'd say 50 TDS or less. The real answer is found through testing though. I hope this helps you resolve the issues. Please take the high road, and do whatever it takes to prevent or minimize eroding profits when producing a failure in the first place. PC Editor's note For further reading, see articles under the Surface preparation heading in the "Index to Articles and Authors 1990- 2016" Reference and Buyer's Resource Issue, Powder Coating, vol. 27, no. 6 (December 2016), or click on the Arti- cle Index at www.pcoating.com. Arti- cles can be bought online. Have a ques- tion? Click on Problem Solving to submit one.