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February 11 - February 17, 2013

Can water be sprayed onto an IOZ coated surface, which has not fully cured due to low humid conditions, to accelerate the cure?

Selected Answers

From Krishnan Swaminathan of Central Electrochemical Research Institute, India, Research in Protective Coating field for 27 years on February 15, 2013:

From Stephen Cantrelle of Concord Terrazzo on February 18, 2013:
     Yes. Allow solvent to flash off first.

From Simon Hope of Bilfinger Salamis on February 18, 2013:

     It is absolutely essential that IOZ is subjected to water, as it is needed as part of the chemical reaction to obtain chemical cure. IOZ will not cure in low humidity even though it seems to be dry; this is one of the most common failures to manifest as an apparent cohesive failure. Water must be present. High humidity is best, but a fine spray applied to the entire structure will work once the IOZ is through dry. It is essential to check the degree of cure using a white rag soaked in solvent, gently rubbed on the surface to ensure no material is dissolved. Once the IOZ is cured, it is imperative that the coating is thoroughly dried before the application of the sealer coat; otherwise, you will have reaction of the zinc to form oxide and the inevitable disbonding again!

From Karen Oscarson of PPG on February 15, 2013:
     Yes, that is common practice in geographically arid parts of the world.

From S. Matsumoto of Abraco on February 15, 2013:
I have similar experience. Spray water but do not wash after a couple of hours.

From Ahmed Abd Ellatif of MOPCO on February 28, 2013:
     Yes, apply water if the relative humidity is below 65% but wait for 2 hours after application and use water with a low salt percentage because  salt will delay the curing.

From Stephen Bothello of Jotun Paints on February 20, 2013:
     Yes, water can accelerate the cure. However, it's better to check with the coating manufacturer before taking this step. Seldom at low relative humidity levels below 30%, even with repeated water spray, it may not cure, depending on the product formula, and  all uncured coating may need to be removed. This can therefore be confirmed only by the coating manufacturer's technical representative. In inorganic zinc silicates the curing/optimum strength development is by the hydrolysis reaction (addition of water) of the inorganic silicate binder/ polymer. A major part of this hydrolysis reaction is executed in the factory during production process by adding calculated amount of water and catalyst. The balance of the hydrolysis reaction has to be completed by water molecules from  atmospheric humidity (after mixing & application). Most hydrolysis reactions are normally standardised by the manufacturers at 60% to 75 % atmospheric relative humidity levels. Lower than this humidity level  will require external water spray (mist spray is sufficient,  not high pressure spray ). At exceptionally low relative humidity levels (generally below 35%), it's better to call the manufacturer's technical representative and ask for technical advise/ intervention before application. Completion of this reaction to optimum levels/ cure state is assessed by the mandatory MEK rub test (ASTM D 4752). A rating minimum of 4 is good enough and 5 considered excellent for cure and strength development for subsequent coating with epoxy midcoat/ other coatings. Coin rub test for burnishing effect can be used as an additional confirmatory test to confirm curing over large/ entire area.

From Jayakrishnan Radhakrishnan of Sigma Paints Saudi Arabia Limited on February 14, 2013:
    Yes, after approximately 4 hours of application, the primed surface should be wetted or soaked with clean water for 2 hours, followed by complete drying.

From Grant Kirby-Smith of Jotun Paints on February 11, 2013:
     Yes, provide it has dried for at least a couple of hours or it will wash off. Always conduct an MEK rub test + coin test to ensure the primer is cured before overcoating.

From Farooq MD of RasGas on February 12, 2013:

From Dipesh Vyas of CARBOLINE on February 15, 2013:
     It is recommended to maintain humidity by sprinkling /spraying or misting of water but not by soaking /immersing after a minimum of 2 hrs of cure ( 23 C), and check after every 3-4 hours to determine if required step can be repeated . It is as good as cement in the way it drinks water till it becomes hard rock. IOZ curing is also more or less similar.

From willem van Gent of corrcon Marine on February 10, 2013:
     I have experience on hatch covers in Korea where we use water spray in the winter time when the humidity is very low on IOZ primer after spray application with a good result.

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Tagged categories: Coating Materials; Curing

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