AU over POR15?

Gentlemen,

I wish to use POR15 on a rusty piece of equipment and want to topcoat it with a two-part automotive acrylic urethane. I want to use an automotive urethane because of specific color desires. My question involves the topcoating process. I wish to topcoat directly to the POR15 without an intermediate primer product. I also wish to avoid any kind of sanding or scuffing of the POR15 surface for the purpose of topcoat adhesion. Since POR15 is a single component, moisture-cured urethane, I am wondering if there will be any cross linking or chemical bonding of the automotive urethane if it is applied before full cure of the POR15, thereby obtaining good adhesion without the need for mechanical abrasion. I would appreciate any comments you might have on this approach, together with any minimum/maximum recommended time period between application of the last POR15 coat and the color topcoat, if such can be done successfully.

Thanks,
Rod

I got an answer from them this morning. A fast response considering the holiday:

Yes it can be done; you will have to apply your urethane over the Por15 when it's dry to the touch with slight finger drag remaining (2 to 6 hours). If you miss that window then you will need to let the Por15 dry 24 hours then sand the surface and apply or you can use our Self Etching Primer, let that dry 45 minutes then apply your urethane.

Further questions call or email

View our products online at www.por15.com Por15

Which is what I sort of expected. I am getting concerned with the actual mechanics of doing this with POR. The job is a 3pt snowblower that is heavy. I will need to use the bucket loader to turn it for painting, even with the second stage impeller assembly and the first stage screws removed and done separately. PO15 has a rather tricky prep to use it as recommended. Wire brush. Marine Clean, then flush with water. Let dry, apply Metal Ready (a proprietary phosphoric acid mixture), then flush with water. Must be absolutely dry before applying POR. Apply first coat, wait 2-6 hours, apply second coat, wait 2-6 hours and apply the topcoat as the response indicates. A very short window. That makes time a problem, especially when I am doing this outside. I could do the prep beforehand. This time of year there is apt to be a heavy dew in the morning and early evening. To have it completely dry, I would probably have to wait until late morning to begin applying the POR. The 2-6 hours is dependent on temperature and humidity. My guess is it will be about 3-4 hours on the best of days this time of year. That gives about 8 hours or so from completion of the first coat to beginning the topcoat. If I should complete the first coat of the POR by 11AM, it winds up to be 7PM before I can apply my 2 coats of urethane topcoat. That's too late in the day for that. I am considering moving the main blower shell into the shed before dew on the prep day and moving it out as soon as possible on the paint day. That could gain me a couple of hours or so in the morning. I am also considering spraying the POR to gain a little time although I really don't want to. Supplied air is not a problem but I am very nervous about putting that stuff through my good gun(s). I am even considering buying a cheap gun from Home Depot for that purpose, just in case. Additionally, I am considering a single coat of epoxy primer on that POR paint day instead of the topcoat. That could gain me a bit more time and I could delay the topcoat until midday the following day (or during the next 3 days). I've read where that has been done with POR successfully, although POR sells their own proprietary "etch primer" for that purpose. I suppose I could just bite the bullet and apply their proprietary etch primer. However, reading the instructions for that stuff suggests that sanding is still needed after full cure of the POR15, despite the implication in the response that it is not. I refuse to get into the scuffing/sanding routine on this piece of equipment. It's a maintenance/life extension task and I have better things to do than mess around with it like that.

I am also looking into Zero Rust as an alternative to the POR. I've used Permatex Rust Treatment before successfully but want to try something different. I've heard that the POR is the best for abrasive service and that is why I am planning on it for this snowblower. However, the tricky scheduling has got me looking at Zero Rust. That promises to be a lot cheaper, a lot safer (no isos), easier to use and to work better than POR. I am somewhat sceptical of such claims. I do see that Len at autobodystore.com has tested the Zero Rust against the POR15. His results are quite convincing that the Zero Rust is superior, at least as far as rust control goes - nothing about abrasion resistance. I have a lot of respect for Len and believe he gives good advice but he does sell the Zero Rust and not the POR as a part of his business. That fact leaves a cloud over any such testing as not being completely unbiased. I've read some comparison user reviews on the net where some are POR believers and just as many others, it seems, are Zero Rust believers. Sort of like the epoxy vs. etch debate. My tendency at the moment is to stick with the POR if I can come up with what I think is a workable schedule considering the limitations. I am open to anyone's thoughts or advice on the subject however.

Rod

Thanks for that input. I may very well wind up doing it that way. No matter how I cut it, going strictly by POR's instructions, it gets real tight timewise. Surely there must be some window beyond their stated single point in time. I could do one coat of POR late in the day and the second coat first thing the next morning. That would be 16-18 hours. That would give me plenty of time the same day to apply the two color coats, which can be done within 15 or 20 minutes of each other.

Rod