epoxy over etch

J

jeremyb

Alright...we all know the right way to do it. Epoxy only and be done, never have to worry about it. But a thread over at hr got me thinking...why are there etch/washprimers that you can supposedly (according to the tech sheets) apply epoxy over, and some that specifically say not to? Seems real confusing to the diy guys.

I dont care if you can or not..i'll never use the stuff but seems kinda odd that you can on some and you cant on others. Atleast that the way for ppg. Sikkens specifically says not to apply epoxy over their washprimer, same with lesonal and utech. Is it the etch/wash....or is it the epoxy that decides?
 
dont know why i even posted. such bad info i couldn't help it. wont happen again.
as for etch i have never heard good about it. we were forced to use it on aluminum and galvanized because nothing else would stick. damn ford trucks spent half their first 2 years in the paint shop. that is when media blasting with acrylic got big. ford paid to strip and repaint. we learned to use a real thin coat.
barry can give us the tech reasons i'm sure but that is just another example of how detrimental the net can be. to say etch gives better corrosion resistance and adhesion that epoxy is just irresponsible.
 
I believe self-etching primer was originally created for production shops to get away from the need to use metal preparation products (Metalprep, DX579, Metal Ready, etc.), to avoid the many problems associated with the improper use of such metal etch products, and (pre-DTM) to eliminate adhesion failure due to no etch procedure being used at all.

Misuse of acid metal etch products and/or improper metal cleaning is one of the major causes of substrate failure.

BUT, in the case where a self-etching primer might be indicated, the PROPER use of a metal etching system (tech sheets followed EXACTLY) will always outperform self-etch primer, and is even appropriate for DTM primers like SPI epoxy.

I know this because in my early days of using SPI epoxy, I experimented with using my old system of DX579/water rinse, DX520/water rinse/fast dry, just like I used to do with the old DP primer. It worked great, but as it turns out, all the extra work did not significantly improve adhesion, so it can be omitted with no compromise.
 
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