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Subject: Re: Post over Pre

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Message Thread:

Post over Pre

4/20/17       
Dan

I know you're not supposed to put post over pre catalyst product.
I have a customer with a 10 year old kitchen top coated with magnamax and they want it redone in white. I prefer post catylist for solid colors. So does sand, clawlock then the white sound good or do I have to use a vinyl sealer over the magnamax first?

4/20/17       #2: Post over Pre ...
RobertJ

Your process sounds fine by me. I would not bother with the Vinyl Sealer. Clawlock will bond once the wood has been thoroughly cleaned and sanded. Post cat over Magnamax is ok; not the opposite.

4/20/17       #3: Post over Pre ...
Dave Edgerton  Member

I second what robertj said

4/20/17       #4: Post over Pre ...
Paul Snyder  Member

Website: finishing.tips

I'd recommend you finish the back of a door, wait a few days, and then do a cross-hatch adhesion test.

The test will tell you if you have a wrinkling or adhesion problem. Pre-catalyzed finishes are not as densely cross-linked as post-catalyzed and may absorb the solvents and swell when you apply a new finish over them. If it passes the test, there's a good chance it will work on all the doors.

Then all you have to worry about is fisheye.

4/21/17       #5: Post over Pre ...
David Thiessen  Member

Website: dtwoodworker.houzz.com

Definitely do the adhesion test. I know someone who did exactly what you are proposing and they came out with wrinkles. It won't show up in the first coat either. Only after the second coat did the wrinkles show up. The ML Campbell folks have always told me never post over pre, hard over soft. Only the other way around.

4/22/17       #6: Post over Pre ...
RobertJ

I stand corrected, David is right. What was I thinking. Magnamax, a softer finish (since it is a pre-cat) cannot be coated with a harder finish, like a post-cat lacquer or 2K urethane. Paul Snyder has the right suggestion if you want to experiment on the adhesion issue. You could just use MLC Magnamax Pigmented lacquer. As such, do look for wrinkling.

4/24/17       #7: Post over Pre ...
Matt

Having sprayed a LOT of Magnamax, Clawlock, Stealth, and Resistant, I would recommend strongly against this.

Especially if the substrate of any of this is MDF. I've seen Magnamax not adhere as well as hoped to MDF and I've seen it cellophane itself off of plywood (granted, I've also seen it happen with several conversion varnishes that I still like).

In your situation, I would spray one coat of white vinyl primer, and one coat of white precat. Maybe one final coat of clear if you want to add a final level of durability and elegance (obvious upcharge).

I've refinished a lot of kitchen doors with this procedure. Works very, very well, even over "unknown-maybe-nitro-lacquer" substrates.

 

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