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Media blasting and priming before carrying out repairs/paint
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jotto



Joined: 12 Jan 2010
Posts: 5

PostPosted: Tue Jan 12, 2010 6:18 pm    Post subject: Media blasting and priming before carrying out repairs/paint Reply with quote

Hi all,

First post!

Im currently restoring my wifes 1969 VW Karmann Ghia and it needs some body work. I have decided that it may be best for me to get the whole shell blasted so that I can see what I have to work with and what needs doing.

I have a couple of concerns that maybe you can help me out with.

After blasting, the guy said he would spray it with a weld through holding primer.

Ideally I guess it would be best to go straight for an etch primer but I dont think that will be an option.
IF I do go ahead and have her blasted and primed, what sort of time span will I have to carry out repairs before needing to get her in for paint?

Also, after all repairs carried out and she is ready for paint, will she need to be sanded back to bare metal to enable an etch primer to be applied?

I'll be honest and say Im not looking for a show car by any means but would like to get her done fairly well. I will be trying to do most of the work myself!

Thanks in advance.
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CMI-Cars



Joined: 21 Dec 2009
Posts: 76
Location: Denmark

PostPosted: Tue Jan 12, 2010 6:38 pm    Post subject: Reply with quote

Well here in DK, its standard to spray primer on after blasting, so it dosent rust away. The primer is to be painted over when repairs are finished.

But again, the diffrence on sand blasters and there primers is very very big.
So to know the guy's work before he does your car, would be a big advandice.
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weldingclassics



Joined: 11 Jan 2010
Posts: 7

PostPosted: Tue Jan 12, 2010 9:02 pm    Post subject: Reply with quote

Hi it depends on how humid your garage is if its damp you will notice the panels gathering rust on an un painted vehicle, ideally as you say spray it in wash primer ie phospheric acid etch and that should do for a while to protect it while you carry out the repairs. I did my apprenticeship a while ago but we were taught not to leave a vehicle in primer to long as most primers are hydroscopic which means they absorb moisture from the air! but modern primers may be different i prefer to work old skool so we dont take chances Smile . we work in a nice modern insulated workshop and are currently working on a vw splitscreen which has been bare metaled 2 months ago we have no etch on it and its fine. hope this helps Wink
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weldingclassics



Joined: 11 Jan 2010
Posts: 7

PostPosted: Tue Jan 12, 2010 9:07 pm    Post subject: Reply with quote

type in soda blasting in "you tube" you'll be impressed..we saw a guy blasting a marcos bonnet with excellent results
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jotto



Joined: 12 Jan 2010
Posts: 5

PostPosted: Tue Jan 12, 2010 10:11 pm    Post subject: Reply with quote

Thanks for the replies guys.

I have thought about this and now my main question is, after having it media blasted and then primed using a non etch 'holding' primer, following repairs would you bare metal again and etch prime and paint as usual?

I too have heard that primer is hydroscopic and is not a sealer.
I assume bare metaling primer would be a lot easier than a full on paint job??

My garage is cold and dry but if raining hard you can see the moisture in the air.

Soda is a great media to blast with. Hardly any heat generated and is probably what I will use when I get around to doing my Corvette restoration.....I promised her indoors I would finish hers first!!
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weldingclassics



Joined: 11 Jan 2010
Posts: 7

PostPosted: Wed Jan 13, 2010 12:09 am    Post subject: Reply with quote

mmm non phosphate holding primer is used by panel manufacturers to make there panels look nice when you recieve them usually called transport paint we would remove this completley prior to phosphate wash coat. To spray a whole car in non phospheric holding paint then remove is not something i would want to do. There are holding primer products out there that contain phospheric i would go down that route as you can then paint over this. the short story is phospheric acid primer coat has to go on the metal for protection against rust first, then your primer filler coats then your colour coats if your bare metaling your motor. hope this helps
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weldingclassics



Joined: 11 Jan 2010
Posts: 7

PostPosted: Wed Jan 13, 2010 12:14 am    Post subject: Reply with quote

forgot to mention any filler work has to go on to bare metal first then spray your phospheric wash coat over the top of the sanded repair Very Happy Dont put your filler over paint as the feathered edges will lift from the solvents in the paint your applying..something you'll never loose right to the top coat!
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jotto



Joined: 12 Jan 2010
Posts: 5

PostPosted: Wed Jan 13, 2010 12:26 am    Post subject: Reply with quote

Thanks, I think I need to ask the guy exactly what he uses a a holding primer...may just be bog standard primer or it may be something more exotic.

I suppose I could just get him to blast it and then blow it over with etch when I get it home.
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