Paint Prep

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Redmoggy
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Paint Prep

Postby Redmoggy » Tue Jul 21, 2015 9:30 am

I'm curious Gents. Lots of posts seem to come up about paintwork and prep. My other hobby that will help fund my 49 Resto is painting vintage Motorbike tanks. Since these are generally quicker to prep than a whole car but the same basic principle would anyone be interested in a step by step?

Regards
Rod

Autobahn
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Re: Paint Prep

Postby Autobahn » Tue Jul 21, 2015 12:04 pm

1) remove all old paintwork, this can be done with a sander or paintstripper.

2) prepare by rubbing down with 320 wet and dry in soapy water.

3) wipe over with pre paint degreasing agent.

4) make sure anything that is not to be painted is properly masked.

5) paint with a good two pack (2K) primer using a suitable primer colour for your intended top coat, or use a etching primer which is recommended for bare metal. Use a fast winter activator and make sure primer is mixed to the correct recommended ratio as they can vary.

6) after minimum of 24 hrs flat with 600 wet and dry in soapy water.

7) wipe over with degreasing agent again and then a tack rag to remove any dust.

8) part is now ready for painting with your top coat, the application of top coats vary depending on type you are using and if solid straight colour, solid base and clear or metallic . Example if 2K solid colour you need to dust a light coat on first, then 3-4 full top coats depending on colour. ( normal time between coats is about 15 minutes.)


irmscher
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Re: Paint Prep

Postby irmscher » Tue Jul 21, 2015 12:10 pm

You have to watch out with two pack as its cyanide based :o

Autobahn
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Re: Paint Prep

Postby Autobahn » Tue Jul 21, 2015 12:25 pm

irmscher wrote:You have to watch out with two pack as its cyanide based :o
Yes obviously proper protective clothing and mask MUST be worn and anything in the area must be covered to avoid overspray and dust sticking.

But I was responding to ops specific question as to the prep process to enable him to achieve a good paint finish which is to professional standard.

It is possible to achieve a reasonable finish with aerosol cans from Halfords which might be good enough for many DIY jobs.


amgrave
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Re: Paint Prep

Postby amgrave » Tue Jul 21, 2015 2:18 pm

I think the OP is suggesting he would post a step by step if there was the interest. I think there is a post already about how to spray synthetic somewhere on here so one for celly would be good I think as it is a different procedure. I think people assume you buy some paint and thinners and spray equipment and away you go but like most things there is a knack to celly. Might be different now but when I was spraying there were three different thinners to use depending on the temperature of the day then there was getting the pressure and spray pattern right etc etc. Once mastered it's easy and forgiving believe it or not. So yes I think a step by step would be good especially if it covered getting over any problems encountered.


panky
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Re: Paint Prep

Postby panky » Tue Jul 21, 2015 3:01 pm

I think a guide would be very useful, if to point out the potential hazards if nothing else :)
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Redmoggy
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Re: Paint Prep

Postby Redmoggy » Tue Jul 21, 2015 7:33 pm

Well, I was thinking more of something based just on prepping for top coat and not using 2K products. That can then cover body filler prep ect.

Rod

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Re: Paint Prep

Postby panky » Tue Jul 21, 2015 7:43 pm

I for one would find it very helpful as my attempts at spraying leave a lot to be desired :roll:
Always glad to hear from those with experience.
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Redmoggy
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Re: Paint Prep

Postby Redmoggy » Wed Jul 22, 2015 10:44 am

Might just be for you then, Panky.

I'm in the process of painting a 70's Triumph tank at the moment. The owner wanted some progress pictures so I'll post them here as well with a description. If it's of no interest or use just say so and I'll stop.

I don't like to use paint stripper, they normally require washing with water which promotes corrosion. Sanding a paint finish can be a long and arduous task and by definition removes a small amount of metal from the surface. Instead I start by using a hot air gun to soften the surface so I can scrape it off.

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Whats left are the primer coats and any body filler. This is then removed with a Clean and strip disc.

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These are designed to remove paint and corrosion without removing metal from the surface. They also give a perfect finish for paint.

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At this point are fresh bare steel is susceptible to moisture in the air that will cause surface rust. If permitted this will undermine everything we do next. As soon as the surface is clean it's wiped down with Acetone warmed with my hot air gun and given 3-4 coats of a rust inhibiting etch primer.

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Two things to note here. I will be using grey primer and a light coloured body filler, and I have not filled any of the surface imperfections.

I've used a black etch primer for contrast when sanding.

Body filler should not be applied to bare steel. This contradicts every how to guide I have ever read. However the reason behind it is that Polyester fillers are some what Hygroscopic. They wick moisture from the air and although can be dried that moisture has already started the process of corrosion on the underlying surface and that in turn will cause the repair to fail.

With the etch primer dry it's given a good key using a coarse Scotch Brite pad on a flexible block. Never sand with just the palm of your hand it will leave a wobbly finish.

Next is to lay the panel up in body filler to sort any deep imperfections. No need to try and do this in one hit, much better to apply two skims and sand in between. This saves you trying to move around thick globs that will ultimately just cause annoyance. So first skim and sand fills are imperfections. The second skim is sanded to give a finished shape and ensure the repair is flat with no high or low spots.

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I've used 120 grit paper dry on a block. The contrasting colour of the primer is used as a guide for sanding, once the painted edge is reduced to nothing you have a smooth transition. Never wet sand body filler.

Once happy with the repairs the panel gets touched in with more etch primer.

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Redmoggy
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Re: Paint Prep

Postby Redmoggy » Wed Jul 22, 2015 10:47 am

It's now roughed out and ready for primer/surfacer and more sanding to straighten up the surface.

Rod

panky
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Re: Paint Prep

Postby panky » Wed Jul 22, 2015 3:02 pm

I'm watching with interest because my bonnet looks like it's been rubbed down with a house brick before it was painted :roll: So a job to do in the near future.
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Mark Wilson
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Re: Paint Prep

Postby Mark Wilson » Wed Jul 22, 2015 5:20 pm

Not just for Panky - I was impressed with Rod's contribution to another recent thread, so watching this carefully before starting my painting stage.

Mark

Autobahn
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Re: Paint Prep

Postby Autobahn » Wed Jul 22, 2015 7:52 pm

Redmoggy ... Body filler should not be applied to bare steel. This contradicts every how to guide I have ever read. However the reason behind it is that Polyester fillers are some what Hygroscopic. They wick moisture from the air and although can be dried that moisture has already started the process of corrosion on the underlying surface and that in turn will cause the repair to fail.

???????? well over 40 years as a qualified panel beater, worked at over 20 body shops, run own business, managed bodyshop for national chain of garages, myself and every car repairer I know has always removed ALL paint and applied body filler to bare metal only, to not do so is considered a bodge job.
guess we are all doing it wrong then? :roll:


tysonn
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Re: Paint Prep

Postby tysonn » Thu Jul 23, 2015 6:31 am

Same here,body filler straight onto bare metal.Its probably a good idea for anyone wanting to learn to paint to start with a small item,bike tank,moggy wing etc.Painting a whole car is a different ball game.
Mick

Redmoggy
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Re: Paint Prep

Postby Redmoggy » Thu Jul 23, 2015 7:24 am

Ok, before you grab the pitch forks. I was taught the same thing and have argued the point. However I have now had several painters / panel beaters along with paint supply reps tell me otherwise. I'm told, and I mean no offence that body filler on bare steel is an outdated practise? I gave in after reading an article in a recent trade magazine describing body filler as needing to be isolated from the bare steel.

http://www.themotorhood.com/themotorhoo ... ion-part-i

Since I said I would not use 2K products to prep this tank I decided to use a simple Aerosol etch.

Regards
Rod

Autobahn
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Re: Paint Prep

Postby Autobahn » Thu Jul 23, 2015 10:17 am

All I can say is I am apprentice served panel beater by trade, over 40 years and can honestly say I have never experienced problems with rust under my repairs unless the repair has been damaged again and cracked to allow moisture in or the panel has perforated and allowed water ingress from behind such as you might find on lower door sections or wheel arches if not properly rust protected inside from new.

On the other hand I lost count many years ago of problems with repairs where the filler isn't keyed and lifted to allow moisture in because the filler was applied over paint instead of bare metal, sometimes being so bad the filler would actually fall out.

My experience has been that often where filler has been applied over painted areas the damage has not been repaired properly either and the dent 'loaded' with body filler rather then being panel beaten into shape, the repair being a basic bodge job by a cowboy or someone trying a bit of DIY.

Obviously body filler is porous and will allow moisture to penetrate into it if left unpainted, but I fail to understand how body filler could retain moisture after being applied considering how hot it gets with the activation process?


Autobahn
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Re: Paint Prep

Postby Autobahn » Thu Jul 23, 2015 10:26 am

Just one more thought on this....

If the repair was finished by wet block flatting prior to primer and not dried properly then this is the only way I could understand any moisture might be retained in the body filler, it would then get trapped by the paint.

I never wet finish body filler so maybe that is why I have never had any problems?


Redmoggy
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Re: Paint Prep

Postby Redmoggy » Thu Jul 23, 2015 10:38 am

So, your objection has more to do with body filler being applied over a poorly keyed top coated surface rather than over a keyed etching primer?

Don't get me wrong here I am not out to convert any one or to knock there professional experience. DuPont is not a back street bodyshop known for dodgy repairs and I have simply tried to follow their advise.

Rod

amgrave
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Re: Paint Prep

Postby amgrave » Thu Jul 23, 2015 11:44 am

Our audience here is the diy enthusiast and as such the advise given is aimed at them. They are more likely not to consider or even know about the absorption of moisture into the filler and more likely to leave covering the filler with a coat of paint for a while after application. Provided the base the filler is applied to is sound and keyed there should be no problem. Out of the two options for applying filler this is the best for the amateur that does not know all the in's and out's of body prep (which is the target audience). Thanks for the post Redmoggy it will help others.


panky
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Re: Paint Prep

Postby panky » Thu Jul 23, 2015 11:49 am

One thing about filler I know from bitter experience is NOT to apply it over rust killer, it lifts every time :oops:
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