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Old 07-04-2008, 02:32 AM
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Basecoat sanding?

Ok guys I purchased a HF 43430 spray gun and sprayed my sons Probe for some experience (btw he did need it so it wasn't a complete test) but I gained some experience with my gun...Nice gun too BTW.

Anyway My BMW 540i rear door is ready for paint tomorrow (July 4) I have all the stuff I need and the door is primed and ready. I have read quite a bit about this process and seems I have run into two schools of thought regarding wether or not to sand the Base coat prior to Clearing?

If anyone could clear (no pun intended) it up I'd appreciate it...the door is smooth and has been sanded with 600 so it is really a nice finish...First I hit it with 400 sanded it smooth, primed it and hit it with 600...so I do believe I am ready ...the Bimmer is definitely ready...lets see how this goes!

Thanks in advance...

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Old 07-04-2008, 07:49 AM
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Basecoat does not need to be sanded before applying clear.

Vince
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Old 07-04-2008, 08:48 AM
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Vince is right, you shouldn't need to sand the base, unless there is some reason you have to. On stuff I was extra picky about, I use to like to spray for coverage, and then denib with 1000, and spray on another coat, but really minor nibs in base, once cleared you shouldn't really notice too much.
Another thing, are you just painting the entire door. Unless it happens to be mixed dead nuts on, you could have match issues. Just because they mixed the paint to what the formula tells them to add, doesn't mean it will match, and sometimes even they are pretty far off. If you panel paint and do not blend either into the existing color on the door, or out into adjacent panels, ie your fender and quarter on that side. If you do intend to panel paint, I'd do a spray out card of your color (or a piece of metal sprayed with your primer), base it, clear it, and when dry check if the match looks like it will be acceptable to you.
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Old 07-04-2008, 11:08 AM
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thanks

Great advice!
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Old 07-10-2008, 09:50 PM
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Yes, basecoat does not need to be sanded...unless too much time goes by before clearing, usually over 12-24 hours. Or if you get a goober in the base and don't want it to show in the finish, you can wet sand it out with 800 grit after about 1/2 hour of the last application and reshoot it with more base.

Krash
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Old 07-10-2008, 10:22 PM
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Of course there is a difference between SANDING and "nibbing" where you are lightly sanding the base. This doesn't pertain to all basecoats, but here in an interesting read. Well, interesting if you skip pages 4 thru 13 where it is basically only fighting about the facts.

Click here for thread on sanding basecoat

Brian
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Old 07-10-2008, 11:31 PM
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Basecoat Sanding...

Well, I am not a painter...although I do have access to a lot of painters in that I work in an auto factory so for me to find a painter that is good is easy to do because there are guys where I work that have YEARS and YEARS of paint experience...both at work and at home. But I did not ask them...

At the advice of the columnist here and disregarded this guys ( http://www.thebugshop.org/bsfqpnt.htm ) recommendations although I did follow a lot of his stuff...it all seemed like common sense...along with great explanations...

So basically I followed the tech sheets, I did not sand the base, and I was exceptionally careful NOT to get a drip or run, if in the event I did I would not have hesitated to sand but I did not go out of my way to create that condition.

So I follow the recommended flash times while 'spraying' air over the panel during the 'flash time'. After the third coat of base I had to switch to the clear so I waited the recommended at least 15 minutes to 8 hours so, I waited 30 minutes for the base to setup...after the base setup I sprayed on the 3 coats of clear + just a smidgen more around the edges... I know for you 'technocrats' the smidgen doesn't work but it wasn't measured and it wasn't a fourth coat...

After the clear sat overnight, I then proceeded to peel the tape, in that the spec sheet said over 6 hours...so I peeled the tape...it didn't look to bad. Kind of shiny but 'textured'...so I waited for 2 days for the paint to set and the clear to harden up more...

Then I did my clear coat sand... here are my results...

Before...
[IMG][/IMG]

and After...
[IMG][/IMG]

Now I may just have gotten lucky...but everyone that sees it can't even tell I touched it...and believe me...I did.
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Old 07-10-2008, 11:57 PM
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Following the tech sheets, you just can't go wrong, PERIOD.

Brian
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