block sanding

[Tscott38]

I read through tons of material on this site and others and cant find an answer.

I'm blocking the car now - has PG DP40LF as a primer, and i sprayed on 3 coats of PPG K38.  I blocked the whole car with 180 grit - there were a number of spots that still needed work so I shot 3 more coats of k38 on and then went at it with 220 grit.  There are now very few spots to deal with.  My big question is, is it better to shoot more paint on and then sand that with 320, or to go at it right now with 320?  My concern is that  1) I may burn thru the paint and expose an area that I'm thinking is OK now.  Then I will have to redo the whole panel right?  If I paint more on the whole car, then this will most likely not happen, and I think that another coat of paint will hide all the 220 scratches better than me trying to sand them all out with 320; and 2) If it is advisable to respray, should I switch to a thinner paint with less solids like k36 to go over the 220 scratches? 

Im thinking that a thinner bodied paint will allow me to put a smoother finish down first allowing me to go with 320 easily.  I was having a bit a difficulty withthe K36 sometimes shooting dry and the gun spitting.   My gun is all I'm ever going to have (devillbiss suction JGA 25 yrs old) and modifying it is not really an option.  Can K38 be thinned?  not according to the data sheet

Im an amateur, but have some skills - I've painted before but not at this level. My plan is to block the car to 400 or 600 and then take to a paint shop that I know does good work to do the color/clear.  Any thoughts would be appreciated.       

[Brian in GA]

I'm not a painter, but try this forum:

http://www.spiuserforum.com/forumdisplay.php?38-General-SPI-Information

This is where I'm planning to get the info to paint mine when the time comes. 

[bill440rt]

When you say apply more "paint", are you referring to primer?

If you applied 3 coats of the stuff, sanded then applied 3 more, I would leave what's on there & keep sanding what you have.
Your last grit is 220?
What would I do? Guide coat the car again, block with 400 just to remove the guide coat & 220 scratches. Any lows/highs should be minor at this point and removed with 400. Guide coat again, final block with 600. Shoot 1 coat of DP mixed as a sealer just before paint, & paint over the sealer wet-on-wet.

[Tscott38]

yes - I meant primer.  and my last grit is 220.  Just finished it. 

Will 400 take out the 220 scratches?   You do 400 wet right?  I was thinking it would be a pain (lots of work), or it may not get it all the scratches out to jump that much in grit all at once, thats why I was thinking of going to 320 first.  I guess I could try and re-guide coat it and see though.

If I wet sand it with 400, then 600 and then shoot thinned DP40 over that as a sealer, will that have to be resanded if theres a month or so gap between it and color?   

The issue now is I have to take it to the paint shop and it may sit a while before the color goes on.  I want to protect the car, if there are any minor burn thrus, so I like the idea of the thinned DP40 as a sealer.  However, the data sheet for DP40 says you have to recoat within 7 days or then you have to recoat again with DP40, and then apply your color..   I may be wrong about that.  the data sheet is a bit confusing. 

Thanks for the reply (s)   

[bill440rt]

Yes, 400 wet.

If DP is not coated within a certain timeframe then yes you'll have to sand it (I believe it's 12 hours?).
It that's the case and there are no cut-throughs then there's no need to apply the DP until you are ready to spray the car with paint. Or, you could always just spot prime the cut-throughs. No need to load more material on the car than what is necessary.

[Tscott38]

bill440rt and brian - thanks for your replies.  It will be a big help. 

[73rallye440magnum]

http://3mcollision.com/3m-dry-guide-coat-applicator-kit-05861.html

^ Great guidecoat.

If you are doing all your bodywork and bringing to a shop for paint, you will want to coat any bare metal with Epoxy primer prior to delivery.

Make it clear to the paint shop that their final prep should include a gentle scuff all over prior to final blow off (compressed air) and wipedown (solvent wash)

Good luck!

[Dreamcar]

Are you epoxy and build primer different colors? That helps when blocking because you know exactly when you've got no build primer left (i.e. sand thru) and you know you haven't exposed any bare metal.

[Tscott38]

Yes dp50 and k38 are different enough to tell. That's been a great help.    The paint shop says they'll seal it.  If I have any isolated spots to re-epoxy won't that leave a spot that will show through the seal coat they will do or will scuffing it up take care of that ?

Thanks for the replies. 

[Dreamcar]

I'm not an expert on sealer, but one of the purposes of sealer is to make everything a uniform color before the paint goes on so it doesn't show through. Just show them the spots you've touched up with epoxy (they should see them anyway) and they should know how to deal with it. You could always scuff the new epoxy spots yourself but make sure its the right grit for the sealer.