Technical Guide Coat

Repainting my Morgan 4/4 (OK, no termite jokes) and have a question about guide coat.

I understand the principle: block sand and the guide coat shows the low spots.
My question is, does the guide coat stay on the car, or do you sand if off before applying filer and/or 2k primer.
Seems to me that if you leave it on, you run the risk of a bad bond under the color coat.
Its crumby single-part rattle-can paint after all.

Sand if off and you've lost the visual id of where the low spot actually is.

What am I missing here?

Thanks in advance,
Warren

 

You sand it all off. You keep sanding until the the lows are gone (meet up with the highs). You may have to reapply filler and or primer to low areas to get to that stage but once you can sand everything without leaving any trace of the guide coat (no lows)you know your have it straight. Think of it like this, the guide coat shows you where you either have to take more product off (highs) or add more product (lows) the preference is obviously to take as much off as you can not to add more. There are actual guide coats available that are dry which will lessen the chance of "crumby paint" contaminating your work.

 

Use this stuff

https://www.amazon.com/Mirka-9193500111-Guide-Coat-Black/dp/B00GTYHCGG

 

Rattle can paint is cheap, sandpaper-loading ****. Use a good aerosol powder based guide coat like SEM 38253 or Fibergl*** Evercoat 711. When you have straight/flat body work, the guide coat is gone after sanding. Any left and you have low spots...


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Yes.

 

If I understand your question right. You are asking if you keep priming over the guide coating that is left in the low areas. Yes. I do prime over the guide coat that is left in lows. I've never had a problem yet. I use spray bombs and I have used the dry powdered stuff. Seems weird to leave it, but it's how it's done. I've been doing it for 34 years now.

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I always thought you just fogged on a very light coat of a different colored primer. Either sand it off or cover with more high build if needed.

 

Yea, that's what I was asking. Just seems strange to me to have guide coat layered-in under the surface once you're done. Maybe the fact that the guide coat is just misted-on, with plenty of surface left for filler or 2k to bond to, is what makes it work.
Thanks to all who replied.

 

It appears to be nothing more than lacquer primer. I always leave it and prime over it, no problems.