I read the sticky on guide coat how-to’s, but have a couple questions, before I try using a guide coat from my spray can. The sticky talks about the powder guide coat, but I think my questions pertain to both. First question is if you sand off some high spots of your high build 2 K primer down to epoxy primer or filler, and decide to add more filler, is it ok to add filler over the high build? The sticky seems to say that’s what he did but it’s not real clear. The guidelines that came with my high build primer do not mention putting filler over it.
What should I do with the guide coat in the low spots? If I sand it off, I don’t know where to apply another coat of 2K, and it seems like a waste of time to give the whole car another coat or two of primer if you only have a few places needing more high build or filler. Seems like the guide coat should be removed entirely. Maybe it would make sense to take a picture if the low spots, then take it off? Thanks

you said--"First question is if you sand off some high spots of your high build 2 K primer down to epoxy primer or filler, and decide to add more filler,"-- why would you want to add more filler? you've sanded down to the epoxy or filler that means that it's to HIGH there. after you apply your guide coat block with the longest board posible to be effective. sand only until the guide coat is gone, look at the panel and if you see a low spot ( still has guide coat) you can sand further to see if that spot will sand out. if you get into your filler you can keep sanding until the low spot is gone. if you sand into your epoxy then i would stop. it needs more filler or another coat of high build. yes you can put filler over the hi build. if your working on a spot or two on a panel, NO you don't reprime the complete panel, you just spot prime the work areas. once you get everything flat on that panel you can then prime it or use a sealer on the complete panel.
Jay D..

Epoxy first, over the bare metal which should be panel beaten to as smooth as you can get it. Fix the big dents, creases, holes etc. first.

Guide coat the epoxy and sand lightly with about P180 to show up highs and lows. Fix highs as necessary and fix or fill lows. You can sand lows a bit by hand to give some "tooth", but it isn't essential to remove 100% of the guide coat. Or use a pencil to mark out the areas you want to fill. You may need to reapply epoxy over rub-throughs.

Guide coat over whole surface and sand until flat, refilling as required. Best practice is to put a final skim coat of a fine filler over the whole lot and sand that until you get down to epoxy on the high areas. This should help ensure you don't have joins visible. At this stage you should be sanding to about P180 after doing the major shaping work with P40-P80.

Now prime. You can guide coat and sand again but this time you're not shaping, just finessing the surface to prepare for your top coats.

The idea is to get the surface flat and/or shaped correctly before primer. Don't fill after priming unless absolutely necessary and then only use a glaze or fine fill keeping it thin as possible or just in spots for pin holes or other very minor imperfections. You'll need to re-prime over any filler or glaze, then go through the guide coat and sanding process again, this time finishing with P600-P800 for solids or metallics, respectively.

Edit: Jay must be a faster typist than I am. He beat me to it, but says basically the same thing.

i'm no way faster i probably just started sooner
Jay D.

badsix wrote:you said--"First question is if you sand off some high spots of your high build 2 K primer down to epoxy primer or filler, and decide to add more filler,"-- why would you want to add more filler? you've sanded down to the epoxy or filler that means that it's to HIGH there. after you apply your guide coat block with the longest board posible to be effective. sand only until the guide coat is gone, look at the panel and if you see a low spot ( still has guide coat) you can sand further to see if that spot will sand out. if you get into your filler you can keep sanding until the low spot is gone. if you sand into your epoxy then i would stop. it needs more filler or another coat of high build. yes you can put filler over the hi build. if your working on a spot or two on a panel, NO you don't reprime the complete panel, you just spot prime the work areas. once you get everything flat on that panel you can then prime it or use a sealer on the complete panel.
Jay D..

Thanks, what I meant by having to add filler in a high spot ( just hypothetical at this point) would be adding around it nit on top of it. Like I do taping a wall. To make a bump invisible. So on slightly high places where I’m hitting epoxy primer ( close to metal)! I can consider that ready for sealer, right? High build is just for flattening, nothing else?

[quote=
Thanks very much. I have got to write this down and remember.
All sounds good, I’m going mostly to bare metal and using top if the line epoxy primer over that.
Don’t know about trusting rattle can guide coat enough to leave it on, but I like your pencil idea for knowing where to fill.
Is 2K two thousandths of an inch? Just wondering where the starting point is for filler. I’m guessing .004”.
Going over the whole lot with thin filler’ means the just the whole lot that is being filled?
BTW this car has nothing flat on it. The roof, fenders, hood, trunk are all bulbous. The doors are the flattest part and even they are curved a little. Like 49 Chevy but the size of a VW bug. So I don’t know if a guide coat is even going to help. Every block I use has to be soft, it seems to me. But I could be wrong. I’ll put up a picture tomorrow. 1956-74 Morris Minor

like a Mini Cooper.
Jay D.

No Jay, more like this - my latest project



Bustedspanner, I understand where you're coming from. Get yourself some blocks like these.

They're a bit expensive so if you can't or don't want to make the investment, next best is to go down to your local hardware store and get some poly drain pipe in 35mm and 50mm diameters. Also get some poly sheet and some glue. Cut the sheet into 70mm wide strips and a series of cuts in the tube, then glue together. May take a little trial and error but you should end up with a block that is firm but flexible - perfect for doing those big curved panels.

Bustedwrench wrote:Is 2K two thousandths of an inch?

Dunno. 2K means "two component", i.e. a base and a hardener. What's an inch? A full wet coat of 2K primer can be 40-50μm.

Bustedwrench wrote:Going over the whole lot with thin filler’ means the just the whole lot that is being filled?

If you just fill the low spots then you'll end up with a series of islands and, sure as eggs, they'll have a shoreline that won't be level with the metal. Guaranteed.

Filling over the whole surface at the end will let you see these and address them before you get to primer which may not have enough depth to cover/fill.

Bustedwrench wrote:Don’t know about trusting rattle can guide coat enough to leave it on

Get the powder guide coat. More economical that the spray cans and won't clog your paper as much. Works better.

badsix wrote:i'm no way faster i probably just started sooner
Jay D.

That's more true than you probably realised.

I posted at 9:25am Sunday morning. You would have started typing at about 4:20pm, Saturday afternoon.

NFT5 wrote:No Jay, more like this - my latest project

20220114_135850_HDR.jpg

Bustedspanner, I understand where you're coming from. Get yourself some blocks like these.

They're a bit expensive so if you can't or don't want to make the investment, next best is to go down to your local hardware store and get some poly drain pipe in 35mm and 50mm diameters. Also get some poly sheet and some glue. Cut the sheet into 70mm wide strips and a series of cuts in the tube, then glue together. May take a little trial and error but you should end up with a block that is firm but flexible - perfect for doing those big curved panels.

Bustedwrench wrote:Is 2K two thousandths of an inch?

Dunno. 2K means "two component", i.e. a base and a hardener. What's an inch? A full wet coat of 2K primer can be 40-50μm.

Bustedwrench wrote:Going over the whole lot with thin filler’ means the just the whole lot that is being filled?

If you just fill the low spots then you'll end up with a series of islands and, sure as eggs, they'll have a shoreline that won't be level with the metal. Guaranteed.

Filling over the whole surface at the end will let you see these and address them before you get to primer which may not have enough depth to cover/fill.

Bustedwrench wrote:Don’t know about trusting rattle can guide coat enough to leave it on

Get the powder guide coat. More economical that the spray cans and won't clog your paper as much. Works better.

I should have shopped around but the only auto paint store in town wanted $42 for a little can of the powder type so I got their spray can. It’s on my list. Thanks. So you are recommending I put a special thin filler over the entire car then sand mist off, just as would be done with high build primer?