That's a lot of sand-thru; how does it feel when you run
a hand across it?

If it is smooth and feels good, I'd spray a sealer coat
and then topcoat it.

 

The spots that I've sanded are really smooth, they only have scratches from the 220 I've been using. The spots I haven't touch yet are rough.

Rather than continuing with the sanding last night, I decided to remove my sunroof panel and finally managed to remove the side view mirror that had been stuck from the cars last paint job (I;'m assuming they painted the car with the mirror on).

I picked up some reducer this morning and plan on doing what you've recommended: finish sanding, seal and top coat. If I had more room, I would remove the hatch as the spoiler (which can't be removed) hangs over the side of the rear quarters. The solution is to keep the hatch open while painting, but it creates a sharp angle where the hatch matches up with the roof line. Consequently, I may end up painting the hatch separately--we'll see.

 

Guaranteed, you will get halos around each sand-thru after spaying sealer.

Which leaves you with a couple of options, sand the sealer (if it's one that CAN be sanded) or, spray your base on top, sand that and then spray a final coat of base.

Some sealers (and some epoxies) are not sandable. I use a reduced epoxy (that is sandable) for a sealer.

Addition:
I just thought of the possibility you are using ss (that you don't intend to color sand) and not bc/cc.
If that's the case, I would shoot a coat of sandable epoxy, block it with 400, then shoot another coat of reduced epoxy as a sealer before your topcoat.

I'm not saying that's the only way to do it. But, it's what I would do.

 

Yesterday was a bad day. I finally finished sanding the car, bumpers, trim pieces, etc,. and decided to spray the second half of the urethane as a sealer (reduced) thinking that it would be much smoother...

While it sprayed much faster this time, it went on too wet (my fault for not setting up the gun properly I'm sure) and it is almost as rough as the first time and has lots of runs. It wouldn't be so bad if it only required a little sanding, but I always have to go really deep as I get little pin holes. What is causing this?

If I have to sand this all the way down again: 1) I'm going to have a nervous breakdown; 2) I'm not going to use this primer ever again; 3) I'm going to pick up more of the epoxy primer and spray a couple more coats of that instead. The epoxy sands WAY easier than the high build and it goes on way smoother to begin with.

It takes me almost as long to clean out the garage after sanding, in preparation for paint; as it takes me to sand the damn thing. I also forgot to spray a couple of pieces yesterday, which just added to the frustration. But, in retrospect, I'm glad I hadn't, because I would have had to sand it all over again anyway.

I'll post some pics later, but basically they will look like the previous ones with way more runs. FWIW, I'm using a 1.7mm tip. Should I have used a 1.4, as the primer was mixed as a sealer?

 

Little pin holes that develop after a few minutes up to around 30 minutes after are called solvent pop.

It's caused mostly by spraying to thick of coat or while doing multiple coats without the proper flash time in between. Improper reducer temperature can play a part too.

Solvent pop is a nightmare. Not as much so with primer but with the topcoat is sure is. Nothing worse than having to sand off all your $300 per gallon paint. At least your primer was cheaper.

Yes, you are better off taking off at least down to where the pinholes are gone. Since you have solvent pop, you probably also have trapped solvents. And that's a really bad thing.

 

Thanks for the insight. Last time I sanded, I just used 220 right off the bat. What is the coarsest grit I can start with that will allow me to get through this process a little quicker?

 

Are you going back down to metal?

Then I'd say 80.

If you're going to try to not disturb your epoxy, you'd have to be pretty careful with that. So, maybe 120. Hard to say, I don't know how you are sanding and how careful you are.

 

Paint.

Hi.
Just thought I would throw in my thoughts. Forgive me if this is redundant to you.

The reason you are sanding through in some spots is because those are the high spots. The low spots are rough because they don't get sanded. of course I'm assuming you are using a sanding block and not just your hand, which will cause even more trouble...
You need to apply more high build primer and sand it flat with a block using 220/320 grit paper. You will need to apply more primer in a different color, or a light coat of a contrasting color until you knock down the high spots and fill the low spots. (called a guide coat)
I have found that if you tint the last coat of primer you can get an idea of how flat and smooth the body is since the tinted primer has a bit of a sheen to it. If it looks good then your final sanding must be with 600 paper wet before applying the top coat. (tinting with your top coat color will also help your top coat to cover quicker as well)
Sealer is not generally needed at this point, just clean with wax and grease remover, tack and spray.

Good luck.

 

I would have to agree with Hemi...............seems like you may have some issues with the body yet .......if you are going to reprime which sounds like a good idea take your time between coats......let it flash..........assuming your using a urethane 4 to 1 type prmer try mixing it 4 parts primer 1 part hardener/activator 1 part urethane grade reducer.....will help it flow out a little and not leave quite as rough.Let it flash off 15/20 minutes between coats....Use a guide coat as Hemi suggested__darker or lighter coat for contrast to your primer.............and start blocking with 120 on a longboard or a paint stick......use the 120 grit just long enough to break through the guide coat with no spots leftif you go through the guide coat and the primer you have some high/low spot issues which you may have to fix. If no issues after blocking with 120 spray a light coat of black for a guide coat again and proceed with 220 /320 or whatever you are going to finish sand with...as fr the second guide coat get a can of Black Lacquer in a spray can.it sands eas sand paper.........

 

I'm sorry I haven't posted in a while. I had to put the project on hold until the weather got nicer.

Before I went AWOL...

Sanded the whole car to 220 and re primed the whole car with high build again. This was a mistake in my opinion. I was back where I started, with a whole car to sand again and the same solvent trapped pitting that made sanding the car the first time such a drag. I did what uhohjim suggested and mixed some reducer in. This helped the flow, but it still got really chunky towards the end.

this week...

I peeled off the masking tape, and learned an important lesson: don't wait 3 months to remove your masking tape after 2-3 coats of epoxy and 2-3 coats of high-build. the trim is going to have to be removed now for sure and hopefully, it will clean up. Otherwise, I will have to open my wallet for some new ones.

i spent all night sanding yesterday with 180 grit on an 18" longboard. I have a lot of pits to sand out, but the panels are looking pretty straight. I also have some cracks in the primer that need to be fixed. I was planning on sanding into them until I hit the bottom of the crack, then widening the crack slightly and filling it in. any recommendations/suggestions?

 

You need to make sure your panels are straight. You're block sanding it so you're doing it right. after you sand your primer with 180 put another 2-3 coats of high build on there and block sand with 320 and then finish sand with 600 grit before your topcoat. Minimum of 400 grit before you seal it.

 

I really don't want to use the high build again. I'd rather use more epoxy, but I guess if the panels aren't straight I'll have to fill somehow. can I jsut apply the high build where I need to?

 

You can apply high build primer in spots yes, however make sure you fill those 220grit scratches with something before seal/topcoat. Sealer is not supposed to go over anything coarser than 400 grit scratches.

 

thanks for the advice! I was planning on sanding with finer paper, it just seems like I can't get ther. Everytime I spray anything I end up back at the beginning again, and again, and again...

I'm going to remove all of the trim tonight and keep sanding. I'll post some pics tomorrow.

 

Hi dr.strangelove.
Sorry you are having trouble. Can I ask a few questions?
What kind of high build primer are you using?
Are you mixing it according to directions?
What temperature are you spraying at?
Is it spraying too dry?
What gun and tip do you have?
Are you waiting between coats?
It is not a good idea to add more reducer to get it to flow. This can lead to a too thick build and solvent popping.

Generally speaking, high build primer should sand easily and level quickly. Assuming your body work is ready for primer, and you are not trying to level deep dents that should have been already been hammered and dollied, or filled.
Epoxy is not meant to be used as a surfacer, so would be an expensive waste.
You should only need to block with 180 once using a guide coat to level.
Prime again with only a coat or two as needed to cover breakthroughs.
Sand with 320 and a guide coat to ensure the surface is flat.
You can spot prime if some areas need more leveling.
When you are satisfied that the body is where you want it, then what I do is tint the primer with the color the car will be and spray another coat over the whole car. This will leave a semi gloss surface that will show any flaws, high, low etc.
If it looks good, (which it should at this point), then just wet sand with 600 and DO NOT break through. if you break through, you need to apply primer in that area. When finished sanding you will have a smooth surface all one color ready for paint.
I do not use sealer nor do I recommend it, if you have a smooth unbroken surface, your top-coat will cover fine, and since its tinted it will cover quick.

I forgot to mention, you should clean the surface with wax and grease remover before each application of primer, and hopefully before you started the bodywork or applied anything! Follow the directions, don't just put it on and let it dry. Spray it on or use a clean white paper towel (bounty) to apply, then use another paper towel to wipe it off, then throw it away.
The idea being the contaminants float to the surface in the solvent then are wiped off with the paper towel. One sheet for each small section. I will go through a whole roll on a big car. Much cheaper to spend a dollar on a roll of paper towels, than to re-prime and sand!

Sorry for the long winded reply

 

Thank you for the writeup, I'll try to answer your questions the best I can...

What kind of high build primer are you using?
ProForm 2K Urethane Primer Surfacer PF 656C

Are you mixing it according to directions?
The first application I used it as high build, the second time I added reducer as per the manufacturers instructions to use as a sealer

What temperature are you spraying at?
-When I sprayed it was about 20 C / 68 F

Is it spraying too dry?
-Yes, even when I used reducer with it.

What gun and tip do you have?
-1.7mm

Are you waiting between coats?
-It went on so thick I only laid one coat.

It is not a good idea to add more reducer to get it to flow. This can lead to a too thick build and solvent popping.
-I'm not sure that I added too much. the first time I sprayed I didn't add any and the surface was not smooth after spraying. Also, it takes a lot to sand down to a surface that is flat (not pitted).

 

I also wanted to add that there are a few spots that are down to bare metal now. I most likely did not fix some dents sufficiently before applying coatings. I was planning on respraying epoxy to seal in the primer, any spots that may require more putty, and protect any bare metal.

One more thing...

I've sanded most of the car with a block and sandpaper, but there are a lot of curves that make this very difficult and I was going through a ton of sandpaper without taking of much material. I switched to a smaller block with some red scotch brite and I went MUCH better. After using the scuff pads I went back to the large block and continued to level the panels with finer sandpaper--much easier than before. Has anyone else done this or is it bad practice?

 

Well, sounds like what you are doing is fine, I don't know why it should spray so thick or dry. Are you setting air pressure at the gun?

Mix 4:1:1 - medium build
Normal shop temp is 77 degrees
Siphon Feed 1.6-2.0mm 40-50 psi
Gravity Feed 1.6-1.8mm 35-45 psi
HVLP 1.6-1.8mm 10 psi

For curved areas you need a curved or rubber block. Basically anything to wrap the paper around.
I don't quite understand how the scotchbrite pads are helping?

Keep at it, you are learning a lot as you go!

Thank you for the writeup, I'll try to answer your questions the best I can...

What kind of high build primer are you using?
ProForm 2K Urethane Primer Surfacer PF 656C

Are you mixing it according to directions?
The first application I used it as high build, the second time I added reducer as per the manufacturers instructions to use as a sealer

What temperature are you spraying at?
-When I sprayed it was about 20 C / 68 F

Is it spraying too dry?
-Yes, even when I used reducer with it.

What gun and tip do you have?
-1.7mm

Are you waiting between coats?
-It went on so thick I only laid one coat.

It is not a good idea to add more reducer to get it to flow. This can lead to a too thick build and solvent popping.
-I'm not sure that I added too much. the first time I sprayed I didn't add any and the surface was not smooth after spraying. Also, it takes a lot to sand down to a surface that is flat (not pitted).

 

the scotchbrite doesn't seem to clog nealy as much as the sandpaper and I wasn't sure if I should wetsand. As I mentioned there are a few spots of bare metal and I don't know if the primer will like getting wet. I read the data sheet for the primer I listed above (high-build), but it doesn't say anything about wetsanding. I've made every mistake in the book, except for that one so far ...and then again I could be making a mistake by not wetsanding too!

My next purchase is going to be a set of flexible durablocks. I find with the longboard it's easy to apply too much pressure to the centre of curves. In the case of my good, which has a slight radius, everytime I go over the centre it is pushed down slightly.

 

I generally wet sand with anything finer than 180 paper. Otherwise it clogs too much. You should have no trouble water sanding that primer.
Sanding is a pain, but has to be done. Its the only way to get a flat smooth surface. Let the paper do the work, using a quality paper helps too.
Just a note, you can use a direct to metal surfacer which will save an epoxy step over bare metal.

the scotchbrite doesn't seem to clog nealy as much as the sandpaper and I wasn't sure if I should wetsand. As I mentioned there are a few spots of bare metal and I don't know if the primer will like getting wet. I read the data sheet for the primer I listed above (high-build), but it doesn't say anything about wetsanding. I've made every mistake in the book, except for that one so far ...and then again I could be making a mistake by not wetsanding too!

My next purchase is going to be a set of flexible durablocks. I find with the longboard it's easy to apply too much pressure to the centre of curves. In the case of my good, which has a slight radius, everytime I go over the centre it is pushed down slightly.

 

Generally you don't wet sand with anything coarser than 400 grit

 

Yes, that's true.
I seem to have fallen into a routine of 180 dry, 320 wet or dry, 600 wet. Just what seems to work for me.

Thanks

Generally you don't wet sand with anything coarser than 400 grit

 

I was thinking about one of the earlier comments regarding line size and decided to look at what I was using at the time. I have 1/2 to the main regulator and to the water/oil separator, then some type of connector that has a 1/2 NPT to a 3/8" air hose, to the regulator at the gun that is 1/4". I measured the ID of the male 3/8 and 1/4 connectors and they were basically the same (i.e. ~.191").

What gives?

What size/type fittings are you guys using?

Sorry for all the dumb questions and thanks for the help.

Mike

 

I should have looked around a bit more. This topic has been discussed here already:

http://www.hotrodders.com/forum/air-couplers-fittings-whats-all-mean-117105.html

 

Just wanted to post some updates.

These pics are somewhat new; however, there have been recent developments. I've gotten through the pinholes and sanded out the cracks. Now I'm trying to flatten out the panels and make sure everything matches up. My friend right now is Metal Glaze by evercoat (i think). It's really smooth but I find it dries too quickly for spreading out on large surfaces.

What's the deal with re-applying additional coats of glaze? sand first or just re-apply within a certain window?