TR2/3/3A "Teeth" to hold the paint

Well I hope this makes some sense, but I am wondering about the scratches left behind on primmer or paint and the problem they might cause after a respray. I used 400 wet and 500 wet and used some of 400 and 500 dry and 800 dry in places where I had tiger strips and heavy orange peel for this respray of the hood. The hood feels and looks smooth, but when the light is just right, I see these little fine scratches. I do not remember seeing scratches in the primmer before I sprayed the paint on--- but primmer is duller. Anyways, at what point are the scratches the "Teeth" to hold the paint and when is it too smooth or too rough. The body shop guys say the paint will fill a wet 400 scratch, but should a person go over the panel with say 1000 or 800 to get a superior surface if they are concerned. I know I am on the lunatic fringe; car painting does that for me. I do not have to be driven crazy. I can walk.
Steve

You're getting into the very detailed questions now, grasshopper, the meaning of life as it relates to painting your TR3.

Some general guidelines...

Most one step paints, like the enamel you are using, will easily cover the scratches made by 220 grit.
Most laquer based color used in 2 step paints will only cover scratches made by 400 grit or finer.
Most show car paint jobs do the final sanding before spraying the color (or the color sanding if re-spraying color over color) using 600 grit, just to make sure the scratches will not show through.

Here is the exception (there always is an exception!?!), you must wet sand and be absolutely sure not to get dirt under your paper. For example...if you are using 400 grit, but you allow a grain of sand to get under the paper, then you can easily leave scratches that will not cover. Likewise, if you do not use enough water, so the dust cakes on the paper, then you can also get large scratches in an otherwise smooth finish. So use plenty of water and pay attention to any feel that the paper is "rolling", instead of rubbing. Also use care to never let the edge of the sand paper or block cut into concave curves. That will also give you scratches deeper than the paper normally would.


As strange as it seems, you can sand with 2000 grit, and that will still leave sufficient scratches to hold your paint. The paint works on a microscopic level, so any scratches are enough. If you rough with 2000, the finish will look smooth to you, but on the micro level it is covered with tiny scratches to give the paint a place to grab.

Lighting is everything when sanding. I work an area wet, and then dry it with a towel to study it closely. The light must be placed so you can reflect it off the panel at a very low angle, with your eye on the opposite end of the panel. Any low spots, orange peal, and scratches will then show. Then work the area wet again. Repeat until the imperfections all disappear...or until you think you are close to cutting through to the under layers of paint. If you get close, use the spot putty to raise the low areas. I use a big halogen work light that I can move around to best study each panel. I start each day by re-studying the panels before I get to work. When your fresh you tend to catch more issues than when your beat after sanding many hours straight.

I have found that liquid dish soap in the sanding water helps a lot to keep the paper clean. I used to wet sand outside and use a garden hose. That worked well too. Usually the poop sheet that comes with the paint tells you how fine to final sand.Bob

Hello Steve

Painting seems to be an exercise in frustration. Imperfections that are not noticed in bare metal standout in primer. Then when they are fixed and it looks great the first coat of finish paint shows a whole new crop of imperfections. It may be we are focusing on smaller and smaller details as we go.

Today I was putting the final coats on the passenger side wings and door. Everything went great till the last coat on the rear wing and door. As I was almost finished the wing I noticed a water drop and thought it is not forecast to rain. Looking at the wing it was covered in small pimples. I am not sure where the water came from as my water traps were empty.
Re-sand tomorrow and get a gun mounted water trap.

David

David, you need a good dryer in the air line also make sure you drain the air tank it could also be temperature related, humidity nothing worse than condensation on the surface.

Graham

Hello Graham

I always drain the tank first thing and last thing when using the compressor. Here in Georgia the humidity is a challenge. I also have the John style copper pipe water trap. (A long length of copper pipe with a drain at the end) Then I have a water separator on the hose connection as well.
Been spraying for the last few weeks with out this issue and in fact it is a little less humid now.

Murphy's law I think. Last coat on the wings lets mess him up.

David

Thank you for taking the time to help John. I totally understand what a small piece of dirt feels like. Theses scratches are the ones you would see at an angle with the light just right. They are very fine. The problem I have with them is that they go in one direction. BUT really, I think I am over thinking this and letting the fear of imperfection affect me. I am starting to think in that kinda light there are always going to be scratches when there is no top coat on the panel.
steve

Yes, the scratches will always be there, and so long as they are caused by the grit paper you are using, that is a good thing!

sp53 said:

I know I am on the lunatic fringe; car painting does that for me. I do not have to be driven crazy. I can walk.
Steve

Click to expand...

You are a funny man Steve ! This made me laugh. You are right though, no matter how many cars I've painted, every time it still feels like I felt the night before a test in school. I don't think it will ever change for me.

I have a separator or water trap at the compressor and have taken to also always using one of those little round thingies at the gun, paint is expensive, they are relatively cheap insurance, as is a splash or two of fisheye eliminator in the paint.

Bummer David the redoing of panel is unsettling, but sounds like you have the paint to do it. Awhile back, I did not have the any extra paint to spare and that just increased the pressure. We have so much rain here that I do think much about humidity, but the summers have been dry it seems.

I drain the air every night also. What I have is cheapie plastic pipe vertical radiator homemade deal about 5 feet high with 6 lines going up and down and faucets at the end of 3 of the lines on T fittings sticking down that I can open and close. The theory is the air is supposed to go up and down and rattle around and leaves the water behind in the lower drains to let out, and it does. In addition, when I restart the compressor I let it run with the all drains open, the one the compressor also for maybe 60 seconds. I also right after the in line regulator where the air hose connects-- just take an open short fitting put that in a quick disconnect end fitting and let the air fly out until nothing but dry air comes out. There always seems to be some mist come out for maybe 10 seconds. Then I try and paint.

Steve

Controlling water in the hoses is really hard in Georgia and Washington with the humidity...both of you have done very well in your set-ups!


We sold our house last month...so we are living in an RV. No projects for a while. I bring that up, as the dude that bought our house low balled first, and then spent 2 days negotiating over my 22 year old lawn tractor and air compressor. He wanted them thrown in...but he is one of those white collar CFO guys. He will never be able to keep the tractor running, and he has no idea the difference between a cheap Lowes compressor and the 100% duty cycle I had. I refused to give either a way until my realtor wore me down and made me feel guilty enough to give in.


I don't think I will ever get over that JA taking my tractor and compressor. Mess with anything you want, but don't screw around with a guy's tools. It's an unwritten law...and this guy proves he's a geek by violating the rule! The tractor was only worth about $500, and maybe $1000 for the used compressor. The problem is I will have to spend about $10k to replace them at some point.


So...you guys keep posting. I am enjoying living through you're projects!

John, if you need a project to keep your hands busy you can park your RV in our driveway. Rent will only be a complete painting of a TR4 with Surry top.

I might have to take you up!

No rust, just a bit of basic bodywork needed.
I'll even keep the cold beverages in constant supply.

My primary water trap The vertical pipe on the left leads to the spray gun connection and the one on the right to a drain.

David

I cannot see your whole water catching system David, so this probably is not relative, but from my perspective the horizontal pipe could help hold water. I was thinking maybe angle it down some towards your drain, but I do hate to be critical, really. The way I see it is we are only probably spraying paint 3 times for 5 minute burst and your water system should give you that much time, so maybe it is not draining.
steve

The horizontal is, i assume, on a slight angle with a trap down length and valve. The importance is the length and diameter of the pipe, allowing plenty of time for condensing the water out of the air. I have a similar system.

The horizontal lines are slightly angled down towards the drain line. The drain line often collects about half a cup of water after a few hours of sand blasting. More of the setup.

David