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Envious
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 Posted: Sat Mar 10, 2012 7:52 pm Post subject: Wet sanding techniques |
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I'm in the final stages of prep before laying out colour. I've heard/read a few different techniques for wet sanding which is different than what I've always done. I was hoping some of the local pros would chime in.
If I'm block sanding, trying to straighten a panel, I dry sand in a typical X pattern. No mysteries here.
I've always wetsanded final undercoat, prior to paint, using parallel strokes along the length of the panel. I've heard of people who circle sand, others who wet sand also in an X pattern, and others who sand parallel along the panel but follow up at 90*.
Opinons or advice??
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VizionCustoms
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schell '59
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| Posted: Sun Mar 11, 2012 7:18 am Post subject: |
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Circles and such are for erasing drag marks or figure f--ks in the body world as they are called...
No matter what you sand like your grit will determine your drag and scratch marks as well as your hand/ block position...primer is very impressionable and can change in one stroke ...and when applying just base over it..it will magnify the blames..this is why you should seal it..the sealer will self level and hide all of these minor drag marks.
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craigman
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| Posted: Sun Mar 11, 2012 11:18 pm Post subject: |
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| Once the car is blocked out and straight, I like to do a final block sand with 600 wet/dry grit on a semi soft foam block with rounded edges. This eliminates any "hard lines" you get with a hard block. |
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schell '59
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| Posted: Mon Mar 12, 2012 5:14 pm Post subject: |
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...water is your friend as well as the correct grits for what your sanding...general rule of thumb is preimer gets 400-600,base coats if needed to be knibbed for light dirt -600-800, and your final sadning for clear and buffing you can go between 1000-2500
All of which need to be gently done with a water/light soap mix and try and cross hatch as much as possible...try to avoid left to rights and up and downs as much as possible..and if needed like say across the length of a door or a long rear quarter,just make sure you " connect" the left to right with a cross hatch top to bottom...make sense?
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theastronaut
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| Posted: Tue Mar 13, 2012 1:34 pm Post subject: |
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I've been using PPG's K93 tintable surfacer on my latest project after the rounds of dry blocking are over. I sprayed three coats, then guide coated and wet blocked it with 280 grit. The 280 gets the primer back flat easily (4/5/600 grit won't get the primer as flat) then re-guide coat and wet block with 500-600. The finer paper takes out the 280 sanding scratches while also smoothing and removing any drag marks from the rougher paper. This gets the panel perfectly flat AND smooth enough to paint over which is hard to do with the usual 500-600. The primer is tinted the same color as the base, so the base will cover extremely well. I like to let the panels set a couple weeks between sanding with 280 and 500 to let the solvents finish bleeding out to avoid any shrinking later on.
The reflections after wetsanding will show any distortion that you'll need to fix before you paint it.
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schell '59
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| Posted: Tue Mar 13, 2012 4:21 pm Post subject: |
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...tintable primers is a different topic.
..we're talking about "average" wet sanding tactics and tricks..thats the point of the thread....so to wet sand "any" primer with 280 is super coarse and not many here will do that.
you take the risk of sinkage and drag marks after the product settles...but as long as the sand scratches of the 280 are gone with the 500 i guess it doesn't matter...
nice truck...but show a vw...that's a paint job most vw guys would never use on there 1972 standard.  . she looks sweet!!
just saying.
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theastronaut
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| Posted: Tue Mar 13, 2012 5:08 pm Post subject: |
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| schell '59 wrote: | ...tintable primers is a different topic.
..we're talking about "average" wet sanding tactics and tricks..thats the point of the thread....so to wet sand "any" primer with 280 is super coarse and not many here will do that.
you take the risk of sinkage and drag marks after the product settles...but as long as the sand scratches of the 280 are gone with the 500 i guess it doesn't matter...
nice truck...but show a vw...that's a paint job most vw guys would never use on there 1972 standard. . she looks sweet!!
just saying. |
It's not a different topic just because it's tinted, because it still builds and sands the same way normal surfacer does. Tintable K93 is a surfacer- just like PPG's K36 is a surfacer. It sands no different. My point was, from my experience 500-600 isn't rough enough to fully flatten the orange peel of the primer, especially once the finer paper starts to wear down any. By sanding with 280 first, the panel can be shaped down flat, then smoothed with finer grit paper. That is technique, and is relevant.
Nobody sands filler with 500 grit and expects it to shape and level the filler. You use ~80 grit to shape and lever the filler to get it straight. Then you start the smoothing process with 180, then high build primer. The primer comes out rough (orange peel) and needs shaping as well, so what sense does it make to try to shape rough primer with smooth paper?
I completely understand you point about that not being a paint job most VW people would use. I posted pics of the truck and not a VW because I've never done any body/paint work on a VW. Most VW guys around here are happy with Maico's services. I'm happy to let them use Maico because they would have a stroke if I gave them a quote of what a show quality paint job would cost. I don't cut corners because a customer wants the job cheaper, they can go somewhere else. Good materials cost more than most guys have in thier finished VW's. Another reason I don't have pics of a VW that I've worked on is, I'm too poor and too busy on other projects to do the body/paint my '66 Bug. 
As far as "average" sanding techniques, between this thread and the one on sanding edges, the OP is obviously interested in spending the necessary time to make his paint job right, so that's why I posted about the way I sand. Read my sig line, I kinda don't like "average".
If I had thought that the OP wanted average advice, I wouldn't have posted. Not trying to come off as a smart-alek, as this is only my second paint job and I'm still learning. But I am standing behind the technique that I've found works well for me.
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schell '59
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| Posted: Tue Mar 13, 2012 5:48 pm Post subject: |
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no need to to get all defensive man,it's all good!!....your 2 examples are far what exceeds what any average vw guys knows and can handle...do you see my point though?
not about your work but if the guys here can understand your sanding grits vs addhesion.
you showing to 10k paint jobs (just so you know)mon two high dollar pick up trucks on a hobbiest vw site...so if the OP poster knew your (our) tricks he wouldn't need to ask,yes?
...i'm not talking about finish for sanding filler, i'm not talking dry sanding, i'm talking about wet sanding...sand scratches will show through if not full removed from the primer, and if 280 scratches aren't completely removed they will need to be dragged out higher with 320,400-500 and this removes even more product...that's what i'm talking about...less product is good for sure but not if your trying to level...you'll be at the filler again before you know it.
just saying,to step from280 to 500 is a lot different than 320-400 then 600.
i don't use PPG or and of the "K" brand primers..i use Azko Nobel Sikkens or Utech that's it and it is all tintable as well but yet can be sanded completely flat with 400 open coat 3M all day long...then finished with 600...have done it over a million times.
again my point was from280 to 500 is extreme...but if it works for you,than it works for you...especially when every brand has different ways of taking their product to the levels needed.
also on those "shiney" pics of the red primer...is that a degreaser or cleaner to allow the shine to be so consistant?...with no sand lines what so ever after it's dry or are there some a bit? for grip on the sealer... how does your sealer stick?
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Envious
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| Posted: Tue Mar 13, 2012 6:11 pm Post subject: |
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All of this is interesting. I'm a hobbiest painter that's done a few cars. I really enjoy the process and I'm looking to bring my skill set to the next level.
You mentioned problems with primer shrinking. What contributes to this? How can I avoid it?
Thanks guys!
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theastronaut
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| Posted: Tue Mar 13, 2012 6:18 pm Post subject: |
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| schell '59 wrote: | no need to to get all defensive man,it's all good!!....your 2 examples are far what exceeds what any average vw guys knows and can handle...do you see my point though?
not about your work but if the guys here can understand your sanding grits vs addhesion.
you showing to 10k paint jobs (just so you know)mon two high dollar pick up trucks on a hobbiest vw site...so if the OP poster knew your (our) tricks he wouldn't need to ask,yes? |
We're on the same page for sure, and I didn't mean to come across as agressive of defensive; if it did I appologize.  He asked, so I posted what I know about wetsanding. Like I said, the red truck is only my second paint job, so I'm still learning too. We're all here to help each other out, and I learn all the time from guys on here. Just trying go give back.
| schell '59 wrote: |
...i'm not talking about finish for sanding filler, i'm not talking dry sanding, i'm talking about wet sanding...sand scratches will show through if not full removed from the primer, and if 280 scratches aren't completely removed they will need to be dragged out higher with 320,400-500 and this removes even more product...that's what i'm talking about...less product is good for sure but not if your trying to level...you'll be at the filler again before you know it.
just saying,to step from280 to 500 is a lot different than 320-400 then 600.? |
I used the example of filler since the principle is the same- flatten then smooth. 280 is fairly rough, but it flattens the primer that much quicker, and it doesn't take much to sand out the 280 scratches with 500 grit. I definitely agree that the thinner the better as long as theres still enough coverage. I always use guide coat to show how much I've sanded, and re-apply guide coat after sanding with 280 so that I'm sure that sanding with 500 removes all the scratches. The guide shows sanding progress to remove the least amount possible.
| schell '59 wrote: |
i don't use PPG or and of the "K" brand primers..i use Azko Nobel Sikkens or Utech that's it and it is all tintable as well but yet can be sanded completely flat with 400 open coat 3M all day long...then finished with 600...have done it over a million times.
again my point was from280 to 500 is extreme...but if it works for you,than it works for you...especially when every brand has different ways of taking their product to the levels needed. |
I used to block my primer with 500 only, but on thin low gloss or satin finishes the "rounded off" orange peel texture of the primer shows through. On something that will get multible coats of clear and will be cut and buffed it probably doesn't matter as much. 280 last longer, and still cuts more when it's starting to wear down than fresh 500 does. Once 500 start wearing, it doesn't cut enough to flatten the orange peel fully. Sounds like we both use the same technique- I'm using 280/500 and you're using 400/600.
| schell '59 wrote: | | also on those "shiney" pics of the red primer...is that a degreaser or cleaner to allow the shine to be so consistant?...with no sand lines what so ever after it's dry or are there some a bit? for grip on the sealer... how does your sealer stick? |
Its just water, right after wetsanding and hosing the panel down heavy. The water hadn't all run off and thinned out yet, so it covered the 280 scratches. I don't use sealer, just spray the base right over the K93. That was my point about using K93, it saves the expense and labor of using a tinted sealer in the booth. 500 grit scratches should be enough for the base to grip onto. They're not as deep, but there's more for the same amount of are.
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theastronaut
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| Posted: Tue Mar 13, 2012 6:39 pm Post subject: |
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| Envious wrote: | All of this is interesting. I'm a hobbiest painter that's done a few cars. I really enjoy the process and I'm looking to bring my skill set to the next level.
You mentioned problems with primer shrinking. What contributes to this? How can I avoid it?
Thanks guys! |
All primer/paint shrinks some as the solvent evaporate out. Problems pop up when there are deep scratches under the primer, and the primer shrinks down into the scratch. If the car is already painted, the line from the scratch shows up as a line in the paint. Using too-rough paper on filler will cause this, or too rough paper sanding the primer before paint. Letting the primer cure awhile before sanding and top coating helps avoid this, but mostly using a smooth enough paper will eliminate the problem. Letting each coat flash the proper amount of time helps keep excessive solvents from being trapped to start with.
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Strive for perfection in everything. Take the best that exist and make it better. If it doesn't exist, create it. Accept nothing nearly right or good enough."
-Sir Henry Royce, co-founder of Rolls-Royce
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'66 Bug
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Envious
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| Posted: Tue Mar 13, 2012 7:20 pm Post subject: |
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| theastronaut wrote: | | Envious wrote: | All of this is interesting. I'm a hobbiest painter that's done a few cars. I really enjoy the process and I'm looking to bring my skill set to the next level.
You mentioned problems with primer shrinking. What contributes to this? How can I avoid it?
Thanks guys! |
All primer/paint shrinks some as the solvent evaporate out. Problems pop up when there are deep scratches under the primer, and the primer shrinks down into the scratch. If the car is already painted, the line from the scratch shows up as a line in the paint. Using too-rough paper on filler will cause this, or too rough paper sanding the primer before paint. Letting the primer cure awhile before sanding and top coating helps avoid this, but mostly using a smooth enough paper will eliminate the problem. Letting each coat flash the proper amount of time helps keep excessive solvents from being trapped to start with. |
Gotcha. The reason I asked is that I reworked my passenger rear quarter and board sanded my high build with 120. I re-primed today and want to avoid showing the 120 scratches.
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schell '59
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| Posted: Tue Mar 13, 2012 7:34 pm Post subject: |
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No worries astro' your doing a killer job...my points were for the average guy who just trying to get the job done with out stressing and using to much product/effort and get the best possible result.
There is a thousand ways to do body work but really only one way to do it 100 percent right and this takes years to figure out and tons of product money and time.
Shrinkage is in all forms of body work from the filler,primer even to the single stage or base/clear
Each layer is as only as good as the original first coat...so thinkmoff this,a panel that has a spot of a good amount of filler and right next to it is perfect steel you can bet the filler will insulate the metal from swelling so the steel next to the filler will skink or swell in sunlight were as the filler will not as quick there for stay sunk....this over time..weeks maybe,will show signs of onion rings,sand scratches etc...even as fine as 220 in the filler through the primer...you can also see 400 scratches sink through base coats if a sealer is not used to insulate the primer from the base.
Sand scratches are also apparent when sanding base coat with the wrong grit...and I don mean 6-800 ,I mean like 1-1500 k. The base will show the drag lines through the clear especially in silvers,golds and most metal flakes.
Just a little tid bit of info there for yooz guys.
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craigman
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| Posted: Tue Mar 13, 2012 7:50 pm Post subject: |
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The only primer i've ever used that does not shrink is Polyester primer. It's not your normal solvent based primer.
I like to bodywork the car, spray 3 good coats of Poly primer, block with 80 grit, then reblock 180 grit, then reblock with 400-600 grit wetsand paper.
I've done it this way for over 10 years. Never once had a shrinking issue.
Not to mention Polyester primer has a great mil thickness, and it won't react to previous paint jobs. |
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Envious
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| Posted: Tue Mar 13, 2012 7:56 pm Post subject: |
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| craigman wrote: | The only primer i've ever used that does not shrink is Polyester primer. It's not your normal solvent based primer.
I like to bodywork the car, spray 3 good coats of Poly primer, block with 80 grit, then reblock 180 grit, then reblock with 400-600 grit wetsand paper.
I've done it this way for over 10 years. Never once had a shrinking issue.
Not to mention Polyester primer has a great mil thickness, and it won't react to previous paint jobs. |
Thanks. I'm using a urethane primer. I plan on letting the fresh primer sit for a few days before starting to sand.
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64 Type 151
63 Type 117 L469 Anthracite
64 Type 361 L575 Nutria
58 Type 113 L41 Black
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59 Heilite Single Wheel Camping Trailer
56 Allstate Single Wheel
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schell '59
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| Posted: Tue Mar 13, 2012 9:56 pm Post subject: |
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Polyester primer is a different animal for sure...actually real poly filler/ primer takes a hardener like fiberglass resin has...this is in brands such as eastwood,overcoat,omni and the real deal Sikkens poly surfacer...all of these are nice ways of leveling out that stubborn panel with out laying on multiple layers of fillers.
They are also different thickness which some of these can and can not be applied...eve coat feather fill the new gen kind,is terrible compared to the earlier stuff.. sikkens by far has the highest build thickness and dries the most dense and is sand able easliy with 180 dry all day long where as the others tend to ball up the paper and drag.
Poly also has minimal if not any,shrinkage as it is caalized harder with a resin hardener and not a liquid hardener/ reducer like normal high build primer.
Prime over it with 180/220 dry scratches...wet snd it with 320-400,seal it and paint it
Some don't use sealer but as a guy who has Seen the difference of a sealed panel vs a non sealed panel after rock chip,adhesion etc I can tell you..it works.
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craigman
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| Posted: Wed Mar 14, 2012 8:20 am Post subject: |
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I agree Schell,
sealer has many great benifits. |
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VintageVulture
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| Posted: Wed Mar 14, 2012 6:39 pm Post subject: |
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I use sealer. I apply sealer over 400 grit wet-sanded high build primer. I always use the afore mentioned soft flat foam block. I prefer to wet sand in a "racetrack" type circular motion and for several reasons. The primary reason is that IF I were to get sand-scratch shrinkage somewhere, that scratch would be less likely to be highly noticable. Typically a light source reveals a scratch right? Well if that source of light is coming from one area, say a lightbulb or the sun you'd have one loong scratch showing up in the reflection of that scratch. If the scratch is round or curved it's less likely to be as visibly devestating to the one stroking their ego over their amazing paintjob.
The other reason is that I've found after so many years of sanding, circular sanding is just easier on my sholuders and elbows
I typically guide coat the primer prior to sanding. I then block on a flat board with DRY 220/240/280 grit (depending on the quality of primer). Then I guide coat again, switch to a DA w/ DRY 320. Then begin wet sanding after that. Hasn't let me down yet. My .02, that's all it is.
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Spridle
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| Posted: Wed Mar 14, 2012 10:22 pm Post subject: |
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As a guy who has been playing with PPG stuff for over 20 years, it's a good idea that you let the K products sit. They shrink a ton. Old technology surfacer high talc content. I like to let it sit for a few days, then just take the top layer off so it can sit for a week. Like someone else said, shit in does equal shit out. Take your time. If you try to bury a 40 grit scratch, you will see it. Eventually.
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