Sanding primer?

[Bucky]

I've been butchering models since 1963. I've got the engineering and execution down fairly well, even when it comes to building a kitbash or full custom. My Achilles heel is the dreaded "Paint Job"! My question to the painting gurus around here is how much do you guys sand the primer before spraying the color coats?  I use Duplicolor primer on everything. I have a couple projects in primer waiting to be covered in color. The paint I am going to use is MCW lacquer. All opinions are welcome.

[Ace-Garageguy]

I wetsand it with 600 to 800 until it's slick...which means zero orange peel.

Depending on how good your eyes are, you may need magnification or a "guide coat".

[Bainford]

After all the body work, filling, and tuning is done and I'm ready for paint (by which time the body will be pretty much covered in primer already), I give the whole thing a light coat of primer, enough to ensure even colour all over. I then let it dry for a day, wet sand completely but lightly with 1000 grit, rinse thoroughly under running water using a soft brush to clear out the panel lines. Then I remove the bulk of the water with a lint-free cloth (to avoid mineralised water stains) and let air-dry completely. When it's time to paint I give the body a quick wipe with isopropyl alcohol and let that dry while I mix up the paint and fire up the compressor.

If the primer goes on a little heavier than I like (which sometimes happens as I still apply primer with a rattle can) then I will block-sand across the panel lines during the final wet-sand, though if the primer coat is light, this shouldn't be necessary. The block-sanding across panel lines, however, is always a part of my initial bodywork and prep.

[StevenGuthmiller]

Sometimes I sand the final primer coat, sometimes I don't.

If there happens to be any dust particles or visible orange peel, (which with Duplicolor primer is almost never) I'll sand it very lightly.

If not, I leave well enough alone.

You shouldn't have any adhesion issues if you're using lacquer over lacquer primer.

 

 

 

Steve

[peteski]

As I understand primer is a special coating designed to adhere well to bare plastic or metal surface, and also provide a suitable surface for the top coat of paint to adhere to it.  Primer already has a satin surface  finish perfect for maximum adhesion of the top coat. Another  function of the primer/filler is to even out any imperfections in the painted surface and also provide uniform color for the top coat.  No sanding should be required to further improve top coat adhesion, but if there are imperfections in the primed surface additional sanding will remove those imperfections.  To me sanding the a smooth primer coat is a waste of time.

[stitchdup]

if its been sat for a while it wont hurt to use an abrasive cleaner and a toothbrush but it is more for cleaning than keying as primer seems to let dust bite into it. the filler primer does need sanded. it dries with a heavier texture so it can be sanded back and i always use a guide coat with it.

[Keef]

2 hours ago, StevenGuthmiller said:

Sometimes I sand the final primer coat, sometimes I don't.

If there happens to be any dust particles or visible orange peel, (which with Duplicolor primer is almost never) I'll sand it very lightly.

If not, I leave well enough alone.

You shouldn't have any adhesion issues if you're using lacquer over lacquer primer.

 

 

 

Steve

This is the way I’ve done it for years.

[Ace-Garageguy]

3 hours ago, peteski said:

As I understand primer is a special coating designed to adhere well to bare plastic or metal surface, and also provide a suitable surface for the top coat of paint to adhere to it.  Primer already has a satin surface  finish perfect for maximum adhesion of the top coat. Another  function of the primer/filler is to even out any imperfections in the painted surface and also provide uniform color for the top coat.  No sanding should be required to further improve top coat adhesion, but if there are imperfections in the primed surface additional sanding will remove those imperfections.  To me sanding the a smooth primer coat is a waste of time.

Golly gee. I've been painting real cars, aircraft, and models for over 50 years.

Sure wish I'd known all that primer sanding I've done to get as perfect a finish as possible was a "waste of time".

I guess all the real-world paint manufacturers that specify final sanding of primer prior to color with 320-600, depending on the specific topcoat, have it wrong too.

Good to finally know the truth. 

Edited Thursday at 12:09 AM by Ace-Garageguy
CLARITY

[peteski]

Bill, my exact statement was "To me sanding the a smooth primer coat is a waste of time. " I guess you missed the "to me" part.  I have models which won awards at the shows with the paint applied over bare plastic (no primer at all) or unsanded primer.  I'm happy with them. Like I said "to me".  Are they flawless? No way, but they make me (and show judges) happy.

For example my 1:43 289 Cobra painted with unsanded Tamiya Fine White primer, nail polish (and white paint for stripes) and Testors Wet Look Clear looks pretty darn good.

 

If your model painting technique requires sanding the primer, have at it!  And I believe the manufacturers recommend sanding the primer to take down any schmutz or other tiny imperfection, not specifically to improve the paint adhesion.  You know opinions are like you know what - everybody has one.

[StevenGuthmiller]

2 hours ago, Ace-Garageguy said:

Golly gee. I've been painting real cars, aircraft, and models for over 50 years.

Sure wish I'd known all that primer sanding I've done to get as perfect a finish as possible was a "waste of time".

I guess all the real-world paint manufacturers that specify final sanding of primer prior to color with 320-600, depending on the specific topcoat, have it wrong too.

Good to finally know the truth. 

No disrespect Bill, but it’s a model car.

The only real requirement is for the primer to be smooth.

If you can achieve that without sanding, I don’t see any disadvantage that’s going to matter with something that’s going to spend it’s lifetime indoors  sitting on a shelf.

 

 

 

Steve

Edited Thursday at 02:47 AM by StevenGuthmiller

[Ace-Garageguy]

D E L E T E D

 

Edited Thursday at 03:12 AM by Ace-Garageguy
PROFANITY

[OldNYJim]

1 hour ago, peteski said:

For example my 1:43 289 Cobra painted with unsanded Tamiya Fine White primer, nail polish (and white paint for stripes) and Testors Wet Look Clear looks pretty darn good.

I always enjoy seeing that Cobra - that’s such a great build

 

I’m in the middle on this discussion, personally…I’ll sand primer when it needs it (to remove peel or imperfections) but also if it looks paint-ready without any extra effort I’ll usually just roll with it.  Whatever works 🤷‍♂️

My two favorite weapons in getting to paint-ready quickly tho are the filler primer that Harbor Freight sells (if I need something thicker to fix or help with whatever needs fixing) or if I need something thinner I like Touch N Tone gray - it lays down like Tamiya gray but it’s $3 for a regular size can

[Bucky]

Thanks for all the info.  I've probably been using a few techniques from each and every one of you. One problem I had to pop up was the Duplicolor primer lifted off the body with the Tamiya tape in spots. This primer had been laid down for around five years on the project. After spraying the roof of the car white, I removed the tape along with some of the primer. Then I had to mask off the roof and respray the primer. 

[StevenGuthmiller]

2 hours ago, Bucky said:

Thanks for all the info.  I've probably been using a few techniques from each and every one of you. One problem I had to pop up was the Duplicolor primer lifted off the body with the Tamiya tape in spots. This primer had been laid down for around five years on the project. After spraying the roof of the car white, I removed the tape along with some of the primer. Then I had to mask off the roof and respray the primer. 

What paint did you use?

 

 

Steve

[Bucky]

It was the Duplicolor primer that lifted off after I painted the roof white. I used Testors Gloss White enamel on the roof. It actually laid down very smooth, which was a pleasant surprise because it is a fairly old can of paint. 

[DiscoRover007]

I sand the primer smooth every time. You don't want to make too smooth though because that can effect how well the paint adheres. But I would consider it an essential step for metallic colors especially to get the grain to lay down smooth.

[bobss396]

I'm using Mr. Surfacer primer lately. It goes on baby-backside smooth.

Usually it takes a few rounds to get everything sorted out.

After the final-ish coat goes down, I'll lightly wet sand with a DM 1800 or 2400 cloth. 

Follow up with a warm soapy water wash, rinse, then 15 minutes in the dehydrator to dry it.

[1972coronet]

FWIW, I made the mistake of wet sanding ( "smoothing" ) Tamiya primer (rattle can) as the final step before colour coats. 
The finish -prior to applying clear- was actually patchy and splotchy ! 
I used Tamiya paints for every step , primer to colour to clear. 

After I stripped the body, I followed the same procedure, this time skipping the de facto burnishing of the primer.
Zero problems - paint laid down perfectly.

I use sandable / scratch-fill primer only where it's needed ( i.e., I tape off the surrounding panels, etc.) , and I keep the filler primer application to a minimum. 

[SfanGoch]

I use Stynylrez primers. They're self-leveling and dry to a smooth finish. No sanding required.

 

[DanL]

A while ago I started using 3000 grit, then 5000 grit to make my primer as smooth as possible and it improved my paint finish a lot. Seems to go against what most are saying but it worked for me. I use various spray paints for my color coats. It seemed to reduce the orange peel.

Cheers

Dan

[StevenGuthmiller]

28 minutes ago, DanL said:

A while ago I started using 3000 grit, then 5000 grit to make my primer as smooth as possible and it improved my paint finish a lot. Seems to go against what most are saying but it worked for me. I use various spray paints for my color coats. It seemed to reduce the orange peel.

Cheers

Dan

Looks terrific!

 

 

 

Steve

[Bucky]

Thanks for showing the great examples, guys! Maybe by using the various tips and tricks posted here, I'll be able to get a little closer to producing paint jobs of this caliber. 

[rattle can man]

It's been decades since I worked in a body shop. Those who are currently in the 1:1 bodywork world please correct me if I'm wrong.  There are different primers designed for different purposes. If your primer is intended as a filler or a sealer, it is thicker because has material to fill imperfections and needs to be sanded smooth. Further, it also is usually porous, which is why you sometimes see primered metal rust. A primer-sealer on the other hand seals all of the underlying materials to help prevent splotches and give a smooth, even surface for color coats.  If you sand a sealer and break through to the paint under it primer, you may see splotchy color coats  because of the different porosity.

[Dave G.]

One category I've noticed it best to not sand the primer. Unlike in 1:1, where typically a clear sealer coat goes over scuffed primer before a hot color coat. In models we tend to put hot lacquers directly over the primer. I've seen in this case, even if sanded with say 1200 micro pads, sand scratch swelling in the color coat driven up from the primer below.. So for me, if to use hot lacquers ( rare for me), Id rather not scuff my primer final coat. So happens, if put down right, Mr Surfacer 1000 goes on baby but* smooth, but being 1000, has a slight tooth, probably microscopic. Never has adhesion problems at any rate.

Another one that lays down that smooth is Stynylrez thinned a little with Createx 4021 reducer. Here I use acrylic or enamels over that unscuffed, except for dust specs.

Speaking of dust specs, I don't sand those but rather use OOO steel wool, which is said to more scrape the surface than sand scratch the surface.. You can actually buff the primer coat up with OOOO steel wool, thus why I use OOO..

Just my .02 cents worth added to the thread..

[bobss396]

I keep an old food container by my kitchen sink with all my wet sanding stuff in it.

DM cloths, #1500 to #8000, some sand papers, sanding sticks.

Also a piece of old flannel and an old tube of toothpaste.