sanding primer

Hi Everyone,
hope all are well. A question, but first a preface. I understand the smoother the coat below something, the better the coat above it comes out. Is it possible to sand the primer coat (tamiya primer, or duplicolor grey auto primer) TOO much? i.e., sanding to a very smooth surface - say, 3200 grit sandpaper - can this negatively affect paint topcoats adhesion? (using tamiya TS spray cans)

thanks in advance for any advice.

SK

just sand away, watch out only not to burn through all the way down to plastic, if you do, re-prime and do all over again. Only thing that is not suitable for sanding is pearl and metalic base colours before you apply clear coat.

is250 - there are two purposes for primer and there are two types - one primer surfacer is used to cover "putty's" and fill small imperfections and blend in the work smooth - the second is primer sealer which seals the surface below the primer chemically so that the paint coats do not react chemically with anything below the primer sealer and to act as an adhesion promoter for paint to "bite" in to. With the (1:1) automotive world primer surfacer is sanded smooth and blended "feather edged" on any work or putty. Primer sealer is not sanded. If you are going to clear coat you paint then do not try to make it any smoother than 1000-1500 it is not necessary. Remember to apply thin coats of the paint to avoid "orange peal" effect the clear can be wet sanded and smoothed to bring out a smooth and shiny finish - hope this helps you some - John

Is it possible to sand the primer coat (tamiya primer, or duplicolor grey auto primer) TOO much?

No worries, it's not really possible to sand it too much or make it too smooth. Even if you polish the primer with 3200 or finer and you can see yourself in the reflection, the paint will adhere (paint may not adhere well to smooth untoothed plastic, but you don't need a rough primer surface for paint to stick to). Sand, sand away until the primer is FLAWLESS. Obviously if you sand through the primer to bare plastic you'll need to reapply (and resand) the primer in that area- but otherwise primer is meant to be sanded and worked until it is perfect. This is the stage to correct all the flaws in the body. You're ready to move on to paint when with careful visual inspection you can find no flaws, no debris, no texture (orangepeel, etc), and no scratches. I spend roughly 70% of my time/effort in painting a body on the primer. The paint gets about 10-15%, and the clearcoat gets about 15-20%. Once the primer is right, applying paint and clearcoat are almost an afterthought.

Never any problems with paint adhering with it that smooth? I've had issues with 1:1 with very smooth primer & also with too smooth of color coat when clearing, but maybe not in scale? 1:1 environment is certsinly harsher...

The 1:1 environment is vastly harsher. Not many of us leave our models out in the weather for months/years on end, on hot bright summer days and cold, snowy winter nights. Extreme temp changes and bright UV puts considerable stress on real automotive finishes. For scale modeling as long as you're using compatible paint/primer (i.e. Tamiya TS paint and Tamiya TS primer), you'll have no trouble. If you're using automotive products for real automotive applications, follow manufacturer's instructions....

No worries, it's not really possible to sand it too much or make it too smooth. Even if you polish the primer with 3200 or finer and you can see yourself in the reflection, the paint will adhere (paint may not adhere well to smooth untoothed plastic, but you don't need a rough primer surface for paint to stick to). Sand, sand away until the primer is FLAWLESS. Obviously if you sand through the primer to bare plastic you'll need to reapply (and resand) the primer in that area- but otherwise primer is meant to be sanded and worked until it is perfect. This is the stage to correct all the flaws in the body. You're ready to move on to paint when with careful visual inspection you can find no flaws, no debris, no texture (orangepeel, etc), and no scratches. I spend roughly 70% of my time/effort in painting a body on the primer. The paint gets about 10-15%, and the clearcoat gets about 15-20%. Once the primer is right, applying paint and clearcoat are almost an afterthought.


I haven't seen any of the finished products of yours - but 1000-1500 for primer is plenty smooth enough. Primer is NOT supposed to be finished to a polished surface unless that is the final finish you would want??? I can send pictures of my work - I never spend too much time or effort to "polish" primer - that defeats the purpose of primer. While I agree that a 1:1 environment is far harsher - the basic chemistry and principles hold true. If in doubt - google primer application of any paint supplier instructions. I agree that Tamiya TS-primer is just about the perfect primer because it has characteristics of both primer filler and sealer. Primer filler usually contains a medium of "talc" which fills in the slight imperfections and allows for the "rough" grabby feel - TS- primer does not contain too much talc unlike "mr. hobby surfacer 500" that needs to be sanded substantially. Additionally if you are using "automotive" spray can primer and it is of the "filler" type you will definitely need to sand it as it is not designed to be painted on directly it is designed to fill slight imperfections and to "feather edge" work below the "filler" primer surface, but 1000-1500 wet sanded is plenty of time spent on "primer". I have no interest in getting into a spitting match with others on the forum - I merely stated "truths" about "primers" and their purpose - if you don't like the opinion posted - please DO NOT READ IT - just skip to the next post. The best advice for anyone new to modeling and the painting process is to experiment on misc scrap plastic "spoons" and see what works best for yourself and your experience level and technical "application" skills. Let's keep the bickering off this forum - John

as other have posted already, why would you even bother sanding primer to such a fine finish, primer is meant for paint adherence and highlighting flaws, not for auto show shine

Let's keep the bickering off this forum - John

Wow, take a step back there, guy. We're not actually bickering. If you reread my post, you may find that it has not a thing to do with either your post or with you. It simply says something different than what your post says.

But since you bring it up- the original poster did not ask "what is primer used for?" or "how is primer used in painting cars?". He asked IF primer could be screwed up when painting a model car by sanding it too much. I answered that. Strangely enough, you didn't.

I'd also like to point out that it simply does not matter how real cars are painted. Even if we're using real car paint, we're not painting 1:1 cars. We're not actually painting cars at all. We're painting plastic toys. This is a bit like using professional grade house paint to paint turtles. It does not matter how houses are painted- if you're going to paint a tortoise (even if you want to make him look like a house), you are going to use a different technique to paint him than you would use to paint an actual house.

I occasionally sand primer with ridiculous grades of abrasive- like 3200 micromesh. When I have, the results have turned out very well- well enough that it justified the effort to do that level of preparation to the primer. There are even applications in modeling where it would be highly advisable. For instance, if you wanted to build a chrome Ferrari-

http://static.desktopnexus.com/thumbnails/403809-bigthumbnail.jpg

-I would recommend that you aggressively polish that primer until you can (nearly) see yourself in it. Spray it with a couple of very light and heavily reduced coats of gloss black, and then lightly spray on Alclad chrome. If you don't polish the primer, it does not matter how much you polish the clearcoat over it- the texture in the primer will forever be clearly visible. In scale modeling if you want a perfect paint job, it helps tremendously to make it perfect from the base up.

as other have posted already, why would you even bother sanding primer to such a fine finish, primer is meant for paint adherence and highlighting flaws, not for auto show shine

Why? Because the smoother your primer is, the smoother your paint will be, especially if you want your color to have an auto show shine. Primer has a texture to it (even Tamiya fine primer has texture), and finished/glossy paint should be without texture. Many colors don't fill that texture in, especially Tamiya sprays.

Primer is used to give a uniform color and surface for the finished colors to be applied upon. 1:1 bodyshops wetsand primer, so not wetsanding model primer makes for an even more out-of-scale texture to color that is totally un-necessary. With modern base coat/clear coat systems, you want that basecoat as absolutely smooth as possible before clear.

I just wetsanded a final primer coat with 4,000 grit Micromesh. It's a perfect surface for the color coats that come next.

From my experience, 3200 is not smooth enough for the base color to develop adhesion problems, especially with the synthetic lacquer like Tamiya that you are going to use. 3200, 3600 or even 4000 can be used to smooth the primer, and a certain level of smoothing is recommended for translucent base colors like metallic/pearl/mica etc, because those colors are more sensitive to the smoothness of underlying layers than the solid colors. (Also the primed surface has to be free from scratches and specks, and that requires some extent of smoothing.)

Things get tricky when you use dissimilar types of paint, like water-soluble acrylic over lacquer-based primer or the very hard urethane clear over somewhat flexible acrylic base coat. Urethane doesn't flex very well, and I had a situation where the clear cracked when I was trying to meet the body with the chassis.

In any case, you have to experiment and develop your own procedure that you can be comfortable with, because everyone has a different painting method, equipment and environment. So, go ahead and spray the base color on the smooth primer, and post what you have learned.:grinyes:

Hi Everyone,
hope all are well. A question, but first a preface. I understand the smoother the coat below something, the better the coat above it comes out. Is it possible to sand the primer coat (tamiya primer, or duplicolor grey auto primer) TOO much? i.e., sanding to a very smooth surface - say, 3200 grit sandpaper - can this negatively affect paint topcoats adhesion? (using tamiya TS spray cans)

thanks in advance for any advice.

SK

Wow, take a step back there, guy. We're not actually bickering. If you reread my post, you may find that it has not a thing to do with either your post or with you. It simply says something different than what your post says.

But since you bring it up- the original poster did not ask "what is primer used for?" or "how is primer used in painting cars?". He asked IF primer could be screwed up when painting a model car by sanding it too much. I answered that. Strangely enough, you didn't.

I'd also like to point out that it simply does not matter how real cars are painted. Even if we're using real car paint, we're not painting 1:1 cars. We're not actually painting cars at all. We're painting plastic toys. This is a bit like using professional grade house paint to paint turtles. It does not matter how houses are painted- if you're going to paint a tortoise (even if you want to make him look like a house), you are going to use a different technique to paint him than you would use to paint an actual house.

I occasionally sand primer with ridiculous grades of abrasive- like 3200 micromesh. When I have, the results have turned out very well- well enough that it justified the effort to do that level of preparation to the primer. There are even applications in modeling where it would be highly advisable. For instance, if you wanted to build a chrome Ferrari-

http://static.desktopnexus.com/thumbnails/403809-bigthumbnail.jpg

-I would recommend that you aggressively polish that primer until you can (nearly) see yourself in it. Spray it with a couple of very light and heavily reduced coats of gloss black, and then lightly spray on Alclad chrome. If you don't polish the primer, it does not matter how much you polish the clearcoat over it- the texture in the primer will forever be clearly visible. In scale modeling if you want a perfect paint job, it helps tremendously to make it perfect from the base up.


MPWR - the reason why I took the time to explain PRIMER in the first place is because if you do not understand the reason for it - you do not understand what and how to use it. This leads to answering the question - rather than telling a person what YOU think is relevant - provide them with the information to make their own decisions. My only advice "telling the thread starter what to do" was that he should experiment on plastic spoons with his primer, sanding , painting, finishing techniques and determine from his material, equipment and experience what he should most likely choose to do. - some people on this forum have some serious ego problems - and the number of one's posts do not determine their expertise. Some people on the forum cannot resist from adding their 2 cents while others choose to contribute when it is relevant. - for those of you that strive to polish primer - go at it - I choose to let the paint system work the way it was designed - nuf said - John

Personally I just sand it enough to take the roughness out of it and make it flat and level. Doing that also makes it less porous so it doesn't suck all the colour coats in like a sponge. I always make sure that it's well sanded as any texture in the primer does show through. However since I started to paint almost exclusively with Zero basecoats and 2K clear, it's less of a problem and some of the slight texture does get 'filled in' to some degree by the 2K clear, so I never feel the need to polish the primer to an absolute flawless finish. Just the way I do things, but there are many different techniques, so whatever works for you...

So having real-world, hands-on experience w/paints and primers, especially Tamiya, is called "having a big ego". Okay, I have a big ego. Let's move on.

The answer to the OP's question is simple. Tamiya primer can easily be wet sanded up to and beyond 4000 grit Micromesh for a smooth finish of the color, which will have no problem with adhesion. Notice I didn't say the word "polish". Just because it is Micromesh and not automotive wet or dry sandpaper doesn't just magically change the task from "sanding" to "polishing".

Tamiya sprays are a lacquer. As long as the primer is a lacquer, adhesion is not an issue if the primer is wet sanded smooth, because TS colors are lacquer and will chemically bond with the underlying primer. Wetsanding through 4000 grit will make your TS painted surface much glossier than not wetsanding. And even wetsanding primer to 4000 grit, TS colors won't lay down as smooth as if sprayed on bare plastic.

You'll really need to spend more time wetsanding automotive primers to use under Tamiya sprays, because automotive primers have more texture than Tamiya primer. If you really want to hate your Tamiya sprays, apply them over automotive primer that has not been wet sanded.

Real world experience tells me that. I'm working on my 16th model of the year, and most of them are shot w/Tamiya TS paints. And truth be told, I try as often as possible not to prime a model if it doesn't need it. In those cases I get the smoothest, glossiest finishes with absolutely the least effort possible. Why waste time and primer? I do clean the surfaces so the paint is sticking to clean, glossy plastic.

Speaking of which, since Tamiya :jerking: us around w/their lack of availability, I've switched to Mr. Hobby primers. Mr. Hobby 1000 is even smoother than Tamiya, especially when airbrushed. Therefore less time is taken preparing the primer for color. And that is a good thing...saving time, when possible.

ZoomZoomMX-5 - not sure if it was your intention, but your post supports my statements about primer and it's use. Primer "surfacer" as I stated is used for filling small imperfections and feather edging uneven surfaces below it - it contains large amounts of "talc" which I also mentioned which makes up for the textured feel and appearance. Most "spray-bomb" can automotive primer is of this nature are "high build" and would obviously require the removal of all the texture bumps - it is meant to "fill" imperfections in the 1:1 world. Then primer "sealer" the other kind of primer is meant to "chemically" seal previous paint and fillers like polyurethane "bondo" etc from interacting with solvents in the new paint above and forming nightmares like crazing - shrinking - checking among other painting chemistry issues. The manufacturers of primer sealer state "not to sand it" because you defeat the purpose of the chemical "sealing" of the surface layer. I can fully agree if one is using "spray bomb" auto primer filler to prime his models with, it is an in-appropriate product for priming as nothing on any model I've ever worked on was so bad that it needed the thick "talc" layer that primer surfacer puts in the coat layer. This would require many laborious efforts to fix - better yet is to use a product as you mentioned that is designed for modeling and models in general like Tamiya primer -"Mr. Hobby 1000 or 1200" and in a worst case "Mr. Hobby surfacer 500". You mention Tamiya being a "lacquer" and it is sort-of - it is no longer a true traditional "lacquer" as in lacquers of the 60's-70's auto era that required 20-30 coats - it is now a "synthetic" lacquer - but sprays thin like a traditional lacquer which has advantages as a flaw is easy to fix because the "layers" are thin. Steve Nobel whom I have the utmost respect for on this forum and consider his opinions and advice worthy of merit - no ass kissing intended Steve - it's simply a fact of your posts and work - makes a good point for "Zero" paints and 2K clears. They are for the most point fool-proof if you have access to an airbrush. They are pre-mixed and come in many colors - many of which are "matched" well that's what it says- and it comes in glass bottles with metal lids so storage problems are reduced. The negatives are shipping if you are anywhere else besides the UK. There are a few paint suppliers here in the USA that serve the "modeler" and sell small quantities of paint, but I have not purchased from any of them. I bite the bullet and pay the exorbitantly high "Royal Post" shipping charges and buy Zero paints from Hiroboy. I have yet to be disappointed by the materials finish or service. - John P.s ZoomZoom, I did not imply "you" have a big ego and coincidentally I am a fan of your work

thanks to all for their input. I did end up sanding to a 3200 grit of tamiya primer layer. waiting to spray it with TS cans. will post some pics. thanks again.

is250 - hope you didn't get to confused with the conflicting replies - each one of us in my opinion has different techniques, skills, equipment, and materials (primer/paint/clear) - so I fully understand the varying opinions you received. Learn from what you have and how you use it and you'll develop your own system - I look forward to seeing some of your work in the near future - John

is250 - there are two purposes for primer and there are two types - one primer surfacer is used to cover "putty's" and fill small imperfections and blend in the work smooth - the second is primer sealer which seals the surface below the primer chemically so that the paint coats do not react chemically with anything below the primer sealer and to act as an adhesion promoter for paint to "bite" in to. With the (1:1) automotive world primer surfacer is sanded smooth and blended "feather edged" on any work or putty. Primer sealer is not sanded. If you are going to clear coat you paint then do not try to make it any smoother than 1000-1500 it is not necessary. Remember to apply thin coats of the paint to avoid "orange peal" effect the clear can be wet sanded and smoothed to bring out a smooth and shiny finish - hope this helps you some - John

I have a third reason to use primer, and thats to create a unified base colour when using different materials (i.e. styrene, resin, pe)

thanks to all for their input. I did end up sanding to a 3200 grit of tamiya primer layer. waiting to spray it with TS cans. will post some pics. thanks again.

is250 - do you use primer for modeling? :mr. hobby or tamiya" primers? They are much better products for using on models than "car" 1:1 spray bomb" can primers, unless you enjoy spending all that time to prepare the primer for paint. If you need to fill large imperfections there is "mr. Hobby" surfacer 500 which fills imperfections, sand and then "1000" or "1200" to use under the paint that requires less preparation. SmokyR67 also makes a good point that is provides an even "color" base for even "color up" build up of color layers. Remember thin layers of the color coat prevent problems like orange peel - checking - crazing etc.so you do not need to sand the paint coats if there are no problems. I'm not a salesman for mr. hobby or tamiya products but they are much easier to use for modeling than 1:1 car primers - and for a beginner will most likely produce a better result. - would like to see pictures of your work added here? - John

Great input here...but mostly if you have an airbrush & access to hobby/model paints...it can be hard to choose a special color online as well as expensive & time consuming to order international just to try out. I'm not against anything said here, just giving a different point of view. I wouldn't use a "filler" primer on a model unless there were special circumstances...

Great input here...but mostly if you have an airbrush & access to hobby/model paints...it can be hard to choose a special color online as well as expensive & time consuming to order international just to try out. I'm not against anything said here, just giving a different point of view. I wouldn't use a "filler" primer on a model unless there were special circumstances...


corvettekid - there are some suppliers for Mr. Hobby primers and clears here in the USA - (Burbank house of hobbies) just google them - there are others and Tamiya stuff (paints/primers) are available at most model hobby stores - Hobbylinc here in the USA is also a good source. As for small amounts of "jar" paints for an airbrush there are some supplies but I like the Zero stuff myself. No mixing thinners with pigments - ready to use and great results. - John

Thanks! But there aren't any hobby shops near me :( I also don't use an airbrush. Perhaps I might get one in the future tho. Will these suppliers ship spray cans?