My primer coat is very delicate

[Guest]

I have just airbrushed my first model (a 1/72 spitfire-like plane) with Vallejo polyurethane primer (recently bought), as it came from the bottle (unthinned). I had previously wiped the whole model with one of those cleaning wipes for glasses. I have learned to prevent any metal tools etc. (tweezers, the metal part of a brush) touching the coat. It comes off. Also, I started to mask a small part of the fuselage and decided that I did not want to do that, and carefully peeled off the Tamiya yellow tape. Some of the primer came off with it. (The primer coat was applied about 3 hours ago and kept in a warm room.)

I thought that a primer coat would be tougher. Is it to be expected that it would be so delicate?

[papa 695]

Hi Steve sorry to hear about the primer peeling, it could be a few things but as it's your first time air brushing i'm willing to bet that you sprayed it a little too thick ( i may be wrong ) . so the top was dry but the underside didn't have enough time to cure so when you pulled the tape away it pulled the primer away with it A tip for you when i use any tape for masking i first of all put it onto my hand/arm or jeans to take away some of the takiness off the tape The good thing about it being the primer you can just respray and it should be fine i hope this helps

[Guest]

It should be very tough. I use Vallejo primer all the time now because it is tough and smooth. WHat worries me a little is what you have used to wipe the plastic first. Are you sure that the wipes for glasses do not leave a residue behind or contain a polish of any kind? If they leave a hint of silicon polish, great for glasses, that would prevent the primer from sticking.

If you need to clean the plastic before spraying you would be better using either soapy water or thinners to match the paint. A compromise would be something like a car windscreen wash which some people use to thin some acrylic paints.

[stona]

Just to add to Graham's sound advice,alcohol is good for wiping down the plastic before spraying. It will also remove any greasy finger prints from that bacon butty you had for breakfast. I use isopropyl alcohol which I also use at work,cleaning electronic bits,sensors etc and which is therefore free. I also have a supply of alcohol wipes which we use for cleaning the fantastically expensive lamps fitted to some of the lights we use.

Good old methylated spirits will do just as well and is readily available and cheap. There's no chance of this damaging the plastic in any way,or removing your carefully applied filler like some solvents.

Cheers

Steve

[Guest]

in the same way that people like myself that don't use primer make sure that the plastic is oil, grease, dust free and has been prepared to provide a good "key" for the paint, primer needs this same treatment. if the surface is "unreceptive" then even primer won't adhere correctly.

sometimes the grease/oil will (can) alter the chemical structure of the primer (especially acrylic) and this will be easily peeled or flaked off.

the same care and preparation should really be taken in model painting/spraying as is in automotive work

[Guest]

papa 695:

To test your comment on too thick and not enough drying time, I placed three pieces of Tmiya tape on to the model just now (5 1/2 hours after spraying) and when peeling it off, no paint came with it. So, progress! However, if I gently scratch the primer with a fingernail, it will come off. Perhaps that is normal.

I will now respray the whole upper side of the model, thinning the primer (if I can find a suitable thinner for it).

== Despite thorough searches, I cannot find anything stated as a thinner for the primer. No supplier (not even Vallejo!) can tell me on their site what thinner to use for this primer. Any ideas?

(I have Vallejo "Airbrush Thinner 71.161 New Formula", and "Xtracrylx Thinners", and of course, water.)

== Should I gently sand the edges of the bald areas to remove any step at the paint edge, or should I just respray?

fanlander, stona and CDW



I got the use of the wipe from someone on a forum. I will use meths in future.

So much to learn!

[BarryW]

Vallejo primer is very tough but you must, absolutely must, let it cure properly not just dry.

1/ Wipe the model with alcohol (IPA)

2/ Airbrush on with light coats, do not flood the model.

3/ Let it be to cure for at least 24 hours before you either apply masking tape to it or overpaint.

I have never had paint peel off with the masking tape doing this and I never reduce the 'tackyness' of it first.

[Guest]

Like Barry not had any problems at all.

Matter of interest Steve di you prepare the surface by wet & dry. The plastic surface of the parts is very shiny. Obviously with wet & dry it scores in minute form the surface which provides a first class surface for the primer to adhere to. The wet & dry will not affect the resulting smoothness of the primer.

Also what temperature did you spray in & what temperature was the paint ? If you sprayed in a cold place after turning the heater on the paint does not reach a good temperature. Add to that was the primed model left in the cold or a warm atmospere ? Did you mist coat (ie thin coat) the original coat ?

You can thin with Vallejo Thinners. But if it is airbrushing OK without clogging I would keep to the full coat. If you thin, depending on the %, the you may have to apply another coat.

Laurie

[Guest]

Steve this is an extract form the Vallejo Site.

7.3. Can I dilute the new Acrylic-Polyurethane Primers for use in an

airbrush?

They seem thicker than Model Air. The new acrylic-polyurethane primers

are especially formulated for use in air brushing. The special quality, the

polyurethane component, which gives it the strength and the resistance

to nicks and scratches, will be diminished by diluting the product, but the

product can be diluted with our Thinner or even with distilled water. To

maintain its special qualities, the less dilution the better.

Laurie

[Guest]

I have to say that I've found Vallejo primer to be very fussy about surface cleanliness, that's why I use Halfords primer exclusively these days, it's hard as nails

[Guest]

BarryW:

I wil follow your 1, 2, 3 (although I will try stona's meths which I have in my garage).

tecdes said:

Like Barry not had any problems at all.

Matter of interest Steve did you prepare the surface by wet & dry. The plastic surface of the parts is very shiny. Obviously with wet & dry it scores in minute form the surface which provides a first class surface for the primer to adhere to. The wet & dry will not affect the resulting smoothness of the primer.

I used wet or dry, but used it dry: 400 grit then 1500 grit. (I have since found info that sanding it wet keeps dust down.) Phil Flory's excellent videos show the use of a sanding sponge then a polishing sponge. But they would polish the plastic and remove the good surface for the primer that you mention. Any comment on that?

Also what temperature did you spray in & what temperature was the paint ? If you sprayed in a cold place after turning the heater on the paint does not reach a good temperature. Add to that was the primed model left in the cold or a warm atmospere ? Did you mist coat (ie thin coat) the original coat ?

My workroom was pleasantly warm before, during and after, and so was the model, the primer and the airbrush.

I did not mist a thin coat. Perhaps I put too much on. A problem that I find is that the primer is very nearly the same colour as the plastic and it is very difficult to see it going on, unlike with colour. I know that you can get black primer, but one day I will experiment by adding a tiny amount of (water-based I think) food dye. But perhaps that would be unwise until I have a lot more experience.

You can thin with Vallejo Thinners. But if it is airbrushing OK without clogging I would keep to the full coat. If you thin, depending on the %, the you may have to apply another coat.

There was no clogging (I have a 0.5 needle). I will respray a full coat over the areas affected.

Thanks for the Vallejo excerpt. Encouraged by that, I discovered a mine of info at:

FAQs

[Guest]

BarryW:I wil follow your 1, 2, 3 (although I will try stona's meths which I have in my garage).

tecdes said:

Like Barry not had any problems at all.

Matter of interest Steve did you prepare the surface by wet & dry. The plastic surface of the parts is very shiny. Obviously with wet & dry it scores in minute form the surface which provides a first class surface for the primer to adhere to. The wet & dry will not affect the resulting smoothness of the primer.

I used wet or dry, but used it dry: 400 grit then 1500 grit. (I have since found info that sanding it wet keeps dust down.) Phil Flory's excellent videos show the use of a sanding sponge then a polishing sponge. But they would polish the plastic and remove the good surface for the primer that you mention. Any comment on that?

Also what temperature did you spray in & what temperature was the paint ? If you sprayed in a cold place after turning the heater on the paint does not reach a good temperature. Add to that was the primed model left in the cold or a warm atmospere ? Did you mist coat (ie thin coat) the original coat ?

My workroom was pleasantly warm before, during and after, and so was the model, the primer and the airbrush.

I did not mist a thin coat. Perhaps I put too much on. A problem that I find is that the primer is very nearly the same colour as the plastic and it is very difficult to see it going on, unlike with colour. I know that you can get black primer, but one day I will experiment by adding a tiny amount of (water-based I think) food dye. But perhaps that would be unwise until I have a lot more experience.

You can thin with Vallejo Thinners. But if it is airbrushing OK without clogging I would keep to the full coat. If you thin, depending on the %, the you may have to apply another coat.

There was no clogging (I have a 0.5 needle). I will respray a full coat over the areas affected.

Thanks for the Vallejo excerpt. Encouraged by that, I discovered a mine of info at:

FAQs

Steve. I would not polish the surface seems to me to defeat the object after giving it a textured surface for adherence.

Mist coat is best.

There are 10 colours of primer in the range. I find it difficult to see when the colours are very similar to the background. I shine a light on to the model when spraying & change position to view as spraying as the light will catch the wet areas.

Wonder Steve if your coats are to thick. I have an adjustment on the A/B which controls the maximum flow. A .5 needle/nozzle will allow a fair amount of paint to be released. Allow that 24 hours if possible between coats. It is a bit of a nuisance but that is the fact it takes time to dry & harden. I have a garden propagator which I have insulated & it has a heater. I keep it at 60 to 70 degrees & this drys & hardens off the paint well.

You are right Steve the Vallejo site is incredible it has so much info it is difficult at times to search it out.

Before respraying Steve I would make sure it is really dry & hard. The areas which have stripped I would gently wet & dry to lose the bare edges otherwise you will end with a hard ridge.

Laurie

[Guest]

Thinning is always a matter of personal choice with Vallejo primer. I use a .3 needle set and I do not thin the primer. I do however, as with all airbrushing, mist the layers on and let it build up over maybe three or four thin coats. I don't let it harden between coats, I just keep going over the model until it is solid.

If the plastic colour is an issue, I tend to use a contrasting primer colour. I think I have them all now which some may think odd but some of the primer colours are spot on for the finish colour (especially the NATO Green and Bronze Green. The German dark yellow is, however, miles out but a good primer for it) at the least I would get a black, white and grey as you can mix them for pre shading to.

[stona]

I don't deliberately sand a model surface to aid adherence but in fact most of my models have had a once over. When seams are fixed,the odd bit of glue in the wrong place etc the area has to be sanded and when I'm happy I give the whole model a very quick once over with very fine (2400 grit) paper just so that it all looks the same. I then give it a rub with some denim material before wiping with alcohol. This doesn't damage any detail.

Cheers

Steve

[Guest]

Like that Graham building up with mist coats before it has hardened not thought of that & seems very logical.

Like the alcohol (more ways than one !) Steve seems a very clean method of prep. Why the denim is it lint free if you get my meaning ?

Laurie