Bad primer job

[Carrack]

I was priming up a rhino a few nights ago using krylon black primer. It has worked well before for me. It appeared to be applied correctly yet when I retrieved it from my covered porch an hour or so later there was a grey filmy residue covering the model almost completely. It was raining and I used the last of the can.

 

Was it the humidity? The dregs of the can? Operator error?

 

Do I need to strip it? It will not wash off, but if I run a fingernail across it it reveals the black primer as it should be. Sorry I don't have pictures.

[FashaTheDog]

Might be humidity.  Fun fact about priming when raining, there is loads of moisture in the air to mess with your spray paint.  Depending upon how bad the residue is, you might be able to still use it by gently washing it off.  This also depends on how good a painter you are too.  A modest quality paint job or worse should be unaffected by a little primer issue provided that you clean it up sufficiently.  For instance, when my primer gets fuzzy from too much humidity, I gently brush it away with a worn toothbrush to smooth and it tends to be just fine (next time it happens to a Carnifex though, I'm leaving it, painting the model white, and giving the Fex bunny ears with the name Fluffy).  If you paint to a high standard, then you may want to strip it.  Since there is a residue, however, you may want to test to make sure your paint job isn't going to flake off as though the model were covered in mold release.

[Carrack]

Thanks I tried washing off with hot water and a rag, I will try with a toothbrush. At least it wasn't the land raider I got the same day. ):

[Stoic Raptor]

Using aerosol spray of any kind on a model (whether it's primer, paint, or varnish) is so dependent upon temperature and humidity.  If it's too cold, the paint will be gummy and thick.  If it's too hot and/or dry, the paint will dry before reaching the model and you get a granular finish.  If it's too wet, moisture gets trapped in the coat and you get what you experienced, or frosting with a clear coat.
 

Basically, the farther the outside weather is from standard room temperature and humidity, the worse your results will be.  To save your model, try gently sanding the primer - not to remove it, but to restore it to a smooth surface.

[FashaTheDog]

Since we are talking about weather and its effect on spray paint I will add this.  You can use cold weather to your advantage.  If you keep the can of paint warm on a day well below freezing and then coat something before the can and paint cools, then the paint will contract while it dries and crack.  On large flat surfaces (like Rhinos) it gives this neat marbled effect.  What is important is that the paint goes on warm and then dries in the bitter cold, which can be tricky unless you spray a small number of parts at a time or have a heated interior spray area.  Fortunately if you lack the latter, you are an endotherm so you can warm that can against your body under your coat between pieces!

[Carrack]

Using aerosol spray of any kind on a model (whether it's primer, paint, or varnish) is so dependent upon temperature and humidity. If it's too cold, the paint will be gummy and thick. If it's too hot and/or dry, the paint will dry before reaching the model and you get a granular finish. If it's too wet, moisture gets trapped in the coat and you get what you experienced, or frosting with a clear coat.

 

Basically, the farther the outside weather is from standard room temperature and humidity, the worse your results will be. To save your model, try gently sanding the primer - not to remove it, but to restore it to a smooth surface.

I fear I will be forced to strip the primer. I have tried gently sanding it with everything from a toothbrush to fine sand paper to no effect. The amount of pressure/ friction required to get rid of the residue will damage the model. Incidentally I also tried rubbing alcohol and a bleach based cleaner, as well as good old soap and warm water, none of which worked.

 

I'm pretty new to the hobby thanks for the advice. Next good weather day I will prime as much as I can.

[Carrack]

Since we are talking about weather and its effect on spray paint I will add this. You can use cold weather to your advantage. If you keep the can of paint warm on a day well below freezing and then coat something before the can and paint cools, then the paint will contract while it dries and crack. On large flat surfaces (like Rhinos) it gives this neat marbled effect. What is important is that the paint goes on warm and then dries in the bitter cold, which can be tricky unless you spray a small number of parts at a time or have a heated interior spray area. Fortunately if you lack the latter, you are an endotherm so you can warm that can against your body under your coat between pieces!

Interesting, I live in a pretty warm place, Texas, and do not think I will see any more cold days this year. I may try this technique with an old freezer I have in my garage though tomorrow. I think I will test it out on some empty sprues or if I can find a flat bit that doesn't have any foreseeable use first though. I'll store the bit in the freezer, take it out and spray it down, then let it dry in the freezer. I'll let you know the results.

[Carrack]

My freezer experiment didn't do anything special.

[FashaTheDog]

For reference I used a Rustoleum flat white and have only done it on days below zero.  I'm not sure what the exact temperature was, but the news said the high for the day was -9^oF when I last did it a few months ago.  Wish I could be more help.

[Carrack]

Thanks for the help. I did get some models primed without the fuzziness by drying them indoors.

[Spazmonkey]

I Live is Queensland Australia very hot and humid place.... I can only paint during the middle of the day, sometimes in the morning if it is dry enough

If i paint in the evening I always have issues with my paint going grey or seperating.

Enamel paints coming out matt instead of gloss. grey paint going black as well.

 

Humidity and heat will have a massive effect on can spray paint.

[Stoic Raptor]

That's why I don't use spray primers any more.  Where I live, it's too cold for 4-5 months out of the year, too hot for 1-2 months, and rainy over 50% of the time.  Needless to say, even during the best months (May-June, September-October) it can be days until ideal weather rolls around for spray painting.  I live in an apartment building and do not have a garage or basement and there's no way I can set up an airbrush station (due to compressor noise and the fact that I paint at the kitchen table).

 

So I typically use brush-on primer - Vallejo makes an acrylic-polyurethane surface primer that is unparalleled.  It comes in a variety of colors and can be brushed on or airbrushed.  It's self-levelling for very thin coats, super durable and has a good surface for paint to adhere to.  If you're having trouble with sprays, try this.  You will not regret it.