Calling All Gurus - re-prime or not?

Like Greg I too order my Stynylrez in warm weather, if it looks low I like to get it in by Oct. In my experience if it came in in good condition it stays that way even if separated down the road but needs power mixing when it does separate. I don't own a mechanical shaker but I use the Badger mixer on my Stynylrez 2-3 times a year on general principals, then it seems not to separate so bad between sessions of use. Just put a mixing stick in there, if there is goo on the bottom or clumps anywhere don't bother mixing with the stick, get out a power something or other. I really believe you'll never put humpty back together again with a stick or hand shaking. But so easy with a power tool.

My secondary primer is Mr Primer Surfacer but it's the real stinky stuff and a topic for another thread. Point being though I always have primer, I guess, well actually I don't know why I brought that up.

Mrchntmarine

So, i was going to do the "tape test" on the bottom. While handeling and rubbing some of the white spots where the primer pulled off, i caused another 1 or 2 belmishes......

I was afraid of that. That can be the problem with re-doing a paint pulled up by mask problem....the bond to plastic is only as good as the original coat (in this case, your Stynylrez)

Also, you mentioned shaking the 'clumps' out of your Stynylrez. This is not a good sign. 2 questions;

1. How old is your Stynylrez?

2. Could it possibly ever have been frozen, including shipping to you?

I've just this summer started tossing my Stynylrez after 2 yrs, and try to buy it only in the summer months to avoid freezing in transit. Not sure what the shelf life is, and I'm just guessing at the two years.

Somebody already gave you the magic bullet advice for Stynylrez above, shake the heck out of it. I broke down and got a mechanical shaker this spring, my Stynylrez sessions have been consistent since.

Good luck with your progress, and sorry about the new paint pull-up. Been there, it's disappointing and frustrating.

Hi!

 Technically, if you wet sand using a circular motion that shouldn't be a problem(Scuff Marks) If this worries you, finish with 1200 or even 800 grit, again,Wet! Eaglecash makes a good point. I have used Comet Cleanser on Car and Ship Models with Great results. It acts like a Rubbing Compound. The nice part? you get a nice dull non swirly finish.I have even used Comet to polish hard to work Clear plastic finishing up with McGuires Classic car polish in some situations. You have doubts? Well, the Mcguires comes off with Dawn if there's any residue

No not the primer but the prep work I believe is your issue unless the primer just wasn't mixed well or got damaged. You want to scuff to where your plastic is dulled out everywhere. 600 should work fine but I prefer 000 steel wool or micro mesh or even a scuff pad. 000 will dull the finish but because of the design of steel wool it doesn't leave directional sand marks, it leaves micro scrapes more than sand marks. And its enough to give paint a grip on shiny plastic. I use 1000 grit micro mesh otherwise or even 1200-1500 ( 1500 is getting kind of fine though). And it seems to me back when I used scuff pads they were the red ones which is a suito 400ish. Now I have not seen scuff marks in Stynylrez primer personally using those methods, I have had them surface if top coating with hot lacquer over stynylrez, so called sand scratch swelling. But a light scuff and reshoot the color and they are gone. But that swelling is why I don't use Stynylrez with lacquers now. I use Mr Primer Surfacer for lacquers. I keep both that in grey and Stynylrez in white and black here. With the Stynylrez I mix my own shades of grey according to my needs when I want grey. I only shoot acrylics and enamels over Styn.

If what you have is 600 it should be fine, I just prefer scuffing with things more pad like than paper. I shot 1/1 for 35 years or more and final scuffing was with red pads supplied by the automotive paint supply stores I used. fwiw. Paper has it's place too just to me not for scuffing prior to paint. But that's me, obviously others are free to not agree.

Mrchntmarine

Question:  Ive asked this before - when ive sanded parts and have scuff marks that can been seen, ive asked, "wont they be visible if i prime and paint if i can see them before priming? " and ive always been told, yes.  So, if i scuff the plastic with 600 grit, the marks will be visible after priming and painting??

Yes, you'll have visible scuff marks if you use 600 grit sandpaper.  I'm currently building a Revell F-100D, and I'm finding that I'm having no issues with primer and paint sticking to it, even doing test fits of the cockpit into the fuselage using non-detacked Scotch tape.  What I did for surface prep on my F-100 fuselage (since its too big to fit in my "bath" containers) was to use my trusty cheap electric toohbrush and a paste I made with Comet and water.  When you use Comet paste like this, its important to use that same cheap electric toothbrush during the rinsing process, to make sure you scrub all of the Comet residue off.  A regular toothbrush is OK too, but an electric one puts far less mechanical stress on any small details you might otherwise break off with the broad motions of a regular toothbrush...the electric one is fast, but the movements are small and gentle.  Once that completely dries, I use decanted Tamiya Grey Surface Primer which I thin with MEK (MEK mixes extremely well with the primer and serves as a really aggressive plastic etchant, but as long as you're airbrushing it and not laying it on in a thick, wet layer, it won't hurt even the finest details).  I have found that the primer is ready to accept paint after a minimum of 2 hours.  I learned the minimum time and techniques above by LOTS of meticulously structured experimentation on spare F-14 fuselage pieces, and finally settled on what I'm posting here as my go-to technique which hasn't failed me yet, and leaves no visible scuff marks, even under the bright light and magnification I always use when building.  For masking, in case I haven't already mentioned it, I no longer use tape of any kind because it always leaves bands of slightly different sheen paint where it touches (again under bright light and magnification...you don't see it otherwise).  I use Tamiya masking sticker sheets, which require no "de-tacking" and they're so thin and strong that they lay down extremly well, even when going over 90 degree bends.  You have to cut them to the size and shape you want, but its not as hard as it sounds.  Using the above techniques and the Tamiya masking sticker sheets (which are essentially the same material as Tamiya and Eduard canopy masks), I have had no issues at all with lifting, and no slightly different sheen to the paint they were touching.

The sharply-defined scalloping between the upper and lower colors on this F-4B, as well as the fairly-complex shape of the bare metal areas, were masked with Tamiya masking sticker sheet material that was cut to the shape of the scalloping.  Also did the masking for the corrogard areas on the leading edges of the wings with this material.  No bleed-under and absolutely no peeling of any kind when the mask was removed.  Surface prep and priming were all done per the above paragraph.

Also used the above surface prep method on the F-100D fuselage.  Its a work in progress, but you can see toward the front that none of the primer was peeled off the plastic by the Scotch tape I'm using for test fits (I had it wrapped tightly around the area forward of the black cockpit area), and Tamiya primer feathers really nicely as well, so blemishes due to schmutz are easy to fix.

Greg, et al.,

So, i was going to do the "tape test" on the bottom.  While handeling and rubbing some of the white spots where the primer pulled off, i caused another 1 or 2 belmishes along the edge of the painted bottom along where the bottom meets the side.  Mind you, 2 tiny specs of red flaked off.  When i applied the detacked purple paint on the bottom and slowly pulled all was good.  When i did the same to one red side - all was not good.  Parts pulled off.

So ive now stripped the sides and bottom of primer and bottom paint.  It all came off VERY easily with IPA - even after a week.  I mixed and re-checked my primer and its all mixed mixed well in the bottle.  No clumps or chunks left.

So i guess ill scuff and reprime. 

Question:  Ive asked this before - when ive sanded parts and have scuff marks that can been seen, ive asked, "wont they be visible if i prime and paint if i can see them before priming? " and ive always been told, yes.  So, if i scuff the plastic with 600 grit, the marks will be visible after priming and painting??

thanks everyone for the help and input!  A work in progress.

oldermodelguy

 

 

Mrchntmarine

Will do. Tks!  Have been traveling since I posted this - so the primer is probably cement now and the bottom paint is I'm sure cured!  Tempted to tape and do 2 coats of black to cover up the peeled primer or just re-spray primer over the pulled spots then black. Not sure I'm up for tangling with the strip and re-do. 

 

 

The question we don't know the answer to yet is is there a better bond now with some curing time ? I mean one has to wonder how good the bond is under that entire paint job.  

now I'm curious. In general you mean why the bond my not be good ( as in not a good primer? )  ? Or based on how I prepped and applied ?    I've always read that stynylerz can be painted over in short time...

Hi!

 That is a REVELL ship, is it  not? Strip, Sand and start over. I have found thet the styrene used by Revell is semiglossy harder finished plastic!. Scuf completey with 600 grit Wet Sandpaper after stripping. Try not to not miss a spot!

Mrchntmarine

Not sure I'm up for tangling with the strip and re-do.

I remember the first time I stripped something. It sounds like such a fuss and I kept putting it off, but there is really nothing to it and the whole process is a lot easier than trying to fix the problem and paint over it.

Just my in case you ever run into something like this again.

Since I make lots of bonehead mistakes, I strip paint quite a bit.

Mrchntmarine

Will do. Tks!  Have been traveling since I posted this - so the primer is probably cement now and the bottom paint is I'm sure cured!  Tempted to tape and do 2 coats of black to cover up the peeled primer or just re-spray primer over the pulled spots then black. Not sure I'm up for tangling with the strip and re-do. 

 

Stynylrez does sand well if you want to try and feather sand the edges of those spots, then spot prime it back in. The question we don't know the answer to yet is is there a better bond now with some curing time ? I mean one has to wonder how good the bond is under that entire paint job. You'll need to tape the red off, is that going to lift is another question ? Course its easy enough to answer, just tape and peel. Remember you need to build on that surface and the kit itself yet.

Will do. Tks!  Have been traveling since I posted this - so the primer is probably cement now and the bottom paint is I'm sure cured!  Tempted to tape and do 2 coats of black to cover up the peeled primer or just re-spray primer over the pulled spots then black. Not sure I'm up for tangling with the strip and re-do. 

Well whatever you do in the next round with this I'm rooting for success ! Let us know how it goes.

Kendra Bell

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oldermodelguy

Just for the record and I'm not endorsing it's use but I've used detacked blue painters tape with stynylrez and not had it lift at all, never mind as yours did. I normally use low tack modeler tape.

mine pulled with the tamiya detacked yellow tape. I like better and have had no issues with the blue painters tape and I like more the purple tape.....  

After stripping I'd scuff the entire hull with micro mesh or 000 steel wool personally, only because you've already had bond issues, not because Stynylrez generally needs it. And I'd power mix that bottle of separated Stynylrez, that stuff is about impossible to get all/fully/100% back together again by hand. But a power mixing will do it in about two minutes. I'd also change from the alcohol wipe down to mineral spirits, some of us here have seen some inconsistencies in the finish of Stynylrez when doing an alcohol wipe down.. Don't know why but we have seen a kind of motor oil on water look to the finish when usin alcohol wipe. It doesn't matter if it makes no sense, it's just there and isn't when using mineral spirits. Could be our particular environments, who knows but it doesn't matter.

Just for the record and I'm not endorsing it's use but I've used detacked blue painters tape with stynylrez and not had it lift at all, never mind as yours did. I normally use low tack modeler tape.

Test

Sorry, not getting notifications- just seeing these now. 

Steps - remove flash, belemishes. 
sand rough spots

wash with water and dawn. Dry

let sit a day

wipe with alcohol. Sit a day

shoot with Stynylrez that was mixed and shaken by hand and stirrer over a number of days as it hasn't been used in a long time. Not thinned and applied by directions on bottle. 

let sit a few hours then taped and primed. Here's the mistake as mentioned above - got my taping drying time mixed with just spraying over time....  

BUT -  this may have contributed too as I remember this happening before. I used Tamiya yellow tape. I did dull the sticky of the tape before applying by pressing it to my pants after I had cut my taping edge with exacto.

i seem to remember having an issue with this tape before with peeling. Like it's too sticky. I'm sure my lack of cure time is the most like contributor here though. But , I've now put the tamiya in a baggie marked "do Not use for painting" and have gone back to purple and blue painters tape. 

I've found that Stynlrez Gray is one of the hardest paints/primers to remove once it sets.  It laughs at alcohol and "purple industrial cleaners."  I usually have to go to EZ Off oven cleaner to remove it.

I have a love/hate relationship with Stynlrez, but mostly I hate it.  I've got to throw-in with MJY65.  Shed yourself of Stynlrez and go to something like Mr. Surfacer.  Much easier to apply and you'll be a happier modeler.  

Once you get the old primer stripped remove any residues or oils with a good wipe down of alcohol. Then prime it. I usually let all paints and primers set overnight just to be safe they are dry. Another good rule of thumb is to make sure the tape you are using is low tack. Tamiya tape and blue painters tape works good, just stick them to your arm or hand before applying them to remove some of the sticky so they are less likely to pull paint up when removed. When pulling the tape, go slow and pull back against the direction of the tape 180 deg. If you pull 90 deg you are far more likely to pull paint up. Take your time and work slow and you should get great results.

BK

Steps for modeling happiness:

1.  Strip old primer

2.  Throw Stynylrez in trash

3.  Prime with Tamiya FSP or the lacquer based primer of your choice

4.  Enjoy

I think its pretty obvious as well that it needs stripping and doing over. But I'm curious about a couple things concerning prep, that you don't repeat whats happened already.

Could you describe your surface prep before priming ? Have you washed the hull, any scuffing of that old plastic ?

And did you mix the Stynylrez by hand stirring or power mixing before use ? Just shaking is often not enough with this primer, so the good stuff of the primer is left sitting on the bottom.

I'm with Keavdog...strip it and start over.  You'll actually save time in the end by doing that.  I don't have any experience with stripping Stynylrez, but I use isopropyl alcohol to strip everything else I have painted or primed with.  It works quickly and doesn't hurt the plastic/resin underneath.

I think I would strip the paint and start over.