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Sep 10, 2019, 03:59 PM
DavidsPlanes
doxilia's Avatar
Greg,

four weeks to cure doesn't sound anywhere close to normal. A catalyzed product will begin to cure as the product is mixed and usually attains maximum hardness within a week. A non catalyzed solvent based clear (e.g., SprayMax 1K) will air dry at room temperature within 24 hours and offgas, again, within a week. Of course, some solvent based paint products such as lacquer can air dry and be ready to re-coat within 10 minutes. In short, anything that took 4 weeks to achieve some measure of stability is NOT compatible with the substrate. The painters likely applied something like epoxy atop urethane or enamel atop epoxy. If you knew what was used to paint the models, it would give us an indication of what was used to clear the model that wasn't finished properly.

As far as using SM 2K, I'd say that any good product used is going to reveal the quality of the underlying finish. The better the clear, the more it will reveal the paint job. In a sense, this is also what it's for. To make the finish "kick". I believe there is also a "satin" finish SM 2K but this might work better with mat type paint finishes such as those you see on European cars nowadays. What I've learned during my painting days is that the more time you spend on prep, the less time you'll spend on painting and the better the result will be. You basically want your surface to be as smooth as you can possibly get it and after having shot your nth coat of gray filler-primer, you want the surface to actually be hard to "detect". In other words, if you see shadows when raised to the light, there is likely an imperfection of some kind (large or small) on the surface. This is where using gray primer helps as it provides the reflectivity required (or rather, lack thereof) to analyze the surface. If it's good to go, you can then wet sand it back down (400 grit or above) and finally shoot a light coat of white sealer primer. The white won't allow you to see imperfections (as strange as that seems) but will provide a good surface for shooting your base coat. The sealer primer is much lighter and doesn't provide coverage like the filler primer does. Instead, it "locks in" the substrate and abstracts the different chemicals used while producing the smooth surface (fillers, primers, epoxy, glass, etc.) for the base coat. Naturally, this sealer primer needs to be compatible with the base coat paint system. This is increasingly critical as you go to "lighter" type paint systems. If you use acrylic urethane paint, then the substrate can be virtually anything. On the other end of the spectrum, if you use water borne paint, then the primer is critical. In between are paint systems such as epoxy, enamel, lacquer and others.

The time invested in the finishing of a model is, in my view, entirely a reflection of the modelers personality and priority. Much like your father recommended, if your priority is a model that flies well but the rest is of less importance, then yes, by all means, I'd say steer clear of paint. Covering is less expensive and faster. Of course, you won't be able to achieve the results that a paint finish offers if well done - bottom to top. On the other hand, if a gleaming pained model is something that makes you feel giddy inside (I'm afraid I count myself as one albeit I don't/can't paint every model I build) upon completion, then I'd say that spending the time to do this yourself provides as much satisfaction as building the model itself. I view the build, finish and flight of a model in equal terms as far as satisfaction goes but this might be a hobbyists perspective. Others, who compete for example, will spend far less time building and finishing (if any) with their main focus being in performing the ultimate pattern. Which camp one chooses is a personal choice and of course one doesn't have to produce a work of art with each model one builds.

I admit though that seeing the type of models that are exhibited at model shows is great inspiration for producing a model of equal or approaching caliber.

David
Last edited by doxilia; Sep 11, 2019 at 11:33 AM.
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Sep 10, 2019, 04:58 PM
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Thread OP
David,
I did not repaint the unknown model at all and it was probably built in the early 80`s, when clearing out dads basement I did find some old Red Baron epoxy type paint that matched but was so old it just went in the bin.
The Curare on the other hand I completely repainted using rattle can automotive Acrylic, at least two weeks after the clear coat was laid I re mounted the engine and could see the thrust lines were off, I laid out guide lines using thin masking tape to aid in getting the thrust correct, on removing the tape, marks were left in the clear coat.

Overall it has been a learning process for me, next time I will do the all the spraying myself, I just need to find a suitable area to work in. I was very pleased with the standard of paint work I managed to achieve , only to be let down by the clear coating but we live and learn.
Sep 10, 2019, 06:16 PM
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Roguedog's Avatar
Yep 90% of a good paint job in the preparation, 10% is the actual painting.
Sep 11, 2019, 11:29 AM
DavidsPlanes
doxilia's Avatar
Greg,

Going the extra step to shoot the clear yourself if you’ve done all the paint work is not a major undertaking. The beauty is that you don’t have to mask much (if anything). I’d say the main concern with shooting the clear is having a way to handle the parts without touching the model and having a dust free place to allow the model to cure. Honestly, if you have a low traffic area where you can leave the model under a table is good enough as far as “dust free”. I usually hang the fuse with a nylon string through the firewall engine mount holes passing into he nose ring. Using dowels into the FW and tail post to “spit roast” the fuse horizontally works too. The wing can normally be held through its mounting bolt holes. In short, imperative the model isn’t touched.

SM requires about 2 to 2.5 cans of clear for a 60 size model. In order not to waste the clear which isn’t given away, I try to prep some other smaller painted pieces in case I have excess. However, you need to estimate what’s needed for two coats which is how the product is applied. First coat is a mist “tack” coat which you allow to cure a short while (I believe it’s about an hour - directions on can) and the second is the flow cover coat. This should go one and have the appearance of molasses. You will see slight ondulations in the flow coat as it’s applied which settle rapidly. The trick is to flow enough on for a deep lustre without over shooting and having a run. I didn’t find it too challenging given the excellent nozzle action and my first round with it turned out great. Should you have a run, leave it be allowing it to cure. Anything you try to do while the clear is wet will result in more problems. You’ll have to sand it out once cured and polish. However, with care and an eagle eye, over shooting is not a problem. Ambient temperature will of course change the viscosity of the flow so keep that in mind. I usually start flowing on the underside for a bit of insurance.

If the Curare was shot with water borne (acrylic paint per se usually is) paint, a urethane based clear should have presented no problem even if non-catalyzed (eg 1K SM). 1K is only suitable for electric models as it’s not fuel/solvent proof. The 2K is considerably more stable however so I don’t bother with 1K and the model is protected in a dual power source fleet. The painters may have simply shot a 1K enamel like product which wasn’t compatible with the auto paint. I’ve had terrible experiences with enamel so I avoid it like the plague.

I hope this helps,

David

PS Nice paint (not clear) job on the Curare!
Sep 11, 2019, 08:40 PM
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Thread OP
[/QUOTE=doxilia;42717937]Greg,



Quote:
Going the extra step to shoot the clear yourself if youíve done all the paint work is not a major undertaking. The beauty is that you donít have to mask much (if anything). Iíd say the main concern with shooting the clear is having a way to handle the parts without touching the model and having a dust free place to allow the model to cure. Honestly, if you have a low traffic area where you can leave the model under a table is good enough as far as ďdust freeĒ. I usually hang the fuse with a nylon string through the firewall engine mount holes passing into he nose ring. Using dowels into the FW and tail post to ďspit roastĒ the fuse horizontally works too. The wing can normally be held through its mounting bolt holes. In short, imperative the model isnít touched
I would have done the clear myself apart from the safety concerns and no suitable area, next time I will do the clear myself

Quote:
SM requires about 2 to 2.5 cans of clear for a 60 size model. In order not to waste the clear which isnít given away, I try to prep some other smaller painted pieces in case I have excess.
Thanks for the estimate on the amount needed, even though I also prepared some small parts that needed clear I`d estimate 80% left in the can

Quote:
If the Curare was shot with water borne (acrylic paint per se usually is) paint, a urethane based clear should have presented no problem even if non-catalyzed (eg 1K SM). 1K is only suitable for electric models as itís not fuel/solvent proof. The 2K is considerably more stable however so I donít bother with 1K and the model is protected in a dual power source fleet. The painters may have simply shot a 1K enamel like product which wasnít compatible with the auto paint. Iíve had terrible experiences with enamel so I avoid it like the plague.
What ever he used it was rubbish, I masked off the area for the aileron servo to re glue the mounts in the centre section to ensure I did not make a mess, I used a very low tack masking tape and on removing it the clear coat peeled away from the paint in that area, there was no chemical bond between the paint and the clear!!! shows that it must be bad really bad product (I fixed it with SM)


Quote:
David

PS Nice paint (not clear) job on the Curare!
Thanks I did try and was quite patient. At the moment I am redoing the servo mounts on the unknown model, it was built up for Simprop housebrick servos, so plenty of room. (some of them still work lol)
I also have an Atlas to finish off, dad started this about 2 or 3 yrs ago when aged 88/89 and it has a few more errr issues to sort out.
No work on them from tonight as I am off to Snetterton race circuit to help my brother out (Im a gopher now these days)
Sep 20, 2019, 08:09 AM
Registered User
Thread OP
Finished at last, will take the unknown model down to my father to for him to see on a visit on Saturday, it weighs just over 7.9Lbs but is tail heavy and would need about 5 oz lead to get C/G but it also has a 14oz fuel tank in the nose so not sure how much lead to add.
here are the finished models and a picture of my brother racing at Snetterton on the weekend, 3 wins and then he did this....... was in 2nd place and pushing for the lead.


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