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Pactra Forumla-U

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Help! Pactra Forumla-U

Post  Dstradt on Fri Nov 10, 2017 4:36 pm

Hi, I have a bottle of Pactra Formula-U, its a polyurethane paint, I want to spray it onto my balsa model. Does anyone know how to thin it, Also what could I do to have a shiny finish. thank you Small Cox Logo

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Help! Re: Pactra Forumla-U

Post  NEW222 on Fri Nov 10, 2017 7:02 pm

I would use Mineral Spirits, or Naptha. If you have any thinner laying around, just put a little bit of paint in a cup or such, add a little bit of what you have on hand and mix it up to see if there is a reaction. As for getting a shiny finish, I cannot comment as I do not know the product that well. You could always use Minwax Polyurethane spray paint, which is great. Back in the day, we did add a half cup of gasoline to Tremclad or Rustoleum paint when mixing it to make it harder and shinier....... As for mix ratio, that can vary itself.
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Help! Re: Pactra Forumla-U

Post  getback on Fri Nov 10, 2017 8:34 pm

https://www.amazon.com/Pactra-20132-PINT-THINNER-FORMULA/dp/B008U2M3V4 This should work , usally 50/50 is about right with Aero/ Sig dopes jsut depines on how much weight you can take ? Huh...
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Help! Re: Pactra Forumla-U

Post  Oldenginerod on Fri Nov 10, 2017 11:20 pm

Looks like Pactra is now made by Testors.
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Help! Re: Pactra Forumla-U

Post  Ken Cook on Sat Nov 11, 2017 7:35 am

Here's my opinion on that paint. It's been out of production for over 20 years now. It more than likely pre dates California warnings. The binders and resins that make the paint harden are well past there expiration. This doesn't mean that it won't work because I've used the same product for touching up my old fleet. However, there were problems associated with it such as fast drying during application but the paint would remain gummy. This new Pactra Formula U thinner would more than likely not be the same product that was offered originally. While this is a enamel product, there were other things in the paint that controlled it's drying and hardness. I had acquired old stock thinner when I used it. Formula U made a brushing thinner and a spraying thinner which I wasn't aware of. What I discovered was that the original Formula U brushing thinner kicked off the paint rather quickly not allowing you to go back into your work creating brush strokes. There was more to this paint then just mineral spirits, I believe tolulene was a ingredient that caused the paint to dry rapidly. If your dead set on using it, I would thin it or at least attempt to use VM&P naptha. General purpose mineral spirits may clean the brush but won't effectively thin the material for spraying.

Recently posted on here was the use of Minwax spray polyurethane over conventional spray colors. I used to do this similar type of finish 30 years ago but have since switched to waterborne finishes. I don't know what your spraying but if you have any attachment or time into what your painting, I would forego the Formula U and use something like the above due to the products certainty that it will dry and provide the proper protection. If your looking for a shine, the Minwax poly in high gloss is going to make a flat paint shine with high gloss. Weight is another issue as this is going to be a heavy product. Almost all polyurethane finishes aside from water based are going to yellow. They just do and the sun makes this happen even faster. Not a big deal with your yellow finish, it will just make it more amber.
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Help! Re: Pactra Forumla-U

Post  roddie on Sat Nov 11, 2017 12:20 pm

Hi Dalton, I would not use that paint. It was a good product when new.. but as "Ken" mentioned.. it's far past its expiration.

I recently bought some "Krylon" #9607 Sun-Yellow gloss in an 8oz. can. I'm not sure if it can be thinned for spraying.. and I can't speak for its resistance to glow-fuel yet.  





This color is available from Krylon in an aerosol/rattle-can.. but my use will be for trim.

It's important to allow the paint/finish to cure completely before exposing it to model-engine (glow) fuel. This can take "weeks".. depending on the type of paint.. and the application of it.

A wise approach would be to finish/paint a few small scrap-pieces of balsa for testing. Experiment a little. You might try testing a gloss base-color alone.. and also a clear-gloss over a flat-base. Let the finishes cure in a warm/dry area. Be patient.. and do some other model-work to kill the time. Smile Once cured (your final finishes..) put a small amount of your model-fuel on a paper-towel and blot/rub the finish to check for color-transfer. This will be an indicator of how resistant your finish is.

If you're using a clear-coat, you might want to try more than one type. If you see any of the base-color transfer when wiping with the towel.. you'll know that the clear-coat as well as the base-color are not fuel-resistant. A clear-coat that's not fuel-resistant is useless and will add weight to the model.

It's a good habit to have soft-clean rags and a bottle of spray-cleaner with you to clean the model after running its engine. I used to use the cheap (blue/Summer-formula) windshield-washer fluid by pouring some into a small trigger-spray bottle. DON'T spray the model or its engine! Spray the "rag" and wipe the oil-residue off the model between flights.. and immediately after your final-flight of the day.

One last thought Dalton; A clear plastic sandwich-bag can be placed over the model's engine (when cool..) This serves multiple purposes. A model engine is "oily" by nature of its operation. It should be protected from sand/grit. This can happen if a breeze blows-through at your flying-field. Some people throw a rag over their engine(s) when waiting to fly.. but wrapping the engine will also help to keep oil-residue from dripping on things like "the car upholstery" on the trip home. Keeping the engine covered when in storage will keep it dust-free. For long-term storage.. put a couple drops of "air-tool oil" in the exhaust-ports and flip the prop a few times to distribute it inside the engine-cylinder.

I wish you the best of luck dude! Thumbs Up
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Help! Re: Pactra Forumla-U

Post  fredvon4 on Sat Nov 11, 2017 3:10 pm

Dalton my young friend, please hook up with Dane Martin and all his friends in your area,,,I know for a fact they have loads of stuff to help you

BUT do not be discouraged at these responses... You are in your teens and learning the important things... what does and does not work and why

When you are my age you will not have to re-learn these important concepts

When I was 55 and searching for info on forums, I prided my self with thinking I was a pretty smart guy... my oh my how I was WRONG

So please keep asking...but at same time find that invaluable local help

Model airplane people seem to be one of several hobbies where people actually like to help and give to others...especially younger friends...take advantage of ----but don't abuse that

Predictably, in a few short years you will be into girls/guys, cars/motorcycles, college, a job, GF or wife, then kids and not much free time for a cool hobby

The things you experiment with and learn--- right now ----will help you a lot in every aspect of your future school and job life

And like many of us, You WILL return to a modeling hobby as you have the time and money later in life

and even perhaps, a desire to share with your own kids, nephews, or others ----and spark their imagination and creativity

Hobbies are fun, spark creativity, learning, curiosity and IMO essential building blocks for so many real world endeavors...



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Help! Re: Pactra Forumla-U

Post  NEW222 on Sat Nov 11, 2017 8:04 pm

Actually Ken Cook, I do find what you say both true, and funny. I am a minwax Polyurethane user, and may have been the one you recalled mentioning it before. The truth behind your statement is that it will yellow over time. I use both spray on and brush on, both in the high gloss. If used on darker colors, you will probably not notice the yellowing as it will be faint. However, on light colors, it is noticiable, as my white homemade fieldbox was white, and now yellow! But here is where it is funny. Minwax Polyurethane in a rattle can, again, high gloss, does not, and has not yellowed in almost three years. And this is sprayed over top of white! I would really like to know what the difference is as to why the brush-on yellows, yet the spray-on doesnt?
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Help! Re: Pactra Forumla-U

Post  Ken Cook on Sat Nov 11, 2017 10:42 pm

The brush on is oil based or oil modified urethane and this is what causes the yellowing. Traditionally, it was developed to offer the wood a deep amber color. Shellac was the traditional method prior and while I'm a fan of shellac, over time this type of finish crazed badly. I haven't used Minwax poly spray in over a decade. I use Zar , but it too yellows. As for spray versions, the main problem with poly in the first place is dry time. The longer it takes to dry, the more dust that can stick to the surface. This suggests to me that the manufacturers are limiting the oil content and increasing the solvent content to quicken dry times. In essence, your not receiving the same protection as you would vs the brush variant. If it's working for your models without issue, that's all the really matters.
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