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foz75

Clearcoat on inside of shell to avoid colour seeping under tape?

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I've seen this in a couple of videos, seems like a good idea especially for areas where it might be hard to get the tape edges fully stuck down. Has anyone tried it? Anything to look out for? I need a can of matt clear for the outside anyway, if I spray on the inside of the shell before coloured paint, is it likely to affect the finish? Does it actually work to seal the edges of masking tape?

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Never tried it, actually. I can see where it might help. But liquid mask also is a thing, and works very well. I've used the old Bob Dively brand, and Parma Fasmask, and both worked great. It dries to a sort of clear rubbery coating, which you cut with an X-Acto blade and peel off the part you want to paint.

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7 hours ago, foz75 said:

Does it actually work to seal the edges of masking tape?

Yes, some static modellers do exactly what you just described.

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I'm a simple guy and avoid extra steps.. so I never do it.  Some folks still end up with bleeds even after this extra step.  

I just properly mask, inject hope, and any bleeds can be removed using motor spray and a fine point swab within one hour of painting,  B)

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@foz75 I've tried it and it really doesn't help much, if not anything at all. You can argue that the first coat of color spray is used to seal the tape anyway.

The key to avoid sipping is understanding what causes it:

  1. Tape not fully sticking to the body, which is sometimes confused with true sip. I'll cover more below.
  2. True sip under a well stuck tape. Not sure about brush painting, but both airbrush (from second-hand account) and PS sprays (from extensive first-hand account) do not suffer from true sip when using Tamiya tapes (either the regular yellow one or the flexible white). If properly stuck, these tapes are 100% reliable.

Back to item 1 above. The worst enemy of masking tape is tension. Always, always, always remove tension from your tape. You have to be very aware of what causes tension and how to eliminate it. Tension (i.e., the tape is under stretch load) will cause the tape to lift, creep and unstick. Some pointers and examples:

  • Never stretch the tape when applying it. At first glance stretching seems like a good idea because it could initially push down the tape well and also helps in getting masking lines straight. However, after a little bit of time, the tape will unstick, and you will not notice it.
  • Tension can occur when:
    • You physically stretch the tape as you put it down. Self-explanatory.
    • The tape is placed above a concave surface (valley) and then it's pressed down.
    • There is a sharp concave corner or edge, on which the tape simply does not have the ability to flex "into" the edge. You might press it down and it appears to be good, but after a bit of time it will relax and lift.
    • The tape is placed above a convex surface (hill) and innadvertly you start stretching it as you progress putting it down.
    • There is a sharp convex corner where the tape doesn't have the flexibility to flatten against the edge (it will create a little bump over it). You might want to apply tension to push it down, but again this tension will be counter-productive on the sections of the tape immediately next to this convex corner.
    • On a place where you introduce a curvature, for example if trying to mask a round line or shape (even if it's on a flat area like a hood). The curvature will have the tape in tension on its outer end and in compression on the inner edge. Same thing, after a little time it will lift.
    • As you paint, the paint itself will contract as it dries. The contraction will in turn tend to "coil up" the tape and detach it on its edges, especially on convex corners where the tape is already bent "coiled down".

How to eliminate tension?

  • Be very mindful and aware of tension when you apply masking. This way you know where it can appear and where to handle it.
  • Minimize stretching the tape at all times.
  • If you need to lay down tape in a straight line, instead of tensioning it, draw guidelines on the outside of the shell (sharpie above the film works well) to check it's straight.
  • On edges where it is unavoidable to create tension, and you can't press the tape down since it will lift up after a little time, simply mask on top and then cut the tape along this edge (valley or hill) with a sharp knife. The tape, now cut, can be pressed down flat on both sides of the cut. There will be a tiny gap left without mask, which you can easily cover with bluetack or similar.
  • If the edges are long and part of a large mask, you can just cut the endpoints of the edge and add bluetack there, instead of cutting the entire edge. It doesn't matter if the rest of mask lifts on the edge at the middle since its already sealed by the bluetack on each endpoint.
  • On larger concave surfaces (but not really sharp enough to be edges), same thing: cut the tape, sometimes even on multiple points to relieve tension, then press down. Fill the gaps with bluetack or small strips of tape.
  • On sections where you have introduced curvatures, sometimes it's best not to cut as this will upset the curve shape. Instead, place a flat blob of bluetack on top of the curved tape. This will hold the tape down. Better yet, instead of masking with straight tape, cut a piece of masking tape that better approximates the curve you want, this way you don't need to bend it much.
  • To minimize tension in curvatures, use the least wide tape you can manage. If you use a wider tape, tension stresses will be higher.
  • For deep holes and edges where it is unpractical to put tape: fill them with bluetack instead of masking.
  • When painting, the first few coats you place above tape will be your sealing layers. It is important that these coats are as fine (misty) as possible to minimize shrinking that could lift the tape. Furthermore, fine coats against bare lexan have a better chance of sticking well and avoiding peeling later.
  • Make a note of the areas where tape could be prone to lifting after a coat of paint. Check these areas after each coat of paint and if necessary, push them down. You will have a few minutes to lay down a new coat of paint before they lift again. You can add some bluetack to hold them down if needed.
  • Small bleeds can be scratched off with a wood toothpick and, if more stubborn, with a small metal pick.
  • The standard Tamiya yellow masking tape can take tension better. The white tape for curves tends to relax tension more severely and requires more of the above techniques applied.

Long story short, tension is your worst enemy and bluetack is your best friend :)

Good luck!

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thanks for the replies! @OoALEJOoO that is a lot of info! must have taken longer to write all that than to fully mask a shell :lol:

I need flat clear for the outside anyway, I have been planning this shell for a while, not started yet but there are some areas where getting the tape in there and stuck down correctly will be tricky at a minimum, which is why I thought maybe this technique could help. I might be able to mask slightly differently and avoid any major problem areas. I have tamiya yellow and white tapes, and also the large sheets which will be better for some of the masking I am planning. I will also practice on some offcuts before I start on the shell proper. The only reason I didn't start yet is because I didn't build the chassis, and prefer to do that first to locate the holes for the body posts in the shell before painting

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What @OoALEJOoO said is correct.

Also, one more thing is to not "flood" the tape, lightly spray away from the edge instead of towards the tape for the first 2 pass. Easier with an airbrush as the pressure and volume is lower.

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