Correct way to apply polystyrene cement

[MarkL057]

Hiya guys,
Another noob question i'm afraid.
After the mess of my first model (USS Enterprise, TOS Star Trek) i did a bit of googling on better ways of gluing pieces together and have found abit of a minefield and mixed opinions.
I'm going to be building the next enterprise out of the kit soon, USS Enterprise Into Darkness.
When it comes to gluing 2 pieces together that would form a seam, like the 2 halves of the secondary hull, would you put glue along the flat pieces of plastic that are going to be touching each other, as one would traditionally glue something onto something else, or would you run the glue along what would become the seam of the full piece? As in holding the 2 pieces together and gluing along the join, as one would traditionally weld?
I've seen both ways done in tutorials, but i'm concerned the second (welding) method would create a messy seam.
I do keep asking stupid questions so hope this one isn't too silly!

Thanks in advance,
Mark.

 

[JHY]

It depends, in part, on which type of cement you're using. The old gel/tube type is probably best suited to being applied to the flat surfaces to be mated, while liquid solvents are best for the seam approach. I prefer the liquid solvents, I haven't used tube/gel for years.

Getting the right degree of flow along the seam takes a little practice, you want a consistent continuous weld with the minimum of damage to the model's surface (none ,ideally!). The liquids come in a range of viscosity and can be applied by brush, needle or applicator (like touchnflow). Best to find an old kit or a cheap kit to rehearse on before you commit to the Enterprise.

If you apply solvent sparingly messy seams are avoidable, but if you get a gooey mess let it dry completely before salvaging it by cutting, scraping, sanding and polishing any scar.

Often on larger pieces you can glue from the inside surface, which can be a benefit.

 

[MarkL057]

Thanks for your reply.
I'm currently using revell contacta as it came with the kit. It has a needle built into the bottle so I assume then by your answer it would be suitable for the seam method?
Will pick up a cheap set before tackling the next enterprise I think.
The only other issue is some pieces of the enterprise are easier to be painted before assembling. Would it be a good idea to mask off the seams to airbrush before gluing then mask off everything but the seams after gluing to airbrush the seams?
I'm probably over thinking it all, I just want this one to look better than the first one, which has messy seams.
Thanks again

 

[JHY]

The liquid solvent applied to seams method relies on capillary action to draw the liquid along the seam. My recollection of Revell Contacta is that the delivery tube is large by hypodermic standards and the cement is quite viscous and will not flow along the seam, so try some liquid solvent and see how you get on; once you get the knack, you won't go back. Some liquid cements come with quite a large "in bottle" brush which is fine for painting solvent onto areas or edges, but not really suitable for applying to flow along seams. Either find a bottle with a fine brush or buy a cheap fine brush solely for applying the solvent.

As for assembling and masking, the points to bear in mind are: 1) cements/solvents work by melting the plastic, they don't stick painted surfaces together, but will probably react badly with paint 2) painting the seams later, you may not be able to match your original paint job and/or the masking lines might be visible.

I've not built the Enterprise, so this is only general guidance, but I'd look for sub assemblies that can be easily placed and glued in position, otherwise I'd build as much as possible, tidying seams as required, then paint the model as a whole, masking as necessary.

There may be areas where other adhesives may be better than plastic cement/solvents. Clear parts are best secured with pva (white glue) which can also be used to fix small surface mounted parts that are not under strain or load, e.g. military modellers often use pva to fix tools, spares, etc to tank bodies and a motorcycle modeller I met used pva to join engine parts that had been airbrushed with various metallic finishes because although the bond was not strong the finishes were unblemished.

Someone is bound to have posted a "Building the Enterprise" video online, that might point out potential snags and provide more focussed advice. Anyway, enjoy yourself, most of want our next build to better than our last!

 

[modelcitizen]

also consider superglue or thicker gel-superglue. the gel type allows more time for alignment.
so many alternatives!
if you use superglue with prepainted parts, plastic to plastic is still the general rule (supergluing paint to paint can be done but will more often than not pull the paint from the plastic and the join may fail if it is under any stress). fumes from curing superglue can frost or "craze" paint and clear plastics but this can be dealt with by keeping the air moving as it cures. good luck and have fun.
(i haven't used plastic welding cement in decades).

 

[Antsnest]

Get yourself a bottle of Tamia Extra Thin liquid cement. Comes with a very fine applicator brush in the lid and gives great results!

 

[MarkL057]

Thanks again for the replies!
I have found Humbrol's poly cement is advertised as solvent based low viscosity and has a needle applicator so i'm going to give that a go i think.
In regards to matching paint, i'm switching to acrylics for this one, just so ive got an enterprise of enamel and one of acrylic so i can see the difference on something relatively like for like, and from what i've read, acrylic being water based, should be ok for storing for at least a short time, so i'll keep it the spare glass jars i've got for my airbrush so that won't be an issue. Besides, i've been quite meticulous with mixing my paints, i mix by the ml with plastic syringes and i've not managed to mismatch any colours even with multiple refills of the airbrush jar.
I'll let you know how i get on, it's wait to payday to restock glues and paints anyway so will be a while off.

Thanks again!