Hi,
I am not sure of the sequence here, so here goes. I am ready to prime one of the Tigers I am working on, but not all pieces have been glued. My question is this: can I still glue the pieces after the primer has been applied? How will the glue react in contact with the primer? Will it have the same strength?
Thanks,

Not really. Poorly. Nope.

maybe if you scrape the contact joints down to plastic it may work?

in the past i have glued pieces on after priming. it really depends on the glue and the primer. for example the tamiya glue will pull off the paint, giving the possibility of a real mess. i typically dont prime anything until it is all glued.

Thanks guys. I'll see what i can do about it. This sucks. I have quite a few types of material on that Tiger, ranging from plastic to brass and aluminium and am worried that Tamiya's paints will not stick on.

A couple of "depends" here.
Most glues are really solvents, and they soften the plastic so that it welds together chemically. This includes liquid glues like Tamiya, Tenax, etc. Depending on the paint you have used (acrylic vs. enamel), these slovents can soften the paint (enamels) and they will blend in with the softened plastic, but they weaken the joint. In the case of most acrylics, they will actually act as a barrier and prevent adhesion.
CA type glues will adhere to the paint to paint surfaces, so the paint adhesion is the limiting factor of the strength of the joint. This may be adequate for adding details such as tools and antennaes and lights, but it will not be strong enough for structural joints (like bogies on a Sherman).
If you scrape away the paint on the joint to bare plastic, you will have a much stronger joint, no matter what glue you use.
I hope this helps.
Norm Samuelson

Thanks Norm. I was actually thinking of scraping off the primer (the white rattle Tamiya Can) from the contact points, then use CA to get the absolute best weld. Problem solved.
Thank you all for your help and input.
Cheers.

Stick to plastic glue. I find that CA doesn;t really work for plastic on plastic

Hi there

if you use MEK as an adhesive and apply it with the tip of a small [quality] brush you will fine that the MEK will easily penetrate the paint, including acrylic and enamels, forming a perfectly adequate bond. will work fine with your Tamiya rattle can primer.

No need to scrape paint or leave an unpainted area.

the secret is to place the MEK at the part to be bonded and leaving it alone whilst the chemical does it thing. takes about 60 seconds for the bond to set sufficiently to move onto the next joint.

also very important to spray a fine layer of primer, keeping in mind that the thicker the paint coat the less effective the MEK.

have fun & stay cool

Bernard

@ Scott
Thanks. I will remember this.
@ Bernard
What is MEK? Never heard of it.

I like to paint as i go, especialy the chassis/running gear,
so what I do is MASK the mating (gluable surfaces) with PVA, (Elmers) tamiya tape, bluetac,etc, then paint. I find this easier than repairing areas wgere youv'e had to scrape.

MEK (Methel-Etheyl-Keytone) is a good liquid adhesive, that welds plastic together, but is getting hard to find in the UK due to H&S & COSHH regs.

It is also used in the print industry, 1 gallon would last a lifetime, but don't breathe it in, or it will be a very short & painful lifespan.

Other Adhesives such as Tamiya Thin Cement, Plastruct Weld(??) work in a similar way.

JON_A_ITS ,
I did just that. I have masked the mating surfaces the other night and now it is ready for the primer. I haven't got the time to take some shots, but will do it in the next coming days, then post them.
Cheers,

For proper adhesion, clean bare surfaces is the key for any type of adhesive.

- Clean before priming with a gentle soap & water wash of the entire model.
- Remove or mask so there is no paint on the surfaces to be bonded.
- For plastic to plastic joints use a solvent based cement (like Testors or Tamiya or Tenax or MEK, whatever, they all have the same MEK base).

DO NOT use CA glues for main structural joints in plastic parts as CA glues just don't have much shear load capacity and have a tendancy to pop open if knocked or stressed wrong.

For small plastic parts you can use it if you like, but liquid cement wil always make a better bond than CA. The reason is that the solvent based cements actually dissolve the plastic at the join line and then, when the solvent evaporates, it leaves a joint that is more like a weld than a bond.

- For dissimilar parts, like PE on plastic or brass to white metal, use CA for smaller or non-structural parts and use 5 minute epoxy for large or heavy structural parts. Epoxy is too viscous to produce really thin joint lines, but is tougher and makes for better structural joints. CA can really give you fine bond lines in teeny parts, but has shear trouble, as I said above.

HTH

Paul