Ineffective glueing

I too have had problems, and seems to depend on the type of cement to the type of plastic. I have had bonding problems with Tenex and Micro Weld with harder styrenes, such as found in older models and found Ambroid and Testors works fine.  Then on softer plastics, the opposite, that too much Ambroid or Testors will melt the plastic and cause it to deform, where as the Tenex, Micro Weld, or Tamiya gives a good bond no matter how much I apply.

I keep a bottle of each brand handy.  And of coarse, keeping everything airtight and free of contamination is a must for any adhesive.  Scott

Patrick

i too notice evaporation with Tenax and Plast I Weld. I try to cap the bottle asap to reduce the effect.

I also thought about surfsce contamination affecting the bond. Possibly release agents, etc.

I have had trouble even with brand new MEK.  Also, I find epoxy no longer adheres to some new kits like it used to.  I suspect some new chemistry in the styrene.

Thanks for the input guys.the glue is fairly new and it works on the harder plastic.I used some on a Hasegawa kit with no problem.and the mystery continues.

I agree with Paul, I have experienced loss of cement volume in bottles unused for a while. Mostly it seems it was Tenax, don't know if it was defective cap seals, or if Tenax is more prone to outgassing and evaporation.

I will say though, my Testors liquid and Tamiya extra thin seem to work with no noticeable change, even though the bottles may be a few years old. I just try to make sure the cap is well secured, when finished with them for the day.

Also, while they are in use I minimize the time they are uncovered. When I'm going back and forth to reload the brush they are open, but if I'm not actually using the cement, even for a couple of minutes, at the least I place the cap on the bottle. That prevents fumes in the air, and loss of volume/or function.

A question to be asked when a cement join fails, is there a possibility that some substance was deposited between the two mating surfaces? And perhaps after filing/sanding a seam, enough styrene was removed that the mating surfaces were just too thin?

Just thinking.

Patrick 

    First:I see that we have a couple of fellow musicians here!

    Second: Here's what I know from experience, and from what I know of chemical adhesion. When any chemical that has to be mixed with another there's always something that will evaporate from it as no two components are perfectly aligned chemically. Much like Paul just said - there is a type of gassing out with most chemicals. However you'll have to also realise that over time some chemicals slowly degrade, and lose their solvency. This also applies to paint as well as glue. When you get this especially with something that sits around for a while after it's been opened this is what you get.

Not always - but in many things that you can buy over the counter will do this even after a couple months. Silicone caulk always does this after the first twenty four hours even if you manage to get all the air you can out of the tube! Just consider this when buying a product for a small project - use as much as you can as soon as you can. Remember, never leave spray paint outside in freezing cold weather as this causes the propellant to gas out of the can. I can't tell you how many cans of paint my best friend and I threw out one year because he left them in the garage.

~ Cobra Chris

I use either Tenax or Plast I Weld with a touch n flow applicator, I run it along the seam then press the parts till I get a squeeze out of melted plastic then I let it cure. I can sand off the ridge of melted plastic that bonded the two parts as a solid piece. No need for putty either. This type of glue melts and fuses the plastic making a strong join. On the other hand, other glues like super glue will just stay on the surface and not bite as much into the plastic. The same thing for tube glue which I find it to have a weak bond and sometimes becoming brittle after a few years.

I have a theory about this, but first a disclaimer: I am not a chemist, just an experienced modeler. I think that most liquid cements are a mix of certain chemicals that will melt/soften/weld most types of styrene plastics, some more than others. I think that the volatile mixture outgasses over time, and some of the elements of the mix that work on this type of plastic or that type of plastic evaporate. I use Weld-On #3, a glue made for acrylics (Plexiglas) and it works on styrene as well. I buy it in a pint can and decant it into a wide-mouth glass bottle with a sealed plastic top. I've found that by the time I have maybe a third of the bottle left that the remaining liquid has less "power" to melt the plastic for an effective weld bond. So, I toss that, decant some fresh from the can, and the "power" is restored. Just a theory.

I've had liquid plastic cements go bad a few times. This was after years (maybe 3 or 5 or so) of storage. There was a discussion about this here somewhere a year or so ago.

I've only been using Tamiya extra thin for a couple years now, and havent' had any go bad yet, so I can't confirm that it will.

First time this happened to me, I thought it was the plastic too.

seastallion53

I was getting a little into my 1/32 special hobby x-15a-2 after a long while by glueing the 2 forward fuselage halves together using Tamiya extra thin but the plastic would'nt fuse together.does the plastic change i.e. get old? I've never hade this happen before.

 

I used to build a lot of old kits (late 50's) and I have never had a problem. I hope you get this issue figured out!

IDK what the reason is for the glue not welding the plstic . I've had this happen to my last 4 models.  Some where rather old kits and 1 new kit as well.  I've had the fsg seams separate using Tamiya Extra Thin and Plastic Weld too.