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Glue suggestion?

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Dan Daniel

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I am looking for a glue or caulk material that is between an epoxy like JB Weld and RTV gasket material. This is for a film chamber wall installed in a camera. It is subject to pressure from the film spools being pulled, so an RTV seems a little too flexible. JB Weld seems too hard and brittle, and not good for any sort of fillet work, not just internal adhesion.

Anyone know of an adhesive that is stiffer than RTV gasket material? Hard to describe but more flexible than off-the-shelf epoxy like JB Weld? An epoxy known for some flex? Maybe a urethane?? And black preferably!

Thanks.
 
Oh my, you are looking for something maybe too exotic too exist, at least for your application. There are many many kinds of epoxies; many are reinforced and not brittle at all. Urethane sealants are generally designed to be just as flexible as RTV sealants. Hard urethanes aren't going to work well in this application. If I were in your shoes, I'd start looking for an aerospace supplier. There used to be one around here in Silicon Valley I once dealt with for my own special sealant needs; but those connections have dried up - they generally didn't sell to the public anyway. I had an inside track because we had our own military sales division.

Take a look at McMaster's selection - they'll sell to anyone in small volume if they have it. That's another source that I've often relied on.
 
That "Flex Paste" is worthless. It needs a sanded surface, has to be glopped on thick like roof patch, and will likely peel anyway.

What has just come back to my memory is black Kampel SeamFill, used for filling and disguising thin Formica seams and small dings. Proper use requires a little practice; but the product is readily available from multiple sources, including Amazon. I always kept sheets of black Formica or Wilsonart in my shop for darkroom applications.
 
I just used some Loctite Flexible Adhesive to repair the leather on some shoes. Maybe a little too flexible for your your use but I was impressed. Cheap from Walmart.
 
  • BrianShaw
  • Deleted
  • Reason: Not worth the breath...
DREW WILEY said:
That "Flex Paste" is worthless. It needs a sanded surface, has to be glopped on thick like roof patch, and will likely peel anyway.
Click to expand...

Just correcting one piece of incorrect information (the rest I'll leave to Dan to research and/or try whatever he thinks may work.

Flex Paste does not require a sanded surface for application.
Click to expand...

In my own work, I've personally used this product and find that thin coats work well too (not for roofing but for similar applications as Dan describes). Peeling is nothing I've experienced in my own work. Your speculation is possible, I'm sure, but it sounds like you aren't completely sure of your statements. I also had access to a government research lab that used it for prototype developments, which gave me the incentive to use it in my own efforts. The biggest downside I've found is that it is solvent-based so cleanup requires a solvent. Oh, and it really can't be thinned with solvent, which might be a bit of a limitation in extremely fine applications.

I've also used a similar product to the formica seam filler. It is tricky to use but seems to work too. Some of those silicone products are sanded, like grout... something to be aware of when researching them for non-standard applications.
 
Last edited:
Dan Daniel said:
I am looking for a glue or caulk material that is between an epoxy like JB Weld and RTV gasket material. This is for a film chamber wall installed in a camera. It is subject to pressure from the film spools being pulled, so an RTV seems a little too flexible. JB Weld seems too hard and brittle, and not good for any sort of fillet work, not just internal adhesion.

Anyone know of an adhesive that is stiffer than RTV gasket material? Hard to describe but more flexible than off-the-shelf epoxy like JB Weld? An epoxy known for some flex? Maybe a urethane?? And black preferably!

Thanks.
Click to expand...

Would you please explain what it is your gluing and what your gluing it to? The materials are important, like if it's mdf, wood, metal, glass, plastic, etc.
 
It is not clear to me what exact properties you are looking for.

Are the two pieces both rigid and dimensionally stable? That is, will the glued joint ever need to flex or bend? If the glue joint will never be flexed, then I don't see how it would matter if the adhesive is brittle.
 
How about hot glue? There are black glue sticks available, but I have never used any.
 
Alan Townsend said:
Would you please explain what it is your gluing and what your gluing it to? The materials are important, like if it's mdf, wood, metal, glass, plastic, etc.
Click to expand...
3-d printed polycarbonate to aluminum and steel. All materials are painted with lacquer. The polycarbonate part is 'trapped' by grooves top and bottom. The concern is that varying pressure on the polycarbonate will lead to flexing that could crack a stiff epoxy or lead to a letting go of the joint.
 
JB Weld, I've used it on about everything, cast iron engine blocks, motorcycle aluminum engine cases, etc . Not brittle at all both aluminum and cast iron changes dimensions when the engine is heated up and JB weld holds very well.
 
The question is, will the lacquer stand up to the solvents in an epoxy itself? Probably not.
Some sanding will be needed.
 
Black silicone. Dimensionally stable and easily as strong as almost any glue. Make sure the surfaces are clean and try to not make a mess.

A second would be elastomeric caulk. It's practically the same as silicone but can get a bit harder (think tough rubber).

Glues are generally meant for applications under pressure. Seam filler is typically not actually capable of being an adhesive. Caulking is engineered to withstand varying degrees of movement and not require pressure to adhere.
 
Don - there are countless version of elastomeric caulk. Most are short-term. All the serious ones have hard engineering spec sheets available and never run TV ads. Products which advertised a 100% modulus of expansion/contraction would lose 95% of it within six months. Consumer caulks tend to come with serious BS Marketing coefficients. Some of the worst of them are from a company whose name rhymes with "crap".

In a former reincarnation, pre-retirement, part of my role as a buyer involved what was probably the largest selection of caulks and sealants on the West Coast at the time (except for high rise and major construction expansion joint sealants, which we only dabbled in - those mainly get pumped out of big A&B containers, and get mixed together in the process).

The best handling silicones for small fussy work naturally come from electronics industry suppliers. Costly for even a small tube; but a camera needs very little.
 
So can you give a concrete and definitive recommendation, Drew. So far all you’ve done is “Dap” on the potentially valid recommendations of others. That’s a bit less than helpful. Someone with your vast experience and knowledge should be able to do better than that.
 
This is the correct glue that fits Dan's requirements of gluing 3-d printed polycarbonate to aluminum and steel.

ACRI-BOND 204 – is a versatile 2 Part Methyl Methacrylate Adhesive (MMA)

Bonds 3D Prints to Aluminium and Steel as well as Powder coated and Painted surfaces

That's the best I could do, I've spent time searching the internet to find it.
If it's still not the right glue, then Dan will be looking for a similar glue that incorporates "flexibility". But flexible glues are generally weak, so it depends on the amount of strength required and the amount of pressure being applied to the separate parts.

Black Silastic is a good suggestion, but surfaces must be very clean and dry, and the Silastic allowed to cure for at least 5 days. Failing this, I think the ACRI-BOND 204 should be used for the job.
 
 
Per Post 16: Sometimes the problem is that "hot" solvents are required to clean up or smooth any overage of the sealant or epoxy itself. A slightly flowable product simplifies this IF it can be very carefully metered out. I've used flowable non-solvent aerospace silicones, which still cure like regular RTV ones.

Gosh, its been a long time since I healed a punctured silk curtain shutter with black silicone; but it worked flawlessly. I always keep some on hand.
 
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