View Full Version : Neoprene or Nitrile... and how to weld/fuse/join either of them

dustin wassner
09-28-2017, 5:20 PM
I am working on a project where I need to somehow glue or fuse two pieces of ~1/32 rubber. I need to join them because a thin rare earth magnet disc needs to be between them that is completely sealed from potential water exposure.

I have narrowed the potential materials down to neoprene or nitrile. I need a material that is roughly the durometer and elasticity of a rubber band and that is available in more colors than tan/black.

If you have any suggestions about a better material to use, or a way to join them it would be greatly appreciated.


Jamie Buxton
09-28-2017, 6:10 PM
Rubber cement comes to mind. It can seal punctures in car tires, or patch inner tubes.

Lee Schierer
09-28-2017, 6:17 PM
Loctite 404 is used to make o-rings from extruded round rubber.

Doug Garson
09-28-2017, 7:55 PM
Not sure about gluing or fusing the two pieces of rubber, but how about coating the magnets in silicone to seal them? Then if the bond in the rubber fails you still have the magnet sealed.

dustin wassner
09-28-2017, 8:16 PM
thanks for the responses. The two pieces cannot come apart otherwise the magnets would fall out. The adhesive needs to have a little flexibility to it as the rubber they are glued to are quite flexible.

Ken Fitzgerald
09-28-2017, 8:18 PM
What about dipping the magnets in the rubber insulating liquids available for tool handles?

dustin wassner
09-28-2017, 8:24 PM
ultimately I would like to coat the two pieces of rubber with X solvent and they melt together... Prob not that easy.

Bruce Wrenn
09-28-2017, 9:37 PM
How big are the disks? If not too large, use two tire patches. But as Henry Ford said. "Available in any color as long as it's black."

dustin wassner
09-28-2017, 9:43 PM
the magnets don't need to be discs. I am guessing they will be either 1/16" or 1/32" thick. ~.5" dia. The rubber will also be about this thick, or 1/32"

Jerry Bruette
09-28-2017, 10:10 PM
I'd use some Loctite 380 Black Max to glue the pieces together. We use it at work for gluing neoprene to steel. It's quick and easy, just keep your fingers out of the way.

Marc Jeske
09-29-2017, 2:01 AM

JK, I would look into the two Loctite product ideas above. Marc

Marc Jeske
09-29-2017, 2:05 AM

I especially liked the "Practical Machinist" threads. Marc

dustin wassner
09-29-2017, 8:39 AM
two things I don't think I mentioned/emphasized:
-The adhesive will have to remain flexible
-It will have to stay strong through many cycles in a dish washer

The latter is what I am most skeptical about with an adhesive, unless I am underestimating them

Ole Anderson
09-29-2017, 9:22 AM
Gorilla urethane adhesive? I used some of their construction adhesive to re-glue the ceramic mosiac trim ring inside my hot tub. Only readily available adhesive (including silicones) I could find that didn't say "not for continuous immersion". So far, so good after five months in 102 degree water.

dustin wassner
09-29-2017, 10:51 AM
is the urethane adhesive flexible?

Also, how thick/goopy is it? The two pieces I am joining are flat and thin and if the material I am using to join them is thick then the neoprene pieces will probably not stay flat... Just a thought.

Jamie Buxton
09-29-2017, 10:51 AM
Why do you keep talking about rubber? Isn't your problem just to waterproof the magnet? If so, just focus on that. Encapsulate it with something that can be rigid, like epoxy or some other plastic.

Stan Calow
09-29-2017, 10:54 AM
Permatex? or maybe that Flex Seal stuff they show on TV? I don't think nitrile will hold up under dishwashing.

dustin wassner
09-29-2017, 11:07 AM
when I say rubber I mean the neoprene. The item I am trying to design is two laminated pieces and it needs to be thin and flat and have small flat magnets between it in specific places. If the magnets fall out the item is useless. Waterproofing the magnets is not really the concern, keeping the joint between the two pieces of rubber is so that the magnets don't fall out.

The ideal scenario would be to injection mold a flat thin piece of neoprene with an encapsulated magnet but that just ins't feasible...

I have read of using contact cement with MEK to reactivate the surface of the rubber... this might allow the joint to retain the elasticity/flexibility that the neoprene normally has

hope that all makes sense

Andrew Joiner
09-29-2017, 12:17 PM
I have used solvent based contact cement to patch neoprene wet-suits for years. On wet-suits in cold or warm water it lasts a year or more. In your application use 2 coats and test it on a sample in the dishwasher.

dustin wassner
09-29-2017, 12:22 PM
thanks, Andrew. Can you suggest a brand name that you have used?

Grant Wilkinson
09-29-2017, 1:34 PM
I've had good results on my dive and kayak wetsuits with this


Mark Bolton
09-29-2017, 1:34 PM
3M Scotch Weld would be my choice for Nitrile.

dustin wassner
09-29-2017, 1:47 PM
thanks Grant. If you were to try to pull apart a repair on your wetsuit with this, could you eventually work it loose? Does it require a large bead of the adhesive on the repaired spot in order to be strong enough?

Andrew Joiner
09-29-2017, 2:45 PM
thanks, Andrew. Can you suggest a brand name that you have used?
Dap 00272 Weldwood

Dave Anderson NH
10-02-2017, 1:05 PM
Neoprene and nitrile (Buna-N, NBR) are thermoset materials meaning that once cured they can' be softened or reshaped like thermoplastic materials. Adhesive bonding layers together is a fine interim approach but won't stand up to multiple dishwasher cycles IF there is any flex. Additionally neither material is injection moldable except by liquid injection molding. As an alternative consider using a thermoplastic elastomer (TPE,TPR) such as Kraton or Santoprene. These are readily injection moldable on standard plastic molding machinery.

dustin wassner
10-02-2017, 1:14 PM
thanks, Dave that is very informative. I actually really don't care if it is neoprene. I just need something that is as close to gum rubber as possible - doesn't need to be as elastic but needs to be grippy. I was going to order a 1/32" silicone 12"x12" sheet from ebay or find a supplier that could send a sample.

Are Kraton or santoprene going to give at least somewhat similar grippy-ness and elasticity as gum rubber?


Dave Anderson NH
10-02-2017, 3:31 PM
Grippiness or coefficient of friction is somewhat a function of surface finish and also the particular polymer. Elasticity is normally expressed as a percentage of elongation to break. Nothing will have the elasticity of pure gum rubber (rubber band material) which is around 400% to break. Silicone (polysiloxane) comes about as close as anything in the lower durometer hardnesses and thin cross sections. Stay way from pure gum and natural rubber since they have poor heat aging characteristics. Silicone will be unaffected by ozone, UV, and has a useful service life beyond 20 years from -75F to + 500F

dustin wassner
10-02-2017, 3:51 PM
the issue I have with silicone is that when I called several local mold shops they all said they could not do silicone. Like literally, all of them said no. I was surprised at that. But if nothing else will work then I guess it is worth a shot...

Is silicone a thermoplastic, and if so, is there a solvent I could use to fuse the two pieces together?

thank you.

Kev Williams
10-02-2017, 4:18 PM
What about food-grade silicone?

Dave Anderson NH
10-02-2017, 4:24 PM
Silicone like all non-thermoplastic rubbers can not be solvent bonded or welded. It can be bonded with a silicone pressure sensitive adhesive. For molding you need to go to a rubber molder who has very different equipment than a plastic molder. Generally the only rubber materials a plastic molder can process are TPE/TPRs. Quantity is key here since the cost of tooling is prohibitive for very small quantities. I might be worthwhile to investigate the TPRs since they an be ultrasonically welded.

dustin wassner
10-02-2017, 4:37 PM
thank you, Dave. Do you think a silicone pressure sensitive adjesive would be strong enough to last through many dish washer cycles?

You had mentioned kraton and sanoprene as options. Do these have elasticity of silicone? I feel like I am running out of options...

Rich Lester
10-02-2017, 5:25 PM
Try googling "silicone casting". There are a lot of different diy silicone casting materials out there. If you need to make a "mold" get yourself some polymer clay from the local craft store and create a mold.
I don't think it would be very difficult to do.

Dave Anderson NH
10-02-2017, 5:26 PM
The TPRs are elastic,but much depends on the durometer hardness, softer beg more elastic. They are nowhere as elastic as silicone. I would be reticent to depend on an adhesive for bonding pieces together except for possibly an RTV silicone. The pressure sensitive adhesives depend too much on the quality of mating surface preparation to be a reliable choice.

Grant Wilkinson
10-03-2017, 7:33 AM
I'm sorry it has taken me so long to reply to your question, Dustin. On my wetsuits, if I try to pull the joint apart, the neoprene will tear before the glue will let go. I don't use a lot on each repair.

Your application is likely too much different to use my results. You want to use detergent and likely hot water. My suits are not exposed to hot water - ever - and only infrequently to mild detergent.

Ronald Blue
10-08-2017, 3:26 PM
Dave is the only one I have saw mention RTV silicone. I know from all the mechanical repairs I make it's a very tough and still flexible material. Certainly worth trying. I think you have a few color choices. Black, red, and blue, and possibly silver.

Dave Anderson NH
10-09-2017, 12:32 PM
Addenda to my previous post. If using an RTV silicone to bond 2 pieces of silicone together first wash degrease,and dry the silicone sheeting. Typical manufacturing (extruding or calendaring) of the sheeting uses mica dust or talc as a release agent and either will interfere with making a good bond. Soap and water or isopropanol both work fine.

Matt Meiser
10-09-2017, 6:53 PM
There are liquid silicone products out there. Years ago I did a project for a company in that industry called Laur Silicone. They made a 1-part liquid and as I understood it could be molded pretty inexpensively since there wasn’t much equipment required.