Gluing aluminum to aluminum or just about anything else

[Gaia]

Originally Posted by a64pilot

Speaking of PTFE, ever wondered how it’s bonded to anything? What kind of glue sticks to Teflon?

Teflon, polytetrafluroethylene, can be glued to but if is difficult. What is done is one removes the fluorine atoms from the surface using very reactive Na, sodium atoms. The liquid containing them is blue and must be used with great caution as it is very reactive.. White TFE thus treated turns brown or black as upon removal of the F surface atoms one is left with a carbon rich surface. That surface can be glued to.with many adhesives. I have no idea where one obtains this stuff. Years ago I had occasion to use it at work but I do not remember if we made it or bought it.

Jim SV GAIA

[Cheechako]

Originally Posted by Cheechako

We used to spray PTFE on aircraft parts. Part of the wing anti icing system. It isn't glued, it's sprayed on as a very fine powder clinging to the metal, then it is baked to melt it to the surface you see like on frying pans.

BTW, we had some "certification out of date" ptfe and I had the guys do a bronze prop with it, unfortunately I didn't keep the boat that long after, but it appeared to be growth free on the sale survey.

[Matt Johnson]

Originally Posted by Cheechako

We tested some special glue offered commercially. It came in a caulking tube, may have been some kind of modified thick CA glue actually, it was clear. They were trying to convince use to use it in lieu of welding stringers inside aluminum boat bottoms.

For the test we glued a stringer 2.5" x 2.5" to a piece of 1/4" aluminum plate. After hardening we had one of our big guys use a sledge hammer to try to break it off. Long story short, it couldn't be done. We didn't go forward with it, but could have probably.
Wish I could remember the product...

ITW Plexus? I think they were the ones heavily advertising this application.

* nevermind, they don't make a clear, so it must have been something else.

-Matt

[Sand crab]

Originally Posted by Cadence

I used Liquid Nails for bonding to aluminum some 35yrs. ago. Still holding. Horrors it doesn't say marine.

I experimented with regular Liquid Nails and the problem was that it would not set up when sandwiched between two sheets of aluminum. It needs some air for that otherwise it's just like being in the caulking tube. I reckon after days it would probably set. Silicone caulk was the same.

[Cheechako]

Originally Posted by funjohnson

ITW Plexus? I think they were the ones heavily advertising this application.

* nevermind, they don't make a clear, so it must have been something else.

-Matt

I think maybe that was it. maybe 10-12 years ago.

[AndyEss]

Originally Posted by Gaia

Teflon, polytetrafluroethylene, can be glued to but if is difficult. What is done is one removes the fluorine atoms from the surface using very reactive Na, sodium atoms. The liquid containing them is blue and must be used with great caution as it is very reactive.. White TFE thus treated turns brown or black as upon removal of the F surface atoms one is left with a carbon rich surface. That surface can be glued to.with many adhesives. I have no idea where one obtains this stuff. Years ago I had occasion to use it at work but I do not remember if we made it or bought it.

Jim SV GAIA

I believe McMaster- Carr used to sell PTFE adhesive kits. I’m not sure if they were multi-part as I never had the need to use them.

[s/v Jedi]

MarineTex is thickened epoxy with UV filters.

I think in the case described by OP I would use JB Weld original formula

[lvictorlucas]

The most important step is preparing the surface and making sure the new part is molded to the surface as closely as possible.

[Ramona]

JB weld is particularly good for aluminium engine parts.

[Sand crab]

I have used JB Weld which is really epoxy with some modifiers but Fuze It is so easy. It's in a caulk tube and it doesn't get any easier than that.

[billgewater]

So why are we not using these adhesives for aluminium boat construction or mast repairs? I had always thought that the welding process was one of the main reasons people did not take to aluminium boats. The welding can cause alloy component separation (I think that is why air craft skins are riveted). The welding can also cause the "hungry dog rib cage look" appearance.
I also wonder about the following: - When a glass fiber, steel, wood or ferro cement boat reaches its end of life, the hull material is near valueless. Aluminium on the other hand has actually increased in value as a highly "recyclable" material ($0.20 to $1.50 per kg) So a ten metric ton empty hull may fetch $15 000. Plus aluminium boats do not necessarily require painting above the water line.

[Reefmagnet]

Originally Posted by billgewater

So why are we not using these adhesives for aluminium boat construction or mast repairs? I had always thought that the welding process was one of the main reasons people did not take to aluminium boats. The welding can cause alloy component separation (I think that is why air craft skins are riveted). The welding can also cause the "hungry dog rib cage look" appearance.
I also wonder about the following: - When a glass fiber, steel, wood or ferro cement boat reaches its end of life, the hull material is near valueless. Aluminium on the other hand has actually increased in value as a highly "recyclable" material ($0.20 to $1.50 per kg) So a ten metric ton empty hull may fetch $15 000. Plus aluminium boats do not necessarily require painting above the water line.

The biggest problem with structural glueing of aluminium is the layer of oxide that forms on the surface of the metal literally within minutes of it being cleaned. It's pretty much like glueing something to something else that has a coating of paint. The glue sticks perfectly to the oxide, but the oxide isn't necessarily well attached to the underlying metal.


In regards to welding, the material used for aircraft is an aluminium/copper alloy (from memory) and cannot be welded. The aluminium used for spars is (most likely) an aluminium/magnesium alloy and is readily welded. Other marine parts made of aluminium are also likely to be the same alloy or an alloy of aluminium and silicon, which is also easily weldable.


The main concerns with welding extruded aluminium components (like a spar) is the softening of the extrusion in the welding zone due to annealling of the work hardened base material and the possibility of distortion. Both these issues are easily designed around. Field welding aluminium is difficult, as only gas shielded processes are useable and this can be tricky in any kind of breeze. This can make repairs using welding impractical when a viable alternative - like riveting - exists.



Welded aluminium trailer boats are notorius for developing cracks in the welds over time, but this is just about always the result of the weld being done by semi-skilled labour which results in the welds having a tendency a initiate a crack. The cracks will rarely extend into the base metal though.

[darrelweb]

Sika Flex and it may be 252, check their web site, is used in the heating and air condition fields to glue aluminum ducts together. Once glued, you can not pull the stuff apart. Check for the correct number to use, but once cured, it will outlast your boat.

Roughen the surfaces to be glued with 60 or 80 grit first, then clamp, screw, or bolt. Its really good stuff.

[Ted and Relinda]

Doesnt sound like anybody else has used it. But it sounds interesting to try. Ted.

[n5ama]

Originally Posted by LakeSuperior

There is a nice article in June 2020 Practical Sailor about low temperature brazing of Al. This is a much lower temperature process and doesn't require the equipment or skill needed for welding Al.

It is more like soldering with a propane torch and can be used to join thin cross-sections. The rods containing the flux can be bought at Home Depot.

Additional flux is available and recommended to help wick the fluid aluminum into the joint. Makes a very strong joint that is usually stronger than the pieces you are attaching especially if they are light gauge. You need to make sure the pieces you are joining are hot enough and clean.