Need to bond EPDM sheeting to Aluminium deck on a yacht 3

Multiple options:

3M Scotch-Weld 4799

3M Scotch-Weld CA-40

Reltek BONDiT

Loctite 496 and others:

Lord Chemlok 6253

Hi Espreeeo51

Irrespective of the adhesive chosen the surface preparation of the aluminium is of fundamental importance. You MUST use a process which inhibits the formation of hydrated oxides in later service or you will experience adhesion failure. Using a different adhesive will only result in a different colour surface on the disbond. Please, please please do not believe that you can use a scuff-sand and solvent clean for this bond.

Regards

Blakmax

I know that the surface prep of Aluminium is vital, but the suppliers of adhesive don't seem to agree. Loctite's rep told me to just clean with MEK!
Can Iask for a recommendation ? Please!

That sort of uneducated sales man garbage really makes me angry. There are extremely few cases where a wipe with MEK is sufficient and that would require an extremely aggressive acid-base reaction with the surface. So you can tell that salesman that he is talking through a part of his body which has functions other than speech.

I have posted my advice on this and other forums many times, but here we go again.

Adhesive bonding is a chemical process which requires chemical reactions at the bond interface. Usually covalent bonds give the best strength. To achieve a chemical reaction the surface must be clean (yes, wipe it WELL with MEK) but it must also be chemically active, so the existing oxide layer must be removed. The most effective method for metals is grit blasting using clean abrasive and clean dry propellant gas. At that stage you will have a clean, chemically active surface. DO NOT solvent clean or you will contaminate the surface. Blow the dust off with clean, dry gas. The surface will instantaneously oxidise but that surface is reactive. Now if that is all the processing you do, the bond will be strong in the short term, but will not last very long. Aluminium has an affinity for formation of hydrated oxides, Al2O3 forms Al2O3.2H2O. In service all polar molecules will attract water by absorption and that water is sufficient to enable hydration of the bonding surface. So for longer term durability you must treat the surface with something that prevents hydration of the interface. (I stress that using a sealant barrier around the bond is not a solution.)

One means of providing hydration resistance is phosphoric acid anodising and application of a chromate based primer (BR 127). The primer contains hexavalent chromium so extreme care is required and your local EPA may prohibit its use without a permit and stringent process controls.

A less risky process involves the use of organo-functional silane coupling agents such as Dow Corning's Z6040. However, if this is a one-off process I recommend you buy a kit. Google AC130 and I am sure you will find it.

Regards

Blakmax

Is this the same as Alodine?
I used this on the boat before.
Can I just sand the surface, whipe with MEK and then wash with Alodine?

No. Alodine works by passivating the surface. You want a chemically active surface.

This reference may be useful for you guys:


Regards

Blakmax

Star for blakmax. That answers a lot of questions I was too ignorant to ask.


Mike Halloran
Pembroke Pines, FL, USA

You can use Alodine as the primer mentioned by Blakmax, there are versions with and without hexavalent chromium.

Again CoryPad, I would not use alodine on a bonding surface. As a corrosion protection it may work well but that is not the purpose of a bonding primer. The primer must not only react with the surface oxides, it must be capable of reacting with the adhesive. Since alodine is a passivator I would not use it where I want a surface to bond onto it. The organofuntional silanes do inhibit corrosion in their own right and are compatible with epoxy adhesives. My experience with a military organisation was that we never used a primer provided we bonded immediately after preparing the surface with a grit-blast and silane. Out of about 4500 bonds since 1992, we had three failures and each of those was traceable to operator errors. In a study of about 180 samples of those bonds, corrosion was found in one sample and that was the size of a match head. We actaully had bonds on steel where corrosion had spread in the steel under the bond by inter-granular progression yet the steel on the bonding surface was not corroded.

It is very simple to determine cases where the wrong adhesive was chosen. The failure will leave adhesive residue on both surfaces because the adhesive was too weak to carry the loads (or the design was poor). If the failure occurs at the surface of one adherend then it is a surface preparation problem. Changing the adhesive without changing the process will simply change the colour of the disbond.

Regards

Blakmax

Fascinating. Alodine primer provides excellent adhesion for epoxy-based coatings (paint), which are limited by the same hydrated oxide failure mechanism described above. I wonder what the differences are.

CoryPad I think it may be that paints do not carry load and hence the interface is never subjected to the combination of environment and loads. I do know from service experience that alodine does not produce durable structural bonds.

Regards Blakmax

Yes, that sounds very reasonable. Looking at this application, the light stresses from sheeting would be intermediate to paint and composite structures.

relatively thin stuff like this?
Acrylic Adhesive backing is an option
I'd have trouble applying a big sheet of rubber without wrinkles and bumps.

Have you looked at with aggressive non-slip strips by 3M with some (acrylic?) adhesive pre-applied?

3M often makes the point that acrylic adhesives require less surface prep than epoxies.
"Acrylic Adhesives - Taking the stresses of tough duty
Two-part adhesives that bond well to a wide range of surfaces including most plastics and metal with minimal surface preparation."
"High strength bonding without the surface preparation needed for epoxies and urethanes."