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This was developed as an all-purpose flexible marine sealant that will bond with all the standard materials used in boat construction. It is a non-structural adhesive, ie light duty, one-component polyurethane, with high elasticity and resistance to weathering, seawater and UV radiation. It has excellent gap-filling capability and can be painted over and sanded, for use above or below the waterline. here
The products purchased from a builders’ merchant were less expensive than those produced for the marine market, and are claimed to stick a wide range of materials. The Bostik/Evo-Stik product performed better than the UniBond but wasn’t as strong as the marine structural adhesives. It’s a good all-rounder though, and is cheap and readily available.
The use of the spacer improved the strength of the bond. Surface abrasion also improved the bond between the adhesive and the substrate for all the specimens.
When it comes to sticking two bits of anything together, I tend to be a belt-and-braces person – or should that be a nut, bolt and glue person?
However, times have changed and so have adhesives. Increasingly, adhesives are powerful enough to do the job by themselves: we have adhesives to hold our car windscreens in place, modern aircraft use adhesives extensively for body parts and even the latest lifeboats rely entirely on adhesives to bond the rubbing strip to the hull.
For the shear tests, most of the metal specimens failed, with the adhesive releasing from the substrate. The acrylic and GRP fared much better, with most of the structural adhesives failing in a cohesive mode.
Other products that Marsh Fasteners supplies to clients that work in the construction field all over the world include stainless steel threaded rod, Stainless steel nuts, marine fasteners and stainless steel bolts among others. We work with a wide range of manufacturer suppliers to ensure that you get high quality products that are delivered within the stipulated delivery time.
To reduce chances of the metals getting corroded reduce the contact the two metals have by creating a non-reactive barrier. The best barrier material is plastic washers which ensure that the metals are sealed at their point of contact. Also, to reduce their contact with water, connecting points can be protected using tape or even paint depending on your preference. [links]
It is no doubt that stainless steel screws are the best when it comes to holding together materials such as aluminum sheets so that when faced with a variety of elements they do not break open. However, the dissimilar nature of these two metals puts them at risk of getting corroded resulting in their destruction altogether. At Marsh Fasteners , we believe that the steel screws can be used with aluminum but some precautions must be taken if they are to work well together.
Salty water is an electrolyte that can easily corrode either the aluminum or stainless steel material when they come into contact with each other. Therefore, it is important to always separate the two metals as soon as possible especially if the environment has salty water or anything close to it. more
Tips to consider when using stainless screws on aluminum
Always ensure that the aluminum part of the material is larger than the stainless steel screws to avoid it being eaten away. Aluminum which has an anodic nature will quickly disintegrate when it comes into contact with salty water, and will do the same when its surface area is less than that of stainless steel. more
In your case, the fittings with the extra bushings shown are done correctly and as the ABYC would recommend in its standards for this type of assembly. Whoever the installer was here may have assumed that the thread sealer would provide adequate separation of the metals, but that is simply not the case. Once the fitting gets tightened properly, all of the sealer will be squeezed out of the threads, putting the brass in direct contact with the aluminum.
Answer: Nice work, you have made an observation that the average boater would never have made. You are quite correct, aluminum and brass should never be in direct contact with one another in the marine environment. The mix is a guaranteed prescription for corrosion, and in the case of fuel fittings, probable breakage of either the tank or the fitting when you attempt to disassemble the connection. [links]
Thread sealer alone won't keep these two metals apart, and they're far enough from each other on the galvanic scale for corrosion to occur if exposed to seawater.
The brass fitting in the middle is screwed directly into the aluminum. This is asking for trouble if salt water enters the mix. more
Question: My boat has an aluminum fuel tank. The other day I was checking out the fuel lines connected to the tank because I could faintly smell diesel inside my boat and I wanted to make sure the connections were tight and that none of the hoses were leaking. Although I didn’t find a leak anywhere, I did notice that the brass fitting in the middle of the photo was screwed directly into the aluminum. It looks like it had some kind of thread sealer on it (the brown stuff). The other fittings you can see look like they have stainless steel bushings that the fittings are threaded into. Those look right to me. I’ve been told that aluminum and brass don’t mix in the marine environment. Any tips on this?
The problem is that the two metals are just too far apart on the galvanic scale. The farther apart metals are from one another on this scale, the more dissimilar they are and the more likely they are to corrode if connected. One will become anodic and the other cathodic. In this case, the aluminum will become the anode, and as most boaters understand, anodes dissolve in seawater. more
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