Bonding aluminum sheets on steel frame for expedition truck body

[2tierradelfuego]

I am building an expedition camper with a steel frame and aluminum cladding. I am planning on using Sikaflex 252 to stick the aluminum sheets (1/8 inch, 3mm) onto the steel frame, but I am open to using a different adhesive. This steel frame is not exposed to the elements and after sticking the aluminum siding on I intend to use spray foam for insulation, so none of the steel is exposed to air.

Few questions:
1. can you use the sikaflex 252 on the bare steel or should it be painted first?
2. If it needs to be painted first do you have to spray paint or can you use rustoleum or some other steel paint with a brush?
3. Do the aluminum sheets need to be clamped or is this Sikaflex strong enough that once you push it on, it will hold?

Any other tips on how to best do this would be greatly appreciated.

Here is a picture, there will be more studs to hold the aluminum sheeting.

 

[Amesz00]

Nice truck mate.
1) sika does advise that the steel should be painted in 'sika primer' prior to using sika on it.
The Ali should be scuffed or orbitaled and wiped with 'sika activator'.
2) see above
3) they will need tabs to hold up the sheets at the bottoms and clamps up top. You don't want to clamp it hard up though.
Side note; you will have almost no window for pulling the sheet off again.

 

[ScottReb]

Welcome to Expo! Very nice truck indeed..

3M VHB tape is very easy to use, stick immediately, good or bad, and is just as strong. I believe it is the more common method in Australia. In Japanese Heavy Truck section, member whatcharteboat and several other are a wealth of info about this type of build. In the states the VHB tape is use quite frequently on various trailer boxes.

I believe Sika recommends that there be a specific separation between substrates. A spacer to keep it at optimal thickness.

 

[tgreening]

One "trick" gluing on sidepanels, park or lift the truck to tilt to its side when applying panels.
Helps greatly to keep the panel in position and flat upon framing members.

That's borderline red neck genius right there. Ridiculously obvious, yet it never crossed my mind. Makes me borderline red neck retarded?

 

[pugslyyy]

Welcome to Expo! Very nice truck indeed..

3M VHB tape is very easy to use, stick immediately, good or bad, and is just as strong. I believe it is the more common method in Australia. In Japanese Heavy Truck section, member whatcharteboat and several other are a wealth of info about this type of build. In the states the VHB tape is use quite frequently on various trailer boxes.

I believe Sika recommends that there be a specific separation between substrates. A spacer to keep it at optimal thickness.

Sika is good but also very particular, I'm becoming more and more of a fan of the 3M tapes.

It's probably worth pointing out that VHB is really a "family" of products, not an individual item. 3M tech support is very good at helping you figure out the best sku to use in your particular application.

 

[Greg]

Please see Robgray.com as he built both his 6x6 motorhomes (Wothahellizat version 1 and 2) using steel frame and aluminum diamond plate skin. If I remember correctly the 1st version used VHB tape and is detailed in his version 1 build diary #23. He was removing the skin and shortening the frame for version 2 and found that the skin installed with VHB came off easier than that put on with Sikaflex (see his version 2 diary Wed 13 Jun). He starts his description of installing the skin in his version 2 diary of Tue 25 Sep.

 

[S2DM]

I've seen a few VHB failures with smaller loads than a skin would see. I'm not an expert on skinning adhesives, but my gut tells me VHB isnt the right choice. I'd consider something like the 252, I believe automotive panels are often applied with one of the hysols. 252 is particular as mentioned, proper prep is paramount. Use the primer, most definitely use the activator, and make sure the substrate is clean and has been scuffed with a scotch bright or similar. Don't clean or wipe down with alcohol first either. Just use the sika products.

Lastly, get yourself a pneumatic gun for applying the sika. Cheap on amazon and will allow you to finish the job before your forearms start to look like popeye's. 252 is harder to dispense than 5200 by a large margin.

 

[AFBronco235]

As someone who's worked on aircraft, I'd recommend using a mechanical fastener in addition to the adhesive. Especially at the corners of the aluminum sheets. Beveled screws with dimple washers or rivets at those points will help keep the skin from peeling over time from simple things such as wind and rain/snow/ice getting in there and pulling the sheets away from the steel frame. It wouldn't be difficult to do either. Once you have the skin on with whatever adhesive you decide to use, then you can drill holes for the fasteners through the skin and frame.

 

[Amesz00]

As someone who's worked on aircraft, I'd recommend using a mechanical fastener in addition to the adhesive. Especially at the corners of the aluminum sheets. Beveled screws with dimple washers or rivets at those points will help keep the skin from peeling over time from simple things such as wind and rain/snow/ice getting in there and pulling the sheets away from the steel frame. It wouldn't be difficult to do either. Once you have the skin on with whatever adhesive you decide to use, then you can drill holes for the fasteners through the skin and frame.

Properly applied sika doesn't peel off on a truck, believe me. Not in a reasonable lifetime. The sheets don't even have to be sealed, they'll still stick hard with water, dirt and crap flowing behind them.

 

[Kevin108]

I don't know - just asking, because I'm a nerd, and maybe you can fill me in - but is there any concern for galvanic corrosion in this application?

 

[Coachgeo]

I don't know - just asking, because I'm a nerd, and maybe you can fill me in - but is there any concern for galvanic corrosion in this application?

If not mistaken the bonding agent is just thick enough there is no metal to metal contact if the bonding agent is spread correctly. Therfore there can be no galvanic corrosion since the different metals does not actually touch one another.

Feel free to shoot holes in this for am certainly no expert on the topic.

 

[loonwheeler]

A minor addition to the galvanic corrosion topic. Two dissimilar metals do not have have to be in direct contact with one another to suffer from galvanic corrosion. They can be physically separated but connected electrically via an electrolyte solution. Examples could include condensation built up in humid environments or a rainwater leaking into a roof / wall joint. That said, if both materials are coated with a non conductive material such as paint or polymers it should greatly reduce any major concerns about an electrical connection being established between the two materials.

That said, the galvanic potential (V) between most low alloy steels and commercially available aluminum alloy sheets is fairly small which further reduces the risk. If both the frame and the cladding were prepped, bonded, and painted - I wouldn't worry to much about galvanic corrosion between the two materials. Just my 2c.

 

[doug720]

3M option - https://www.youtube.com/watch?v=qgKl0FBVTg0

 

[Coachgeo]

A minor addition to the galvanic corrosion topic. Two dissimilar metals do not have have to be in direct contact with one another to suffer from galvanic corrosion. They can be physically separated but connected electrically via an electrolyte solution. Examples could include condensation built up in humid environments or a rainwater leaking into a roof / wall joint. That said, if both materials are coated with a non conductive material such as paint or polymers it should greatly reduce any major concerns about an electrical connection being established between the two materials.

That said, the galvanic potential (V) between most low alloy steels and commercially available aluminum alloy sheets is fairly small which further reduces the risk. If both the frame and the cladding were prepped, bonded, and painted - I wouldn't worry to much about galvanic corrosion between the two materials. Just my 2c.

Great info...... much thanx

 

[KE7JFF]

I'm trying to remember what I was watching but there was some engineer showing how I think commuter rail train cars were built and surprisingly they were using adhesive bonded aluminum; the trick was to spray the adhesive on if I remember right.