Originally Posted by
peteeng
Hi Jerry - Your first options would have worked, maybe not up to what you think. Re: aluminium bonding with epoxy. The type of epoxy you describe is quite thin. If you laminate with it and clamp it you can create a zero thickness bondline that obviously has no strength. This sort of connection is perfect for contact cement but since you have epoxy.
1) I'd firstly do a small test piece to understand how the epoxy soaks into the timber or not and to time its gel time. You need to know that it does not leave a dry surface and when the epoxy gets tacky. You can also use a "primer" coat on the timber so it seals and allows a consistent epoxy film when you do the join. I'd do a primer coat on the timber.
2) scotchbrite is good for wet sanding the AL surface but any fine wet and dry paper is OK (240 or 320G). And yes you apply the mixed epoxy to the surface (use a V spreader). Wear gloves!! I suggest butyl gloves latex tends to tear
3) If you want to get technical you should use a glass fibre tissue or some very light cotton cloth to create a consistent bondline thickness. Glass tissue is 0.25mm thick. The perfect bondline thickness for structural components is 0.25 to 0.5mm thick. You can achieve this without a scrim by applying the epoxy to the timber, allow to get tacky then apply the wet AL to the surface. The tacky epoxy then can't be squeezed out of the bondline. Do a small scale test to get to know the timeline
In this application the bondline strength required is tiny so I'm sure if you dived in and did it it any old way it will be fine. Peter
To get a little more technical the most common reason epoxy and aluminium bonds fail is surface moisture. Epoxy does not like water. If you have ever TIG welded you will see the moisture coming out of the metal. So a waft with the hot air gun (or propane torch) before you coat the metal is a good idea but this can change the gel time. Automotive and aerospace now use flame (plasma, corona) treatment to prime surfaces prior to bonding. And laser prep have you seen laser cleaning of rusty surfaces aaaaaaaaAMAZING!! I expect Dakota is dry air however compared to where I live. The deserts in USA are full of aerospace component makers for the dry air and cheap land.
re laminating plywood and LVL - I'd prime coat these as well before laminating the result is much more consistent.