Filling in Holes on an Aluminum Boom

[The Froon]

I understand the technique for filling in unwanted holes (old tapped or rivetted hardware) on an aluminum boom (or mast) is to fill with thickened epoxy. As I approach this project, in my mind I am seeing no way to prevent the thickened epoxy from sagging into the interior of the boom itself...and possibly never filling the holes, or creating a terrible mess within. I plan on tapering the old holes to allow as much 'hold' as possible for the epoxy.

Is there a way to create a 'backer' (e.g. tape) for the hole as the epoxy is applied? Should I simply mix the epoxy with enough thickening agent to create an extremely viscous batch, then apply? Which of the West System products should I use (403, etc.)?

Lastly, I am concerned that this process of filling holes will eventually produce cracking and chiping in the new paint application: pettit metal wash /prime, pettit ti-coat, pettit easypoxy. I have a number of holes to fill on the boom, so should I just go ahead and buy a new boom, drill and tap? Should I be confident in the adhesion strength of epoxy to aluminum and charge forward?

Thanks!

Brian

[Tim]

Mill a countersink at each hole location to hold the epoxy over a wider area (this is probably what you meant by "tapered", so you're on the right track). Mill these holes shortly before you plan to fill with epoxy, and abrade them if possible to ensure bright white metal; aluminum will oxidize quickly, so you don't want to mill the holes too far in advance.

Mix your epoxy with microballoons (407) and cabosil (406) till it's stiff and it won't run out the holes at all. A small amount will press through as you apply pressure, but this is not a concern. There's no way to back up the holes, nor should you worry about it or spend time trying to figure out a way.

In terms of paint failure, chipping: I filled numerous holes of this nature in my mast some years ago before painting, and have not experienced issues or paint failure around the holes, or elsewhere. I painted the spar with Awlgrip chromate primer and Awlgrip topcoat. Check out Awlgrip's online user guide for valuable aluminum preparation tips regardless of the paint system you end up using.

Be sure to purchase the thinner that goes along with that Pettit tie-coat prime, if you must use these items. I have been involved in its use once, and it's thick gross stuff that goes on about as smoothly as drywall compound if you don't have the thinner. Note that in this same experience, the topcoat seemed to adhere poorly to the primer too, so I'm not sure I'd recommend that set of products based on this single experience.

[The Froon]

Thanks, TIm. I am going to give this method / product selection a shot since I have already purchased. I spoke to Pettit, and they recommneded a slight scuffing of the tie-coat primer with 220 prior to application of their easypoxy product - not sure if you had done this through your use of the product, as you noted poor adhesion to the topcoat. They also recommended thinning with 97 epoxy thinner - which I did purchase. As always, appreciate your's and the forum members' feedback.

Brian

[Quetzalsailor]

I filled heaps of 3/16" or so holes in bright, shiny steel using polyester resin and 'glass back in about 1967. Many failed in the ensuing 20 years. This was on a black car body. Do y'all think that epoxy fillers would have survived?

I think that very little filler will extrude through. I'd taper the hole more for cleanliness and an easier transition between the smooth extruded aluminum surface and any burr at the lip of the hole, than for bond or preventing squeeze through. I'd aso wet out the nice clean aluminum using as little neat epoxy as possible (a Q-tip?) so that the filler would stay thick and would have enough free epoxy to make a bond.

If I were gonna' close a half inch hole, I think I'd taper from both faces (with a pocket knife and burr), poke a bit of 'glass through, tied with a bit of glass to hold it from falling into never-neverland. Wet out and fill against that, with microfibers for stiffener and reinforcement. Like patching a hole in plaster.

I have also filled many fastener holes in aluminum by welding 'em shut. I also butt-welded a bunch of aluminum extrusions with reverse polarity DC stick welding. Unfortunately, the heat expands the aluminum enough to craze a clear anodizing coat. This was on architectural aluminum and the anodizing is there for appearance and is thicker. I painted the raw aluminum patches and welds, and the crazed anodizing, using old fashioned aluminum paint; the result was entirely adequate.

[Commander-147]

I'm looking a rehabilitating the mast on my commander and one option is to send it to JSI in St Petersburg and let them weld the holes up that are no longer wanted. At the same time they would weld winch bases on both sides and a fixed gooseneck bracket and pivoting vang bracket. Then they would paint with Awlgrip. The total bill would run me approx. $2,500.00

Is there a reason I should not go this route or anything I should be careful of if I do? These people have a good reputation here locally and they weld a lot of masts.

[Tim]

I spoke to Pettit, and they recommneded a slight scuffing of the tie-coat primer with 220 prior to application of their easypoxy product - not sure if you had done this through your use of the product, as you noted poor adhesion to the topcoat. They also recommended thinning with 97 epoxy thinner - which I did purchase.

I didn't do the work, but the mast was here on site. The failure to have the thinner on hand for the tie-coat primer was certainly a problem in terms of the primer's application, but I don't know if this also caused the poor topcoat adhesion.

In any event, I was unimpressed with the Pettit system--from green chromate to topcoat. One bad experience does not a bad product make, but it should make one extra careful about following the application steps properly, if nothing else.

[Tim]

I filled heaps of 3/16" or so holes in bright, shiny steel using polyester resin and 'glass back in about 1967. Many failed in the ensuing 20 years. This was on a black car body. Do y'all think that epoxy fillers would have survived?

Probably, assuming proper surface preparation, etc.

Remember: epoxy is an adhesive. Polyester is not. This is a significant difference.