Hello 1mancrew, I would simply say that even under the best of conditions SMAW on aluminum is a son of a gun. The second thing that you were likely fighting here is the fact that this was a trailer for an 18 wheeler. It has had plenty of time to pick-up any number of nasty surface contaminants to play heck with welding it. Any time that you have cracks, connection points that involve the lapping of two surfaces or spots where dirt and other contaminants can be trapped, they will make the welding of these very difficult. Whenever possible in these situations, grind, chemically clean, or otherwise clean out the crack or junction point. If using chemicals for cleaning, only use non-residual cleaners(acetone is a good general choice), but never weld on the part until the residual chemicals are completely gone. I don't actually believe that it is anodized, however if it was you would definitely want to remove this surface condition before attempting to weld on it. I myself have been at the welding game for a number of years and have played around with the SMAW process on aluminum stick and have actually used it in industry once. I didn't have any impressive results then either. It simply isn't the same as GMAW or GTAW aluminum and you can't expect to see similar results. If you anticipate having future opportunities to work on aluminum trailers you may want to invest in the necessary equipment to perform GMAW. There are some of the gas drives that will accept spoolguns directly while others may require a control box to be used in conjunction with the spoolgun. You can either purchase these set-ups new or possibly used through a rental yard, craigslist, or ebay. I have made the assumption that you are using an engine driven welder of some sort and that's what I have based my reply on. Also, don't forget that no matter what sort of welding process you are attempting to use, you will need to pay special attention to the preparation of the material and keeping it as clean as absolutely possible. Sorry to hear of your troubles. Best regards, aevald

I was stationed aboard a minesweeper in the last months of my Navy career, and most everything there is either stainless or aluminum.  No high-freq allowed, and didn't have room for a decent wire feed machine.  So I had these SMAW sticks, can't remember the manufacturer or class; 3/32"x16", the flux was rough and white.  I have had to weld handles onto doors and hatches; this is 1/2" 6061 round bar onto 3/16" 6061 sheet.  After some practice, I was able to make fillets resembling some of my earlier work with E6011 on carbon steel.  That is to say, it wasn't pretty but it was passable.  Allan is dead on when he says you have to get your base metal clean.  And when it's clean, clean it again. 

i know in gmaw there is a huge defrence between dragging and pushing would that be the same in stick.

understand your grief, played around with this about a week ago, i used a SS brush like they taught us in TIG class. and fired up the Hobart Champ, set the current to 90 amps, decided real quick to turn that down some. but all in all it wasn't that bad, but i think the better deal for my attempt would have been preheat, since the heat transfer of aluminum is so high. and the last post speaking of push instead of drag, i wil try that, might help.... the weard part was you take a 14" rod and get to weld 2" and you need another rod.... not the same with 7018. i thought if i had to weld anything other than playing around trying to teach myself, this would get expensive. so i agree a TIG or MIG Plugged into the Champ. would be ther best bet.

Mike

Use a carbide burr with a pencil/die grinder and hog out a clean groove/surface for the weld to fuse to.
Miller makes the Spoolmatic 15/30A spoolgun and when connected to the  WC-115A Control it provides a volt sensing wire feeder which works with any dc stick welding machine. It won't do short circuit from a stick machine but it will do a very nice job with spray transfer. This is the preferred transfer for aluminum.
Remember amperage is controlled from a stick machines output control and the voltage is controlled by arc length. Therefore with the volt sensing wire feeder; the voltage is controlled with the wire feed speed. Increase wire feed speed and the arc length decreases, the resistance decreases and the voltage is also decreased. Amperage is penetration and the bead profile - the height & width is controlled by the voltage.
Set the amperage for material's thickness and penetration; once set, leave it alone. Then set the voltage for the bead profile. High & Ropey Beads requires an increase in the voltage by decreasing the wire feed speed. Fine tune the arc with voltage not amperage.
This extra equipment may be pricey but if the job can't be done it gets real pricey. The customers find shops or rigs which can do every or at least more/varied projects.