[DLCeveryday]

I have searched and cannot seem to find this information. How would I properly remove paint from aluminum I plan to tig weld ? Specifically an aluminum boat transom patch ? it is .125 aluminum . I do not want to sand it because I might drive impurities and paint into the aluminum. I am not sure if a chemical remover would create toxins or a problem welding. thanks.,

[cj737]

You can chemically strip it, then clean the chemicals off with Acetone. Or, you can use a flap disk and remove the paint then use Acetone to clean the ally before welding.

As long as you don’t use anything with chlorine on the surface then weld, you’ll be fine. If you must use a chlorine-based Cleaner, you have to clean that off before welding.

[DLCeveryday]

Thanks ! The more I learn , the more I realize how much I dont know !

[noddybrian]

If you have an air compressor I would sand blast it - does'nt have to be be a big elaborate setup as your only doing a narrow band where the weld will be so just a syphon gun style & regular kiln dried paving sand will do in a pinch - depending on the type & age of paint when trying to sand it there is a high risk some of the paint will get hot enough to melt & smear into the metal surface - much like the glue from worn flap discs does - this is very hard to get rid of & plays havoc trying to weld over.

[cj737]

If you have an air compressor I would sand blast it - does'nt have to be be a big elaborate setup as your only doing a narrow band where the weld will be so just a syphon gun style & regular kiln dried paving sand will do in a pinch - depending on the type & age of paint when trying to sand it there is a high risk some of the paint will get hot enough to melt & smear into the metal surface - much like the glue from worn flap discs does - this is very hard to get rid of & plays havoc trying to weld over.

Pardon my dissent here, Noddy, but sandblasting aluminum before welding is a poor choice. Especially with paving sand. The media will become embedded into the aluminum and create quite a mess. Soda blast, sure, that will work, but it’s messy outdoors and kills the vegetation nearby depending upon how heavily you spray.

The paint on these boats is very thin, and a light scrub with a disc, or even a chemical wipe will generally remove the paint sufficiently to weld them. I’ve done several repairs to these with very good success using either of these methods. Worst scenario is if the boat has spent its life in brackish, alkaline water. That really makes a mess and is a MFer to clean.

[Poland308]

I like to use the citrus based gel paint remover.
https://www.homedepot.com/p/Citristrip- ... lsrc=aw.ds

[noddybrian]

@CJ737.
Totally respect your views as I believe you do way more aluminum than I do - my comments are always based on what has worked for me in the past - as such I'm largely self taught - if something works I tend to stick with it ( but maybe mis-guided in what I'm doing ! )- I had nothing but trouble anytime I got a flap disc near aluminum - maybe I'm heavy handed or unlucky or they were poor quality - I always had good success with localized blasting using whatever I had by me - often aluminum oxide - sometimes copper slag - occasionally flint but mostly plain sand - I always blast casting repairs too & never had problems - I think you will find Peter Zilla on You Tube does the same - only boat work I get has always been in sea water is as much white corrosion as base metal & has usually been over-painted by owners with many layers of cheap household gloss paint so everything is against getting good results - Tig is my least favorite process anyway & on this boat stuff it usually boils more crap out than welding & constantly has junk jump on the tungsten ! so I blast - cook it with an oxy torch - wire brush then spool gun - unless I can get it up to my mates place where he has a push pull with pulse - on cleaner material completely different approach.

[DLCeveryday]

noddybrian , I was concerned about those flap discs the same as you. I like Poland308 suggestion on the citrus paint remover, then acetone . Seems like a good plan . Thanks everyone.

[noddybrian]

Never tried the chemical cleaners as over here there is very little choice - only kind I've seen is particularly nasty & leaves a terrible mess behind unless you can do it so any residue falls clear of the job - I guess there are now more eco friendly versions if you live in the right place - on the flap wheel debate there are specific just for aluminum types though I never found any locally - if used with care with a fairly course grit & not too worn they likely will work ( flat fiber discs present less of a glue issue )- still very easy to remove more material thickness than desired & probably won't reach all the surface imperfections created by corrosion - as to embedding sand - I never seen it happen - even if a small amount remained I think it would simply float on the pool surface then solidify leaving a similar removable deposit to silicon islands on steel Mig welds - however you tackle it I hope it goes well for you & perhaps you can report back what worked best for you.

[cj737]

Noddy - no doubt you have had decent results after blasting if you’re MIG’ing it. Your pouring so much filler in there so quickly that you end up welding over it for sure. Yeah, you must be ham-fisted if you tear up ally with a flap disc Or, I have the most gentle touch Strip, blast, flap, it doesn’t matter. Whatever works is all that’s imoprtant panda that you follow it up with some Acetone or Laquer Thinner before welding. Heck, even a Brown or Red ScotchBrite Roloc works.

[noddybrian]

I blast no matter which process I use after including Tig & have had no issues - but I like to follow that with a quick cook with oxy followed by stainless brushing prior to welding - I sometimes use solvent but never find it makes a noticeable difference - I do wipe the filler though - that is always filthy with oil from manufacture & shop dust.

[aeroplain]

I'm sure you're done with this, but boats are all I get to weld on and red scotch brite roloc is all I use; an acetone wipe doesn't hurt. On the transom can be a bitch tho, with wood behind the weld.

[DLCeveryday]

aeroplain, thanks for answering, I only have a Tig welder, do you think I should have someone Mig weld it instead ? I have transom wood removed , floors removed , gas tank removed . just the actual aluminum transom left. I am learning to Tig right now , mild steel. I have never welded aluminum before so it might be a minute. Judging by the difficulty on mild steel, I think I could try some aluminum in a month or so , but...we are talking a Boat transom on a 18 footer. It needs to be water tight, but structure wise its not really a factor. The new plywood transom and knees are going to bear the burden so to speak. The outboard bracket that is getting bolted over the patch is fiberglass. some people have installed them right over the hole. I just cant bring myself to do that, lol. And I dont want to bolt a plate over it either. So its either Tig or Mig , lol.

[cj737]

MIG welding would be the ideal process for thin aluminum sheet to thin sheet. The amount of wire being spewed out helps cool the puddle as you go. You still need to be mindful of distortion, so neither process is idiot proof.

Both methods want numerous tacks spaces apart. If TIG, your tacks want to be more than a single dab, usually I use 3-4 dabs with a thinner wire than I’ll weld with. There’s just not a lot of strength in ally tacks. With a single dab tack, and MIG welding over them, you’ll notice opposing tacks will tend to crack before you get there.

The distortion you’ll see is the transom warp inward and the outer panel will warp outward. So you end up with larger gaps than your initial fitment. By interim tacks, you keep the panels together so the weld bead spans a more consistent gap. TIG or MIG, just take your time and you’ll be just fine.

(For TIG settings, I’d be running about 100Hz, 65% Balance, a 3/32 tungsten and tack with a 1/16 wire. Weld it out with 3/32 or 1/8. I’d have my machine set for up to 140 amps, but using a pedal, I’d likely be closer to 90 after I get my bead rolling along. It’s difficult to say because I can’t watch my machine and my work puddle at the same time).

[DLCeveryday]

MIG welding would be the ideal process for thin aluminum sheet to thin sheet. The amount of wire being spewed out helps cool the puddle as you go. You still need to be mindful of distortion, so neither process is idiot proof.

Both methods want numerous tacks spaces apart. If TIG, your tacks want to be more than a single dab, usually I use 3-4 dabs with a thinner wire than I’ll weld with. There’s just not a lot of strength in ally tacks. With a single dab tack, and MIG welding over them, you’ll notice opposing tacks will tend to crack before you get there.

The distortion you’ll see is the transom warp inward and the outer panel will warp outward. So you end up with larger gaps than your initial fitment. By interim tacks, you keep the panels together so the weld bead spans a more consistent gap. TIG or MIG, just take your time and you’ll be just fine.

(For TIG settings, I’d be running about 100Hz, 65% Balance, a 3/32 tungsten and tack with a 1/16 wire. Weld it out with 3/32 or 1/8. I’d have my machine set for up to 140 amps, but using a pedal, I’d likely be closer to 90 after I get my bead rolling along. It’s difficult to say because I can’t watch my machine and my work puddle at the same time).

cj737 , you have been a wealth of information ! Thank you !

[aeroplain]

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[aeroplain]

Dang! Sorry I got back so late. You're probably right if nervous about Tigging it. I figured you were done by the time I posted. You could go after it just the same since the wood is out because you can get to both sides. That will allow you to grind the outsides flat again and still have the thickness you need. Most hulls are pretty beefy and lend to tig welding well. Most companies use a 5000 series alloy. I weld with 4043. Do some bench testing to get your setting right and give it a go.






My guess is that you'll tend to weld too cold when you start on alum. It's not as hard as you might think, just different.
Stomp the pedal at 135 amps and push some rod in the shiny puddle and see how it looks.

[DLCeveryday]

nice , Im gonna try that .