The undercoating will most likely burn off. The problem is where the remnants go. Likely some of it ends up in the welds and a long the weld boundaries, and that's how you get weld defects. Letting the undercoat burn off in the welds is lazy and can bite you later if those welds crack because of it. Metallurgically speaking, it's a bad idea.
Welding is like painting: how well you clean and prep the part will show in the final product. I used to work with a guy who mostly ran his mouth to make up for poor skillsets/knowledge. Refused to clean and prep anything he welded (no beveling, burn through paint, rust, grease, scale, ect), then blamed "junk" equipment for the poor results. Just about everything he made failed for one reason or another.
QUOTE="05snopro440, post: 15562314, member: 144657"]To be fair, he didn't say how much he was paying them.[/QUOTE] Paying by the hour. Over $100/hr.
Check this Guzzi Fabrication video out at the 10 minute mark. Guzzi has lots of good information in his videos/ Here is one source for the spot blaster. https://www.aircraft-tool.com/Detail?id=ATS201
Over $100/hr for them to tell you stuff like this is fine? Yeah... Not cool. I'd have a hard time trusting their work.
Grind it, desolve it with lacquer thinner, scrape it then hand sand. Try and see what works best for you. Kinda simple really. Have you ever tried removing paint before?
Flap disk, grinding disc, sometimes you can just scrape and peel, depending on how long it's been on there. Just use an old flap disc or grinding disc because that stuff can sure gum up and ruin a new one. Although I've never heard of it being discussed, I can see it causing a grinding disc to explode like gumming one up with aluminum? That is purely speculation on my part. Probably overkill but better safe than sorry.
Just because a shop charges you for their services does not make them professionals. There are people with jobs, people with careers and finally, people that are professionals. The workers the OP is referring to I would land firmly in the first category and the very reason the majority of us do our own work. If you don't know how to weld and clean metal and you don't have the time or facility to learn you end up at the mercies of these folks. You have an advantage in that you have the HAMB and some excellent advice on how to proceed by members that have done this before. Heed their warnings and listen to their instructions. They are not being paid, they are offering assistance with nothing to gain.
Think of it this way: if the surface isn’t clean enough for you to feel comfortable laying your sandwich on it between bites, it might be too dirty to weld.
Most people I think just care if the paint is shiny. I need to work with the shop and try to fix these problems. I'm not sure how to best approach the shop. I'm at the mercy of the shop. Things I've asked to have done were not done and it is too late to fix. I'm not expecting a high end restoration. I realize that some short cuts will need to be made. At the end if the weld is strong and corrosion resistant that is what matters.
Short cuts should only be made if that’s what you are paying for. You should get what the contract specifies.
If they are doing a piss poor job, get that car out of there! I have no idea about your car or situation but if you are already questioning what and how they are or aren't doing a good job, you are only at their mercy if you leave the car there. Just my opinion, as I stated I know nothing other than you saying you are at the mercy of a shop that already hasn't done what you asked of them. I will go back to being "it's none of my business" now....
You are asking an awful lot of questions here on multiple threads. If you are not happy with the shop pull your car out and take it else where. I can guarantee one thing if you start questioning everything they are doing, which it seems like you might doing be based on all your threads, the work will only get worse as they tire of you questioning everything they do. If they are doing shoddy work you going in and saying a bunch of people on the internet told you they are not doing things right is NOT going to improve the situation.
I agree, pull the car out of the shop, take it home, do some research both on repairs performed and other shops in the area. Once you do all of that then start looking at other cars the shop you researched fixed to see if your happy with that work along with the customers thoughts on that work then talk to the shop, tell them what you want, what you expect and then let them start on your car OR start researching another shop until you find one that does repairs to your satisfaction... Your money... your choice.... ....
And that is the point of my response. Being at the mercy of the shop is a tough position for you. High end restoration is not the point, quality repair is. It is your money, it is your car, make the best decisions you can.
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