Just out of interest, whenever I have seen (or had done myself) a finished welding job on a car, it is invariably covered with some "black stuff". Is it just a smooth underseal or something special they use ? .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

Waxoyl/Schutz/Stone chip. Helps to protect the bare metal after welding etc

If you are wanting to prtect new bare metal, I'd personally spray it with Hammerite paint first and then the Shutz/Waxoyl stuff, or in a high impact zone, stonechip too. Discovery 4 HSE
1998 110 TUM HS FFR Hard Top XD WOLF
1982 Series 3 Hard Top

*Gone:L462 D5 HSE LUX, L663 Defender 110 HSE, Discovery 3 HSE, 2014MY Range Rover Sport 5.0 Supercharged AB Dynamic; L405 Exec Vogue SE 4.4, 5.0 Supercharged Autobiography, Defender TDCi XS CSW, Defender TD5 HT, Vogue SE TDV8, Vogue TD6, RRSport SC 4.2V8, Classic 3.9 Vogue Auto, Land Rover Series 3 SWB

I use Mio-Guard. It is a dark grey coloured paint (Micaceous Iron Oxide) it prevents any rust forming on new steel and is the same stuff they use on North Sea oil rigs, bridges etc. Not too easy to get hold of, but really does the job well. Mike
Gone:-
2004 V8 Autobiography
1998 2.5 DSE
1993 200Tdi Classic

All good answers, many thanks, and apart from the Mio-Guard, stuff I have in the garage, somewhere....  .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999