Hi,
I'm about to start preparing the underside of my body. I'm currently undertaking a full restoration and the entire shell is in etch primer. I wasn't sure whether to use bituminous body deadener, but have hesitations due to the lengthy drying times prior to putting body colour down. The other option was that I do it in stone guard, but I was concerned that this option wouldn't give me the protection that I was looking for. When I asked the paint shop which to use they didn't fill me with confidence either. They told me that if I go for the body deadener (Septone), I need not worry about painting the underside with the body colour, as there were issues with colour going over it.
I'm seeking advice from those of you who have been there and done it before me. Which path shoud I take?

Regards,
James.

Stone guard is good.
I painted Stone guard and then 2K under my Cooper S over 15years ago and it still looks great. Did the same for my most recent project and it also turned out great.
I spent weeks removing the old body deadened so I wasn't about to put it back again.
For the seams I used an acrylic seam sealer, Sikaflex, which is paintable

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1969 Cooper "S"
1967 Mini Deluxe
1973 Clubman Van (the fleet spare)
1978 ex 1275 LS ("Wizard" Eaton Supercharged)
2015 HSV GenF GTS(occasional drive & tow car)
2019 MINI F55 Cooper S

Anything bituminous will seep through a top coat and not look right, I believe 68rusty had this problem in his build thread.

I haven't heard of any issues with stone guard especially if you are going with a quality brand. I haven't had the mini on the road but the bits I have covered in stone guard have stood up well to belts with a hammer and jaws of the vice so I'm confident of its road holding conditions.

Just another option. I used U-POL Raptor ute-bed liner, tinted to the colour of the car. Been on for 12 months with no problems. Cost was $260 plus whatever your painter charges you for the tint, and it's easy to put on yourself with a shultz gun. That way your painter only has to paint the top half of the car saving you money

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Dalmeny

Stoneguard should be the easiest for the job. I prefer to use the water based ones over the solvent based ones. They smell less, dry faster, clean up easier, and last just as long. They are perfect to paint over. I did it on hundreds of cars back when I was Spraypaing.
If you don't paint over it , it will not be as durable. Ie. Petrol spill would soften it or even wash it off. The paint shop you talked to just sound lazy and obviously don't care about the quality of your resto.
Septone one is pretty good, and not too pricy.

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Tim
Dusk Blue
1964 850