Underseal recommendations

[hunker7]

I'm in process of giving my UrS4 some long overdue TLC. Plan is to wire brush the wheel arches, then follow up with Bilt Hamber Hydrate, Primer, Bilt Hamber Chassis Epoxy and this is where I'm undecided. What underseal would people recommend? Something satin/matt preferably.

POR 15 underseal seems to be the go to from the older posts I've seen, is that still the case?

[tango123]

Tractor Dave He’s your man for this kind of stuff.

[Tractor Dave]

Under the arch liner, bilts underseal is good but brown. Rustbusters is self healing and black, also very good.

[hunker7]

Under the arch liner, bilts underseal is good but brown. Rustbusters is self healing and black, also very good.

Might be stupid question but is Rustbusters same as Dinitrol?

[Tractor Dave]

No, but Rustbusters sell dinitrol as well. I hear that's good but haven't tried it.

[Tractor Dave]

https://www.rust.co.uk/product/1ltr-techshield-underbody-wax-black/

[hunker7]

https://www.rust.co.uk/product/1ltr-...ody-wax-black/

That looks spot on. Can it be used on suspension components (driveshafts, subframe etc?) or best using chassis paint for that application?

[B5NUT]

I would not touch Por-15 these days. Not the stuff it used to be.

Depends on the look your going for under the arches. I like factory colour of the car so use I 2 coats of epoxy followed by 2-3 coats of base then 3 coats of 2K clear. For the underside I like to use epoxy & 3M Schultz. Down side to the above is there is a lot of masking involved and you really need a compressor. Also if your removing the factory seam sealer then it best to reapply with a brushable version.

[hunker7]

I would not touch Por-15 these days. Not the stuff it used to be.

Depends on the look your going for under the arches. I like factory colour of the car so use I 2 coats of epoxy followed by 2-3 coats of base then 3 coats of 2K clear. For the underside I like to use epoxy & 3M Schultz. Down side to the above is there is a lot of masking involved and you really need a compressor. Also if your removing the factory seam sealer then it best to reapply with a brushable version.

I am happy with satin black finish. Mine is by no means as bad as S6 Tractor Dave was working on, and years ago I cleaned it up and covered in Hammerite underseal.

This time round car isn't a daily so have more time to spend, I'm not sure if I should take all the original underseal off on blue part as it all seems solid but also don't want to be returning to wheel arches again.

Seam sealer goes over welds correct?

[B5NUT]

You only need to remove factory underseal if the rust is creeping behind it, if it all looks solid then leave it. If you have sprayed Schultz type underseal before then that will need to be removed as nothing will stick to it other than more Schultz based underseal. If you want to remove the Hammerite underseal then your going to need cheap thinners to get it all off.

[hunker7]

You only need to remove factory underseal if the rust is creeping behind it, if it all looks solid then leave it. If you have sprayed Schultz type underseal before then that will need to be removed as nothing will stick to it other than more Schultz based underseal. If you want to remove the Hammerite underseal then your going to need cheap thinners to get it all off.

I'll leave that alone then, it all seems very solid. Wouldn't think the car was sat on a grass verge for 2 years before I bought it.

Plan is to clean it back to nearly bare metal in the red part I circled, then follow procces in first post. First time round I didn't do any of that.

[B5NUT]

Personally if the factory paint is solid, just leave it. You will get a better Idea once the arches are cleaned up. Just remove all the rust spots then put some sort of primer on first (an epoxy based primers would be the best option) then apply the underseal.

[steve briance]

I really rate dinitrol products and have used them a lot in the last few years.

If you decide not to reproduce the painted finish, i think you will struggle to find a better product than 4941. Covers well, flexible, self heals and for me - most importantly it dries to a non sticky finish so it won't get road dirt stuck in it. Can't paint over it though so, if you go that route, check out 447. It's paintable and gives a finish that is similar to the factory stuff.

[hunker7]

Turns out there was some, luckily, surface rust under drivers side wheel arch. I wire brushed it all and treated with Hydrate 80. I will use seam seal on the parts that have been welded. Do I need epoxy mastic or can I go straight in with dinitrol 4941?

[Tractor Dave]

If you have cleaned off back to bare metal you need to 're paint before using underseal.