Undersealing recomendations

What would be the consensus on a single product to treat the rust and coat it, or a product to deal with the rust first and then another product to protect afterwards?
 
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the biggest issue is that the bitumen type stuff doesn't really work as well as people think, they tend to peel away with stone chips and hold water in.

schutz and waxoil used to be the go to, but there are now products from other manufactures like bilt hamber


frost restoration also have a number of products that work really well, but again they all need to be applied pretty much from new to be of significant use.

stone chip protector is significantly less flexible than the traditional bitumen type underseal.

when we restored our mini we done the sills and wheel wells in stone chip, then done the chassis in schutz. the schutz didnt work out to well, it seemed to not adhere so we peeled it all off and used the bilt hamber https://bilthamber.com/product/dynax-ub/ , this will do both stopping further rust and stop any new rust, saves having to purchase more than 1 product. it wont convert rust however
 
Does anybody do that nowdays? in the old days you would coat the underneath with old engine oil! I haven’t seen a blowing exhaust for years now - when I first started driving you would cut up a coke can and use a couple of jubilee clips. Failing that you'd use gun gun or an exhaust bandage.

OP. What car/age are you talking about?
Much of that improvement in exhaust life has come from the removal of sulphur from the fuels. Doesn't form as much sulphuric acid to corrode the exhaust. I too, can remember when 3 years was a good innings for an exhaust!
 
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What would be the consensus on a single product to treat the rust and coat it, or a product to deal with the rust first and then another product to protect afterwards?
With a car that already has surface rust, my thought is that is exactly how to deal with it. I like XCP, the original one not the clearcoat. It soaks in well to old rust but leaves much less residue than some of the more waxy rust proofers. I tend to buy a top up every month or so too and spray the suspension components, wheel arch lips etc. I use a tube up through the door and sill drain holes too but I do that about once a year or so
 
Quite a lot of info on this site:


As Burnerman says, it's incredibly important to wash the underside first, and leave to dry fully. Any road salt, oil, grease, even some oily underseals, will stop any of the preventative products sticking properly. A god degreaser is absolutely essential. I prefer detergents to solvents, because the latter seem to dissolve it and spread it over a larger area.

If there is already any surface rust at all, it's worth using a converter. There are loads around and they all work on much the same principle. The FE-123 on that site is as good as any. However, it can't get inside bubbles and under flakes, so you really need to wire brush the surface carefully first.

After that, I quite like the epoxy mastic products, like EM121. It's messy, you have to mix the two parts and it goes on very thick, but it sticks very well and isn't as permeable as many other coatings so water can't get through it as easily.

After that, just spray whatever black, "stuff" you fancy under the car to make it all look uniform. None of them (on its own) has ever worked terribly well for me, the rust just carries on underneath.

For the insides of box sections, I'm a fan of Dinitrol ML. You can buy extension nozzles for the cans. Just feed the tube down a convenient hole in the chassis member, press the aerosol button on the can, and pull the tube out whilst holding the button down. It will make a mess of your drive, though, because the excess drips out everywhere for several hours!
 
Much of that improvement in exhaust life has come from the removal of sulphur from the fuels. Doesn't form as much sulphuric acid to corrode the exhaust. I too, can remember when 3 years was a good innings for an exhaust!

The longer life from exhausts, coincided with my switching to diesels, so I always assumed it was diesel being more oily, which made them last longer. Thanks for that.
 
I think most problems come from spraying it over rust expecting it to stop bit in most cases in does not.
Certain products are much better than others.
I'd probably use this first but it's not cheap.

Lashings of oil on rust, will stop rust instantly. The problem is preventing that oil from being subsequently washed off. My car has about 5" of exposed brake pipe at the front, inside the wheel arches. I soaked the exposed pipes with oil during dry weather, wiped the oil off, greased them with heavy grease, then slipped some of that split corrugated plastic conduit over the top, held in place with tiewraps.
 
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