I plan on buying rust convertor for the underbody of my 84Z28....im gonna wire brush the big stuff off then apply the rust convertor. What steps do i need to do for this stuff, any idea how much ill need for the whole underneath of my car, any spots i should not do? can i do the control arm, axle tubes ect ect? Thanks

 

Id say try and use a sypon snadblaster and get the under side as good as you can. Get it striped down to the metal and coat the complete thing with por15. Id say 1qrt. will do. I did a engine bay shooting it out of a gun thined 5% and have 1/2 quart left.

and I did 2 coats. You can do the rear end, lca's etc..

 

syphon sandblaster? how much are those?

 

Be careful with a sandblaster, and a wire brush for that matter.
How bad is the underside, is it just surface rust of rust rust, bc if it's deep rust then a sandblaster will make a hole out of it and a wire brush is dangerous too if you apply too much pressure. Go over it with a wire brush and get all the loose rust off, if you happen to develop small holes get some POR 15 Patch and fill the holes in. I'd recommend the POR15 system if your car sees the elements. That stuff does not chip and is ceramic based so it provides a good seal from moisture. The rust converter that is made by someone like Permatex is great but I prefer it for just real light rust, and then I topcoat it with something.
In any process you will need to degrease the metal real good and with PO15 they provide a solvent to etch the metal to make sure that the POR15 adheres real good. POR15 also has a good staff of tech advisors, they can help you out.