Side rail rebuilding

[june2009]

Ed Dzwilll and I are rebuilding our separate 1972 MGBs. He in north Jersey and me in south Jersey.   We both have the same issues with rust that is common to MGBs. Ed has an unique proposal below.  Have you ever heard of anyone trying this ?  What is your opinion?
 
Question: When rebuilding the side rails on the MGB, painting the sheet metal before assembly with POR-15 or similar paint is a given. Has anyone foamed urethane in these areas after assembly to preclude future penetration of water? The urethane would also act as a sound deadener.
 
Thank you
John Roberts

[Art]

Using POR-15 and other stronger rust preventatives on the sill components, floor pans and inner fenders before and after assembly is a very good idea.  The only problem is with the components you would coat before you weld them together.  Like any paint or coating, you run the risk of damaging or burning the paint off some areas with the heat, leaving them vulnerable to moisture intrusion and rust.  Mainly this would be the sills and rear quarter, where you cannot get back inside to touch them up.  One person had said they had gone so far as to "fill" the sills (and drain them, of course) as you would wax oil to coat the sections after they were completely welded together, much like a Ziebart or other rust proving treatment to address this.  The front wings and even the floor pans can be repaired after installation as necessary, as the areas are mostly accessible.  It has to be better than the usual approach, especially when combined with traditional maintenance procedures.

Urethane foam has it's own issues.  I have worked with it in commercial buidings and even clothing (foam bra and shoulder pads).  For one thing, it is not really waterproof.  And it is flammable, burning like a liquid if ignited and "gases off" toxic fumes while setting.  It floats because it is low density, which is why it is used in boat floataion devices and hulls, but is porous and not the best moisture sealant.  Other than the expensive marine application foam (which lasts somewhat longer, but is still usually sealed in fiberglass pontoons to extend its life further), most will deteiorate with continued exposure to air and moisture, even trapping moisture against the steel.  It is also not as fluid as oil- or water-based sealants, so impossible to ensure it will fill all the cavities in the sills and other areas you might use it.  And it cannot be removed without cutting the sill assembly apart. In short, it could potentially do more damage than good and I would reccomend avoiding it.

John may have other thoughts, experiences and suggestions that I would like to hear as well, but I hope what I've said helps you.  Good luck.

Art