Sounds good to me. 3m does state in the instructions to cover both surfaces completely but for these purposes it would be a good test of less than ideal situation and also allow you to split it open again. Can't remember what grit it wants the surfaces to be keyed to though would be worth a GoogleI received some 3M panel bond in the post today, generously donated by @onthames . Does anyone have any thoughts on what might make a good test for it?
My first thought is that it can't be tested in the same way as the other samples I made up as I will probably struggle to separate it neatly. So I'm thinking perhaps something like this:
1. Spread a wide ring of it on a piece of mild steel
2. Sandwich the ring with another piece of steel, tightly fitting the two together
3. Spot weld the centre of the ring
4. Immerse in salt water like the others
5. Cut open after a week or two to see if the ring was breached, and salt water got past it
My rationale would be you'd have an unglued inner part to the ring that you might be able to prise open and look into
I think it would potentially make it easier to inspect the quality of the weld, my previous method effectively destroyed the spot weld which is not ideal. For inspecting corrosion protection, I'm not sure. I would want to see the steel that had been covered by the panel bond, but even panel bond cut in half would still be masking the steel underneath (which may be rusty, may not).
I did some reading today on testing porosity of coatings on steel and there seem to be a lot of standard tests (mainly adding specific acids), though the only ones I could find were for when the coating consisted of another metal. It would be neat to be able to test coating porosity without immersing it in salty water and waiting for rust.
I guess that must be the UPOL ones, incredible price to pay for a spray can of paint isn't it.I looked at weld through primer spray in Halford yesterday, £25 a rattle can.