I'm not sure if anyone's experienced problems with this?

I recently had reason to grind off some areas of POR-15 to allow me to install my new MII lower suspension arms,there's a support tube and gusset required on the front crossmember.

Despite good clean back with hard and soft grinding discs I just can't get good weld penetration.
By comparison the supplied (untreated)upper shock mounts had great penetration but where they butted onto the chassis the weld looked like chickensh*t....

Does the POR affect the metal this much?
Any advice/suggestions welcome.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.