[MARTINSR]

Originally Posted by MP&C

The Weld Through primer is not really true to it's name, it will contaminate the weld. If cleaned back as Eric and I suggested, the heat from the spot weld will still liquefy the WTP surrounding the bare metal within the plug weld hole, and much like soldering copper pipes, wick toward the heat to surround the weld. Most people will use the WTP to cover the entire flange, which as you've read, is not the intent. It is not as good at rust prevention as the epoxy.

Perhaps Brian can add to this, and my comments are not meant as a slight to anyone in the collision industry, but many of the products/processes recommended by I-CAR for repairs such as these also revolve around useability within a narrow window of time. You can't expect a repair to be completed within three day window if you're waiting on Epoxy primer to fully cure for seven days. If I-CAR can develop a process/use a product that still fits within their prescribed time frame for a particular repair, then the body shops are more likely to not skip a step due to what may be perceived as wasting valuable time. Having said product in a convenient spray can also makes it more likely the technician will adhere to the process and not skip a step. If Epoxy primer were used and someone needed to adhere to a seven day full cure window prior to plug welding (if that's what the process directed) then you would likely see a body shop or two that skipped that step in the interest of getting the job done in a more timely fashion.

So in a similar thought that OEM spot welds aren't the best welding methods for panel attachment (these create voids for moisture and rust traps, but get the car through the assembly line much faster), I'm suggesting that the I-CAR method of using weld through primers may not be the best method for long term rust protection, but given the parameters listed above, it's the best compromise for them to insure a given standard is followed.





Why use a spray can, get some epoxy primer in quart/gallon cans and mix up what you need for what you are working on, for minimal waste. There's nothing that says you can't use brush or other similar application methods, especially those areas that will be hidden that you mention. (note the brush strokes in the green epoxy primer above) Even for exposed areas, are you not going to block out the primed surface? Be sure you still follow flash times, etc as if you were spraying. But IMO you are still using the better product even if the application method seems rudimentary. Especially for the home project, you are less concerned with the time constraint and now you would get the job done with one product throughout, eliminating the need for multiple primers.

Robert, first off MAGNIFICENT work there, just beautiful! I think you are right on the mark with the collision industry and weld through thoughts, yep, right on the money. I do believe the weld through is one tiny step up from nothing, but it's that one tiny step, better than nothing. I do typically remove the weld through primer similar to how you do, I also have a spot blaster that works awesome for that. But yeah, I think I need to move up to epoxy for my truck.

Brian