Okay so the title is a bit misleading. Yes, I worked on the cowl, no, it wasn't holey but I just couldn't resist the play on words so... there.
When I looked into the cowl through the grill, I could see several curled up paint chips and some rust. I removed the vents from below the dash, crawled under there, shone a flash light up at the cowl, and inspected it very carefully. Up to that point I was worried that I'd have to do a complete cowl repair like a large percentage of people have to do when restoring these cars. My inspection purged that fear and I rejoiced in my uncommon luck. It's kind of like when the doctor diagnoses you with some fatal disease on a Friday and then calling you Monday to tell you that he made an error and that you only have mono. Well, the rust I saw in the cowl is the mono. Not bad enough to replace the cowl but bad enough that I had to find a way to service it.
I decided to cut access holes in the front of the cowl that I could get my arm into to clean it out. I marked the cut lines with blue masking tape in such a way that they followed existing bends and/or didn't disturb features like the windshield fluid ports.
I marked and cut the passenger side in this way:
And then chose a similar cutting path for the drivers side:
I'm going to show these next two pictures out of sequence because they were actually cut after I had completed some cleanup work in the cowl through the holes I had made above. I realized that although I could come close, I could never get all the way around the vent hats so I cut another, less intrusive hole in the passenger side to allow access to the back of the hat:
After working through the above small hole, I found it useful but time consuming to maneuver the brush or tools in the space. So on the driver side, I cut a somewhat larger hole. This one proved just right for outside access:
I stuck my digital camera in the front access port and took a picture from within the cowl. It definitely would not be a good idea to leave this unattended. The good news is that I think this cowl was replaced during this car's restoration in the 80s. There was paint, probably from through the grill, but also primer inside the cowl by the cowl hats. I don't know if Ford primered the cowls at the factory, I thought they were left bare metal:
An inside shot of the passenger hat. See the remnants of gray primer?:
Some mouse decided that the driver side hat would make a comfy little mouse home. I found my missing seat cushion batting:
Fast forward past all of the tedious labor of cleaning out the cowl. I used hand-held wire brushes and an air angle grinder with a wire brush and a 2" abrasive disc. I then cleaned the debris from inside the cowl and sprayed it down with Ospho worked in with a scotch brite pad:
After the Ospho dried, I went over it again with the scotch brite pad and then went to work with the ZeroRust. Now, spreading ZR in a cowl takes some special planning. For instance, I wore latex gloves and then duct taped my cover-all sleeves to the latex gloves so they wouldn't roll up and get ZR all over my arms. Also, I put a strip of duct tape across the knuckles of my latex gloves so avoid ripping them (or my knuckles) open on the underside of the cowl grill. Lastly, I cut the handles of my 2" wide paint brushes off to about 1" long. I reached in with my left arm through the passenger front hole and my right arm through the driver front hole doing a half cowl at a time.
After about an hour I had the middle area done:
Then I did the driver vent hat, first from the inside...
...and then from the outside:
Followed by the passenger side hat in the same way:
The next day, I scuffed it all down and painted on another coat.
24 hours later, I went in with seam sealer. First laying down a bead and then spreading it with an acid brush soaked in lacquer thinner:
And made sure to get the outside:
I did a similar treatment from under the dash. Wire brush, Ospho, and then ZeroRust. I kept the work close to the cowl vents though. I'll treat the rest of the dash when I get it apart for paint later. Driver side:
Same for the passenger side:
Before I could weld the cut-outs back into place, however, I had uncovered a bit of rust on the driver side and needed to repair it:
Like the other patches I had done in the past, I cut out the rusted metal:
And then fabricated replacement patches, welded them in, and ground them down:
I then welded the cut-outs back into place. This proved to be tricky since the cowls are galvanized. The metal definitely didn't weld easily and white zinc residue collected on the welds. I had to do this in a series of spot welds. It took quite a long time:
Same with the passenger side:
I then ground the welds down on the driver side:
And then the passenger side:
A note about this process if you're thinking of doing something similar: If you look at the pictures of the front access holes, you'll notice that I cut them about 3/16" down from the top of the cowl. I did this to minimize the damage to the top of the cowl. However, this is guaranteed to damage the paint on the top of the cowl since the heat can't be controlled from the other side of the weld. I tried keeping a wet rag on top of the cowl and that may have helped a little but I still managed to burn the paint and leave slight warps in the vicinity of the top weld joint that will have to be leveled with filler. Another caveat is that the weld beads are unprotected on the inside of the cowl and may be harbingers of rust in the distant future which wouldn't be a problem if you remove the entire cowl top.
Benefits to doing it this way, though, include not having to remove the windshield like you need to do to remove the entire top of the cowl and also leaving a majority of the sealer in place including the factory sealer between the top and bottom cowl panel joints which was allowed to remain except in the places where I cut my access ports.
So, the cowl is hereby protected for an unknown duration into the future. At least my feet will stay dry.