What glue do I use to replace my doors' weather plastic sheeting?
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It's called "butyl tape". It's a gummy, gooey, stretchy substance that, despite its name, is actually round in cross-section, not flat. This stuff is available from any glass shop. About $10 buys you 15 feet, which appears to be enough for all the doors in most Honda 4-door cars.
Normally, it's used on non-structural auto glass that's held in place by bolted trim. Things like pickup truck sliding rear windows, some Corvette glass from the '70s, that kind of thing. It never hardens or goes rubbery like silicone. These things mean it's ideal for what we want to do with it, and it's almost certainly what Honda originally used. It took me some sleuthing to end up at an auto glass shop, but when I described what I wanted to do to the glass place's proprietor, he knew instantly that I needed butyl tape.
A couple of limitations:
1) It's black. The original Honda stuff is usually white. I can't find white anywhere else. Is originality that important to you? I didn't think so.
And
2) It's 3/8" diameter. But that's not a real problem, since you can stretch as you go to (roughly) achieve the 3/16" that fits in the channels provided in the door frame.
You can still buy the proper white Honda stuff at the dealership. The part number is 08712-0003, and it's about $12. I don't know how much comes on the roll, but it's probably just one door's worth.
I understand newer Hondas use low-density polyethylene as their weather sheeting, but older cars used vinyl. Vinyl was probably used because it is softer and makes less noise, but it shrinks! Vinyl is made soft by the use of special oils called plasticizers. Those plasticizers have mass, and bulk out the plastic with their mass. But as the vinyl ages, the oils evaporate off, the vinyl loses mass and shrinks. When it shrinks, it pulls away from its adhesive. When it does that, you start getting water leaks, most noticeably on your door sill scuff plates.
I used poyethylene here for my fixup. It was just house vapor barrier plastic from Home Depot.
It starts out looking a lot like this...
...but we're going to make it look like this:
So what's butyl tape look like anyway?
In the package...
...sticks like snot...
...and it's stretchy!
The hardest part is scraping the old adhesive out of the channels in the door frame so as to prepare it for the new. For me, after 15 years, some of it was pretty firm. Not hard, mind you, but firm. A heat gun, the corner of an old credit card, and some auto body cleaner did the trick, along with some time and scrubbing. You could just use a screwdriver, but I'd be worried about scratching what little primer and paint there is. A shaped piece of wood is probably better if you need more oomph.
Before I did that, though, I got some house vapor barrier plastic from Home Depot, which is just thick polyethylene. I cut a piece bigger than the final size, taped in place over the old vinyl, and used a marker to trace (as close as I could) the size and shape of the original vinyl sheeting (watch for the door trim panel clip holes!). I made a few reference marks so I could lay the new sheet back down in the same place that I traced it, then untaped it and cut it out with a utility knife. You'll also need to cut holes for such trifles as the window crank shafts. Make sure your knife has a fresh blade!!! It is MUCH easier to shape the plastic with a new, keen edge, rather than the one you've been using for the last three years.
I then removed the vinyl and as much of the old butyl as I could. Once you've done that, it's really obvious where to stick the new stuff. As I went around the channel with the new butyl, I stretched and stuck, stretched and stuck, until the entire channel was lined with butyl tape, most of it the correct diameter. Remember to default to too little stretch, rather than too much. You can always squish it flat if the tape is too big, but you'll have trouble getting the plastic to stick if there's not enough tape.
However, if you don't stretch quite enough, your 15ft roll may not suffice to cover all 4 doors (if you are blessed with that many doors), and you'll need to rob your piggy bank for another $10.
With the new butyl in place, you can lay your new plastic in place, and press it firmly and evenly into the butyl with your fingers. Job done! Button it all up and say goodbye to water leaks in your doors.
