Butyl rubber is a synthetic rubber, a copolymer of isobutylene with isoprene. The abbreviation IIR stands for Isobutylene Isoprene Rubber. Polyisobutylene, also known as “PIB” or polyisobutene,n, is the homopolymer of isobutylene, or 2-methyl-1-propene, on which butyl rubber is based. Butyl rubber is produced by polymerization of about 98% of isobutylene with about 2% of isoprene. Structurally, polyisobutylene resembles polypropylene, having two methyl groups substituted on every other carbon atom. Polyisobutylene is a colorless to light yellow viscoelastic material. It is generally odorless and tasteless, though it may exhibit a slight characteristic odor.
FROM A FORUM POST BY crackodawn
Make life easy. If you don’t want to go through the hassle and expense of dealing with windshield replacement for whatever reason (I am not advocating ignoring the root cause fix) and you just want to stop the water leak, here is a 100% solution.
Get some butyl rubber. Anyone not having this handy is missing out on what is probably the best emergency and long term sealant ever invented. It puts any silicon to shame.
There are many forms, some in a caulk type tube but most commonly you can find it in rope form at many auto parts stores. Marine supply stores have it too because it can be used under water to seal holes and leaks and needs absolutely no cure time.
Butyl rubber is non-permanent but can provide a permanent fix. I mean that you can remove it but you can also leave it in place for tens of years and it will not degrade. Pontiac used to use this material to seal windshields and even after 30 years the material remains pliable and can be reused as good as new.
Back to the fix. You get the rope form, try the thin rope style as opposed to the thick. If you get the thicker rope you are going to pull and twist it until thinner, about an 1/8″ thick.
Butyl rubber will stick to nearly anything but oil. Before using it to do anything cut off a small piece and just play with it. Get used to its properties so you don’t make a disaster of what should be something simple.
For your windshield: (you can do this in the rain if need be) It will be almost invisible to anyone looking at your coach.
Clean you windshield gasket with a mixture of water/alcohol 50-50. Wipe it dry. Also make sure that the immediate area of glass is clean (same cleaner) and also the coach frame/paint/whatever. Just get the dirt off. This should take about 5 minutes tops.
Put lengths of butyl rubber along the windshield gasket (the one outside that you can see and touch) on both the topside and underside with the underside being the side which touches your windshield.
What you have now are two ropes of butyl rubber traveling along the windshield gasket.
Now press the butyl rubber down a little and make sure that there is no gap between the butyl rubber and the windshield gasket. You do not need to make the butyl rubber flat, just enough to stick and seal any gap between the windshield gasket and the butyl rubber.
The above should take about 3-5 minutes to complete for half the height of the windshield side and about 1/4 the distance across the top.
You are done unless you want to go onto the next step.
Water WILL NOT leak past this seal no matter how hard it rains. You can fire a high pressure water hose at your windshield and it will not leak. You can throw buckets of water on it and it will not leak. This seal will not harden, it will not fall off, it will not crack.
5 years from when you put it on, it will still be there as good as when you put it on.
Next step but completely optional and only for the topside seal, not the side touching the windshield:
Butyl rubber is black. If you didn’t use a 1″ diameter rope of the stuff you can probably forego this step. But if you want to completely hide the seal, you can go to a fabric store and find some very thin fabric close to the color of your paint. Cut a thin strip just enough to cover the butyl rubber. Place it on top and press slightly. It will stay there and hide the thin black rope of butyl rubber.
In most cases, no one will be able to tell you have this fix in place so that last beauty step isn’t necessary.
Like I said, you can use this in the rain. It can be pouring rain and this will do its job as good as if it was sunny outside. In most cases it is unaffected by the temps you will encounter in an RV. Hot or cold it doesn’t matter.
There is no cure time. When you are done, you are done.
There are 100s of uses for butyl rubber. You can use it as a temporary tack in place for just about anything. It can hold things of high weight too, just put a blob onto something, hold it against something else and it stays there but you can remove it at any time.
Want to put a mirror on something. Use butyl rubber. It will stay there unaffected by vibration or flex yet can be removed when needed.
Butyl rubber will mark some porous fabrics. It will stick to your hands. Wearing plastic gloves will insure you mess things up.
If you get it in your hair, have scissors handy.
For a leaking roof, nothing can compare to butyl rubber. All those miracle emergency repair products are a joke compared to what butyl rubber can do. Here is a super fast fix that works in the dead of night when it is pouring outside:
Length of butyl rubber rope. Plastic sheeting. Cut a piece of the plastic sheeting. A ziplock bag or plastic trash bag also works. Just cut it to the size patch you need. Outline the patch with the butyl rubber rope. On the roof, wipe the area with a sponge. Do it quick and easy, nothing fancy. The roof area does not need to be dry-obviously.
Press the patch down and press over the rope all the way around. Leak fixed. A hurricane will not pull the patch off yet you can remove it easily when you want. Just pull it up slowly.
What else can this fix? A hole in a plastic water pipe. Knead some of the butyl rubber into a patch and stick it on. Unless it is 100psi, it will hold. Fix the pipe permanently when you can. Works on metal pipes too.
Loose body parts like wheel well covers, trim etc. Use it instead of some silicone or other glue. It is instant. You stop, put the trim back in place and drive on. No need to every remove it and glue it. 20 years from now it will still be in place.
Hope this helps someone.