Obvious cracking, peeling and chipping is the number one problem with old seam sealer. As I mentioned before over time the seam sealer becomes brittle and starts to crack. This is usually very clear and easy to see in the drip rails above the side windows. The bead that is applied in this area likes to come off in chucks, leaving large section that is obviously missing material. If this is happening there is a good chance you will have at least some surface rust underneath.
Finding places of misuse is another reason to remove all of the old seam sealer. It is common to find seam sealer in rust holes is a low quality paint job or restoration. Seam sealer is a great way to prevent rust from seeping into and through seam on the bottom of a deck lid or door, but it is not a form of rust repair as seen in the below picture filling the rust holes on the Camaro deck lid. When the seam sealer is used correctly you should see signs of the lip or metal edge and not a heavy build up hiding these details.
In some cases the seam sealer may actually be intact and look as though it is in good shape, but it could be hiding rust. In the picture below of the Mustang, the black seam sealer was fairly intact until we took chisel to it. When we did this it all fell off revealing the rust underneath. If this were to have been just sanded and painted, we would have just sealed in all of that rust.
You will find seam sealer everywhere on your car. On almost every welded body seam, on floors, quarter panels, deck lids, and doors the old seam sealer needs to be removed and reapplied to prevent rust and leaks. Just as with any other repair, replacing old seam sealer with new ensures a long lasting restoration.
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