Why do we need seam sealer in our cars?

Seam sealer is best applied after a good epoxy primer is put over the seam. The intent is to SEAL the gap and try to prevent any moisture from wicking inbetween the two layers of metal.

Spot welds leave spaces in between and all around them water can wick into.

Any weld has gaps that water can get into and start the rust process right away.
Paint never survives welding...so the best way to deal with it is to cover all the seams with a waterproof sealer to keep moisture out.

Its not just our cars, but any car that needs seam sealer.

Rich

failure to properly seam seal is a sure way to get seam rust, seam rsut can at times be incurable. if your painting your car, you NEED to make sure it is seam sealed, no gaps, think of your car as a submarine, no leaks in the seams allowed!

Both my cars seem to have alot of rust under the seam sealer.

old seam sealer can fail, or be inproperly applied. seam sealer some times cant cope with standing water for long periods of time, one flaw in teh sealer can allow water to get in behind the whole bead,a dn rust from behind. that is why application and material choice is so important. I concur that a good epoxy pint is needed before seam sealing.

unfortunatly the nanny state no it alls at CARB have outlawed the epoxy paint of choice in many areas of the peoples republic of california

remember bondo (filler) is NOT a seam sealer. you usually want a flexable seam sealer one that wont crack.

Ray - remember that our 914s & most older cars of the era were not treated with rust preventative, galvanized, etc., & so are rust prone. Also, it could have been a damp or humid day, or moisture otherwise introduced to the sheet metal surface prior to seam sealing.

IIRC it was Sir Andy who posted once that the Karmann plant could've been damp/humid & had moisture under the paint on my 914, causing the rust from under the paint but on top of the metal.

I saw on the Wurth website (sold by their USA suppliers) that they make/sell the seam sealer in large sizes to sealer gun cartridge & squeeze tubes, both paintable & paste consistency.

I realize these cars started rusting from day 1. Most cars made 30+ years ago are not on the road unless they have been restored. I'm just wondering if its worth putting the seam sealer back on a car that is going to continue to rust from the inside out.

I know/saw many East coast 914's that were rusted through by the mid 80's.

well lets assume you rinse all the salt out of the rusty seams,with HOT water,Dry, then with somereally thin epoxy paint,you get the seam painted,thin paint can can pennitrate the seam best,then use sealer. This can arrest the rust a good deal, the new seam sealer willhelp keep out more water. fail to seam seal will mean repair wont last as long.

Of course more extensive rust will return if the old rust gets wet again.

the best repair may not be economical, that would be to split the seams and treat/replace the metal

How about seam welding instead?

the process I seam to like (no pun) is to seal the car with an epoxy primer, then apply seam sealer....then primer/paint from there.

Rich

That seams to me to be the process I like too.