With the doors dismantled I could see the state of my door innards with regard to rust. There was some surface rust but nothing that had yet started to damage the door skins. The bottom of the door skins are one of three main rust vulnerabilities on early 308s (the other two being the panel behind the front wheels and the panel behind the rear wheel). The problem with the doors is that water enters past the window glass and runs down inside the door and cannot always find its way out.
There are two drain holes at the bottom of the doors but they are covered by the weatherstripping on the outside so water cannot drain away easily. Furthermore, the drains are not necessarily at the lowest point of the door so water can pool without ever reaching the drain holes which is what had happened in my case.
Ferraris had no significant rust proofing until a basic process was introduced towards the end of 1983. Nowadays, significant rust protection can be achieved using a product called POR-15. POR-15 is an anhydrous urethane paint that cures on exposure to moisture. It is extremely effective at encapsulating the rust forming a glassy, hard finish over the metal/rust that is chemically impermeable to water and oxygen… the necessary ingredients for rust to develop.
POR-15 requires a systematic preparation procedure. If it’s not followed I have found the final results can be variable. However, if the instructions are followed to the letter, the results are remarkable. There are two downsides. The first is POR-15 degrades in UV light. So anything painted that is exposed to sunlight needs to be further protected with a UV-blocking top coat. Not an issue for the inside of my doors. Secondly, the stuff is really not nice to use. It is highly volatile producing solvent-heavy fumes. It cannot be thinned when wet or removed once dry so gloves and neat working are a must. Finally, once the tin is opened it starts to cure even if after the tin is closed. Once curing has started and the tin closed you will never get it open again once the paint has gone completely off. For this reason I only buy small tins that will be consumed within a day or two of opening.
Step one is degreasing for which they provide a product called Marine Clean. This is an OK, but not a great, degreaser. Step two is to prepare the area with a product called Metal Prep which seems to contain both an etching primer (to prepare the good metal) and phosphoric acid (to convert the rust). The final step is to paint on the the POR-15. It has good leveling properties so even when brushed on, it leaves a smooth, glossy permanent barrier to rust. Hopefully, enough to keep my doors rust free for a few more years.
Disclaimer: This website describes the restoration work I perform on my car and only my car. I am not a professional mechanic. The website content is presented for entertainment purposes only and should not by seen as any kind of advice, information, instruction or guidance for working on any other car. The opinions stated here are my own and no-one else’s.
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