What's the Best Rust Removal Method for Inside Floor?

[BeachKing]

Ghia was stored for 30 years. As you can see, the rear floor is rusted through, but the front seems to be relatively solid, only heavy surface rust. I'm very new at restoring rusted metal, so I'm not sure of the best way to proceed with this. I watched a few videos on how to replace the rear metal. But I was wondering what the best way to remove the front rust. I see many rust removers, but not sure which is the best product and method.

[viiking]

For heavy rust the best method is to use a knotted wire brush on a grinder to remove as much loose rust as possible followed by vacuum cleaner. Getting stuff out of looks and crannies is always a challenge, but get as much out as possible.

Why? Any chemical method to remove rust will not discriminate between loose and strongly bonded rust, so the more you remove mechanically the better your result and less chemical you use.

ANY acid will remove rust. That is, it REDUCES (in chemical terms) the oxidised steel (rust). The problem is of the speed, corrosiveness, danger of use and the by-products of the reaction of the acid. You could use pool acid (HCl), citric acid (food acid), oxalic acid (timber bleaching), vinegar (acetic acid) or phosphoric acid (Ospho, most rust converters) to mention most of the common ones. For small parts that are rusty, I make up a batch of 10% citric acid in a bucket and immerse the part for a few days. I like it because it is relatively benign and I can safely put my hands in the solution without burning. (But each to their own). However for pans this is not practical.

The benefit of using phosphoric acid is that the reaction product between it and rusty steel produces a phosphate which is a very stable base for subsequent painting.

Most of the rust converters use phosphoric acid and another polymer which might re-seal the surface from continuing rust. However you should always paint the part immediately after rust converting. Any paint is better than nothing. Some rust converters specifically say NOT to use a zinc containing paint. But you need to check the instructions.

Most people on here will use a three-step proprietary product. The two most common are POR-15 and Master Series. I lean towards MS because of the issues that many people have with POR-15, but a search on the SAMBA should give you plenty of information (and contrary views of each one's pros and cons).

The three step process is basically:

1. A cleaning step with alkaline based degreaser, to remove any trace of oil and grease. This should be standard practice for any sort of painting.
2. Rust converting (phosphoric acid)
3. Encapsulating (sealing) the metal with a paint such as a polyurethane which uses the moisture in the air to cure the paint.

In both cases you end up with a rock hard and excellent surface to prevent future rust.

In every case you need to follow the instructions and in particular for the timings as once you convert the rust, the surface of the metal can be very reactive to being re-oxidised quickly. This is called "flash rust".

In your case you should clean the excess rust off, then inspect the areas that need to be replaced, then install new sheet metal and then finally paint. The products above are not resistant to welding heat, so the welding has to be done first. You also want to do the paint job in one contiguous layer so there are no borders between wet and dry paints.
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1968 1500 RHD Lotus White Beetle since birth. In the hospital for major surgery
1966 Lancia Flavia Pininfarina Coupe - in the waiting room
Discharged: 1983 Vanagon, 1974 1800 Microbus,1968 Low Light,1968 Type 3

[BeachKing]

Thank you so much for your help, I really appreciate it!

[carlos_magnum]

Evapo-Rust is another effective solution.