Floor Tar Mat Removal Opinions

[CanTechZ]

As one of the first steps in the restoration process of my '70 240z I'm trying to determine the full extent of my rust issue and I'm looking for opinions regarding floor tar mat removal. I plan to have "all" rust removed and have a complete paint job back to the original 918 Orange. I know that the safest method is to remove all of the tar mats but most of mine are in such good shape I am hoping that will not be necessary.

I have started to remove the undercoating below the floors to identify rusty areas and found that rust in the floors is mainly in areas with damage and the undercoating had cracked or had loosened allowing moisture in. For a test I removed a small area of tar mat that was bubbled and directly over some rust on the underside of the drivers side floor. It was 30°C today so I used a 1" scraper to lift the tar mat and then used a rag with varsol to remove the excess, no sanding was done. I was expecting to see a lot of surface rust, or worse, adjacent to the rust holes but was surprised to see how clean the bare steel was. Here are a few pics of what I found.

Passenger Side

Drivers Side, with tar mat removed in rusted area

Close-up showing clean bare metal adjacent to rusted areas

Close-up showing what bubbles in tar mat looked like

previous to removal

The area of tar mat I have removed is not the full extent of the issue but I don't want to blindly remove all the tar when I am trying keep my car as original as possible. I value any input or suggestions you may have.

Thanks

Mike

[Mark Maras]

i would remove it but if keeping the tar mat is a goal, I'd go at the otherside with an ice pick & don't be gentle. They are a great tool for finding soft spots. If you don't remove the tar, you'll never know what is under there slowly eating away at your Z. You'll never determine the extent of the rust nor get rid of it all. You can remove the tar mat now or later.

[grannyknot]

Mike, you are wise to go slow but removing the tar mat from the floor is not a bad thing, that is where the rust starts. From your pics it looks like a well taken care of Z but the rust spots that you show are directly above where the rails are spot welded in. If you remove the rest of the tar mat on the floor, driver and passenger side, you will probably find the same rust spots in a parallel strip on both sides.

Chris

[EuroDat]

By far the easiest way to remove tar sound deadening material is the dry ice method.

Its easy to do. Heap it on a small section to start with to get use to the technique. About 1 to 2" thick and wait a couple of minutes. You will hear the tar cracking and then its ready to remove.

Pick the pieces of tar out of the dry ice and move it the the next section, add more dry ice when needed.

Use a good pair of leather gloves when handling dry ice. Its very cold and can cause nasty cold burns. Welding gloves work fine. Keep the doors and hatch open and well ventilated.

[CanTechZ]

Thanks for the replies so far, if/when I decide do a complete removal I will definitely use the dry ice method. Either way I will also use the ice pick idea to check the extent of rusted areas. Here are a few more pics as I wanted to investigate the areas that Chris pointed out, its looks like I have been somewhat lucky as the rust on the area of the spot welds is only surface, due to a crack in the tar mat as indicated by the arrows in the third picture

Any other opinions, suggestions, comments are welcomed.

Mike

[AZ-240z]

Mike,

I second removing all of the tar mat insulation. It will not only give you unencumbered space to repair the rust,

but you will be certain that there is none left. The same tar mat insulation can be purchased at a quality

colllision repair shop that has an adhesive backing. I would take pictures of the old mat before removing

to accurately document for a replacement pattern, then paint it the original body color and it will look showroom new.

[240dkw]

I agree with the other posts, it will be very hard to stop the existing rust from growing without removing all of the mat. I would make a pattern of the mat, remove it all and the cut new ones and have them repainted when you do the car. I had the same issue on the underside of my car. the only rust was where the undercoating was chipped,cracked or scraped off. I removed it all,cleaned up the rust and re-coated it all.

Dan

Looks like AZ-240Z was faster on the keyboard than me.

Edited August 4, 2014 by 240dkw

[CanTechZ]

Thanks for all the advice, when I am ready to have the repairs done I will do a full removal of the tar mats in the floors. For now I will make patterns and continue with the spot checks to expose the worst of the rusted areas so that I know what I am getting myself into.