Soda Blasting Body. Alternative to sanding?

[EuropaTC]

Add methylene chloride to your stripper. Standard strippers used to have it until the EPA got involved. I add 10 % by volume to the junk you can get now and it strips as it should.

Yep, methylene chloride is one heck of a paint stripper. So good that it got banned..... 

In the UK we used to have methylene chloride thixotropic strippers and they were absolutely excellent in getting anything off, unfortunately that also included the gel coat if you weren't careful. For that reason they weren't advised for GRP bodies but I still used them up to a point. If you're stripping a car with multiple re-paints (my Marcos had 9 (yes, NINE) different coats of paint on it the first time I did it) then it's reasonably safe to use it to get rid of the outer layers.

I'd certainly use methylene chloride if I could get it but with caution. I'd never apply and leave it because the rate of attack on bare gel coat will upset you, been there, done that.  The strippers I used to get would wrinkle the top couple of layers within 15-20 minutes and at that point I'd start scraping.

Incidentally, it will also attack you if you're not careful and it smarts a bit. Gloves, arm and eye protection are essential.

[Richard48Y]

Walnut shell blasting experiment done.
For this experiment I was mostly removing the thin paint/primer film patches left behind after chemical stripper.

Cost at HF, $30.00 for a 25 Lb. box.
Can be used from an inexpensive standard sand blast rig.
Consumption rate is high.
No Baking Soda odor but you may need to sweep or vacuum as it will not dissolve in water or the next rain.
Does not appear to etch Gel-Coat but does leave a coarser finish on remaining Bondo® and old repairs.

If you really want to avoid Soda Blasting and are not going through several layers of paint Walnut Shell media should work.
For cost savings I would use it as a final finisher after chemical stripping but that may just be me.
I think it is a little slower, and certainly more expensive per pound.
The "Good" stripper is $82.00 -$109.00 per gallon depending on purchase location.

Next experiment will be a final light coat of chemical stripper followed by coarse steel wool and water rinse.
I hope this removes the final remnants of old paint without having to run the big air compressor or deal with media blast residue.

[Bryan Boyle]

Was talking with a local shop which specializes in marine fiberglass repair/renovation here in the southeast MA area...while busy (obviously...getting the yachts and cabin boats ready at the marinas around here...has no openings until July), he is willing to take a look at what it would take if he's in the area.  He mentions that after soda blasting, it's important to neutralize, with vinegar, the remnants of the soda that remain on the surface (which makes sense...sodium bicarbonate is highly basic, and vinegar acidic...so one would cancel out the other (with a little foaming) followed by a strong soap and water rinse, then let the surface thoroughly air dry in the sun. 

Also mentioned that he's had good luck with micro glass beads (not the type that are usually used in blast cabinets, but down at the micron level...) and turning the pressure way down on stubborn top coats such as urethanes and catalyzed enamels.  One of the caveats is that any glass that remains in the car has to be covered with aluminum foil, then two layers of masking paper (shiny side out), and any trim masked with duck tape (not paper painter tape) and ALL chrome removed, since the micro glass bead WILL etch the windows.  And, it can leave a slightly 'toothed' surface, which would probably require a high-build primer to properly smooth before standard primer, sealer, and top coat. 

I mentioned that the body thickness is NOT the 1/2" or more that a boat hull is constructed from; it's a polyester resin chopped strand slurry shot-gunned into a female mold, not hand-laid epoxy or injection-molded (IIRC, some builders licensed Lotus' VARI system to build their hulls...I may be wrong), so that has to be taken into account. 

Figure, if he stops by the house (the soda method is environmentally friendly....wash down the drive with water), he's willing to test on the boot and bonnet lids, which would be the easiest to rectify if it all goes sideways.  If it comes out ok...will schedule for after when I can get the doors dismounted and the shiny bits off the car. 

Oh, BTW, he also uses this method at a couple airports near me for folks that want to strip their airframes without having to use the aggressive chemicals that are usually employed to get back to shiny aluminum (aluminium) in preparation for their refinishing.  So, he seems to Get It, when it comes to helping in the renovation of high-dollar conveyances.  We'll see.

But, first...just have to get the beast to the Brits at Bristol (RI) show on 6/10 at Colt State Park.  Entered in the "Diamond in the Rough" class. 

[Richard48Y]

Vinegar is an inexpensive rinse but the "Best practice" industry standard is Holdtight 102.

https://holdtight.com/products/holdtight-102/

[dakazman]

 Cleaning is key, however the loose fibers created by the stripper are still in play, Europa TC said it best, veil and wait times  .  I am testing different veils that hide all hidden voids in the glass that I could not detect. After 1 year my upper body panels show signs of the loose fibers that are shrink wrapped by the clearcoat, luckily for me sanding down the clear and rebuffing solved the problem in the mirror reflection.
 Dakazman