|The MGA With An Attitude
PAINT STRIPPING, Chemical or Mechanical - RT-202
These days it is increasingly rare to find an MGA that has not been repainted at least once on the outside. If the original paint or first repaint is in generally good condition, you might decide to wet sand it and repaint over the existing base. More likely the original paint will have given way to some rust, and much of the panel work would have to be power sanded to remove the rust before repainting. Any cut and weld repair work would of course be done before repainting. The point in question here is, what do you do if a prior repaint was done badly, or is cracking and checking, or there are too many layers of paint, and it has to be removed?
If the car was never repainted underneath, but only on the outside, you might opt to remove the outside paint by power sanding. For this it may be a good idea to keep the car body mostly assembled for rigidity while you do most of the work. Steel body panels can be power sanded, but you must be very careful with the parts which have aluminum skins. The two doors, bonnet and deck lid will have aluminum skin over a steel shell. A front valance panel might be fiberglass or aluminum if it has been replaced. Fenders could also be fiberglass replacements, or aluminum in very rare cases. Very few people will have enough time or patience to hand sand a lot of paint from the body panels. Power sanding on the aluminum skin is tricky work and requires some finesse to prevent overheating and warping. For those panels it may be better to do chemical stripping.
Maybe you have tried a little sanding for paint removal, and you soon figure out it will be very time consuming, so there must be a better way. Chemically stripping the entire car manually can also be time consuming as well as moderately expensive for the chemicals, and very messy. So you may want to turn to professional services for the paint removal job.
Media blasting is quite popular these days. Assuming you find the right professional who knows the business, there are many types of blasting media for various applications. For removal of heavy rust scale from structural parts the abrasive blasting may be done with sand or steel shot or ground slag from a steel mill. Less aggressive blasting on steel body panels might be dome with pulverized walnut shells, glass bead, or any number of different plastic bead materials. For the finicky aluminum skin parts the gentler method may use softer plastic beads or baking soda. I am NOT an expert in this area, couldn't begin to expound on all the different blasting media materials available, and will leave this up to your friendly professional blaster if you choose to go that route. One thing which media blasting cannot do is to clean inside of box sections such as body sills and door posts.
Another possible method of paint removal is a full body chemical dip. One problem here is finding someone who can actually do it, as it requires very large tanks of nasty chemicals, and will be subject to local environmental considerations, state and federal restrictions and various taxes. The process begins with soaking for as much as a few days in chemical paint remover, possibly interspersed with a few short sessions of hand scraping in a few tough spots. The next step may be electro-etching to remove any rust. This works similar to electro-plating but in reverse. The car body is immersed in an electrolytic fluid while iron oxides (the rust) is electrically etched off of the sacrificial car body and plated onto a collection electrode. End result of all this should leave bare sheet metal, quite clean, with some pit marks anywhere there used to be deep rust. Following all this the parts need a bath in an acid neutralizing fluid, a good rinse with water, maybe a quick dip in alcohol to remove the water and give a quick dry. This should be followed by application of a thin water soluble coating to prevent rusting for a reasonable time before it gets painted. Pay the piper on the way out.
When I had this done the final coating held up quite well for a couple of months in a controlled temperature garage while I was finishing up a little sheet metal repair. Prior to painting this coating has to be washed off with water. This requires a bit more of a rinse then just sloshing at it with a garden hose. A high pressure spray washer should make short work of it (being careful not to warp the aluminum skins). I used a garden hose sprayer and a stiff bristle brush. Pay attention to getting into all the nooks and crannies and spot weld seams as best you can to remove any remaining chemicals. Do this on a low humidity day, and maybe blow out the spot weld joints with compressed air for quicker drying. You will need to apply primer paint very soon after this cleaning job to prevent immediate rusting of the bare steel surface.
There is a bit of contention here about some chemicals possibly hiding in the spot weld joints which may come out later to disturb the new paint. I had no problem with this whatsoever, but I was very diligent about cleaning and drying and the method of application of the paint. To the underbody I applied a thin caustic etching primer using paint brushes and plenty of time to poke into every little corner and all along the weld joints in the process. This was followed by two brush coats of 50/50 black epoxy paint, to be followed later by spray painting in body color. The entire underbody was painted in this manner (as well as all of the chassis parts). The outside of the body shell got more traditional spray on primer. The final color coat covered everything inside and out so it is finished all one color as original.
To this I can add a historical report. After putting the car back on the road, twelve years and 124,000 miles later (including at least 10,000 miles of gravel roads) the car was partially disassemble for a repaint. I am happy to report that there was no rust anywhere under the fenders or along the piping joints. There were just a couple very small spots along the bottom edges where road sand and gravel had abraded paint away down to bare metal. Higher up in the wheel well some of the colored paint had been chipped off leaving the black epoxy paint exposed, but nothing gone through to bare metal. I am quite happy with this result and expect it to hold up as well until it needs another repaint. The main point here is that there has never been any problem with chemical disturbance of the paint along the weld seams. I would do this again, as long a economics would allow it.