I was wondering I own an old bronco and it needs paint and body work has some rust.Do body shops sand the old paint off before they paint?or do they just paint over the old paint?how many coats of paint do they use to paint your truck?do they just paint it once and thats it or do they paint it twice 2 coats?just wondering before i go talk to someone at a body shop i know a little more then I do now.what do body shops use to fill in dents bondo?how long does bondo last before it starts to crack ?thanks any info will help

 

it all depends on the situation and your expectations and budget.
If modern paint is on the vehicle and it is in sound condition, and there are not too many layers (mil thickness), you could just sand the existing paint and paint over it.
The amount of coats depends depends on paint type and how well the paint coverage is. Old lacquer, which no one really uses any more for good reason, required many coats to be sprayed on and where many get the idea like something like 10 layers of clear would be a good thing. With modern urethanes, 2 to 3 coats of the clear is all that is really needed, and more isn't an advantage, and too many would only lead to problems. The base coat is applied till you have coverage, how many coats that amounts too. Most time it is done in 2 to 3 coats, but some colors are awefully transparent and don't like to cover, even more so in cheaper bases. Most places now spray a base , urethane clear system where the base contains the color/pigments and effects such as metallics or pearls, which isn't sprayed to achieve gloss, and the clearcoat provides protection and gloss, and contains uv protectors to protect the color from fading and chalking. Most basecoats are basically a lacquer, which kind of makes it the weakest link, which is why many say single stage urethanes are a bit more durable, but a good quality base clear urethane should last many many years with little maintainance needed. Most metallics expecially are sprayed in a base clear for the added ease, and for the ability to buff. Single stages have both the color and provide the gloss in one coat (actually usually a couple coats, but no clear layers are needed over it for gloss and protection). Some places still spray enamels, it should be cheaper, is not a terrible system, but outdated today and not as good a system as a urethane. Generally can fill a bit coarser scratches and only need a few coats applied and is often still used on some fleet equiptment and at the cheapy production shops. Both enamels and urethanes can be applied as a single stage (no clear coat is applied over the color, gloss and protection is provided in the color coats). Metallics in single stage can't be buffed out afterwards if needed, as the metallic would be disturbed when color sanded. There are also some factory colors and also custom colors that are three stage , involving a base color, and a midcoat consisting of a candy, pearls, metallics or flakes, ect, and then final coats of clear. Application of the midcoat especially must be very consistant and and as clean of dirt specs as possible.

On something older like your bronco that has rust, it would be best to strip to see the true condition of everything under the paint, and start off fresh with modern materials. You didn't say what year it is, but all manufacturers in the 80's and 90's also had problems with paint delamination, and around those years and prior likely were using 1k materials that are outdated today. Your paint is only as good as what it is put over.
Bondo-plastic filler gets a bad rap because it is often abused. Used correctly in a proper application, and not abused trying to apply to thick, it should hold up fine. It can crack if it gets a sharp blow or if applyed over an open seam. It should not be stuffed into a rust hole, if you have rust holes, the metal or piece needs replacement first, and if a little finishing work is needed with filler after replacement thats okay. Plastic filler absorbs water, so you don't want any water able to get behind it, so welds should be done well. Metal work-dents should be worked out of the metal as much as possible, and if plastic filler is used, keep the application as thin as possible, within its recommendations. But I am guilty of abusing applying thicker then should be, and it usually holds up pretty well unless that area gets hit or something. This work is labor intensive and quality materials are expensive, so don't be too shocked if you hear some big numbers for a paint job. Also be leary of too low a price. Know what exactly what you will be getting for your money, and try to get some references about shops you are considering have do the work, what there quality is like, and if they stand by there work if they happen to have a problem. Every shop can have something go wrong now and then, but they should be willing to fix anything on there end. You not very likely to get a warrenty on rust repair, and its getting harder to find places that still do complete paint jobs and rust repairs on vehicles, collision work typically brings better money and ties up shop space for a shorter time.

 

I agree with kenseth. This guy knows what he is talking about.

A couple of years ago I had a 1972 F100 2wd long bed. I had taken real good care of it. It had a ding in the left front panel, and the left rear panel. I figured 1500 bucks to get them banged out and painted. Well............
not so, the body shop wizard said, depending on what I wanted it to look like. Problem is, that materials and things change over time. I wanted a good repair job, so you "couldn't see it from a couple of feet away".
Really my truck needed a whole new paint job, which took, (see above post). I was not prepared to pay the amount asked.
I did do a settle for, only because I was wanting to sell the truck. I know, I know I will regret selling it, but some things ya just have to do.