Body prep for paint

[Rainer S.]

I know this question has been raised before, but cant find the thread in the archives.
I am restoring the body of my 63 coupe. (orig sebring silver). The body is stripped completely.
My question is: What is the best, current product to use to fill areas, which have been repaired earlier, and need to be repaired again. The body has some damage in the wheel area (tire damage ?) and on front and back. I have heard of 3M short strand reinforced filler. Is that a good product, or are there better filler I can use ? I am planning to paint the body with poly-urethane paint.
Any suggestions ?

[Chuck S.]

Re: Body prep for paint

Rainer, you don't describe the damage in your wheel well, but the only function of filler on a Corvette, or even a metal-bodied vehcile, is to be applied over repairs or superficial nicks to finish the area to contour.

The body filler with fiberglass strands is not intended for use in repairing cracks or other damage in fiberglass panels. If the fiberglass is cracked, then you need to vee-grind the cracked area (preferably both sides of the panel) and use resin and mat to repair the damage. If necessary, filler is then used to finish the area to a smooth contour. The only damage suitable for body filler alone is building up and smoothing superficial nicks and gouges.

After using both types of filler on a conventional metal-bodied vehicle, I found it easier to obtain a smooth surface with minimum pin holes using the non-reinforced filler. My experience was that the fiberglass reinforced body filler was more susceptible to pin holes. Any pin holes have to be filled with glazing putty before painting...my experience is that primer or primer-surfacer will not fill them. Fiberglass reinforced body filler may have more strength in thick applications, but the objective with body filler is to keep it as thin as possible.

[Tracy C.]

Re: Body prep for paint

Rainer,

I agree with Chuck. If you have a fracture in the panel, you need to remove material from at least one side of the panel surface and preferably both if accessable. Taper grind along the crack to about an inch out creating a "channeled groove" to fill with fiberglass and resin. Be sure to use random fiber mat and NOT woven cloth.

Don't worry about overfilling the area during the repair. You can grind the area flush with the surface when it kicks off. I like to wait at least 24 hours.

Use any good grade of bondo to sweep over the patch and block sand to contour finish the repair.

If all you are doing is filling a scratch or gouge, bondo alone is fine but try to limit build up areas to less than .1 inch thick.

Good luck,
tc

[Richard G.]

Re: Body prep for paint

Chuck/Tracy

I agree with each of you said, but I have a quick question. What is the best way to smooth over bonding areas i.e fenders, etc.. I've heard of people grinding them down and laying fiberglass in there back in the day, panel adhesive etc. any thoughts?

Rich

[Chuck S.]

Re: Body prep for paint

Rich, it's called "glassing the seams". I haven't used it yet, but if you have seams that are significantly below contour from shrinkage, or if they are cracked from collision damage, the seam area is ground down and resin and mat is applied just like any other fiberglass repair. The technique is covered in Eckler's "Complete Book of Corvette Fiberglass Repair".

[Tracy C.]

Re: Body prep for paint

Rich,

I've never done this either.

Some seam shrinkage is typical and wouldn't loose any points.

Unless the shrinkage is extreme and/or the gap between the panels exceeds 1/4 inch, the glassing operation isn't required unless you want to ensure the seams will never show.

Haven't seen he procedure Chuck refers to, but I suspect you want at least a 1/2 inch wide taper to the gap on each panel edge.

tc

[Chuck S.]

Re: Body prep for paint

Tracy, I am pretty conservative (liberal?) with the taper grinding...I usually use about 1" - 1 1/2" on each side of the repair (seam). It makes sense to me that the bonding area should be larger to reduce the stress where the new material joins the old material.

[Terry F.]

Re: Body prep for paint

Bevel the edges of the repair about an inch each side of a crack. Try to reinforce the crack from the underside with a bonding strip that is 2 1/2 inches wide. You can make your own out of old broken panels. If you don't uses a bonding strip then you will need to bevel a wider "V." Be as precise about this as possible for strength. I outline any area with blue masking tape to keep the area defined and keep the job neat. A nice gradual "V" bevel will minimize problems with the repair being seen after painting. But, the best thing you can do is to use very good products when making repairs. Best products will simulate the original structure that you are making the repair to. They will expand and contract the same, etc. I use the panel adheisve that is sold by Corvette Immage. I think they sell the same stuff to Eckler's and others. It is polyester resin and short strands of glass. It has a higher composition of fiberglass to resin than you can ever get with just using seperate fiberglass matt and resin. The end result is less shrinkage, which will occur over time (couple of years)and eventually show up in the final finish. I have also used this product by pushing it into random fiberglass matting and had great results with it that way. Your goal is to make the repair strong and look good a long time. Remember, resin shrinks a lot, fiberglass does not shrink. Strength and flexability comes from the fiberglass not the resin. Resin is hard, shrinks and brittle. Use a heat lamp to strink the repair when finised. I would especially do that on seams. Use a heat lamp after the repair has sat a couple of days. Be carefull doing this. Don't burn your car to the ground. You can also use plastic wrap to cover your repairs and shape them. This can reduce the amount of sanding/labor of finishing the repair. You can also use a small roling pin to contour the repair to the panel when it is covered with plastic wrap. Grind the repair with 80 grit just prior to filling and rub the bonding adheisive into the open fiberglass with your fingers, use vinyl gloves and change them often. Again, tape the area off that you are working in. Consider using a couple layers of tape just around the repair. I do that when I am clamping something or using the roling pin to finish the repair. It leaves the repair slightly above the surface of the panel and greatly reduces the pinholes and having to add more repair material.

Practice on broken panels. Use safty equipement. Use those flexable plastic spatulas to apply the material. The list goes on but it is mostly common sense. Sorry if I over elaborated on this. These are just suggestions. You need to do what works best for you. Have fun, Terry