Bondo over bondo

[mofosheee]

Performed a sheet metal repair............now it's bondo time.
Put on an initial thin coat, another required
Should I sand between coats or would the following layer over the initial layer (UN-sanded) result in better adhesion ?
Thank you

 

[34_40]

Yes, sanding between "coats" is preferred.

 

[Buffalo21]

Depends, are we talking about a car or to even out the side of an mill castings?? On my 1940 Bridgeport the bondo I took off was between 1/4” to 3/8” thick, in certain areas, a friend‘s HF 6 x 26 mill‘s bondo depth made that look like a skim coat.

 

[raven7usa]

Need to sand to remove "skin" on the bondo for good adhesion.

 

[RJSakowski]

Bondo is permeable to water. It is imperative for rust prevention to have a solid steel backing before applying Bondo. Water w3ill permeate from the underside and start rusting This is usually done by welding a patch that would be below the surface and then buildiing the surface with Bondo. If that isn't practical to weld a patch, an epoxy seal layer will prevent water intrusion. The epoxy should be made to good metal. Fiberglass cloth can be used with the epoxy as long as it is well wetted.