1979 Baja 180BR restoration

[BlueArcher]

I currently in the demo stage of transom area I got all wood out and when I pulled it out I seen this adhesive/ bonding substance on the outer skin of the transom on bottom of hull area and the sides following up both sides of the outer skin of transom. Can anyone tell me what this is and what can I do other than chisel it out or grind it down bc the area I am working in is a small area that will not allow me to maneuver tools very well?
Thanks

 

[Bondo]

Ayuh,...... Welcome Aboard,..... My guess is, it's a resin based filler,.....

 

[BlueArcher]

When I was attempting to get it out by sanding a whole lot of white dust came out of it but If it is what you say it is how would I remove the resin based filler?

 

[Bondo]

Ayuh,..... Any way you can,.....