im having to patch the bottom of my seat and when i took it off i noticed one of the wholes that mounts the seat to the frame is super wallowed out, will the bondo fibreglass patch stuff be strong enough to use and have the bolt go through to mount the seat.
Welcome!
I’m unsure if Bondo Fiberglass will be strong enough to hold up to the consistent strain a seat experiences.
Power Republic has a good video on seat repair but someone else should have some insight. I just milk mine till the Swiss cheese holes become one massive hole 
. Then it’s to the graveyard.
If you do it right it can be stronger than the original. I have quite a bit of experience with composites in aerospace application and have patched a number of seats. Here is my advice.
- Sand and clean area to be bonded really good (60 grit and acetone)
- Use a good laminating epoxy (System3, Pro-Set, West Systems, etc.) Bondo is primarily a polyester resin which prioritizes affordability and sandability but sacrifices strength and stability.
- Composites transfer load through shear so provide sufficient overlap between the patch and existing seat. i.e. minimum 3" piece to patch a 1" hole (bigger the better).
- Compress the patch while curing to ensure good contact with existing seat and squeeze excess resin and air from within the patch itself. A pro would use a vacuum bag. At the track I’ve used packaging tape to cover both sides then a credit card like a squeegee which worked OK.
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Some great advice posted above. I have patched almost every seat we have at least once. Generally from a bolt coming loose and a weight moving around a little or sometimes the previous holes are just a little bit too close to where you want mount it. Put on a pair of disposable gloves and have at it.
Some good tips here! Though I am curious why you choose to use epoxy resin to repair what is (usually) a polyester part? I have fixed many a seat over the years and I always used polyester for no other reason than to fix like with like. As much as I enjoy a good ole fashioned polyester, stir-cup melting hot batch, I prefer to work with epoxy…
I was a motorsports composite guy in a past life, so I get the materials and techniques, but always eager to learn more… You aerospace guys are next level with the sticky stuff!