Can I bondo my aluminum transom?

Can I bondo my aluminum transom?

I’m about done w/ the structural part of my new transom rebuild before painting I’d like to smooth it out a bit.image


Can I use automotive Bondo to smooth the splashwell an transom top caps?



Thanks for advising

 

Yes, and then it will soon fall off.

 

+1
Aluminium takes an extreme amount of prep to accept any permanent adhesive or filler. If you just want to make it water-tight, use a butyl tape or caulk.
Why corrosion resistance matters for the adhesive bonding of aluminium https://www.shapesbyhydro.com/en/material-properties/why-corrosion-resistance-matters-for-the-adhesive-bonding-of-aluminium/

 

No. Maybe epoxy on a keyed surface, but Bondo takes on water and will fail fast.

 

before I mounted the engine pod which is now a sealed pod.I added flanges on bottom w/g/flex an sides glued flanges to pod w/ JB epoxy it seams very stronge bond.
bottom flange note not added side flange yet.note pod manufactor didn't much of a flange I applied almost full 10oz tube of 5200 to flanges.

side flange

side flange port mount flange glued to transom skin w/ 3m 5200

side flange star mount flange glued to transom skin w/ 3m 5200

I cleaned the primed aluminum w/ isopropyl alcohol prior to glueing both the JB an the 3m.

I want the bondo on the transom cap it's 45"s above the waterline. not for structure just cosmetics. using butyal tape inbeween the transoms splashwell skin.

thanks

not much sticks to aluminum.Bondo is very strong it's really just this small corner next to rigging tubes, opposite side won't need any cosmetics. thanks

 

Bondo is always a bad choice for boats.

The bond strength is about 50% of epoxy. And regular Bondo is not waterproof.

You asked, we answered, you argued.

Bondo has a labelled marine product that is waterproof.

 

not arguing just said"bondo is strong" I was unsure of it's bonding capabilities were. additionally I knew it wasn't water proof I think that's why is must be primed an painted to protect it. I've only used it once on my vans plastic grille damage this stuff was impressive.
I'll take you'rs
jehardiman and
ondarvr
advise an use something else to smooth out this small area. is this your suggestion?
it claims to stick to aluminum.
https://www.3m.com/3M/en_US/p/d/b40067468/
can you please suggest a generic version.
maybe this
Amazon.com https://www.amazon.com/TotalBoat-Polyester-Structural-Repair-Putty/dp/B07C9D2GFJ/ref=pd_ci_mcx_di_int_sccai_cn_d_sccl_2_2/144-3857527-0201307?pd_rd_w=tcu4K&content-id=amzn1.sym.751acc83-5c05-42d0-a15e-303622651e1e&pf_rd_p=751acc83-5c05-42d0-a15e-303622651e1e&pf_rd_r=3HXEWE5RN7TYVKNGARG2&pd_rd_wg=mGsZT&pd_rd_r=0d63d345-cb2b-4153-af6b-f40b55509e76&pd_rd_i=B07C9D2GFJ&th=1

thanks fallguy

 

The problem with most "bondo" is that it is a porus polyester, that if not sealed completely, will allow oxidation at the metal/filler interface. As common on steel auto bodies as aluminimum boats, the real issue is the "open" back side of the joint. Once the metal surface is preped...no water vapor can be allowed at the bond, which means the whole lap joint needs to be sealed.

 

I've decided to just extend the transom top cap an trim the underneth green piece.
as it is right now won't stop the inaugural splash of new transom rebuild an repower.

I also wanted to use the bondo over those ladder attachment holes in transom skin. I've got a nicer ladder w/ a platform as 1st step so I'll probably only reuse the top section of original ladder.
thanks

 

Just use epoxy and cabosil. Higher bond strength, or if you think it’ll flex, use 5200, or if you need to fair, epoxy and microballoons/cabosil about 80/20

 

I've never set eyes on Bondo as they don't sell it here,but I am familiar with a few types of polyester filler.I think categorising it as porous polyester may be a little inaccurate as low cost fillers tend to have a porous powder in a polyester resin base and it is the porosity of the filler powder that allows moisture to be absorbed.for this particular application one of the early hurdles to overcome is achieving a good level of surface preparation and you will have that regardless of filler type,so maybe an etch primer will be necessary.Another potential source of trouble could be differential expansion as temperatures fluctuate.I tend to use epoxy only where really necessary as it is quite a bit more expensive than polyester and I prefer not to have to take extensive precautions to avoid becoming sensitised to the chemicals involved.

That Total Boat repair paste isn’t what you need as it has strands of glass mixed with resin and won't allow a good finish easily.If the filler was being used to seal holes or cracks,epoxy would be the only way to go,but if all you are planning is a bit of cosmetic work with a few ounces of polyester,what is the worst thing that could happen?A bit of filler might flake off and you wouldn't win prizes for best paint job until a repair had been done.The boat looks functional,rather than a contender for the title of prettiest boat on the river,so if you can tolerate the ignominy of being seen in a cosmetically flawed boat,make an informed choice and deal with any problems if they arise.A boat headed to the Monaco Superyacht show would have no expense spared,while a workboat would be lucky to have the biggest dents hammered out.Where on the spectrum would you place this boat?

 

The idea one would base the quality of the repair on the quality of the boat brings us to ‘just throw some house paint on it’.

Others read this content..

 

Well you won't stay in business too long if you do Rolls-Royce work-and charge for it-on a 30 year old Chevrolet.Maybe your customers are charitably inclined when you turn their boats into visions of perfection,but few are so benevolent.