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 Helmet Question: Bondo Cracking

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Helmet Question: Bondo Cracking
« on: Jul 11, 2018, 01:46 AM »
Hello all!

I've been working on my helmet on and off for quite some time now (about a year or so), and I'm getting down to the final stages of bondo-ing and sanding. However, I am running into a problem where the bondo keeps cracking along the base of the helmet. I read up about bondo cracking on helmets on the forums, and it seems that this is mostly an issue with the material underneath the bondo being too supple. My helmet is made of poster board and cardboard re-enforced with fiberglass resin on the outside and a layer of fabric on the inside. How should I go about supporting the problem areas at this stage?

Not gonna lie this is kinda disappointing because I was really hoping to be able to choose some paints this week, but now that might not happen  :( I know I need to be patient to make sure everything turns out well; it's just a bit  discouraging to hit yet another roadblock.

Thanks in advance :)

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Re: Helmet Question: Bondo Cracking
« Reply #1 on: Jul 11, 2018, 07:37 AM »
We will be able to give you more specific answers if you provide photos. But some use 6mm sintra as bracing on the inside.

Re: Helmet Question: Bondo Cracking
« Reply #2 on: Jul 11, 2018, 01:29 PM »
We will be able to give you more specific answers if you provide photos. But some use 6mm sintra as bracing on the inside.

Oops! I posted this very late at night after working on my helmet for a few hours and completely forgot to add more details. Thanks for the tip though  :D I'm planning to go out and find some sintra today to re-enforce the problem areas. Hopefully that'll stiffen it up so it can set without cracking. I've also read some suggestions to fill in cracks with an epoxy filler because it's more flexible, so I might try that as well.

The cracking is almost entirely confined to the back - definitely the most flexible part of the helmet. It seems to like cracking especially in the inch or so after the earcap connects to the back bit of the helmet. I've tried going over it with filler putty, but that just cracked on top of it too - wouldn't say that worked out too well.

The cracks are quite small, but they might not stay that way if the helmet is stressed any more than it is while I'm sanding, which is a very real possibility. I superglued the cracks last night to try and hold it together, though I realize that's probably just a temporary solution.

The other part where there is a fair amount of cracking is the part right by the connection to the keyholes, but oddly enough, only on one side.


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Re: Helmet Question: Bondo Cracking
« Reply #3 on: Jul 11, 2018, 04:10 PM »
That area by the earcaps is definitely prone to cracking.  I've got a crack there.  After stress testing, I eventually just made it be weathering.  I don't know about an epoxy filler -- but you could use something like Kwik-Seal -- it's not sandable (because it's flexible) -- so smooth it as perfectly as you can with a wet finger before it cures.  It IS very paintable.

Re: Helmet Question: Bondo Cracking
« Reply #4 on: Jul 11, 2018, 10:30 PM »
That area by the earcaps is definitely prone to cracking.  I've got a crack there.  After stress testing, I eventually just made it be weathering.  I don't know about an epoxy filler -- but you could use something like Kwik-Seal -- it's not sandable (because it's flexible) -- so smooth it as perfectly as you can with a wet finger before it cures.  It IS very paintable.

My local sign shop only carries 1mm sintra, but they told me the name of their supplier which is only about 20 mins away, so I'm heading there tomorrow morning. Once I've re-enforced the problem areas, I'll try to finish up sanding without aggravating the cracks further.

is Kwik-Seal just caulk? I looked it up and appears to be so. Once I'm done with sanding I'll probably go over the cracks with caulk and smooth them out just so I cna be sure my helmet will stay structurally sound. Thank you so much for the advice  :D

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Re: Helmet Question: Bondo Cracking
« Reply #5 on: Jul 11, 2018, 11:04 PM »
Yeah, just make sure whatever you get is paintable, not all caulk is.  Kwik Seal is also convenient cause it's just a tube, and oyu don't need a caulk gun, and it's a smaller quantity, cause you're gonna end up needing like a teaspoon of it...

Re: Helmet Question: Bondo Cracking
« Reply #6 on: Jul 12, 2018, 07:18 PM »
Yeah, just make sure whatever you get is paintable, not all caulk is.  Kwik Seal is also convenient cause it's just a tube, and oyu don't need a caulk gun, and it's a smaller quantity, cause you're gonna end up needing like a teaspoon of it...

I'll check what I have to see if it's paintable. If not guess I'm making another menard's run   :D

 


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