Epoxy on bolt threads for use on grp frames

[Durcott]

Hi Folks,

I was reading a thread elsewhere on the web, which mentioned refitting bolts into a grp frame.

These were fairly hefty bolts - screwing in to a hole size of just over 1/2".

The writer mentioned smearing epoxy over the threads before re-fitting.

I have a similar situation, but the bolts are also being backed by a nut, though the bolts still need to screw into the grp frame.

I just wondered if anyone had a view on why this smear of epoxy was mentioned?

I don't think I've read anyone else doing this, but it seems like a reasonable thing to do - I'm guessing it would replace any material lost in the grp frame, while probably not bonding to the bolt sufficiently to stop it coming out again.

What does the forum think?

Jeff

 

[TQA]

Give the bolt a wipe with an oily rag first.

Otherwise removing it at some future date could be challenging.

 

[SHUG]

I think that the idea is that the smear of epoxy will seal any exposed glass strands and prevent "wicking".
A more thorough way to do this might be to put even more epoxy into the hole and then re-drill it to the required size.

 

[PaulMcC]

I'm pretty sure there is a section on epoxying threads on bolts and screws in one of the west system guides - which are all free to download. From memory the argument was that the epoxy binds to the surrounding fibreglass and creates a strong threaded hole which is perfectly matched to the screw so you end up with much higher pull out resistance. There was also something in there about wiping the threads with something prior to epoxy if you want them to be removable but I can't remember what west recommended.

 

[Concerto]

Coating the threads with wax or mould release will stop the thread sticking.

Full details here:
http://www.westsystem.com/ss/bonding-hardware/

 

[Tranona]

Can't quite visualise why you need a nut if the bolt is screwed into the frame, buy no reason why you can't take the load direct to the frame with a well cut epoxy thread instead of a nut. As Concerto's link shows you can cast the thread with wax to stop the bolt from sticking so you can remove it when the epoxy has cured. No need to coat the thread with epoxy unless you never need to remove it.