Screw holes in GRP

[morgandlm]

What is the best way to repair screw holes in GRP when the thread has been stripped? I have tried several techniques with varying degrees of success. My current problem is the holes for side window fixings where there is no access to the back of the hole. I need to re-use the same screws so cannot upsize. I have tried stuffing epoxy filler into the hole and then drilling a pilot hole for the screw. This works but is not as good as putting a blob of epoxy behind the hole and drilling into that. Any ideas please?
Morgan

 

[rob2]

It will depend on how much clearance there is between the frame and the side when installed. GRP is a totally unsuitable material to support a threaded fastener - the material is too friable and has very little tensile strength. If you are simply screwing the frames on with self tappers, then the sealant is probably doing most of the work in holding the windows on! To improve the fastening you would need some form of blind fastener, like a rivnut, or a surface bonded type. I'm not that familiar with the "Big Head" threads, but if they are available in a flanged version, they might be mounted through a clearnace hole and glued by the flange. So long as the protrusion is not too great and the positioning is within the sealed width of the frame, it should seal successfully but might require new fasteners unless you're lucky enough to find some with the same thread form as your original screws.

Rob.

 

[John the kiwi]

Just a thought. Did you drill out the original holes to a larger size before "stuffing with epoxy filler"?
If you didn't you would have two problems:
1 trying to bond to possibly/probably contaminated material.
2 by the time you screw your screws in you are expecting the new material to be replacing only the bits of old material that had been stripped out. The new material will thus only be a miniscule amount and bonded over a tiny, possibly contaminated area.
Does this make sense? Try drilling out your stripped holes to a larger diameter and then filling with an epoxy mix with microfibres. (which are tougher than micro balloons i think.)
Your new material will be well bonded to clean original material and when you drill and tap new screws in the entire thread will be in homogenous material.
Good luck.