Bonding Stainless to Fiberglass

Little Dorrit

Little Dorrit

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In an attempt to avoid the sacrilege of screwing wood screws directly into fiberglass (to secure a cabin sole) I decided to use some rivnuts and machine screws. I want to secure the M6 stainless rivnuts into the hole made in the fiberglass cabin floor. The rivnuts just need to resist turning motion as they are inside the hole when a machine screw is tightened . Any suggestions on a suitable adhesive? I considered heating the rivnuts so that they would expand in the hole but the expansion coefficient of stainless is minimal so I don't expect to be able to use that technique.
 
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Propery set Rivnuts should work well.
They grip a bit like pop rivets.

Wellnuts are a bit fraught IMHO, the brass insert corrodes to any fastener, be it stainless, brass, plated steel, then shears from the rubber bit and won't undo.
They are used a lot to hold motorbike fairings together, I normally have grief with one or two at each service.
 
I just used standard 10min epoxy, I lightly abraded and then cleaned (degreased) the rivet nut with IPA. If the hole in the GRP is freshly drilled and clean it should be OK and long as you blow out any dust or shavings.
I think rivet nuts epoxed in are great, very quick and easy to use and the take standard bolts, set screws or whatever.
 
If you want to drill a hole to take the rivnuts, why are you averse to drilling a hole to take a self-tapper? I would have thought you will have a lot more problems with nuts coming unbonded and jammed threads than you ever will with self tappers.
 
Just buy a tap for the size of screw you need. Drill a suitable sized smaller hole and make a tapped thread for the hold down screw. A low speed battery drill is ideal for running the tap in. olewill
 
duncan99210 said:
All the deck sole plates on my yacht are simply fixed down to the grp bearers by self tappers. Not sure why the op wants to introduce a level of complication beyond this.
Click to expand...

Hi thanks for your interest.

I probably should have explained that the boards don't sit flat so needed a really good screw fixing as they needed to correct an uneven floor. As they may need to be removed from time to time I was concerned that eventually they would strip the fiberglass.

I have actually finished the job with rivnuts which cost very little and with a 8.5mm drill I managed to bang the nuts home so they are now perfectly tight. With the countersunk M6 screws going through the wooden floor and into the rivnuts the flooring can now be screwed down and importantly removed and put back with ease plus no risk of stripping the fiberglass.

Everyone to their own I guess but it really was quite a minimal amount of extra work and cost... good luck with the self tappers but they were not the best solution on this job IMHO.
 
lw395 said:
Propery set Rivnuts should work well.
They grip a bit like pop rivets.

Wellnuts are a bit fraught IMHO, the brass insert corrodes to any fastener, be it stainless, brass, plated steel, then shears from the rubber bit and won't undo.
They are used a lot to hold motorbike fairings together, I normally have grief with one or two at each service.
Click to expand...

Thanks the jobs been completed and the Rivnuts worked well. I actually put them in from above which bis not the conventional way but they never-the-less work well. I think I was just looking for some assurance that I had not missed something obvious. A few posters suggest self tappers but I'm not a great fan of using them in fiberglass unless it's absolutely necessary.
 
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