Replacing bilge switch, and filling old mounting holes.

[scgunner]

A & K,

I don't know who'd recommend a slow hardener especially for a job as small as filling screw holes. The reason for using a slow hardener is if you've got a big job and you need to mix a large batch and need a lot of working time. Even on hot days using fast hardener in small batches of epoxy you'll have at least 3 to 5 min working time, which should be plenty to fill screw holes.

Ken,

"That highly depends on which plastic -- there are ones that epoxy will not stick to", while that may be true, I have yet to find anything epoxy won't stick to, aside from maybe waxpaper. If that were the case however, roughing the surface with a course sandpaper would solve the problem.

[KWKloeber]

I have yet to find anything epoxy won't stick to, aside from maybe waxpaper.
roughing the surface with a course sandpaper would solve the problem.

I'll let West Systems' testin' do the talkin' about simply sandin' (mechanical treatment) "to solve the problem." 
These are using G/Flex 655 and 80-grit on plastics:

HDPE
sand  400 psi (i.e., didn't work)
sand, flame treat  1890 psi
Alcohol wipe, flame treat  2312 psi  (no sanding is better)

ABS
sand  1535 psi
sand, flame treat  1813 (i.e, didn't help much)
Alcohol wipe, flame treat  3288 psi (no sanding is better)

PVC   
sand  1780 psi
sand, flame treat  1813 (i.e, didn't help much)
Alcohol wipe, flame treat  2081 psi (no sanding is better)

Again, the above adhesions were using G/Flex.  West 105 is NOT recommended for plastics but on PVC the result was:

sand  892 psi  (i.e., didn't work)
sand, flame treat  (not tested)
solvent wipe, flame treat  1585 psi (no sanding is better)
Alcohol wipe, flame treat  2081 psi (using G/Flex)

Plastic non-adhesion is why West's application tools are plastic, its syringes are plastic (reusable) and many mix epoxy in Rubbermaid shallow containers (doesn't adhere, reusable, resin pops right off of the surface.). It's also why leaks in our potable and black water tanks can't be "reliably" repaired with epoxy without modifying the molecular properties of the polyethylene surface.

Your boat, Your choice on the epoxy technique to install a pc of critical safety equipment.

The elephant in the room question (which initially I intentionally did not ask is, *Why adhere with permanent epoxy, a switch that one might need to remove to service or replace it?*

[scgunner]

Ken,

I'd remind the elephant that I said "a few dabs of epoxy". If the switch required removal a hammer and chisel could easily pop it off, any epoxy remaining in the bilge could be sanded off so the process can be repeated, and look still haven't drilled any holes!

Since I love West Systems products I will defer to their expertise, but have you ever noticed when you use their tools and pots they clean up nicely at first but as you continue to reuse them and they become progressively more abraded it becomes harder and harder to get them clean to the point where you just have to replace them.

Speaking of critical safety equipment, aren't you the guy with the slippery decks?

[David Comando]

I don't know if I missed it but what brand switch did you get? My Guest, non mercury float switch failed in under 2 years. I replaced it with another Guest, non mercury switch. At least the holes matched!

[Sailing Amok]

I don't know who'd recommend a slow hardener especially for a job as small as filling screw holes.

It was suggested in a Practical Sailor https://www.practical-sailor.com/boat-maintenance/a-stronger-screwhole-repair article. The argument is that the fast hardener creates bubbles which reduce strength, but I believe from other comments here that is only an issue in rather large holes. Also, it looks like Maine Sail suggests fast hardener in his Marine How To article.

I don't know if I missed it but what brand switch did you get? My Guest, non mercury float switch failed in under 2 years. I replaced it with another Guest, non mercury switch. At least the holes matched!

David, I went with a Johnson 36152 as it was very well reviewed in several sources. It's a bit more expensive than the typical mercury switch type, but should be less prone to clogging and contamination. It just arrived in the mail, so I'll have a go at this project later this week.

[Ron Hill]

Aaron : I replaced the float switch?? with a Jabsco "Super Switch" and it has not failed in over 15 years!!

A thought