Originally Posted by George DuBose
I have started using butyl rubber in various dimensions. I recently installed a large Lewmar
hatch on my foredeck using a 1/2" x 1/16" or so grey tape to bed
the hatch and it was so easy. No tubes, no guns
, so Sikaflex up to the elbows...
I will use butyl rubber tape to rebed all my hatches next month.
I don't know the life expectancy of butyl rubber, but I am sure it would be easy to remove and replace if it ever fails due to age.
Butyl rubber will last indefinitely, and stay flexible, within the seal itself. Its one downside is that whatever is exposed will accumulate dirt and grit. This grit may rust or discolor over time. This grit may also harden, crack or shrink sections of the exposed butyl rubber.
Butyl has a long history
of good performance in many navies. They tend to paint
everything. This seals
the exposed butyl and eliminates the grit problem.
In many of the recreational boat applications we dont tend to paint
as obsessively as the military. Choosing a good tube based sealant
is the next step.
Barium based sealants work well but Barium has some health
issues with regular exposure. Probably not an issue for us part timers.
Take notice of the advice for specific applications. Shrinkage is the usual failure mechanism that leads to leaks
From an engineering perspective the following points are worth remembering.
1) compatibility between old and new sealants, and mating surfaces is not well understood. Therefore cleanliness is paramount. Mechanical and chemical cleaning
of the mating surfaces is mandatory. No exceptions.
2) Repairing leaks by adding a bit of goop never works. You must replace the entire seal
3) check flatness of the mating surfaces. Often screw holes will bulge inward which will reduce the effective tension across the joint.
4) flexible seals
will usually fail by peeling as long as the mating surface has enough surface area. Think at least 10x the final compressed seal thickness. When breaking an existing seal peal the surfaces apart. It will take a lot of force and time for a good seal to fail.
5) dont final tension on initial fitment. Final tension after the sealant
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