Butyl remains pliable over time. For this reason you want the joint to bottom out so you can torque the fasteners. Once torqued there is no need to retension to maintain the seal using butyl.
If your joint relies on the compression
between the butyl and the fitting and parent material you run the risk of squeezing the butyl out of the joint if you keep tensioning.
If however you are using a sealant
that will set, such as life calk, then it is good practice to not fully torque until set. Then torquing will apply compression
to the joint thereby effecting a good seal.
Joint design dictates whether buytl is appropriate or not. In all cases the joint load should not alter the compression joint of the sealing material. The key is to not unload the seal (seperate it) or overload it (displace it).
One final note, all elastomers fail from peeling before they fail from tension or compression. No joint should introduce a peeling load or displacement
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