Tip tip

This post originally appeared on Windborne in Puget Sound

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Have trouble with polysulphide, silicone or 5200 curing in the tube tip between uses?  

Here's a tip: wipe the tip clean before you snap the cap back on. See that thin ridge that goes around the tip?  That is supposed to seal, plastic to plastic, with a mating groove inside the cap, making a *snap* when you push it on.

None of the compounds I listed above "dry" - instead they harden by reacting with water vapor present in the air.  And the reaction is designed to propagate over significant distances of the material, so that thick layers will cure all the way thru. Therefore if there is a continuous layer of material reaching from outside the sealing ring and past it into the tip interior, the reaction will proceed into the tip and then eventually into the tube itself. 

Thinking of this as if the tube were filled with polyester resin, and the air was saturated with MEK peroxide catalyst will give you a clearer picture perhaps. 

Just before the final capping, extrude some of the contents, flushing the end bit which has been exposed to moisture. Then thoroughly wipe off the tip and install the cap. You'll be surprised at how little in-tip curing there has been the next time you need to use the material.