Why would silicone caulk not cure?

Question

I re-caulked my shower on Saturday afternoon, using GE Silicone II Kitchen & Bath Caulk. I left it alone until Monday morning, when I showered in it. I assumed it had plenty of time to cure so did not check before using the shower. When I used a squeegee to clean water off the walls of the shower, I hit a corner and discovered the caulk was still as soft as when I had applied it over 36 hours earlier. I could wipe it away with my finger.

What would cause my caulk to not cure?

Some possibilities:

• Humidity is about 100% right now. I live close enough to Hurricane Harvey to get lots of rain.
• The silicone caulk tube says to use by 2014. Does this caulk really expire?
• I smoothed the caulk application using my finger dippped in warm water, based on a YouTube video I watched to give me confidence. Was this a bad idea?

Answer 1

Expired caulk

You bet it expires, and fast. That is because of the chemistry of this type of caulk. The stuff is nearly magic, but that comes at a price.

Extremes of temperature are not kind to it either. That's not a surprise, even latex paint has that problem.

I have had your experience myself, grabbing random caulk found around the shop and going "this must be OK", only to have to redo the project. Removing the old material completely is a huge chore, and the job will fail if you don't. Never again!

Answer 2

The answer will depend on the exact type of sealant you used.

For the standard silicone sealant (acetoxy- condensation cure or "acid cure": smells of vinegar as it cures), the curing reaction actually requires water to take place. So high humidity or use of water in smoothing should not have prevented the curing. This type of sealant usually uses organotin catalysts which are non-volatile; the most likely degradation in storage is premature hardening in the tube. Acid-cure silicone is known for being resistant to cure inhibition ("Next to nothing stops a condensation cure setting"), though this reference states that isopropyl alcohol and some Lithium compounds can inhibit cure.

For addition-cure silicones which contain a platinum catalyst, there are many substances which can interfere with curing (see "Platinum catalyst poisons" on this page for a complete list), including rubber, latex, previously cured silicone and PVC.

Answer 3

GE Silicone II caulk is not an acid cure (vinegar smell) caulk. Once it is past its expiration date throw it away. Be sure to check when you buy it too that it is not past the expiration date. Stores are not good about rotating the stock for items like this. I was just burned by this caulk. I went to use it after it was sitting in my basement for quite a while. I checked it and saw that it did not harden and found it was still very soft, so I thought all was good. Not so much though, 2 days later my little job is a clean up and redo.

Answer 4

1. Humidity can definitely affect cure time (for latex caulk especially)
2. Caulk can expire, but that usually means it's spoiled (i.e. hardened). Still, some rely on a curing agent, which evaporates, and caulk tubes are not necessarily 100% airtight
3. Not at all. It's a good idea to use cleanup solvent/water (in moderation) to spread caulk

Try staying out of the shower a couple of days. If it still fails to cure, get some fresh caulk and start over.

Answer 5

I have experienced the non-drying silicone a couple of times. Both times it was black, last time was with the GE product. First time was an old tube from the local small hardware store and it was years past the expiration date. I used it to install a bathroom sink so one can imagine the work to clean both surfaces to redo the job. Last time was an old tube from my garage shelf. It was oily on the outside (first sign it’s gone bad) but it flowed perfectly. Next day I had to remove it because it hadn’t cured even slightly. So to sum it up, watch that black GE silicone. I have never experienced any issue with curing when I use small permatex tubes like automotive gasket material.