The general issues in selecting a caulk are:
Silicon or urethane usually performs best overall. It lasts longest and holds up best, but is harder to apply (can make a real mess) and isn't paint able. Silicone "Tub and Tile" caulk has a mildewcide -- use in areas that get wet, but don't use it in area where it will contact food or drinking water. There are other versions without the mildewcide for these applications. [A possible exception to silicone being the best caulk is urethane caulk which may be as good and is paint able. See discussion below.]
Elastomeric latex sealant (caulk) comes next in durability and is paint able.
Latex, silicone/latex (siliconized) and acrylic is next, but there's a lot of variation in quality within and between brands.
Latex is easiest to apply and cleanup.
Butyl rubber is dead last.
Silicone is essential to seal around bathtubs, showers, lavatories, etc. There's a special bathroom formulation for this that has a mildewcide. This poison has been known to be hazardous if used inside dishwashers because the high heat outgases the poison onto the dishes and is then eaten. The implementation of every caulk and latex product is given in www.fixallroofs.com
If silicone does not cure it makes a godawful mess. Most manufacturers specify a shelf life of 1-year from date of manufacturer for silicone caulk in unopened tubes. I've not seen times for partially used tubes. Silicone will last longer than a year, but if it's old you must test it to see if it is going to cure. Silicone does not air dry, it has a curing agent. If a sample placed on a non-porous surface does not cure in 24 hours don't use it.
Tips
Tip1: Cold caulk can get stiff and hard to squeeze out of the tube. If it's cold, put the tube it in a pan of warm water for 20 minutes or so.
Tips2: Here are some ways to reseal partially used caulk tubes.
In the past I used a large nail stuck into the tip. This works good for keeping the tip clear, but the nail sometimes rusts causing you to have to pump out a lot of caulk to get rid of the rust.
Right now I'm using a large wire nut (used to connect electric wiring) to cap the tip if I'll be using it again within a month. The gray wire nuts are about the right size. For longer term storage I use a piece of plastic (Saran Wrap or plastic bag type) over the tip, held in place with masking tape or a rubber band. Squirt a little caulk into this sock covering the tip -- it will harden first, helping seal the caulk in the tube. Some people use a piece of duck tape instead of the plastic wrap but it doesn't seem like it would be airtight enough.
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Original source: http://www.articlesbase.com/diy-articles/issues-in-selecting-a-caulk-339259.html
