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Old 08-31-2004, 07:34 PM   #4
cx
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Epoxy Grout, Caulk, and Other Pookey (a collection of posts)

Chris the Rep
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Join Date: Aug 2004
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The most commonly used silicone sealants in the construction trade fall into 2 groups with regard to their chemistry and cure method. If it says on the label that it is "acid curing" or "liberates acetic acid" it is known as an acetoxy silicone. We've all used them, they have that pungent, distinct vinegar odor. If you read the tube and/or the data sheet, they are generally not recommended for use on masonry or cement based surfaces. The acid that is liberated during the cure can attack the cement, or in some cases the stone, potentially causing bond and seal failure. As a tub cauk, it works great because it bonds extremely well to the more-often-than-not glazed surface of the tile. As it relates to shelf life, when it gets old, it hardens in the tube, so there is no question as to whether it is bad or not.

Neutral cure silicones used in construction often use an alkoxy cure method. They are used often in the glazing and curtainwall trades. Since they don't liberate acid when they cure, they work great on masonry, stone, brick, and other acid sensitive materials like anodized aluminum, galvanived surfaces, copper, etc. Urethanes are often used with metals, but for glass and structural glazing, neutral cure is the best. Unfortunately, neutral cure silicones have a short shelf life, unless refrigerated. 6 months is the usual. However, unlike the acetoxy that gets hard in the tube, neutral cure will gun out of the tube like a dream, it will just never cure. What's worse than removing caulk? Removing caulk that didn't cure.

Most of the limitations regarding acetoxy silicones aren't a huge concern to the average tub surround job. But when you're essentially gluing in 500# panes of glass a couple of hundred feet or more up the side of a building, you tend to get a little picky about such things.

Neutral cure is a good choice for the tile trades, but it is more expensive. Buy it from a caulking/waterproofing wholesaler that sells a lot of it, that way you'll know that you're getting fresh material.

Chris
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Last edited by cx; 09-20-2004 at 09:08 PM.
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