Caulking Acrylic Fixtures

Dear NH,
You have a great site but the information on tub and tile caulking overlooks the issue of acrylic fixtures. For example, GE Silicon II says it bonds to plastic. However, it fails to tell you that it is worthless when it comes to acrylic. I thought acrylic is plastic! It has taken me a while to discover this problem and I'm somewhat frustrated with Kohler Company because they have not been able to suggest a specific product for this job.
TW from Brookline, MA

I can't speak to Kohler's lack of help. One possible reason might be that some acrylic fixtures have a slight amount of almost undetectable lubricant on their surface when removed from the box, a residue from processing. They should be cleaned with soap and water prior to caulking to insure adhesion. (This is actually a good idea with most surfaces prior to caulking.)

That being said, any non-silicone bathroom grade caulk should adhere to clean acrylic products. If you've read any of my other comments on caulk, you'll see that I am not a big fan of silicone caulks, at least for indoor applications. In fact, I can't think of an interior application where silicone caulk would reliably outperform latex caulk, so I don't recommend using it unless the manufacturer of the item specifically demands it.

Acrylic, by the way, is a "plastic," but the term plastic is a catchall for many products derived from petrochemicals. The variety in plastics is such that no adhesive is truly universal. Many plastics cannot be glued successfully unless the correct adhesive is chosen. With thousands of types of plastics (and more formulations every day), no product label could possibly list the exact types it can stick to, except for industrial or commercially-labeled products used under stringent conditions.

Latex caulks can seal effectively on a variety of materials, including many plastics, but may not be adequate for gluing purposes since the surface adhesion is good but not extremely strong. Since caulks are supposed to be removable (especially in bathrooms where they need to be renewed every few years due to mildew staining), this is a positive, not a negative.
Take care,

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