Thanks to Randy Leasure for this heads up about 3M 4000 UV. 

See the article on line at Practical Sailor

Six years ago (“Marine Sealant Adhesion Tests,” published November 2016) Practical Sailor began exposing samples of marine sealants to weather and sunlight to compare how they retained adhesion and flexibility, and how well they resisted mildew. Periodically and at the end of five years, we examined the samples and awarded final grades. Near the end, we tested removing mildew with a deck cleaner and dilute bleach. Eventually, we took the sample panels down, but we didn’t throw them away. We put them in a storage area, in case we needed to refer back to them.

Recently, we’ve received several reader reports that 3M 4000 UV used to bed hardware had become sticky and begun to leak. We went back to our sample rack, and sure enough, the 4000 UV had lost all strength, the surface had become slightly sticky, and the center had become liquid, with the same gooey feel it had the fresh out of the tube. It was a complete failure and a mess. It was a shocking change from less than a year before. It was as though the polymer had suddenly unzipped and returned to its uncured state.

The rest of the samples on the rack were performing exactly as we left them a year ago, just one year stiffer, as expected. The other polyether, Loctite Marine, was unchanged.

The response from 3M was as follows:

“Thank you for your inquiry regarding 3M™ Marine Adhesive Sealant 4000 UV, Black. We are sorry that the product did not meet your expectations. At 3M, we aim to continuously improve our products. Your feedback indicates that you have product that is prior to our reformulation in late 2018. We appreciate your interest in the product and are happy to send you a sample of the reformulated product.”

We’ve asked for a sample and will be re-testing it alongside competing products. But we won’t know anything definitive for five years. Meanwhile, we’re not going to be using 3M 4000 UV. Inspect projects where you used it, specifically anything pre- 2018. Until we know more, we’re recommending Sika 291 as the Best Choice for all-around sealing of fiberglass and deck hardware, and Loctite PLS40 Door and Window as our Budget Buy. We’ve been using these for decades and they’ve never let us down. Our 2016 Marine Sealant Adhesion Test” highlights other standouts for specific jobs.

We are currently following up with 3M to get more details regarding the failure of its product. Some posters on online forum threads report similar failures. We’d like to hear from anyone else who has had a similar experience with 3M 4000UV or any adhesive sealant. You can email us at practicalsailor@belvoir.com