3M Marine Adhesive Sealant 4000 UV, PN06580, White, Medium Strength Flexible Waterproof Adhesive Sealant for Boats and RVs, UV Resistant, Cures in 24 Hours, 295 mL Cartridge, 10 Fl Oz (Pack of 1)

This is THE product to use for marine applications when you don't want a permanent bond. The issue for me is, it's quite expensive and I only tend to use a fairly small amount at a time for repairs (e.g., installing a replacement stanchion). They tell you that you need to use it within one week of opening. This is only true if you want to dispense it through the nozzle. What I do for small jobs is punch a small hole in the side (I use a nail set or a nail), squeeze a little out using a caulking gun, and spread it with my finger (in a nitrile glove), then slap some tape over the hole. I've now been using one tube of a year on 6 small jobs, and I expect to do more.

This is an excellent product overall. While marketed as a marine sealant, it can be used in other applications where a waterproof, UV resistant seal is needed. I previously used this to seal around mounting brackets for solar panels on an RV roof. Now, I am removing dicor sealant around vents and other openings on the roof and using this instead. Based on my experience with it around the solar panel mounts, it seems to be far superior to dicor and similar products sold as roof sealant. It sets up quickly and acts as both a sealant and an additional bonding agent. I suspect it is strong enough to hold the solar panels by itself (I used VHB tape as well). The only downside I have found is it does not keep its shiny white appearance over time; it gradually turns dull aand yellowish, but as long as you use it where the appearance does not matter it is a great product.

Worked well and is very strong.

The 3M Marine Adhesive Sealant 4000 UV delivers excellent performance for sealing and bonding in tough outdoor conditions. Its UV resistance ensures it won’t degrade or discolor, even with prolonged sun exposure. The adhesive is flexible after curing, making it ideal for marine use and projects where durability is key. It’s easy to apply and provides a strong, lasting hold. A dependable choice for anyone needing a sealant that can withstand water, weather, and time.

I used this product during the repair of a Suzuki outboard. It works great but I wish they sold the 4000 in the smaller squeeze tubes like they sell the more permanent version.I also wish they sold this in black.Product is very easy to work with and you mold it with your fingers just like caulk.

This stuff saves the day even if applied underwater. But do wear nitrile gloves as it will seal to your hands for awhile. That just proves it’s a great sealant!

So good, only brand and formula I really trust

Moving to a new house, we unknowingly let a vinyl lined hot tub (Softub) sit in the summer air upside down for three months. BIG mistake. This resulted in several rips and tears (including one 2 feet by 6 inches!) in the inverted sagging of the long-water-dependant vinyl. We thought our hot tub was a goner. Tried numerous hot tub rip repair kits, and none of them worked well enough for this major repair job. The hot tub was aging and had served us well for nearly a decade, so we didn't want to purchase a complete replacement liner because of the price - either fix it or toss it.Vinyl patches provided were strong enough, but none of the vinyl patch kit adhesives were able to really withstand the stresses of a full 300 gallon water load on the stretchable vinyl. We made all repairs while tub was empty so as to obtain the best seal. In addition to vinyl-specific glues and patch kit adhesives, we tried vinyl contact cement, shower pan liner adhesive, and every single type of PVC/vinyl glue at the local home improvement store. Not even Loctite plastic bonder would hold once the hot tub was full and chlorine was added to the water.As a last resort, we decided to give this "below the waterline" "hull repair" "permanently flexible" sealant a try - and WOW! it sticks to everything. We gave it a good cure of several days (this was outdoors in winter, so took a bit longer). We used this to adhere the vinyl patches to the tub' vinyl liner, to each other, and to feather around the edges so as to prevent bathers from tearing up the sides or water working the sides loose from the jets.2 months in to this repair, from which no other product/system/glue previously lasted longer than a week.Much impressed by the miracles of modern petroleum strength commercial chemical derivatives - nicely done 3M!