The caulk paradigm: permanent vs sealant

[maury]

This past few days I have extensively tried to better understand which product is best and why. What I am seeing as a fundamental often ignored issue is permanent, semi-permanent or sealant. Other then a major structural fix never to be taken apart why would anyone use a permanent grade caulk? My bigger question is how to differentiate when to use a more semi-permanent vs sealant blend. I understand the challenge of removing parts in the future can be a significant issue when adhesives are used

If something is periodically taken apart every 5-10 years for rebedding it would seem that it comes down to the need for added adhesion power between the two or more parts being caulked and sealant needs. Given screws and bolts are holding everything together is it mostly for added redundancy one would go for more adhesion or can one go heavy into the sealant grade products without significant loss of benefits. For this discussion lets strictly talk about marine grade polyurethane caulks.

When do you choose products which emphasize semi permanent vs sealant?

[Benz]

A sticky caulk that acts like glue will be less likely to be lifted off or gotten past by water. It is actively stuck to the surfaces it's trying to keep dry. A sealant that's not really stuck to either surface is depending on being squeezed to keep water out. That means that as it dries or shrinks or the surfaces change/oxidizes/wick water, whatever, it's not positively grabbing them.
That's why I prefer 5200 in most places I want water to stay out of.

[rslifkin]

If the assembly is extremely rigid, it shouldn't matter much if the sealant is adhesive or not. But if there's any chance of flex or movement, an adhesive sealant is likely to hold up better for all of the reasons Benz mentioned.

I generally default to using 4000UV as bedding compound for that reason unless there's a good reason to use something else in a specific application. The stuff is generally removable enough that I haven't found the adhesive aspect to be a problem.

[SailingHarmonie]

Originally Posted by Benz

A sticky caulk that acts like glue will be less likely to be lifted off or gotten past by water. It is actively stuck to the surfaces it's trying to keep dry. A sealant that's not really stuck to either surface is depending on being squeezed to keep water out. That means that as it dries or shrinks or the surfaces change/oxidizes/wick water, whatever, it's not positively grabbing them.
That's why I prefer 5200 in most places I want water to stay out of.

This is the same silly argument that comes up over and over.

If you showed up on my boat to rebed a winch base, window, or piece of deck hardware with a tube of 5200 in your hand I would send you home right quick. Do not pass Go. Do not collect $200. Do not get paid. To me, that is the very definition of amateur hour.

If your deck hardware is moving around enough that standard sealants will not work, you need to fix the securing of that hardware before you bed it with anything. 5200 is NOT the right fix for a winch or cleat that wiggles under load!

Proper marine sealants do NOT "dry or shrink." And if they are sealed properly, they don't corrode or wick water.

Think about it this way: Sealant for deck hardware (in almost all cases) should simply be a convenient way of making a gasket. It is just easier, simpler and less labor than cutting a good fitting custom rubber gasket. Doesn't matter what product you use, if you could not seal the resulting joint with a rubber gasket then something is wrong. (There is a small exception around through bolt holes, but I stand by the substance of my argument).

Think about all the places we use rubber gaskets to seal water, or fuel, oil, or some other fluid out of something (or inside something) PERMANENTLY. Without a thought that this is a short term fix. There is no reason that this shouldn't work with deck hardware, unless someone is sloppy and lazy.

The amount of time I have spent removing adhesive sealants that were used inappropriately has cost my clients a LOT of money. I make sure they know WHY it took me three times as long as it should have to fix piece of hardware.

[Bowdrie]

I believe that it's a little more complicated than that.
Probably the parts on a boat that are most subjected to the combination of water and flexing are the bases for the bow/stern pulpits and the lifeline stanchion bases.
You can easily see that typically there is perhaps only ~1/4>3/8ths of an inch of metal between the edge and the bolt holes, and the bases are rather small in area.
In that application, (metal to fiberglass,) a product with high flexibility is desired, as well as good adhesion, (really a Polysulfide).
The "rub" today is that the Urethanes have taken over everything and the Sulfides are harder to source.
Now take something like a teak pad that goes between a cabin top and a winch.
In that application, (lots of surface area surrounding the bolt holes,) and large area in general, high adhesion is not so important.
For that, something soft and gooey is a better choice, (even Dolphinite).
The "need" for very high adhesion products, (think 5200,) is actually fairly limited, (like a hull to deck joint).

[rslifkin]

Bowdrie's comments align with my thoughts. On something like a winch base, it should be a solid enough assembly with enough contact area that just about any remotely suitable sealant or gasket material will work. The time where I like adhesive sealants is for the more challenging applications like stanchion bases. Something with 5200 levels of adhesion is overkill though.

[Benz]

Originally Posted by SailingHarmonie

This is the same silly argument that comes up over and over.

If you showed up on my boat to rebed a winch base, window, or piece of deck hardware with a tube of 5200 in your hand I would send you home right quick. Do not pass Go. Do not collect $200. Do not get paid. To me, that is the very definition of amateur hour.

If your deck hardware is moving around enough that standard sealants will not work, you need to fix the securing of that hardware before you bed it with anything. 5200 is NOT the right fix for a winch or cleat that wiggles under load!

Proper marine sealants do NOT "dry or shrink." And if they are sealed properly, they don't corrode or wick water.

Think about it this way: Sealant for deck hardware (in almost all cases) should simply be a convenient way of making a gasket. It is just easier, simpler and less labor than cutting a good fitting custom rubber gasket. Doesn't matter what product you use, if you could not seal the resulting joint with a rubber gasket then something is wrong. (There is a small exception around through bolt holes, but I stand by the substance of my argument).

Think about all the places we use rubber gaskets to seal water, or fuel, oil, or some other fluid out of something (or inside something) PERMANENTLY. Without a thought that this is a short term fix. There is no reason that this shouldn't work with deck hardware, unless someone is sloppy and lazy.

The amount of time I have spent removing adhesive sealants that were used inappropriately has cost my clients a LOT of money. I make sure they know WHY it took me three times as long as it should have to fix piece of hardware.

Why is everyone assuming deck hardware? Though incidentally, I prefer 5200 for deck hardware as well--anything else is just not as good. But look at what most reputable boatbuilders use below the waterline: 5200. Why? Because it's the most reliable sealant goo available.
You can use what you like, but in my experience nothing beats the 5200.

[Flatswing]

Just say “No” to 5200 unless you are mating ‘permanent’ underwater surfaces like keels or Stabilizer assemblies, or a hull to deck joint. Everywhere else a sealant with appropriate UV properties or Bed-it Butyl tape is the way to go. acrylics or glass must be bedded with Dow Silicon or equivalent (not the big box store silicon that smells like vinegar). Remember every bedded structure is probably in need of rebedding every 10-15 years. Why make it harder by using an adhesive which doesn’t seal better but is just harder to remove?

[Bowdrie]

We should acknowledge that 5200 has been on the consumer market for ~50 years.
And in the beginning, it was touted as the "Wonder stuff" for all kinds of bedding/sealing applications and was aggressively marketed to the boating industry.
It might be noted that at that time there were still large numbers of wood boats around and 5200 became a staple in wood boat repair.
So anyway, all the boat builders in the '70s>'80s, and later used it lavishly for just about everything, including a lot of applications where it shouldn't have been used.
It became the "go to" product to replace many other products that were previously carried in inventory.
It was also cheaper than the 2-part products and saved labor costs.
It has its place and always will, but we've learned a lot about where we shouldn't use it.