3M 5200 Marine Sealant et al

I can only answer one of your questions. Once silicone caulk is applied, it works well for a long time. But it eventually needs scraped out and replaced. Unfortunately, even if you do a great job removing the silicone, and it looks spotless, there is still a film of silicone on the roofing/trim/whatever you scraped it from. Nothing will stick to that film, not even new silicone caulk.

Ranger Tim wrote:
I know people scream not to use silicone but I never hear why. Where is the holy grail of information on all things RV caulking?

Everything I've read on the forum about not using silicone is because nothing will stick to silicone, including other silicone. So, in theory, if you need to recoat a seam the new silicone will not stick to the old.

Maybe that was true with the original silicone caulks? And maybe the newer silicone caulks don't have that problem? I don't know.
I've had good luck with Dicor caulk but, I would consider using a different product if I knew there was not an adhesion problem.

The RV Industry probably uses what works and is the cheapest.

As for finding the Holy Grail on caulking, opinions are like other body parts, we all have one.
I don't know if there is a one size fits all answer.

Silicone is just base material, when caulks have advanced formulas and silicone roof coating makes the best material it is.
I tried all kind of caulks on my RV and marine caulks would turn yellowish within couple of seasons, not mentioning their adhesion to rubber roof was poor.
Their internal strength played no role.
The best caulk I experienced is the pictured below. It will stay flexible, is paintable and relatively easy to apply. Then what really made my rubber roof leak-proof was mentioned Henry's silicone roof coating, who will stick and feel gaps around all caulking.

I used 3-M UV 4000 marine sealant on compartment doors and horizontal seam on our Bigfoot. I believe Bigfoot and Northern Lite use this product at the factory.

Most of the recomended caulks are polyurethane basied, they dont get real hard like silicone and other caulks. This allows them to stay flexable. Silicon, is what they said above, not a great idea. You like the 3m , use it , its poly baised. I dont k ow what the quad is, but its miniral spiret clean up so probably the same. Polyurethane caulks you can clean up with miniral spirats and it becomes tacky again, so you can go over existing caulk if its adhered well. The others you cant. And always try to use the same stuff. Some may not play well with others.

5200 is great stuff. I use it to seal screws and sink drains. Never tried using as a caulk.

Ranger Tim wrote:
When I was on the east coast I grew up using the 3M sealants for marine industry, notably 5200 and 4200 caulks that came in squeeze tubes and cartridges. These lasted for many years in salt water. They would also go through season after season of abuse from freezing and vibration. I can't believe there is anything that vibrates and moves more than a boat pounding the waves. Those sealants are tough, last for a long time and don't let go. I even used them to mount lighter weight things to fiberglass hulls with no screws with success.

A lot of world cruisers HATE 5200 !

First, let's start by saying all caulks/sealant fail. Some last longer that others, but they all fail. Proper preparation will make them last longer, but still, they will fail.

Many (most) world sailing cruiser will bed things in butyl tape. It stays pliable for a long time. Any "squeeze out" can saved and reused. If the seal fail, remove the item and the butyl, clean and re-apply butyl tape. Butyl is not an adhesive.

Second, once 5200 is on a surface and cured, it is next to impossible to remove. If you need to re-seal something, it ALL must be removed. There is no solvent (that I know of) that will remove 5200 although low heat makes it easier to scrape.

Last, the RV industry uses what is CHEAPEST.

Thanks for all the input. I understand the feedback on silicone. I also watch the butyl caulk squeeze out occurring on the camper seams and worry about how much is left. I don't mind using the Dicor but it seems to only last a year or so before beginning to show signs of sun damage/cracking. I will be switching to Sikaflex in the short term, but was looking for input on longer term solutions. I figured there had to be others that are as fed up with continual maintenance as me - and I don't even have any real problems... yet.

There are two reasons the 3M and equivalent Sika products are not used in the RV industry: cost and installation time (in other words, cost). No one would use the common RV products on a boat, and no one responsible uses silicone.

Silicone lasts forever as a lump, but is a very poor adhesive, so it really only works when clamped between two rigid flanges. These conditions rarely exist on an RV, and the usual method of slathering it on the outside of a joint is pointless. It simply fails, collects dirt and water, and prevents resealing the joint properly.

5200 is as much an adhesive as a sealant, strength is around 700 psi so it is for things you want to mount permanently. It can be removed, but you will need to put some effort into it. There are now polyurethane debonders that help. 4200 is another polyurethane, with about 1/2 the adhesion of 5200 (300 psi). Both take days to cure, though both come in a "fast cure" formula that takes about 24 hours. This is one of the reasons they are not used in RV production. Both of these will yellow in the sun and eventually (years) degrade from UV exposure.

4000UV is a polyether, and is highly resistant to yellowing or degrading from UV. It is a bit stronger than 4200 but not as strong as 5200 (400 psi). It cures a little faster than the "fast cure" polyurethanes. This is the product I would use on an RV, unless the strength of 5200 was needed.

Any of these is far better than typical RV sealants: better adhesion, more flexible, and retain flexibility longer. Properly done, a vent or window frame should be good for 15 - 20 years without attention. On boats 30 years to reseal hatches is not uncommon. I cannot understand the tolerance of RV owners to having to pour snake oil on the roof year after year. There are better ways.

I personally don't like butyl tape. It doesn't harden, but it doesn't cure or stick to anything either. When it gets hot, it oozes out of the flange making a mess, and now it is gone when things cool again and you've got no pressure on the seal. I've seen many things sealed with butyl fail, including the shower skylight that I am right now fixing on my Bigfoot.

Part of the reason for the post was the disconnect between the boating community and the RV side of things. I'm after people's perspectives and have appreciated the responses so far. Much obliged!