silicone sealers

Silicone is for bathtubs or landfill.

It has absolutely no place in sealing anything exterior, including RV's.

OK

One word, ProFlex.

I've had so many leaks to repair that I tried many types. No leaks now after using everything from silicone to the poly's. One place in particular I used only rv type byutle (sp.) type tape/rope caulking without any sealant around the outside.

I discovered actual Vulkem lasts a long time. Discovered removing the part, cleaning and caulking between mating surfaces is key since the sun/ weather cannot get under there.

Also discovered byutle tape is made in varying degrees of quality and the industrial grade from heating and air conditioning parts supply houses are the stickiest/ best to use. Hardware store, rv store quality is usually just non professional grade by comparison.

Last, the byutle tape is loads easier to clean off and redo. Because of this I have left off the perimeter caulk that is so hard to clean off for redoing it later.

Good hint to buy the tape from heating and air conditioning parts supply houses. Do you have another hint about the best sources for sealant like Vulkem?

I used silicone for years making fish tanks and it worked great for that and bathrooms / kitchens. Not a fan of it for anything else. Went in to a RV place a year ago for new furnace and guess what he used to seal the furnace vent, you got it silicone. Says that is all he has used for 30 year and would not use anything else. As soon as I need to redo it will use something else, but to be fair it is still on there and not separating.

jimh425 wrote:
Good hint to buy the tape from heating and air conditioning parts supply houses. Do you have another hint about the best sources for sealant like Vulkem?

Vulkem is a caulk that is in the polyuerethane family but with a fiber reinforcement that causes it to have more of a textured surfac. It may be one reason it has lasted so long, perhaps acting like a reinforcement in the caulk. Many types/ brands fall into this 'poly' family or catagory that are usually considered the better types. Labeled under many brand names, they each have their own differing viscosity and behaviors based on proprietary formulas with polyeurathane bases.

I tested Vulkem only because I'm in the building industry and was just another brand to try out on hand. It's been on there for over ten years and is still not come loose nor cracked. I used it to seal between metal to plastic, metal to fiberglass. Those seams still are holding well.

Vulkem is available at most building supplies and is the least expensive of all the poly type caulks out there, but, does turn a bit off white over time. I don't mind as leaks have been the biggest exasperation in buying my new rv.

Vulkem is murder to get off. Any polyeurathane will be so I'm right now leaning toward only using the industrial grade byutle caulk which is easier to redo.

I will only use Butyl tape, PLAS-t-COTE and ProFlex.

I have bought the Butyl tape from several different RV supply stores, but have had clerks try to give me the clay type tape.





I have bought the PLAS-t-COTE from RV supply stores and Box hardware stores.



I purchase ProFlex from RV supply stores. It is great, but very difficult to remove, and does not bridge gaps very well. It easily goes into cracks. I have used the white, black and clear.

My 1988 Bigfoot was sealed with Butyl tape, PLAS-t-COTE and Silicone. All of the Silicone has failed years ago. It was only stuck where it was not needed. I have had no failure with the PLAS-t-COTE. The only failure with the Butyl tape was poor application, as can be seen in the following photo.

Polyurethane sealants in general have far greater adhesion than silicone. If you look at a company that makes both (like 3M) they list the adhesion to different substrates of all of their sealants.

I think those in the industry like silicone because it is easier to handle and clean up than a good, sticky polyurethane. Also quicker curing than most good polyurethanes. On the RVs I have owned, they must have bought silicone by the boxcar load, because it was used in copious quantities, inappropriately. And in many cases did nothing to seal out moisture.

Polyurethanes can discolor in the sun, that is why I use 3M 4000UV for exterior. It does not yellow - the UV is for UV resistant.

If polyurethane must be removed, there are products that will do that. "Antibond" is one that seems to work pretty well (you can get it at marine stores like West Marine). I have tried a couple of others that don't seem to work as well. Another trick with polyurethane is that it will creep: apply some force (for example with a wedge) then wait a couple of hours, tap it in further, wait, etc. With patience, you can separate it.

Finally, many (most?) sealant joints are improperly designed, whether you are using silicone or polyurethane or butyl. You need some thickness of sealant to allow the two parts to move relative to each other, especially when they are different materials, like aluminum and plastic. These will expand at different rates, and flex at different rates. If you squeeze the joint so that there is a thin bond line, there is not enough flexibility in the sealant to accommodate the motion. Lets say you have a sealant capable of 100% stretch before failure, and a joint of 1/16". The parts can only move 1/16 before the sealant fails. If you instead have a 3/16" joint, now it can move 3 times as far before failure. Many times this can be done by inserting small spacers inside the joint to guarantee the sealant thickness.

HMS Beagle, I like your post very much.

I have heard of sealing all mating surfaces screw it down but, not quit all the way. Wait till the caulking is cured, then tighten the screws. Sort of like forming your own gasket. But this sometimes requires a strong frame for even pressure or adding more screws.

I'm going to stay with the butyl tape because I've had great success, usually doubling it, even triple it in some places and on a warm day it'll squish into a good seal. This means having to add screws to a compartment door frame for 'pressure fit' if they don't already.

I like sealants on jack mounts for strength and to seal screws/ bolts.

If you don't seal bolts/screws/threads on a jack mount having only perimeter caulk, it'll will act like a funnel. That's the problem I had with my new camper. Screws were not sealed to fiberglass body and leaked everywhere.