3M 5200 Marine Sealant et al
I currently go over my camper religiously looking for chances of leakage at least every six months. Seams on the roof, windows, etc. are checked for any signs of cracked sealant or separation. I treat...
Forum Discussion
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.
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.
