Installing a Fantastic Fan

[boomer]

I finally bought a Fantastic fan for our Silver Shadow. I cut the hole in the roof and wired every thing in. The roof has a curve to it and it obviously does not sit flush. It did not come with any gaskets. I went to a RV store and bought a roll of putty tape that they recommended. I asked if I should use Butyl tape ( I think I spelled that right ) and they said no that the putty is what I should use. I put a couple of strips of the putty tape where it should go and mounted the fan in place. I figured the tape would fill in the 1/4 inch gap between the roof and the fan. It looks awful and very sloppy. I am going to remove it and take all of the putty off. Are there any reasons why I can't use silicone instead ? I do not think that the putty will leak, it just doesn't look very neat. Thanks for your advice, Ed.

[MtnDon]

The only disadvantage to silicone is that new silicone not stick to old silicone. So if there ever was a need to remove and replace all the old silicone has to be removed. Less of a factor these days is the reaction of the acetic acid in the silicone with metal; years ago there was more acetic acid in the silicone than today. The acetic acid helps it cure. However a high quality latex caulk seals as well, does not react with metal and can adhere to itself.

[KennethW]

I would use polyurethane it sticks better.

[tony.latham]

I use silcone II (it isn't corrosive like I is) and have a love-hate relationship with it. Don's absolutley right about new silcone (or anything else I think) won't stick to where silicone has been before. A good polyurethane would be best I think, perhaps someone could chime in here and suggest one.

T

[MtnDon]

Sika makes high grade sealants. I have used Sikaflex 1a; an elastomeric sealant. I get it from a local metal roofing wholesaler. FWIW, generally a product called a sealant is superior to one called a caulk.

[dales133]

Sikaflex pro is a polyurethane sealant a though it's not an adhesive by rating it's a very good sealant and half the price of of sikaflex 252 11fc and it's other full adhesive rated counterparts

[KCStudly]

Is there any way to caulk or seal a 1/4 inch gap without making a mess?

I would consider making a contoured shim flange to level the mounting location, seal that and the fan flange and screw them in a sandwich. For weather resistance you could consider making the shim out of vinyl trim material or other plastic stock. This shim could be made from 3/8 x 2 inch stock front and rear, and the side pieces could be sanded into saddle profiles tapering to 1/8 inch thick in the middle. You might have to use slightly longer screws.

[boomer]

I went to Home Depot and the only Sikaflex that they had was in tan or gray. I bought some Dap caulk for windows and doors. I went to pull the vent back out and the putty tape that I used was apparently pretty strong and the fan would not come out without forcing it. I did not want to distort the metal so I left it in place. I ran a strip of painters tape around the roof approximately 1/4 inch from the lip of the fan. I carefully trimmed all of the excess putty that squeezed out from between the roof and the fan. I then ran a strip of painters tape around the top of the lip on the vent. I caulked all the way around the fan then ran my index finger around the lip between the 2 pieces of painters tape. I carefully peeled the tape off and it came out perfect. I let it dry over night and will check it tonight. It now has a double seal with the putty tape and the caulk. I saw a factory job that was done and they had warped the metal when they tightened everything up and I was so afraid that this would happen to me but thankfully it did not.I wasn't in a hurry. Thank you everyone for your advice and comments. Ed. ( next project a deep cycle battery so I will get a few days of use out of the fan. Any advice on that one? )