Caulking replacement roof vents

[BobBeery]

On 87 Dolphin, I found 2 roof vents were leaking because they had all-plastic frames which had cracked in two or four places. I decided not to try sealing the cracks because on one frame the cracks were too long. They would probably flex a bit and the seal would not hold. So I bought new vents with metal frames. The question is how much of the old caulk has to be removed to get a reliable seal with the new caulk. I bought caulk tape to use. Scraping the old caulk will not get it all because the roof top is aluminum and embossed with a pattern similar to wood grain. I can use a plastic scraper to get down to the embossed ridge tops but all the valleys still have the old stuff in. I can't scrape too hard because the aluminum is too soft (and painted). also the old caulk is two kinds, a softer material which can be pulled and stretched is under the flange. A different material was put on later in a swath an inch wide or more over the flange and onto the roof. This stuff is very firm and hard to get up. I have tried using a metal putty knife with a thin blade to get under it but it cuts into the aluminum roofing where the high spots are, so I would rather stick with the plastic scraper. Is there anything else I can do, such as a solvent? Oops I didn't mention I also have 100% silicon caulk to apply after the new roof vents are screwed down. (And MaxAir hoods go on too)

[Diesel_Aggie]

I've read in another RV forum that Coleman camping fuel works wonders on getting the old sealant loose. I'm real curious about your roof as the only aluminum RV roofs I've seen are just a big sheet of smooth aluminum. Would be interesting to see a picture. Is the silicone you are using UV resistant? I can't recall the recommended roof sealant on my old aluminum roofed Lance camper but on the aluminum sides clear Geocell 2300 was recommended. It is UV resistant and stays flexible. It is commonly used on house roofs and can be found at most roofing suppliers. I've read in several other forums to avoid silicone as it collects dust. I used it before I read about it on an old 5th wheel and it did collect dust. Probably not an issue on the roof but it sure is ugly on the sides if a white camper! Another though just occurred. If the Coleman fuel works well, maybe that and a firm toothbrush would get down in the pattern.

[BobBeery]

And a big thanks to Diesel_Aggie. I tried the Coleman fuel and it worked great on the soft sticky caulk. On the other hard caulk it was possible to remove some but it was slow going and a lot of scrubbing. However, it got the dirty surface layer off so that fresh clean stuff was there for the new caulk to stick to. The first new roof vent is installed and I am completely confident I'll be leak free for many years. I'll do the other vent tomorrow.

[86rader]

i've had pretty good luck with lighter fluid. i was under the impression that coleman fuel was basically just unleaded gas. i think they called it white gas a few hundred years ago when i was into that backpacking thing.

[WME]

Technically speaking lighter fluid and Coleman fuel are closer to each other than Colman fuel is to unleaded gas

[Gulfstream Greg]

Oops I didn't mention I also have 100% silicon caulk to apply after the new roof vents are screwed down. (And MaxAir hoods go on too)

Silicon is a NO-NO. Lap sealant is what you want to use, available from any RV parts house. The silicon will eventually come loose and then nothing else will stick to the surface after that. As far as getting the old stuff off try some acetone or lacquer thinner. After you screw down the new vent let it sit for a couple of days then trim off the excess tape then apply the lap sealant along the edges and over the screws.

Here is a link to some sealant http://www.pplmotorhomes.com/parts/rv-roofs/rv-rubber-roof-lap-sealant.htm

[flatspin]

Silicon is a NO-NO. Lap sealant is what you want to use, available from any RV parts house. The silicon will eventually come loose and then nothing else will stick to the surface after that. As far as getting the old stuff off try some acetone or lacquer thinner. After you screw down the new vent let it sit for a couple of days then trim off the excess tape then apply the lap sealant along the edges and over the screws.

Here is a link to some sealant http://www.pplmotorh...lap-sealant.htm

Oh yeah, silicone is unfriendly stuff. On my Sunrader when I bought it I discovered a slow drip coming in the black water tank vent (which sneaks up through the closet to the roof). Turns out a previous owner had installed the vent cover entirely with silicone. No butyl tape, etc. And then when it clearly hadn't been water tight, just added more and more. It looked like a cowpie of silicone on the roof. What a nightmare to remove.

And the best part is that the butyl tape and dicor are much easier to deal with than silicone too... big win win.

[BobBeery]

Thanks everybody for all the info. I got the old caulk off with scraper followed by Coleman fuel followed by a clean dry cloth. New vents are installed with butyl tape. The silicone will go back to the store unless I find a use for it somewhere around the house. Have a tube of Dicor non-leveling caulk on hand but leave tomorrow (Sat. Sept 4) for a week in Michigan's upper peninsula. Plan to walk my wife across the Mackinac Bridge Labor day. Then I can finish the caulk. BobBeery