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Old 02-27-2016, 01:55 AM   #51
GeorgeRa
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Default Re: Caulking for roof vent/fan?

Use zinc loaded primer which you could cover with paint, than wait until fully dry before putting a butyl tape down.
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Old 02-27-2016, 02:04 AM   #52
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Default Re: Caulking for roof vent/fan?

Quote:
Originally Posted by Aqua Puttana View Post
You really should determine whether silicone caulk was used. If no silicone your life becomes much easier.

Did the caulk that you removed feel stretchy and slippery? Did it come off in very small pieces? If not, then it probably isn't silicone based.

Butyl tape/caulk will stick to cured sealant if it isn't silicone based. You don't need to clean off every scrap before installation.

I would not use razor blades. I feel a bit differently about scratching off perfectly good OEM paint. If it is intact I leave it alone. Try using mineral spirits (paint thinner) with a Scotchbrite scrubbie pad. That should remove all that is needed.

If you do use mineral spirits I would give a rub off with acetone before installing any sealant. Acetone leaves no residue, but it is nasty stuff so my advice is to use the mineral spirits first. Mineral spirits is about as user friendly as solvents get.

vic
I don't know what the caulking/adhesive is. The caulking around the vent that I removed was soft, rubbery, and stretchy. At one point I did go over the original caulking and screw heads with Sikaflex though. The stuff that was put under the gasket and subsequently smashed down tight when the fan was screwed on, is not like hard rubber. It's still kind of soft but impossible to get off without the heat gun, or maybe razor blades which I have not tried to use yet.

The thing is that with using the heat gun and putty knife, sometimes I end up removing the adhesive and the OEM paint down to bare metal. :(

It's supposed to rain for at least a week here so I doubt I can do anything to it for awhile.

I've decided that I'm going to go ahead and have Line-X put on the roof like Jon Caples did to his van, only I'm going to go with white instead of gray. I should have done that years ago! I spoke with Carl, the owner of Tucker's Line-x in Burlington, WA about it today. He said that all of the adhesive needs to be removed before I bring the van in, but it doesn't matter if the paint is scraped down to bare metal because they will remove the rust and prime any bare metal before they spray on the Line-X. Because I want white, he said he couldn't get me in for a couple of weeks. In the meantime, I'll just get up on the roof whenever there is a break in the rain and go at it with the heat gun and putty knife (or razor blades) until I get it all off.

I want the fan to be removable (in case it needs to be replaced), so I think I'll use the butyl tape over the Line-X and stainless steel sheet metal screws in the existing holes. Then I'll probably use a good caulking around the edges and on top of the screw heads. Someone mentioned putting on enough caulking and feathering it out over the flange and the screw heads, so I might do that. I like the idea of the Eternabond tape, but I don't know if it would be easily removable in the future. If so, I'd rather do that than the caulking.

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Old 02-27-2016, 02:08 AM   #53
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Default Re: Caulking for roof vent/fan?

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Originally Posted by OrioN View Post
To minimize the gouging, I round the corners and concave the front profile of the metal 'blades' .



.
Yeah, rounded corners would most definitely help! I'll have to keep that in mind for the next job. I'm going to have Line-x put on the roof asap, and the installer said that he will deal with any bare metal or rust as part of the preparation process. Because of that, I think I'm just going to go ahead and scrape (or gouge) away and not worry about it.

Kat
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Old 03-12-2016, 07:13 AM   #54
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Default Re: Caulking for roof vent/fan?

if you read sikaflex specs carefully you'll note that it doesn't bond to plastic--i learned this the hard way with a leaky roof vent as well.

i've since used dow 795 which does bond to plastic & has high UV/sun resistance, no leaks in 6+ years of parking outdoors.

http://amzn.to/1RFl6LK

http://www.dowcorning.com/DataFiles/...fe801a7bbe.pdf
"Available in 13 standard colors;
custom colors also available
 Excellent weatherability – virtually
unaffected by sunlight, rain, snow,
ozone and temperature extremes of
- 40°F (-40°C) to 300°F (149°C)
 Excellent unprimed adhesion to a
wide variety of construction
materials and building
components, including anodized,
alodined, most coated and many
Kynar®1
-painted aluminums2
 Ease of application – ready to use
as supplied
 Ease of use – all-temperature
gunnability, easy tooling and lowodor
cure byproduct"
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Old 03-13-2016, 07:26 AM   #55
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Default Re: Caulking for roof vent/fan?

Several different Sikaflex were mentioned by others as there many kinds. Which Sikalflex were you referring to?

Silcone will can cause rust on bare metal:

"Since the acetic acid is released during curing, it can attack the
underlying substrate material. This can cause corrosion of certain
metals and prevent the proper adhesion of the silicone. However, on
other materials, the acid can etch the surface slightly and increase the
adhesion. Aluminum is one such material. Copper and zinc, however, are
corroded by the acid. Thus brass and galvanized steel should not be used
with silicones which release acid. Dissimilar metals can form
electrolytic couples and corrode severely underneath a covering of acetic
acid releasing silicone. Silicones do not adhere well to all other
plastics either."
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Old 03-13-2016, 08:31 PM   #56
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Default Re: Caulking for roof vent/fan?

Quote:
Originally Posted by shenchman View Post
if you read sikaflex specs carefully you'll note that it doesn't bond to plastic--i learned this the hard way with a leaky roof vent as well.

i've since used dow 795 which does bond to plastic & has high UV/sun resistance, no leaks in 6+ years of parking outdoors.

http://amzn.to/1RFl6LK

http://www.dowcorning.com/DataFiles/...fe801a7bbe.pdf
"Available in 13 standard colors;
custom colors also available
 Excellent weatherability – virtually
unaffected by sunlight, rain, snow,
ozone and temperature extremes of
- 40°F (-40°C) to 300°F (149°C)
 Excellent unprimed adhesion to a
wide variety of construction
materials and building
components, including anodized,
alodined, most coated and many
Kynar®1
-painted aluminums2
 Ease of application – ready to use
as supplied
 Ease of use – all-temperature
gunnability, easy tooling and lowodor
cure byproduct"
I run away from any silicone sealant like from a plague. As long seal is good it is OK, but if you have to reseal or replace a component it is a nightmare. Nothing will stick to silicone sealant and its removal is painful.

In regards to using polyurethane sealants such as Sikaflex or 3M products like 5200 they actually stick well to most plastics, but there are plastics to which no adhesive will stick well like Teflon or Silicone Rubber.

I used extensively 3M 5200/4200 and lately Sikaflex 252 and never had an issue with adhesion to plastics. It would be nice to see which Sikaflex you are refereeing to and perhaps see the text that polyurethane doesn’t stick to plastics. You can use primers to improve adhesion to some materials, see attached.

Personally I don’t like using polyurethane on any components which could require replacement like for example a roof fan but this is just my view. Polyurethane is used on windshields and windows and there are easy methods to cut through with a wire but I prefer just an easy butyl tape with a self-leveling sealant like a Dicor.

I am attaching 3 polyurethane pdfs sealants and primers with specifications including adhesion strengths to different materials.

George.
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Old 11-20-2019, 09:15 AM   #57
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Default Re: Caulking for roof vent/fan?

Quote:
Originally Posted by NelsonSprinter View Post
If you have a smartphone here's the locator app
https://usa.sika.com/en/group/Media/mobile-apps.html

the product should be Sika Hyflex 150LM
Thanks for the link, but I think I'll go with a silicone sealant instead.
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Old 11-21-2019, 01:51 PM   #58
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Default Re: Caulking for roof vent/fan?

Silicone sealant should not be used on vehicles. They prevent any subsequent sealant from adhering. In the event you need to patch, replace, or change the sealant, you will be forced to mechanically remove the paint to get a good bond for the new sealant.
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Old 11-21-2019, 02:11 PM   #59
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Default Re: Caulking for roof vent/fan?

I didn't go back and review the thread, so this may be repeating.

I agree with avoiding silicone caulk.

It is the roof. Nobody sees it.

For a repair I would use Eternabond tape to overlay the original sealant. Clean the surfaces as best you can and press the tape on.

I wouldn't choose 3M 5200 sealant. It is a great product, but it is a strong adhesive. 3M 4200 seals well, but is a less aggressive adhesive.

Just the other day I sealed some leaks on the 2004 vent. The sealant and Eternabond didn't fail. It has a plastic flange. After over a decade in the sun the flange has small cracks in various places that run out and up. I used roof repair mesh and sealant to address those cracks. So far so good.

I will never install a plastic flange vent unit again. The 2006 vent fan that I installed has a galvanized metal flange/base unit. If a plastic flange unit is the only option in your choice of vent unit, I would definitely use a flange adapter of some type. I believe that Hein offers them. https://www.ebay.com/itm/132298140143
The steel bases don't necessarily need an adapter.

vic
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