Sealant schooling

[ripperj]

I am putting new aluminum skins on the roof and lower section on my Alaskan camper. The original windows and vents were sealed with butly tape. In most cases it lasted 30 years, so I am planning on using it for the primary seal. I want to seal the edges of the butyl and screw heads with something white from a caulk tube, lots of choices, I know not to use silicon.
What should I use to secondary seal the edge of the buytl tape?, 5200 looks pretty much impossible to remove.

Also on a roof vent, should I use Dicor lap sealant over the screws and the joint between the roof and vent?( with buytl tape underneath the vent flange)

What about places that have a light aluminum corner bracket over aluminum siding corners, the tape is too thick, so it would have to be some kind of caulk. The corner trim gets screwed on.

Thanks for any input

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[silversand]

When I completely reconditioned our Caribou pop-up this summer (just completed it last weekend: about 180 hours of labor), used several lap sealants: Dicor flowable caulking (when re-doing the roof vents x2: 1 aluminum flange; 1 plastic flanged, caulked to pre 2010 TPO), Dicor non flowable (caulking the TPO roof fascia to aluminum); ProFlex bright white for my "under-wing trim" (which I had to remove and reinstall to replace rotted under-wing plywood), and SicaFlex 221 multi-part urethane for bedding screws (this includes dipping all the new stainless steel screw threads). Then, I removed and resealed both the battery and propane hatch (radius) frames (butyl strips, then caulking using contractor-grade Flextra Expert white INSIDE the re-install and the exterior perimeter on both: these standard RV hatches leak like a sieve, so I had to drill weeping holes along bottom of the hinged hatch doors). I also replace EVERY soft steel RV screw (I replaced literally hundreds, many rusted beyond recognition or usefulness) with high quality stainless steel screws of the correct size (and our camper is 100% aluminum framed, imagine?), and I bedded and thread dipped every new screw.

I use the caulking for the job (does the part/structure you want to seal flex? If so, by how much? Thermal expand? If so, by how much? Have a base plastic or membrane that is negatively affected by certain caulking formulations? Is the caulking for bedding screws? Spanning an unusually wide "gap" ? ).

One thing you must be aware of when buying caulking: ALL CAULKING HAS A FINITE SHELF LIFE ! Buy caulking directly from the manufacturer, or, from a large RV repair shop that goes through hundreds or thousands a tubes over summer, or from a distributor. Retail stores and on-line vendors may not rotate their caulking in a timely manner, and you may end up buying tubes of solid block dried caulking, semi-dried/semi-cured, or caulking so stale, the caulking may not function as it should (or at all). Learn how to squeeze the tube to determine if a particular caulking is drying inside the tube, and how to de-code the date/manufacture stamps on the various brands...

 

[silversand]

....oh, you mention 5200 caulking/sealant (3M products): 3M has a very wide variety of caulking! Dozens. You have to buy the 3M caulking for your application: skin time, tensile strength, cure rate, elongation properties needed, etc, etc, etc.

Some 3M caulking/sealants cure flexible -- like for bedding screws, or for flexing (to cope with thermal expansion of same or differing materials caulked), etc.

I have used the 3M 4000 series for bedding screws but not for direct UV exposure. Also, if your 3M caulking will be taking in incoming solar radiation (UV A & B, etc), you need to buy the 3M caulking actually rated for UV exposure ! Otherwise, the exposed caulking will crack and dry in 2 years or less.

 

[ripperj]

Silversands - that's an awesome reply, I need to digest that and look up some of the products, I'm not familiar with most of them.
Thanks!

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[shanz3n5]

im following.....can i ask what are bedding screws

 

[ripperj]

Bedding screws is covering the head underside and threads of a screw before you insert it in the hole, seals the underside of the head and the threads to the parent material.

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[silversand]

Ripper described the process perfectly. I have a photo of the bedding underway (after bedding, a cap of the same caulking is applied, and smoothed). Every stainless steel screw (and socket) was cleaned before application of sealant, and I used cotton gloves during the process, so that my skin oils weren't coating the screw, potentially usurping the sealant's effectiveness. I have to upload photo apparently (to my photobucket space, and link), before posting...will do this later...

Flextra (Supra Expert):

http://www.mulco.ca/sealants/doors

Geocel Pro Flex:

http://www.geocelusa.com/product/all-rv-aftermarket/pro-flex-rva-flexible-sealant-detail.html

Sikaflex -221 - Sika AG:

http://usa.sika.com/en/industry/industry-home/01a004/01a004sa05.html

Dicor self-leveling and non-sag sealants/caulking:

https://dicorproducts.com/catalog/roof-products/replace/epdm-lap-sealants/

 

[shanz3n5]

perfect. thank you. been doing that, just new term for me. looks like i will be hitting giant rv for sealant today. thanx to all the info and the sealant question post.