Sealing Screws -- PMF

Finishes, paints and coatings

Sealing Screws -- PMF

Postby Belmo » Thu Sep 05, 2019 8:00 am

I'll be skinning my teardrop soon, and I have a question.

The main reason I am doing PMF is because I like the notion of a continuous waterproof skin on the teardrop: I like it so much that I'm even going to skin the kitchen, the shelves and all that. I am intentionally overbuilding this thing, in terms of watertightness, because I don't want to have to deal with a leak down the road. I also like how it looks, and the ability to paint it any color I want, but utility is the main reason I'm going that route.

But I am wondering about screws going through the canvas and the camper frame behind it: I'm going to keep these to an absolute minimum, but I can't avoid attaching at least a few things to the outside of the camper: I need brake lights, and I'm going to need to fasten a license plate holder to the back. And I'm toying around with the idea of putting cross bars on top of the camper, and even a fishing rod rack in the front -- I may or may not do these, but if I do, I want to put them in now, rather than trying to retrofit them later.

What did those of you who have used a PMF skin do to seal screw holes? Do you do what boat guys do on fiberglass, which is to use 3M 5200 around the screws/bolts? Or did you do something else? And how have those results held up?
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Re: Sealing Screws -- PMF

Postby RJ Howell » Thu Sep 05, 2019 8:25 am

This is a great question as I'm headed towards that as well. Mine is mainly for hinging, like the widows. My thoughts are on Butyl tape, Dicor, or even silicone.. Dicor is on the top of the list as it's what I used around my roof penetrations on my other trailer. Dicor also comes as a tape (which I haven't used yet).

Curious as to what others have used as well.
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Re: Sealing Screws -- PMF

Postby tony.latham » Thu Sep 05, 2019 8:56 am

But I am wondering about screws going through the canvas ...


I'm not a PMF guy but I use a syringe to squirt a 50/50 mix of oil-based poly in each screw hole. Sealed. It should work well on a PMF skin as long as you do it before you paint.


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Re: Sealing Screws -- PMF

Postby Tomterrific » Thu Sep 05, 2019 12:50 pm

Dipping the screws or getting some sea
lent in the hole will work and I have done that. I also used finish washers with the screws which highlight the build rather than covering them. The inside of the washer was filled with a oil clay caulk called rope caulk. Like modeling clay. This caulk squeezed out when the screw was tightened super sealing the fastener.

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Re: Sealing Screws -- PMF

Postby RJ Howell » Thu Sep 05, 2019 2:50 pm

All things being equal.. My mind goes towards not allowing water to get trapped behind... whatever your mounting. I do like the idea of dipping the screws into sealant. Why not! This conversation is selling me on Dicor tape.
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Re: Sealing Screws -- PMF

Postby TimC » Thu Sep 05, 2019 3:29 pm

On this page I describe the way I made silicone gaskets to bed different attachments. They are all on PMF. Not sure it'll help or that you wish to go to this length. I've stayed away from bedding with butyl tape (messy) and wet caulking (difficult to remove) to seal fastening points.

http://tnttt.com/viewtopic.php?f=50&t=63575&start=120
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Re: Sealing Screws -- PMF

Postby RJ Howell » Fri Sep 06, 2019 7:02 am

TimC wrote:On this page I describe the way I made silicone gaskets to bed different attachments. They are all on PMF. Not sure it'll help or that you wish to go to this length. I've stayed away from bedding with butyl tape (messy) and wet caulking (difficult to remove) to seal fastening points.

http://tnttt.com/viewtopic.php?f=50&t=63575&start=120


Nicely done! I like very much!
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Re: Sealing Screws -- PMF

Postby swoody126 » Fri Sep 06, 2019 8:01 am

5200 is a permanent adhesive/cauk

butyl tape is elastic and can be removed when needed

4200 is a cross between the 2(somewhat elastic adhesive/caulk)

the above mentioned "rope" caulk is what we used2 call "dum-dum" and has an oily base

caulking/bedding IMHO should allow parts to be removed/replaced when needed

on boats we countersink holes(slightly) and fill them w/ the chosen goo then when running fasteners thru the hole the goo not only seals around the edges of the fixture it coats the inner sides of the hole thus sealing them too

also IMHO sillycone has no place on boats or trailers(campers) that are left in the elements... it gets wonky(wonkier when in contact w/ aluminium) and looses it's ability to seal properly over time

sw
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Re: Sealing Screws -- PMF

Postby Belmo » Sun Sep 08, 2019 6:20 am

swoody126 wrote:on boats we countersink holes(slightly) and fill them w/ the chosen goo then when running fasteners thru the hole the goo not only seals around the edges of the fixture it coats the inner sides of the hole thus sealing them too


I think this is what I'm going to do. I like how it's easy, and I think that it will work. I will NOT use 5200 -- I want to be able to remove these later, if need be. Either 4200, or a high-quality exterior caulk, should work.

I did a sample bit of PMF on a scrap piece of plywood. I wanted to see how it would look and feel first -- I thought I'd like it just fine, but I didn't want to do it on the outside of the entire camper, and find out I hated it. I also wanted to make sure that I could get a drill through the finished/painted canvas -- I was curious whether the canvas would tear or bind or anything (it didn't -- drilling holes through it is fine). But now that I have this scrap piece of PMF lying around, I can use it to experiment with sealing screws.

Thanks for the tip.
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Re: Sealing Screws -- PMF

Postby swoody126 » Sun Sep 08, 2019 7:17 am

Belmo, you're welcome

we have also begun using exterior latex calk for attaching some decks when we think there might be a need to remove/replace

latex calk is being used for hardware on boats that get painted w/ gloss exterior latex house paint

TiteBond III, gloss exterior latex house paint & latex calk all having a primarily water base haven't needed all the curing sanding 2nd coating ... process

in some cases we end up "hot coating/assembling" which allows for quick builds(4.5 days) and immediate launching of painted boats

so far it's working/holding up

the only element i haven't personally factored in is the canvass as in PMF which is an absorbant natural fiber(like wood) and i can't imagine any issues raising their ugly heads

btw, rememberize... sailboat decks were traditionally canvassed way back when

many of them lived/survived entire summers out in the elements

sw
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