Need Help Selecting Appropriate Sealant

These top skin covers were initially sealed with proseal, which was applied to the lower countersurface and the covers had vaseline applied as a release agent while the proseal cured with the screws installed. Unfortunately, they have always leaked a little.

There is no room for a gasket here - is there a more appropriate sealant to use? Something that seals well, but still allows for cover removal for inspection and service?

Old modelers trick.

Lay a bead of RTV on the doubler, cover it with saran wrap.

Attach the cover with all screws and go away for a day.

When you remove the cover, the saran warp will just peal off, and a conforming seal will be left in place. Trim off any excess that has squeezed out.

Done.

Thanks Mike.

Given that my plane is not yet painted, I have a pretty strong aversion to using silicone based RTV because of the contamination issues it can cause when painting. Is there a better choice out there? I wonder what the airlines use for sealing inspection panels like these?

Look up access panel sealant. It's a form of the stuff that's designed specifically for this situation. Here's some:

http://www.skygeek.com/prc-desoto-pr-1428-access-door-sealant.html

Put it on as if it were a fuel tank, without plastic wrap, Vaseline or other contaminates.

Dave

Gasket/sealant

This is how I did mine: Riveted in a .032" spacer ring between the top skin and the nutplate flange to allow for a gasket. Masked area around the openings and top surface of cover with packing tape. Scrubbed the flange with scotch brite and cleaned well. Put proseal on the flange then stretched a sheet of Saran Wrap over the opening. Punch small holes in saran wrap with a pick then screwed cover down carefully into the proseal using a straightedge to get the cover edges level with the adjacent skin. Ran a razor blade around the cover to remove excess Saran Wrap then used a hotel room key as a scraper to get most of the squeezed out proseal off the packing tape. Let dry then removed cover and all masking tape.
I thinned the proseal with mek so it would flow better and mixed with a little less activator than normal to allow more working time.

Don Broussard
RV 9 Rebuild in Progress

1. Try latex caulk instead of silicone

2. What did you do to seal the nutplates? Any chance the small leaks are around the screws?

If folks want to do this type of access,, your might consider that virtually every business jet has access panels to the wet wings. You might consider contacting Cessna or Bombardier or who ever and get a gasket and make your access panel work with the gasket they use. I have only seen a couple weep in my entire life. You can also contact a maintenance shop that works on this type of equipment for their advice on making a gasket.


Smilin' Jack

The trend these days (in 4 prop military transports built in Marietta, GA, at least) is towards avdec gaskets, which are thin sticky clear plastic membranes with some conductive material built in. They have to be specially cut so....$$$

I wonder if you could get the same effect if you could find some really thin, really soft rubber sheet and cut some gaskets out with an xacto knife.

Some white lithium or even wheel bearing grease might also work, added to what's there already.

Put a piece of automotive vinyl over the whole top (black if you want the traditional black antiglare look). It will peel right off if you need access. Then put a new sheet on. OR

Do the above and just cut the seams around the access plate, peel that section just over the access panel when you need access. Replace with a small patch.

It will be tight as a drum.

Bevan

Scott Card made a nice gaskets for similar setup years ago. I hope he will chime in Noah.

Gasket

The skin thickness on biz jets and even wet wing Mooneys is a lot thicker than what's on our RV's. On those planes the fuel tank covers are typically installed with a low adhesion pro-seal type sealant. To get those covers off it takes enough force to damage RV skin so I wouldn't glue them on.


Don Broussard

RV 9 Rebuild in Progress

Sealant

Why couldn't you use plumbers putty? Just an idea, not necessarily a good one.

I don't know if this material is compatible with aluminum.

Appreciate all the comments on this.

David Paule, I didn't realize they make sealants specifically for this purpose, I think you are on the right track. Skygeek does have a good selection, with quite a range in pricing:
http://www.skygeek.com/access-door-sealants.html

There is no extra thickness built in for a rubber gasket in my case, so unless I want the covers to stand proud, I am thinking I need a sealant that can be squeezed with the screws before curing down to almost nothing in spots. These sealants seem to have low adhesion, making the panels hopefully not too difficult to remove. Does anybody have any experience with these? Preferably the cheaper ones like:
http://www.skygeek.com/ac-tech-ac215b1-2-2-5oz-215b-low-adhesion-sealant-2-5oz.html

Latex caulks also seem like that might be worth trying, if the panels can be removed without too much trouble. I'm definiteley concerned about damaging the panels when removing them as CajunWings hints at.

Charlie, I'm not sure what to do at the screws, goop it up I guess!

Smilin' Jack, I am hoping some of those jet mechanics are also building RVs and frequent this site!

Fuel bay panels will have sealed nut plates. I'll bet the leaks are around the screws. i would use clear aviation silicone under the panel and run the screws in wet with silicone.