Need help, replace rivets or try to seal?

[timzog]

So I patched all the obvious holes, replaced missing rivets, and went out and sat in a rainstorm last night to check things out. The good news is that all my new bucked rivets and patches are water tight. Yeah! The bad news is there are a couple of leaks at the top of the main ribs. In some places, I noticed there is a pretty big gap up there between the ribs and the outer skin. So the question is: Do I just tr to seal up all the gaps with vulkem on the inside and Sikaflex on each rivet or do I replace the rivets and try to eliminate the gap? It would be easy to just squeeze vulkem into the gap, but I don't want to miss the opportunity to fix this properly while I have access but I also don't want to replace every rivet on the top of this thing.
Any thoughts or experience would be appreciated.



Thanks,
Tim

[Sodbust]

Not a AS expert,, but looks to me loose tin is loose tin and needs to be 'nailed down"!

I fear just putting putty in the seam will just stretch and work lose again..

Some real body people need to chime in here.. and help this fellow.

Sodbust

[timzog]

Originally Posted by Sodbust

Not a AS expert,, but looks to me loose tin is loose tin and needs to be 'nailed down"!

I fear just putting putty in the seam will just stretch and work lose again..

Some real body people need to chime in here.. and help this fellow.

Sodbust

I think you're right. I just wish you were wrong. I'm getting tired of going backward before I can start going forward. I'm thinking I will add rivets between these rivets and then drill the loose ones out and replace them. The space between rivets where the outer skin attaches to the ribs is 3 times what it is where there are skin overlaps over the ribs. The more closely spaced connections are still perfect after all these years so maybe a few extra rivets will be better for the years of vibrations ahead.

You've also got one more rivet than me, so you must know what you're talking about. Thanks for keeping me honest in a moment of weakness, Sodbust!
Tim

[Kevin245]

So your new bucked rivets are holding fast, but you have a few old leakers? Speaks well of your work. How does the seam look from the exterior?

Before squeezing, riveting or sealing, stand back and see if you can determine the separation cause, and more importantly the effect pulling open gaps together may have on the skin. If it was fabricated this way then pulling the gaps closed may cause some unsightly waviness in the seam between rivets. Also installing new rivets in between the existing ones then drilling out the old ones may cause a slight shift in the hole pattern, leaving you with offset, or oval holes. This may be better left alone and sealed in that case.

If not, then pull the plies together and re-fasten.

Keep us posted.

[barts]

I'd consider a sealant that wicks into gaps. Vulkem/Trembond seems to work well when placed between panels, or into a large gap like one can find around some of the vista windows, but for skin/skin joints something that wicks into the gap and then hardens seems far better. Acryl-R is what Airstream uses and recommends:

http://www.airforums.com/forums/f456...ply-32894.html

I have not used it yet.

- Bart

[timzog]

Originally Posted by Kevin245

So your new bucked rivets are holding fast, but you have a few old leakers? Speaks well of your work. How does the seam look from the exterior?

Before squeezing, riveting or sealing, stand back and see if you can determine the separation cause, and more importantly the effect pulling open gaps together may have on the skin. If it was fabricated this way then pulling the gaps closed may cause some unsightly waviness in the seam between rivets. Also installing new rivets in between the existing ones then drilling out the old ones may cause a slight shift in the hole pattern, leaving you with offset, or oval holes. This may be better left alone and sealed in that case.

If not, then pull the plies together and re-fasten.

Keep us posted.

Kevin,
I see your point. If the current radius of the skin is greater than the radius of the rib, then attempts to secure the two together would cause some kind of buckling for sure. I think I know the separation cause. When I bought this, the interior skins were removed and there were fiberglass panels installed as the interior skins. Also the axle is in bad shape. I will fix all of this before I pull it so the whole system should be more stable. The gap is 2-3 mm in some places so it will be easy to squeeze in sealant, but I am not sure what would be the best choice for that. I think Vulkem works well on large gaps like this. Barts, do you recommend AcrylR for gaps this large?
Thanks for the advice.
Tim

[barts]

Originally Posted by timzog

Kevin,
I see your point. If the current radius of the skin is greater than the radius of the rib, then attempts to secure the two together would cause some kind of buckling for sure. I think I know the separation cause. When I bought this, the interior skins were removed and there were fiberglass panels installed as the interior skins. Also the axle is in bad shape. I will fix all of this before I pull it so the whole system should be more stable. The gap is 2-3 mm in some places so it will be easy to squeeze in sealant, but I am not sure what would be the best choice for that. I think Vulkem works well on large gaps like this. Barts, do you recommend AcrylR for gaps this large?
Thanks for the advice.
Tim

Vulkem is what you want for large gaps; Acryl-R is for gaps where capillary action will draw in the sealant. If you can squeegee in the Vulkem, use that... but for small gaps (less than .030" say), a wicking sealant is the only choice.

- Bart

[timzog]

I think I will try to add a rivet or two in between the existing ones especially on the flattest part of the roof. If I squeeze in some vulkem and then pull it together with a rivet, I don't think it will buckle the skin on the flatter parts. If that works, I'll move down the roof toward the smaller radius curves and see what happens. Then I'll try and replace a couple of the rivets in the worst parts. The other option is to try and rehammer some of the existing rivets. Can you take the rivet gun and bucking bar to an old rivet and squeeze it back together if there is a gap between the skin and rib? Are the rivets work hardened after 30 years? Will the tail of the rivet squeeze the two pieces back together or does the rivet just bulge in between the skin and the rib?
It's raining right now so I have time to think about it.
I have spent many hours scraping off the old white sealant so I could see where there are problems. I can count 4 areas with leaks and they are all where the skin is attached to a rib by rivets space many inches apart. I see no leaks where the skins overlap on top of a rib, but those rivets are spaced more like 1 1/4".
I just threw away a 5 gallon bucket mostly full of that white sealant. I hope to make things as leak free as possible before applying any sealant on the outside of the joints. Buck rivets are supposed to seal their hole without sealant right?
Tim

[barts]

Originally Posted by timzog

I just threw away a 5 gallon bucket mostly full of that white sealant. I hope to make things as leak free as possible before applying any sealant on the outside of the joints. Buck rivets are supposed to seal their hole without sealant right?
Tim

I dip them in Vulkem for good luck... it gets a little messy, but that's ok. I like to see the Vulkem oozing out both sides; a quick wipe w/ a solvent rag and we're in business.

- Bart

[timzog]

So I did an experiment with one of the ribs today. I installed pop rivets in between the buck rivets that connect the main ribs with the outer skin. The original rivets are between 5 and 6 inches apart so I drilled a 1/8" hole midway between the buck rivets from the inside. The gaps between the ribs and the skin at the point of the new holes was as much as 6 mm in some places. I filled the gaps with vulkem and installed 1/8" pop rivets from the outside while pushing down firmly to close the gap. From the inside it looks really good. The vulkem gets squeezed throughout the rib. There is no sign of buckling in the skin. When I can get a buddy to help, I'll drill out the pop rivets, expand the hole with a #21 drill and install buck rivets. At that point, I think I'll drill out the original buck rivets and replace them as well. I have only 3 ribs that have this problem so it shouldn't require more than 40 rivets total. I am worried that vulkem alone will not be good enough if the rivets leak even a little since water will get in and do freeze thaw cycles that have a way of finding a path through any sealant. This is going to add a week or two to my project in real terms but what's a few weeks if it saves tracking down leaks in a couple of years.
Tim

[timzog]

In the past week, I've been removing sealant and preparing to fix the attachment of the 3 main ribs to the skin. Yesterday I injected vulkem into all the gaps between the rivets. The original rivets were spaced 5 to 8" apart and the gaps varied from a mm to 5 or 6 mm deep so it was easy to inject a lot of vulkem in there. Here is a picture of the existing gap.





I then drilled 1/8" holes midway between every original rivet and installed aluminum pop rivets in all of the holes compressing the gaps down to essentially nothing and squeezing out lots of vulkem. I then drilled out all of the original rivets on the roof. To drill out the existing rivets, I used a nail punch to center the hole.
Then I used a 1/8" drill to drill right down the center of the rivet. As long as you are centered, this works great.
After the rivets came out, I pushed up on the outer skin with my finger while I squirted in a little vulkem in each of the smaller gaps where the original rivets were.
Here is what it looked like from the top after I drilled out the original rivets.



I drilled out all the holes with a #21 drill bit and my friend Derek came over and we installed buck rivets in all the holes. I then drilled out all the pop rivets with a 1/8" bit, enlarged the holes with #21 bit and then Derek and I buck riveted all the new holes. In the places with the largest gaps there was a small amount of dimpling



but I think this was the right thing to do since things were so loose. The gap is gone!!




Now I can't wait for rain to check it out. Should come tomorrow so we'll see.
I also patched up the hole from the former kitchen vent. I really like round patches.