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Old 02-03-2004, 09:23 PM   #1
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Need help removing plywood floor section

Hello all, My '69 overlander 27' has the usual rear end seperation and I have removed the interior to restore it and the bad section of flooring. I got some advice fom Andy at Inland when I bought a lot of parts to replace the flooring and holding tank but much is still very unclear. First when I remove rivets from the rear exterior panels to remove them, the tail lights are still quite firm and I can't find a way to remove them, if i have to. I would like to take off enough rear skin to remove the afflicted section of 3/4 plywood from the bathroom area, in fact the entire rear 6 feet at full width and slide a new section in. I am not sure how to proceed. I thought of installing 2 sections for ease of installing but I think it would not be strong enough over the unsupported area above the holding tank. I suppose i need to remove the interior skin as well. Why didn't the factory rivet the bottom of the interior skins to the floor channel? It seems it would have been much stronger in supporting the rear end wieght.
Any thoughts and advice gratefuly welcome,
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Old 02-04-2004, 04:46 AM   #2
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Re: Need help removing plywood floor section

Quote:
Originally posted by brentleew
...I am not sure how to proceed. I thought of installing 2 sections for ease of installing but I think it would not be strong enough over the unsupported area above the holding tank.
It sounds like you are thinking of two sections roughly the same size. How about cutting one section big enough to span from curb-side over to the middle of the street-side C-channel? This should give enough support over the holding tank.
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Old 02-04-2004, 08:13 AM   #3
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It's been refered to Clam shell repair.
DO NOT remove exterior pannels unless it's the last ditch effort. The body is mostly assembled when it is dropped o nthe frame and deck at the factory. The rivets are bucked and it's very noticable when they have been replaced. The lower rivets will hide under the rub rail so not noticable.

Once you drill out the rivets to the first rib under where the rub rail attaches and remove everythign above the bumper then lower the belly pan pan to get at the bolts. You will need to remove the inner lower pannel.
Once everything is free you can put about 200lb on the ends of the bumper and cause the frame to drop about 1-2 inches from the body. This is just enough room to slide in a new peice of deck.


You can only get away with this to the first rib . At the First rib the U-channel has a second lip that wraps under the deck and makes it near impossible to slide wood in and out.

If you hit the search buttom at the top right you should be able to find quite a few posts on how to do this. Many ofe these folks have some pictures if you hit the Photo button at the bottom of their post. use key words like rot, floor repair, clam shell, etc.

I would also look at the posts about Sag or trail droop. Many longer coaches have this problem and there are repairs for it that would be easy to do as your replacing the flooring.
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Old 02-07-2004, 02:03 PM   #4
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I agree with the previous poster about removing exterior rivets only as a last resort. I repaired my frame separation (on a 68) by removing only the interior aluminum. And the only piece of that which I took completely off was the narrow strip under the service hatch. The other pieces were carefully pulled back. This gave more than enough room to place aluminum angle (reinforcement) and tighten the new bolts.

I removed the plywood from the rear up to the first floor rib. I cut all the seams on a 45 degree angle with a spiral saw (God bless the guy who gave me that tip!). I put the new plywood back in three pieces. The seams ran along the back edge of the first rib and the insides of both frame rails. The rectanular middle piece went first and the corners last. If you visualize it or make some sketches, you'll see which way the 45 degree edges need to face for all of this to work. Take your time, start with oversized pieces and work down gradually. If you get a tight fit, everything will be in compression and you can stand on the new floor BEFORE you even screw it down. Epoxy the seams for good measure and you'll be good to go!

Good luck and don't give up!

Jon in SC
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Old 02-07-2004, 07:36 PM   #5
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Quote:
Originally posted by fitzjo1
I agree with the previous poster about removing exterior rivets only as a last resort. I repaired my frame separation (on a 68) by removing only the interior aluminum. And the only piece of that which I took completely off was the narrow strip under the service hatch. The other pieces were carefully pulled back. This gave more than enough room to place aluminum angle (reinforcement) and tighten the new bolts.
Don't see how you could pull back any interior or exterior panels without removing rivets> Please explain more fully.


Quote:
I removed the plywood from the rear up to the first floor rib. I cut all the seams on a 45 degree angle with a spiral saw (God bless the guy who gave me that tip!).
Is a spiral saw the same as a Circular (Skil) Saw?
or a sabre saw ?
or is it one of those things they use to cut out sheetrock openings etc with? Sort of looks like a dremel with a recip blade?

Did you make your first cut along (over) the floor-cross-joist at that angle?
How'd you get up against the walls?
How'd you locate the joist?


Also did you find that the "U-channel" had the added lip to catch the edge of the plywood underneath?

Was the channel rusted all the way thru? And did you add the reinforce plates inside the channel at same holes or make new holes for floor bolts?
Did you have to grind off the old bolts?

Thanks
your answers will help many of us.
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Old 02-08-2004, 10:58 AM   #6
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Thanks all for the advice, I'm still trying to sort out what everyone is trying to convey. I'm fairly mechanical but visualizing these cutting and fitting processes isn't easy. It was mentioned that the outer skins might have to be pulled back enough to allow the plywood to slide out- I can't get my outer skin to budge no matter how many rivets I remove. I know I'm not supposed to remove any more than above the rubrail, but peeling back the skin isn't going to happen unless it's clear to bend up. and it's held under by overlaping seams and compound curves.
Also if you pioneers in this operation had a picture to show this imagination challenged newbie, it would be incredibly helpful. Perhaps even a penciled sketch showing the names of pieces described.
You all are a great help to us- Thank you
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Old 02-08-2004, 12:07 PM   #7
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Sorry, I didn't mean to suggest that you wouldn't have to remove any rivets to peel back the interior panels--you do. However, there are, IMO, four advantages to removing only interior rivets:
-They're easier to drill out, since they have "pilot holes" in them
-You can put back exact replacements with common tools
-You don't compromise the strength of the shell
-And best of all, you haven't created new opportunities for leaks

I would urge others to remove exterior rivets only as a last resort. You simply can't do as good a job of replacing them as the original work (unless you have the equipment).

The spiral saw is the tool used to cut openings in drywall and tile. The bit spins, but does not reciprocate. It is a lot like a laminate trimmer. I made a jig out of plywood to hold it at 45 degrees. It was two planes glued against a 45 degree wedge. I simply laid the tool flat against it and slid it along. The angle jig was butted up against a wooden strip that I screwed to the floor. This kept the cut straight. This arrangement gave me the freedom of movement to cut partly into the wood that was in the U-channel. A chisel and some grunting did the rest.

My U-channel was, well, a U-channel : ) The edge of the plywood could enter or exit only from one side. It was a close fit. In fact, I had to push in some bumps in the channel that were created when the assembler put staples through the channel and into the wood.

The channel was formed sheet aluminum. So, there was no rust, though some areas were noticably corroded. It went along the entire perimeter of the plywood, including the section where the frame was attached. There were "Vees" cut out of the inside of the curved sections.

The frame was attached via a different channel along the underside of the access panel. This channel faced up. It was attached to the inside and outside skins. It was the primary point of load transfer to the skin from the steel rib that spanned between the frame members. I would strongly urge you NOT to drill out the rivets that attach it to the outer skin.

I would draw a sketch, but I don't have a way to digitize it easily. Just think of three "U" channels. One faces in to and surrounds the edge of the plywood. One (steel) faces/opens down to the street and is welded at both end to the steel frame. One faces up and is riveted to the skins. Steel bolts go through the top of the down-facing U, the sides of the inward facing U, and the bottom of the top facing U.

The steel bolts were mostly rusted out, and the rest made big holes in the channel when they pulled through. I put some heavy (1/4" web) 1" Al angle into the the top facing/opening aluminum U. This was much thicker than the original and helped spread the load more evenly.

I know this sounds complicated, but it isn't. Go have a look at your unit and you'll figure it out.

One last tip--seal all of the new plywood with penetrating epoxy. Do the sealing after drilling holes, etc. This way, even if there is a leak--who cares?

Jon in SC
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Old 02-10-2004, 08:09 PM   #8
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Here is a rough drawing of what I am presuming the Airstream
floor/wall cutaway is set up like.

Obviously not to any scale.

Perhaps all wrong! But this is what I deduct from what I have read here and at other threads and even other forums and groups.

We have some really talented architects and CAD guys on this forum, I wish they would get interested in this .

I will remove or try to correct the drawing as soon as I get some clarification on how it really should look. Please notify me here if it is all wet so I can remove it before it misleads some other poor soul.

(This represents a section along the straight side of the trailer not the setup in the rear (or front) curved end).
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Old 02-10-2004, 11:56 PM   #9
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Here is a sketch I did of the existing condition of my 1969 floor assembly. It doesn't call out the peices, but basically:

green=extruded perimeter floor track
yellow= interior, exterior, and banana wrap skin
grey = beltline trim
orange = plywood
red = rivet
cyan = finished flooring

I replaced the last 4'x8' of my rear floor recently, and feel your pain. I added washers where I added new bolts. The biggest change though, was rather than using 3/4" plywood, I used 3/4" plastic (King Starboard XL), which cuts, drills, and holds screws like wood. It is a bit more flexible, but it works for my setup... and it WILL NEVER ROT AGAIN!

You can get Starboard or generic equivalents at most boat repair shops, like West Marine.

Just my two cents.

Christopher
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Old 02-11-2004, 12:59 AM   #10
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Quote:
Originally posted by gerbermania
I used 3/4" plastic (King Starboard XL), which cuts, drills, and holds screws like wood. It is a bit more flexible, but it works for my setup... and it WILL NEVER ROT AGAIN!
Whoa, you just got my attention! How much more flexable is this stuff? Pretty expensive?
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Old 02-11-2004, 07:51 AM   #11
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Thumbs up Jaco & Grebermania -

Great Drawings! -- Karma to you both.

The limited exposure I've had to "Plastic Wood" has convinced me that it is pretty heavy.

That might be a concern if you are doing a large area, and are close to max weight already.

I have only seen a couple examples, though, and there may well be a "light weight" product out there.
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Old 02-11-2004, 08:35 AM   #12
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thanks

Thanks, both of you for posting these pics. I have the same repair in front of me and these drawings will be a big help. I appreciate the time you put into drawing and posting these.
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Old 02-11-2004, 10:51 AM   #13
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As far as the plastic:

Weight is always an issue in travel trailers. However, so is indoor air quality and maintenance.

Standard HDPE and PolyPro plastics are heavier and more flexible than plywood. However, specialty panels designed for use as subfloors are lighter weight and stiffer than standard plastics. Because the plastic panels do not absorb water, delaminate, swell, support mold growth, degrade in UV, or offgass chemicals like plywood. Two products worth investigating are:

CoDeMo Panels: www.codemo.com : These have small, closed, micro-bubbles in them to make them lighter weight and maintain strength.

King Starboard XL: www.kingstarboard.com : The Starboard XL product is lighter weight than the original, and is still quite stiff. It is more commonly available than CoDeMo because it is carried a larger boat repair shops.

For those non-technical types in the audience, to compare the properties of Plywood versus CoDemo or Starboard XL, you need to look at "Density" to compare the weight, and "Modulus of Elasticity" to compare the flexibility.

In a 3/4"x 48" x 96" panel, the Starboard XL weighs 82 pounds, which is only 4 pounds more than Douglas Fir AB Marine-Grade Plywood. That same panel has a Modulus of Elasticity of 0.5, whereas the plywood is approximately 1.5, so it *is* noticeably more flexible.

I added an extra support channel underneath, running diagonally from the rear-most steel outrigger to the main frame channel. It may not be necessary for you, but I have the opportunity to stand in the rear corners, so I wanted to be sure the floor's flexibility didn't add extra strain on the monocoque shell. The extra support channel is wholly contained in the belly pan, so it is completely hidden from view, and did not require the re-routing of any infrastructure like gas or waste piping.

Christopher
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Old 02-11-2004, 12:06 PM   #14
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I made Autocad drawings of the tank frame and floor repairs. Unfortunately, most folks don't have a means of displaying or printing these files. They do not include views of the aluminum channels anyway.

A few thoughts on flooring:

I would try to keep the floor as stiff as practical. It plays an important role in transferring loads between frame and shell.

I had negative clearance between my floor and black tank. IOW, it was force fitted (and there are creep rupture cracks in the plastic as a result). Keep this in mind when adding reinforcement.

The tail end of an Airstream is the worst place to add weight, IMO. I'll admit that I go overboard in this regard. But, all those classes in dynamics, stress analysis and fracture mechanics will do that to a person!

I can't say enough about the wonders of epoxy. You can get 2 quarts of penetrating epoxy for about $25 from www.fgci.com. That's enough to seal a LOT of plywood, yet it weighs less than 10 pounds. I sealed every square inch of the replacement floor. I believe it optimizes the combination of cost, weight, stiffness, and rot resistance.

I need to post my pictures of the floor repairs I did. I just haven't gotten around to exloring the user interface for this site. Presumably, I could post them all permanently and save myself time in the long run. But, I seem to stay preoccupied with two toddlers and all my airstream repairs...

Jon in SC
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