Floor Support & Frame - Fiberglass RV


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Old 09-28-2010, 06:07 PM   #1
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Floor Support & Frame

I have removed the inteior hardware and floor as part of my Lil Bigfoot renovation, but am torn as to how to address future floor sag. I'll be installing 3/4" medium density overlay (MDO) for the new floor, but it appears to me that floor sag may be inevitable due to the lack of lateral frame support. I really don't want to attempt to raise the shell off of the frame and have supports welded. Does anyone know of a way to provide support without frame modification? I will be glassing the floor to the wall. Would glassing the entire floor (side to side) to the wall help? Of course, this might be a little costly due to the amount of resin. Any other ideas?

Also, will painting all exposed areas of the frame (all areas except where the frame touches the body) be sufficient? There is light surface rust but nothing excessive.

Thanks,
Carl
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Old 09-28-2010, 06:39 PM   #2
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Is there no way to bolt on lateral support?

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Originally Posted by Carl G View Post
I have removed the inteior hardware and floor as part of my Lil Bigfoot renovation, but am torn as to how to address future floor sag. I'll be installing 3/4" medium density overlay (MDO) for the new floor, but it appears to me that floor sag may be inevitable due to the lack of lateral frame support. I really don't want to attempt to raise the shell off of the frame and have supports welded. Does anyone know of a way to provide support without frame modification? I will be glassing the floor to the wall. Would glassing the entire floor (side to side) to the wall help? Of course, this might be a little costly due to the amount of resin. Any other ideas?

Also, will painting all exposed areas of the frame (all areas except where the frame touches the body) be sufficient? There is light surface rust but nothing excessive.

Thanks,
Carl
I would think if you didn't want to weld you may be able to drill and bolt some lateral support braces to the existing frame without taking the body off.

Any pictures so we can see what you're up against?
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Old 09-28-2010, 07:12 PM   #3
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I was thinking about the potential to glass on some support, but I, too, would like to see some photos. We need to visualize!
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Old 09-28-2010, 08:21 PM   #4
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I was thinking about the potential to glass on some support, but I, too, would like to see some photos. We need to visualize!

These aren't the best pictures, but I think you can see enough to get an idea. The frame is basically in the shape of a big letter A -- two beams running lengthwise with a cross member at the very back and the axle.

Carl

Click image for larger version

Name:	<a title=Axle 2].jpg Views: 35 Size: 29.7 KB ID: 31484" style="margin: 2px" />

Click image for larger version

Name:	New 2008 <a title=Axle.jpg Views: 30 Size: 50.0 KB ID: 31485" style="margin: 2px" />
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Old 09-28-2010, 09:06 PM   #5
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Am I seeing correctly that there is already a fiberglass "under pan" to the floor?

If so, what did you remove inside? And how were things originally put together?

Did it sag due to inadequate original construction? Or was there rot or something else untoward contributing?

Lastly, I'm not familiar with the "stiffness" properties of MDO, but I would want to know how that stacked up against other materials.

You could potentially go with a sandwich construction or a cored sheet good for your new floor, for more rigidity and (potentially) less weight, but I would want to understand the answers to the previous questions, if it were me (and heck, I am curious now even though it is not me!)

Raya
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Old 09-28-2010, 09:19 PM   #6
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From looking at your pictures, it seems to me that you could use 2" angle iron to span across from frame rail to frame rail. You would only have to cut the one side so that it could rest on top of the frame rail and against your floor and the verticle piece of the angle iron would be flush with the side of the frame rail where you could weld it if so desired. My Burro has spanning supports factory built into the frame from the factory and this is where the floor gets its support on my camper, it seems as though your camper is built very similar, with exception to these supports. My supports are spaced every 2 feet apart and my floor is rock solid.

Mark
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Old 09-28-2010, 09:24 PM   #7
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The axle looks pretty solid.

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Originally Posted by Carl G View Post
These aren't the best pictures, but I think you can see enough to get an idea. The frame is basically in the shape of a big letter A -- two beams running lengthwise with a cross member at the very back and the axle.

Carl

Attachment 31484

Attachment 31485
Why not fit a spacer between the floor and the axle beam you could do something that was square and sat on the axle tight to the bottom of the floor, then with flat plate four pieces you could bolt them to the square tube hanging down in front of and behind the axle sandwiching the spacer onto the axle. That way you wouldn't have to drill or weld the frame at all and if you ever wanted to remove the spacer you would only have to remove the flat plate sandwich pieces.

Hope that was descriptive enough.
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Old 09-28-2010, 09:50 PM   #8
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Originally Posted by Raya L. View Post
Am I seeing correctly that there is already a fiberglass "under pan" to the floor?

If so, what did you remove inside? And how were things originally put together?

Did it sag due to inadequate original construction? Or was there rot or something else untoward contributing?

Lastly, I'm not familiar with the "stiffness" properties of MDO, but I would want to know how that stacked up against other materials.

You could potentially go with a sandwich construction or a cored sheet good for your new floor, for more rigidity and (potentially) less weight, but I would want to understand the answers to the previous questions, if it were me (and heck, I am curious now even though it is not me!)

Raya
I removed the original wet and rotted 3/4" plywood floor, Beneath it is a fiberglass bottom, which is very thick between the outside wall and the frame, but very thin between the main frame members that run lenghwise. I cannot say for sure if the new floor will sag, but a lack of cross member support just appears to be inadequate, especially in the middle of the trailer.

I don't know the exact stiffness of MDO, but do know that it is supposed to stiffer than regular 3/4" plywood. It is not the easiest stuff to find. I had to go to wholesale lumber company that carries a wider range of material than a place like Home Depot or Lowe's.
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Old 09-28-2010, 10:05 PM   #9
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Well if you have a lower skin (the shell), and then there was originally a non-rotted plywood floor and (even better) an upper skin, then I can see how the floor would have been rigid enough. This could explain how there are no additional supports than what we can see now. Once your "filling" was rotten, and the lower skin de-bonded, all the strength was lost. A cored boat deck works similarly.

So, I think you could make a very rigid floor, by creating (perhaps re-creating) a cored sandwich. In a nutshell, you would prep the inside (upper side) of the bottom skin, spread on some thickened epoxy, apply your core (balsa, nida core, plywood, etc.),and then put a top skin of fiberglass over that. With all layers well bonded, this would make a tensioned "sandwich" that is quite strong and rigid for its weight.

I can't speak to the MDO, as I'm not familiar with it for cored construction. For a boat, balsa or Nida core (or Klegecell or a number of other foam cores) would typically be used, with plywood being used less commonly (slightly less preferable). Balsa (vertical grained - comes on special sheets with a scrim) is very stiff for its weight, and is a good core material.

With any type of sandwich or "bathtub" construction you want to make sure to keep water/moisture out of the core (as you have found out). There are some pretty simple ways to do that, which I can elaborate on if you decide to go this route.

Raya
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Old 09-28-2010, 11:24 PM   #10
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Carl---- honestly, the only way to really get a solid floor is to remove the body...... Then weld in more crossmembers/supports. Another weak spot is the door area, without more strength there, it will start sagging. You need to find the rebuild thread by Roger (of Bonnie & Roger in WA- their Lil Bigfoot is listed in the For Sale forum). He rebuilt the frame properly and no sag will ever reoccur. Larry
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Old 09-28-2010, 11:40 PM   #11
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You need to find the rebuild thread by Roger He rebuilt the frame properly and no sag will ever reoccur. Larry
Is this the thread?
TOTAL MAKEOVER - includes pics
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Old 09-29-2010, 07:52 PM   #12
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Well if you have a lower skin (the shell), and then there was originally a non-rotted plywood floor and (even better) an upper skin, then I can see how the floor would have been rigid enough. This could explain how there are no additional supports than what we can see now. Once your "filling" was rotten, and the lower skin de-bonded, all the strength was lost. A cored boat deck works similarly.

So, I think you could make a very rigid floor, by creating (perhaps re-creating) a cored sandwich. In a nutshell, you would prep the inside (upper side) of the bottom skin, spread on some thickened epoxy, apply your core (balsa, nida core, plywood, etc.),and then put a top skin of fiberglass over that. With all layers well bonded, this would make a tensioned "sandwich" that is quite strong and rigid for its weight.

I can't speak to the MDO, as I'm not familiar with it for cored construction. For a boat, balsa or Nida core (or Klegecell or a number of other foam cores) would typically be used, with plywood being used less commonly (slightly less preferable). Balsa (vertical grained - comes on special sheets with a scrim) is very stiff for its weight, and is a good core material.

With any type of sandwich or "bathtub" construction you want to make sure to keep water/moisture out of the core (as you have found out). There are some pretty simple ways to do that, which I can elaborate on if you decide to go this route.

Raya
Thank you Raya! Now I understand what originally happened. The back of the rotten 3/4" plywood floor did have glue and so was bonded to the lower shell at one time.

I do believe I will go with the sandwich construction as I don't relish attempting to lift the shell off of the frame. Also, there should be no reason to monkey with the frame design, which was most likely engineered with a rigid floor incorporated as a integral part. And, I agree with you that my 3/4" MDO acting as a core between a top and bottom layer of fiberglass ought to be quite rigid, especially since it will also be glassed to the side walls of the trailer. I'll use epoxy resin. What type of glass cloth do you recommend?

Please do share your ideas about preventing water from ever entering the core. I do plan to glass over all of the original holes that were used to run cable, gas lines, etc. What do you suggest for running these types of things through the new floor material as I can certainly see this as a possible point of entry for water. I've thought about using Ancor or Perko wire seals. Will these do the job?

Thanks,
Carl
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Old 09-29-2010, 08:40 PM   #13
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Quote:
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Is this the thread?
TOTAL MAKEOVER - includes pics

YUP-- that is it. Larry
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Old 09-29-2010, 10:41 PM   #14
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Hi Carl,

It's nice to have some idea what happened, isn't it? I always feel better repairing or improving something if I think I understand why it originally worked and why it failed.

I will write up something and post it tomorrow - I wanted to let you know that I did see this, but I just don't have time to respond tonight.

I won't say the MDO won't work; I just don't know enough about it to know if I would recommend it as a top choice (but, perhaps I will investigate it before tomorrow so that I can say something more definitive about it ).

Raya
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