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Old 11-17-2010, 07:08 PM   #1
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Problem with Bigfoot Floor Renovation

I am close to glassing in a new Medium Density Overlay (MDO) subfloor into my Lil Bigfoot and have run into a bit of a snag. Raya, you have been a huge help (Thank you!). Not only could I not determine how to attach picutures in a related private message, but also I figured others might want a look at what I am facing in case it is helpful. Essentially, the bottom fiberglass "pan" had detached from the original, badly rotted subfloor, and had apparetly "stretched" over time. (picuture #1). You are seeing the fiberglass "pan" after it has been prepped with a grinder. The MDO floor is white due of a layer of paint that I had applied a few months ago as part of a plan that I have long since abandoned. The paint has already been sanded off. When attempting to compress the floor pan against the new MDO floor (see picture of jack set-up), the result is two thin pockets running the length of the trailer between the central portion of the floor that has been raised and the two frame members that run the length of the trailer (picture #2).

My plan is to reinforce the bottom pan with a layer of epoxied glass cloth that will cover the entire floor and be adhered to the walls of the trailer. The I will adhere the pan to the new subfloor with a layer of thickened epoxy. I will address the pockets by sandwiching a thin layer of lumber between layers of thickened epoxy to fill the gap. I may also be able to reduce the size of the pockets by adding one more 2"x4"x8' board to the jack setup, which is 4 scissor jacks in two sets, each of which supports 2x12 boards that, in turn, support the 2x4x8 boards that run the lenght of the floor. After the bottom is complete, I will then glass entire top of the floor to the walls of the trailer, thus sealing the subfloor from below and above. The goal is to prevent water from reaching the subfloor in the future. Let me know what you think.

Carl
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Old 11-17-2010, 11:57 PM   #2
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Carl,

It looks to me like the weight of the body is pushing the floor pan up at the frame.
I see a dip between the frame and wheel well wall.

I'd be tempted to lift the body off the frame, place plywood (temporarily) that has been cut to fit - between the floor pan and frame and then see how your interior floor fits. Perhaps supporting the center similar to your pictures above.

Alternatively, a series of 1x2's slightly spaced (like a deck) running from side to side might be cheaper and easier to fit than the temporary plywood underneath.

I also question if the MDO is strong enough to support everything without warping itself as it does not have the long fibers of plywood structurally arranged in a crossing pattern. Overlays are usually meant to level something, not support it.

It is interesting that your axle says "Cerka" on it. That is the name of a Dexter dealer up here in Ontario, Canada.
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Old 11-18-2010, 08:31 AM   #3
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Originally Posted by Carl G View Post
I am close to glassing in a new Medium Density Overlay (MDO) subfloor into my Lil Bigfoot and have run into a bit of a snag. Raya, you have been a huge help (Thank you!). Not only could I not determine how to attach picutures in a related private message, but also I figured others might want a look at what I am facing in case it is helpful. Essentially, the bottom fiberglass "pan" had detached from the original, badly rotted subfloor, and had apparetly "stretched" over time. (picuture #1). You are seeing the fiberglass "pan" after it has been prepped with a grinder. The MDO floor is white due of a layer of paint that I had applied a few months ago as part of a plan that I have long since abandoned. The paint has already been sanded off. When attempting to compress the floor pan against the new MDO floor (see picture of jack set-up), the result is two thin pockets running the length of the trailer between the central portion of the floor that has been raised and the two frame members that run the length of the trailer (picture #2).
My plan is to reinforce the bottom pan with a layer of epoxied glass cloth that will cover the entire floor and be adhered to the walls of the trailer. The I will adhere the pan to the new subfloor with a layer of thickened epoxy. I will address the pockets by sandwiching a thin layer of lumber between layers of thickened epoxy to fill the gap. I may also be able to reduce the size of the pockets by adding one more 2"x4"x8' board to the jack setup, which is 4 scissor jacks in two sets, each of which supports 2x12 boards that, in turn, support the 2x4x8 boards that run the lenght of the floor. After the bottom is complete, I will then glass entire top of the floor to the walls of the trailer, thus sealing the subfloor from below and above. The goal is to prevent water from reaching the subfloor in the future. Let me know what you think.

Carl
Carl,

I am currently replacing the floor in my Burro and have the new plywood installed and glassed in on the outside. I will put it back on the frame before glassing the perimeter on the inside. I did the wheel well areas yesterday. I faced a similar decision when replacing my floor. The old plywood was completely rotted, although the fiberglass skin on the bottom of the plywood was intact and in good condition. I decided to cut out the fiberglass skin as part of the replacement process because I could not see a good way to insure proper bonding of the new floor to the old skin and the perimeter at the walls.

As far as I know, fiberglass does not stretch very much, so your sagging floor may be because the walls pulled in and are not far enough apart. As the old floor rotted, weight on the floor could have caused it to sag by pulling the side walls inward. I won't get into the all details, but each pound of weight on a sagging floor can pull the walls in with tens or hundreds of pounds of force. If this is what happened, spreading the walls back out could take out much of the sag. Just be careful of causing damage if you try to spread the walls. Even if you take most of the sag out, it will be very difficult if not impossible to get a good bond, without gaps, between the old fiberglass and the bottom of the new floor. Water will leak into these gaps where the floor is bolted/screwed to the frame and eventually cause rot. The thin fiberglass at areas of gaps will be unsupported and easily damaged.

I would recommend removing the old fiberglass floor and glassing a new one directly to the new sub-floor. This is best done by removing the fiberglass body from the frame. Removing the body is easier than you might think and in the long run will save time and result in a stronger, more waterproof structure. You could easily jack the body off the frame with the jacks I saw in your pictures. I only used 1 jack to remove the body from my frame. With the body off the frame you can easily clean and repaint the frame and add extra floor support in the sagging areas.

If your replacement floor is made from particle board rather than plywood, I would strongly recommend switching to plywood. Particle board and flake board are not very strong and should not be used as sub-floors. Some current manufactures use flakeboard for the floor, but it is an inferior product and only offers modest cost savings over plywood. It is also heavier.

Good luck,

Andy
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Old 11-18-2010, 10:01 AM   #4
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Thanks for posting the photos, Carl. That's interesting.

I've never seen fiberglass "bag" like that without breaking (i.e. if forced to "grow" it just cracks instead), so I would also be interested to know if the walls have shifted somehow (probably inward?) and that has caused the apparent "stretch." Floppy fiberglass I've seen - it's actually a fairly floppy material; I just have not seen it "stretch." I wonder if you "tugged" the walls apart at the bases of the sides if things would suddenly fit. Or are you going by holes that went through the floor into the frame and you can see they are lining up?

On the MDO. I might not choose it myself, but it's not particle board. Also, in a cored panel, the core itself does not have to be strong enough to support the load - it's mainly there to keep the upper and lower skins separated and bonded. It's the sandwich that gives it strength. Vertical grain balsa is a very good and commonly used core material for fiberglass sandwich construction, and of course it's not "strong" in the usual sense.

Andy, if I'm understanding you correctly on what you are trying to bond: You can get a good secondary (mechanical) bond to existing fiberglass. Epoxy resin does this better than polyester (and I think even better than Vinylester although V is better than Poly). You just need to properly prep (provide tooth, solvent wash, etc.). Of course a primary (chemical) bond is great, but if secondary bonds did not work no-one could repair 30-year-old boats, and that is commonly done. Actually, even a new boat will often have secondary bonds, as everything is not done within the primary "window" for one reason or another. If I misunderstood what you were saying... never mind!

Raya
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Old 11-18-2010, 12:29 PM   #5
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Originally Posted by Raya L. View Post

Andy, if I'm understanding you correctly on what you are trying to bond: You can get a good secondary (mechanical) bond to existing fiberglass. Epoxy resin does this better than polyester (and I think even better than Vinylester although V is better than Poly). You just need to properly prep (provide tooth, solvent wash, etc.). Of course a primary (chemical) bond is great, but if secondary bonds did not work no-one could repair 30-year-old boats, and that is commonly done. Actually, even a new boat will often have secondary bonds, as everything is not done within the primary "window" for one reason or another. If I misunderstood what you were saying... never mind!

Raya
Raya, What I ment about the difficulty in getting a good bond was the mechanics of the assembly not the actual bonding power of the resin. There is floppy fiberglass hanging below a "to be installed" solid floor. It would be difficult to have the old fiberglass floor smoothly pressed against the bottom of the new floor so there is a good bond without air bubbles. Unless something mechanical holds the fiberglass to the new floor, it will flop away before the resin sets. I thought about using soft foam on plywood with jacks underneath to press up on the fiberglass as a way to get even pressure on the fiberglass as the resin sets. I decided it would be easier to cut out and replace the fiberglass than to try and save the old fiberglass and bond it to the new plywood floor.
Andy
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Old 11-18-2010, 03:38 PM   #6
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Hi Andy,

Thanks for clarifying that. Sounds like a situation commonly encountered when re-coring boat decks, although they are usually not as wide (except in a few places). There, it's most common to use prop sticks and plywood or other forms from below, then to possibly reinforce the lower skin, and then to proceed with the re-coring and new top skin.

Since you are right there with your trailer project, I'm sure you've figured out the best way for your job. Sometimes a way can sound good theoretically but then when you get your hands on it you can see a better one
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Old 11-18-2010, 05:38 PM   #7
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Hi Andy,

Thanks for clarifying that. Sounds like a situation commonly encountered when re-coring boat decks, although they are usually not as wide (except in a few places). There, it's most common to use prop sticks and plywood or other forms from below, then to possibly reinforce the lower skin, and then to proceed with the re-coring and new top skin.

Since you are right there with your trailer project, I'm sure you've figured out the best way for your job. Sometimes a way can sound good theoretically but then when you get your hands on it you can see a better one
Thanks everyone.

For clarification, MDO is far from being a particle board type of material. It is essentinally phenolic resin impregnated paper laminated between layers of ply(11 layers of wood in a 3/4" sheet). After working with it, I can tell you it is quite dense and doesn't appear to flex as much as standard 3/4" plywood.

In terms of the sagging, it is a bit of a mystery. I too thought that the weight of the trailer may have caused what looks like extra material in the portion of the floor between the frame members, but I don't see how that would have been possible with bolts (4 in the rear and 2 in the front) clamping the plywood subfloor and fiberglass pan to the steel frame. I just can't see how "extra" fiberglass could have crept from the outside of the frame members, past these bolts and to the middle of the trailer. Additionally, the fiberglass over the frame members and extending outside of the frame members is considerably thicker than the central floor. It too has sagged around the frame members to an extent.

I actually think that removing thebody from the frame might be counterproductive at this point. The fiberglass in some of these areas around the frame members is quite thick. It is not going to simply lay flat with the body removed. Instead, I plan to exert pressure in many areas around the perimeter of the body, which will most likely remove some pressure being exerted on the middle. If I can reduce the depth of these two "pockets," I believe that my idea of a thin lumber spacer sandwiched between layers of thickened epoxy will fill the void nicely. I may not be able to eliminate every single air pocket, but I think I can sufficiently bond the bottom to the new floor. I plan to prevent water intrution by overdrilling all bolt points and all penetrations for electric and water lines and then using thickened epoxy to form annuli. I will then drill the correct diameter holes through the epoxy for bolts, etc., thus eliminating the possiblity of water reaching the wood interior (Thanks for that tip Raya!). I'll send more pictures as I go. With all of the surfaces that I plan on exerting pressure, the bottom of the trailer will most likely look like scaffolding around a building. Should be interesting.

Carl
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Old 11-20-2010, 11:44 AM   #8
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Have you considered removing the body, cutting out the floor leaving a 2-3" tab all the way around then attaching the floor pan to the MDO? Then you could glass it all back together. One might even consider leaving the majority of the cuts / repairs so they line up with the frame.

Someone sent me a link to info on MDO, which I now understand to be quite different from MDF.
Medium Density Overlaid
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Old 11-20-2010, 11:51 AM   #9
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Thanks Roy. If it looks as if my plan to apply pressure around the entire perimeter and the center portion between the two main frame members is not going to sufficiently press the lower pan to the MDO, I may consider removing the body. I'll keep you posted.

Carl
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Old 11-20-2010, 08:31 PM   #10
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Carl,
Looking at your picture with the floor toggled to double ridges, it seems that your floor is compressed between the frame rails about 0.4. I am basing this assuming that 2 folds are about 1 wide each, with 1.25 deflection peaks making the radius of each of these two curvatures about 16.5.
If I would be in your shoes, I would likely relax one side of the chassis and let it move 0.4 then make a tight floor sandwich using sacrificial bolts going through the floor and support structure below. After the sandwich is fully cured, I would remove the bolts and fill their holes with silica filled epoxy.
George.
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Old 11-22-2010, 11:32 PM   #11
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I think you might need to get some steel crossbeams under there to support the floor, whether you weld it or bolt it in place.

Regards,

Matt
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Old 11-23-2010, 11:11 PM   #12
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Matt,

At this point, I am going to go with the MDO sandwiched between Fiberglass. I will be adding a layer of new glass cloth covering the existing glass pan and extending up onto the walls of the trailer, followed by thickened epoxy. After adhering the pan to the bottom of the new MDO subfloor, I will then glass the entire top of the MDO floor, extenidng about 7 inches up onto the walls of the trailer. It should be failry substantial.
Carl
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Old 11-25-2010, 11:40 AM   #13
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Update: Yesterday, I placed almost all of the supports for the fiberglass bottom; it looks like adding pressure along the perimeter, outside of the main frame members is having a positive effect. I still have several more to place. I had planned to do the glassing this Saturday, but the temperatures are going to be a bit on the low side for resin. I'll shoot fot he next weekend. Happy Thanksgiving everyone!
Carl

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