Floor Support & Frame

[Carl G]

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

[Rick n]

Originally Posted by Carl G

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?

[Raya]

I was thinking about the potential to glass on some support, but I, too, would like to see some photos. We need to visualize!

[Carl G]

Originally Posted by Raya L.

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

Axle 2].jpg Views: 36 Size: 29.7 KB ID: 31484" style="margin: 2px" />

Axle.jpg Views: 30 Size: 50.0 KB ID: 31485" style="margin: 2px" />

[Raya]

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

[Mark Shaffer]

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

[Rick n]

Originally Posted by Carl G

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.

[Carl G]

Originally Posted by Raya L.

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.

[Raya]

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

[Larry&Carrie]

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

[Roy in TO]

Originally Posted by Larry&Carrie

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?
http://www.fiberglassrv.com/forums/f...ics-27107.html

[Carl G]

Originally Posted by Raya L.

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

[Larry&Carrie]

Originally Posted by Roy in TO

Is this the thread?
http://www.fiberglassrv.com/forums/f...ics-27107.html

YUP-- that is it. Larry

[Raya]

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

[Raya]

Okay, so, cored floor repair.

I have to start out by saying that I would still really like to see photos of the inside of the floor, and where it meets the walls/shell. Since I can't see that, I'm going to be a bit more general.

Also, I'm coming from a boat perspective, so some of the materials I'm suggesting are a bit of a step up from original egg construction.

So, for starters (again, I'm making some assumptions here since I can't see your details), you want to sand off any "gunk" from the top of the lower shell. Also, if it's weak (and it probably is), you may need to shore it up from below while you work (say, thin sheets of junk ply held up by something; you just want to make sure to establish and keep the flatness while you work, and you will need to be able to put pressure on the floor).

Once you have the shell clean and smooth (I would probably use something like a Porter Cable 7335 with 40 - 80g paper; of course be careful and test gingerly before you go whole hog), then vacuum and wipe it with denatured alcohol or acetone. This should all be taking place on the "raw" (not gelcoated) glass. I would also sand about 4" up the sidewalls. If there are any damaged or too-thin areas, you can reinforce them with fiberglass now.

Next you would mix up some thickened epoxy (cabosil) and spread it on the inside of the lower skin with a notched spreader. Then you place your core on the epoxy (no need to use one huge piece - actually balsa core is made in about 3" squares - the skins and epoxy will bond it all together - one huge piece would be pretty unwieldy).

I checked with someone about the MDO, and apparently it is just plywood with a paper facing bonded to it and could probably be used, although not ideal. Personally, I would not use it or plywood, because that is just extra weight. I would use either balsa or foam core. I'm not sure exactly what thickness you need; but a boat deck of about 4' or more in width would probably use 5/8" or so core. The further apart you space the skins (with the core), the stronger they are, but it's not actually the core that is making it stiff; it's the space between the skins and the bond. Did you say what thickness was there originally?

Once you are sure the core is in and properly down, you can fill any gaps with more thickened epoxy. Then you can either let it cure and clean/sand, or you can keep on going as long as it is still "green" (dentable with a thumbnail) and get a chemical bond without sanding. But, you have to watch for heat buildup if you are getting really thick/large areas of epoxy curing. Also, you may need to stop and cure/sand at this point if things are too lumpy. This is a bit of a judgement call. Being new at it, I might stop here and let things cure, then sand/wipe, continue. Less potential for a big whoopsie that way.

Next, you coat with neat epoxy, and then lay on the top skin, working epoxy thoroughly into the weaves (white cloth should turn totally clear). I would use something like 1708 biaxmat, a couple of layers, although that is probably slightly overkill. You can use a layer of something like 6-10 oz cloth on top if you want a smoother finish, and/or fair with thickened epoxy (microballoons and a bit of cabosil). Roll/squeegee out all of the air (they make little spiky metal rollers for this). Then I would probably let things tack up to the green stage, and then go back with some ~5" strips to tab up onto the sidewalls. After this gets "green," you can go back with thickened epoxy to fair the surface if you need it smoother.


There is some good information on the web at either WEST System's site (they have a great usage manual online), or System Three's site (another great free manual).

Some places to buy supplies:

www.raka.com

Boat Building and Woodworking Supplies (Jamestown Distributors)

Fiberglass Coatings Inc. Your Single Source for All Your Fiberglass Needs

This was really not as detailed as it could be, but.... there is a lot to say, and numerous little details that depend on the exact situation and how things look, how they go, etc. which I don't know right now. I wanted to give you an idea what to do, but I don't want to feel too responsible either, since there are numerous ways to do it, experience counts, etc.

If you do plan to go ahead with it, feel free to PM me if you like and we could talk/call, etc.

Oh, and for sealing core penetrations. If you have an area you know will be a largish penetration, you can lay it up now with solid glass. But for fastener and other smallish holes, I would just go back after you are done, "overdrill" them with something like a 1" bit, and then fill in with thickened epoxy (cabosil). After that cures you re-drill the (smaller) hole through the center for the fastener (or, if you want to be extra smart and not have to have someone on the bottom holding a nut, you can tap the holes, then go back and put the nut on at your leisure).

This should keep leaks from getting to the core. Then you can use caulk or whatever to bed your stuff, and if there is ever a leak it is "just" a leak, not something seeping into the core and insidiously ruining it.

There are "waterproof" cable pass-throughs too, like these; it kind of depends on what you are actually running.

CableClams - Blue Sea Systems

Raya

PS: I'm sure I forgot or misstated *something*; I would recommend reading the free guides from WEST and System Three, and comparing notes. They are the pros.

[Carl G]

Originally Posted by Raya L.

Okay, so, cored floor repair.

I have to start out by saying that I would still really like to see photos of the inside of the floor, and where it meets the walls/shell. Since I can't see that, I'm going to be a bit more general.

Also, I'm coming from a boat perspective, so some of the materials I'm suggesting are a bit of a step up from original egg construction.

So, for starters (again, I'm making some assumptions here since I can't see your details), you want to sand off any "gunk" from the top of the lower shell. Also, if it's weak (and it probably is), you may need to shore it up from below while you work (say, thin sheets of junk ply held up by something; you just want to make sure to establish and keep the flatness while you work, and you will need to be able to put pressure on the floor).

Once you have the shell clean and smooth (I would probably use something like a Porter Cable 7335 with 40 - 80g paper; of course be careful and test gingerly before you go whole hog), then vacuum and wipe it with denatured alcohol or acetone. This should all be taking place on the "raw" (not gelcoated) glass. I would also sand about 4" up the sidewalls. If there are any damaged or too-thin areas, you can reinforce them with fiberglass now.

Next you would mix up some thickened epoxy (cabosil) and spread it on the inside of the lower skin with a notched spreader. Then you place your core on the epoxy (no need to use one huge piece - actually balsa core is made in about 3" squares - the skins and epoxy will bond it all together - one huge piece would be pretty unwieldy).

I checked with someone about the MDO, and apparently it is just plywood with a paper facing bonded to it and could probably be used, although not ideal. Personally, I would not use it or plywood, because that is just extra weight. I would use either balsa or foam core. I'm not sure exactly what thickness you need; but a boat deck of about 4' or more in width would probably use 5/8" or so core. The further apart you space the skins (with the core), the stronger they are, but it's not actually the core that is making it stiff; it's the space between the skins and the bond. Did you say what thickness was there originally?

Once you are sure the core is in and properly down, you can fill any gaps with more thickened epoxy. Then you can either let it cure and clean/sand, or you can keep on going as long as it is still "green" (dentable with a thumbnail) and get a chemical bond without sanding. But, you have to watch for heat buildup if you are getting really thick/large areas of epoxy curing. Also, you may need to stop and cure/sand at this point if things are too lumpy. This is a bit of a judgement call. Being new at it, I might stop here and let things cure, then sand/wipe, continue. Less potential for a big whoopsie that way.

Next, you coat with neat epoxy, and then lay on the top skin, working epoxy thoroughly into the weaves (white cloth should turn totally clear). I would use something like 1708 biaxmat, a couple of layers, although that is probably slightly overkill. You can use a layer of something like 6-10 oz cloth on top if you want a smoother finish, and/or fair with thickened epoxy (microballoons and a bit of cabosil). Roll/squeegee out all of the air (they make little spiky metal rollers for this). Then I would probably let things tack up to the green stage, and then go back with some ~5" strips to tab up onto the sidewalls. After this gets "green," you can go back with thickened epoxy to fair the surface if you need it smoother.


There is some good information on the web at either WEST System's site (they have a great usage manual online), or System Three's site (another great free manual).

Some places to buy supplies:

www.raka.com

Boat Building and Woodworking Supplies (Jamestown Distributors)

Fiberglass Coatings Inc. Your Single Source for All Your Fiberglass Needs

This was really not as detailed as it could be, but.... there is a lot to say, and numerous little details that depend on the exact situation and how things look, how they go, etc. which I don't know right now. I wanted to give you an idea what to do, but I don't want to feel too responsible either, since there are numerous ways to do it, experience counts, etc.

If you do plan to go ahead with it, feel free to PM me if you like and we could talk/call, etc.

Oh, and for sealing core penetrations. If you have an area you know will be a largish penetration, you can lay it up now with solid glass. But for fastener and other smallish holes, I would just go back after you are done, "overdrill" them with something like a 1" bit, and then fill in with thickened epoxy (cabosil). After that cures you re-drill the (smaller) hole through the center for the fastener (or, if you want to be extra smart and not have to have someone on the bottom holding a nut, you can tap the holes, then go back and put the nut on at your leisure).

This should keep leaks from getting to the core. Then you can use caulk or whatever to bed your stuff, and if there is ever a leak it is "just" a leak, not something seeping into the core and insidiously ruining it.

There are "waterproof" cable pass-throughs too, like these; it kind of depends on what you are actually running.

CableClams - Blue Sea Systems

Raya

PS: I'm sure I forgot or misstated *something*; I would recommend reading the free guides from WEST and System Three, and comparing notes. They are the pros.

Raya,

Thank you for the great information! Here are a few additional pictures so that you can get a better idea of the project (The pink stuff is the original adhesive that Bigfoot used to bond the lower shell to the 3/4" plywood subfloor). I did a little research on MDO. Although heavier than needed, it is different that normal plywood from everything that I read. The layers "overlays" and outer covering are resin impregnated, resulting in increased stiffness as well as durability in exterior environments. Although I would prefer something lighter, I own three 4' x 8' sheets of MDO, and so it will have to work as the core.

I do have a few addtional questions. Do you suggest making the thickened epoxy by adding the Cabosil to the same West 105 that I'll be using for normal glassing? Just follow the mixing instructions? Also, what about the penetrations for the bolts that hold the shell to the frame. I'm a little unsure about overdrilling these, adding epoxy, and then redrilling for bolts. Is this what you recommend?

I'm excited about getting started. I've struggled for some time to find a good, long-term solution to the floor. It is such a relief to know that it will be both durable and strong. Thanks again!

Carl

[Raya]

Okay, I guess I have to write something outside the quoted area, or my message is "too short."

Originally Posted by Carl G

I do have a few addtional questions. Do you suggest making the thickened epoxy by adding the Cabosil to the same West 105 that I'll be using for normal glassing? Just follow the mixing instructions?

Hi Carl,

Although you can now buy pre-made thickened epoxy, I like to mix my own. You can do it as you go along, use various thickeners (strong but hard to sand, for structural stuff; less strong but easier to sand for fairing, etc.). Also you can easily vary the texture according to what you are doing (i.e. mayonnaise consistency; peanut butter consistency; "oops, that's too much" consistency , etc.).

Seriously, the exact texture/amount of thickener is not critical. I mix my resin and hardener thoroughly first, then start adding thickener and stirring a bit at a time until I have it how I want it.

You'll see that in the WEST System guide, they also describe the consistencies in terms of well-known food products, to make it easier.

If you don't want to buy every thickener in the book, I would probably go with colloidial silica (cabosil), for strength, and microballoons, for fairing (if you need to fair). Note that colloidial silica can be very "fly away" and you don't want to be inhaling it.

When you are wetting out the cloth, you can just pour some resin on and then start spreading it around. Or, for smaller pieces (like when you tab edges), I wet them out ahead of time on a sheet of plastic laid over cardboard, then roll them up and move them into position.

Also, what about the penetrations for the bolts that hold the shell to the frame. I'm a little unsure about overdrilling these, adding epoxy, and then redrilling for bolts. Is this what you recommend?

Yes, that is what I would do. Not only does it seal off the core, but it provides a rigid epoxy annulus so that when you tighten down on the fastener, you aren't going to crush the wood. If you want to go whole hog you can tap the annulus, but just re-drilling the normal type fastener hole is fine too. You just want to end up with a decent sized ring around the fastener hole. I usually use something like a 3/4" or 1" bit, depending on the fastener size. Coat the inside of the large hole with neat epoxy, then thicken it and fill the rest of the hole. Tape off around it. A syringe or straw works great so you can fill from the bottom and avoid trapped air, but not entirely necessary. You can trim off overage at the green stage.

I'm excited about getting started. I've struggled for some time to find a good, long-term solution to the floor. It is such a relief to know that it will be both durable and strong. Thanks again!

On the campers I have looked at closely (Boler, Scamp, Trillium, Compact), you won't have any trouble exceeding original factory strength or methods. Just plan it out like a stir-fry, so that once you get going you have everything ready. And like painting, don't rush to the last step.

Raya

Carl

[Carl G]

One last question. All of the cabinets were screwed to the floor. If I replicate this method, I will be placing numerous penetrations into the core. What are your thoughts on this one.

Thanks,
Carl

[Raya]

Well, realistically, unless you get a bunch of water in the interior, things would probably be fine with the screws going directly into the core (presuming MDO has good holding power), especially with some bedding (a slightly chamfered hole helps with this, but of course exposes more core).

On the other hand, if you want to be SURE, you could overdrill-fill-redrill where the screws will go.

If you want to help some, you could coat the insides of the plain holes with neat epoxy (say, with a pipe cleaner or something), but it's debatable how much better that would be than plain holes. Some, I suppose.

It's one of those things where you have to balance your expected use/abuse of the trailer, how much extra effort it would be, whether you would lose sleep over it if you didn't do it, etc.

Raya

[Carl G]

Sounds good. I'm most concerned first with the holes that penetrate to the outside of the trailer; cabinetry screws less so. I'm planning on completely re-working the windows and will monitor them in the future for any potential leaks. That should do the trick. Thank you again for the help. I'll be sure to post pictures at various stages.

Carl