Joining Wall to Floor....Yet Another Dumb Question!

[SteveH]

Shil,

Thanks for your input. Grant also mentioned the dado and I think it's a good idea, but my only problem with it is the accuracy required on such a large piece of wood. I do have a 10" table saw and a dado set, but the table is not near big enough to handle 4 X 8 sheets. How did you do it, do you have a table extension, or a good willing helper?

[shil]

I used a router. My favourite tool.

[SteveH]

Gotcha!

[Arne]

When I built mine, I bolted a furring strip along each outer edge of the floor (standing upright), from front to back. Each wall unit, which was pre-built on a table, and an outer and inner wall with furring strips as studding. I left a gap along the bottom of the wall unit 1/4" higher than the furring strip bolted to the floor. When the time came, I slipped the wall down over the strip on the floor, kind of a tongue in groove design. It was glued and power nailed in place....

[BrianB]

Only thing even potentially bad that I can see is that it creates a place for water to accumulate and possibly soak into the plywood wall.

Well if you're skinning yours with aluminum, keep an extra 1/2" of aluminum hanging on the bottom of your wall so that when you bolt it down, you simply wrap the extra aluminum around the bottom. That way as water runs down the sides or splashes from the road, it can't get at the wood. i.e.:

[Arne]

On my plywood walls, the outside extends down about 1/4". Everything is coated with deep penetrating expoxy primer and epoxy paint..... the water can sit there for a week and never be absorbed.

[BobR]

I have seen floor and walls attached in many ways. So here is how I did mine with an insulated floor. The frame supports the shear load and water is not a problem with proper sealing. Before installation the bottom edges of the walls were sealed with polyurethane and a bead of silicone caulk was laid on the frame rail. The bottom ply was coated with a liquid latex product called Mercote (expensive). The standard RV flat insert molding covers the gap between the frame and the wall and give a nice finishing touch. If I do it again I will use the same method only I will go to insulated walls and reduce the thickness of the floor plywood to 3/8" since the weight inside is distributed and supported by the framing members and the foam insulation.

[Guest]

Steve H,
That's not "...another dumb question." It's a very good question.
I'm reposting my response because I failed to see that you asked about 3/4" solid walls and floor.

Here is how I would do it, if I was concerned about the shear stress from the wall placed upon the bottom wall anchoring screws;

[SteveH]

Dean,

Thanks for your input. Very nice method. Wish I had a way of posting a picture of what I've decided to do, but I'm not a computer wiz, or any other kind of wiz now that I think of it!

Anyway, I plan to dado the side wall and join it to the floor and have the floor AND the wall on top of the frame at the joint. Maybe it's not called a dado if it's at the end of the piece, can't remmeber, maybe it's called something else. Rabbit joint maybe?

Then, since it is only the appearance of the side covering the frame that I am after, I plan on having the aluminum extend over the side of the frame also. By doing it that way I get the "look" I want, and maintain as much interior height as possible with 48" wide plywood.

How's that sound?

[Guest]

Steve H,
Building with a dado joint would be stronger and easier than using a rabbet joint at that paticular location. (IMHO)
What profile shape are you going to build, and how tall is it?
If I was commited to using 3/4" solid walls that were going to be skinned over with sheet metal on the exterior... I wouldn't be willing to nix the dado joint, just to save 2" in overall height. (Again IMHO)

If you are going to use a rabbet joint at that location, have a good selection of bar clamps on hand and make sure the sidewalls are perpendicular to the floor when gluing/screwing up the joints. (Make sure that everything is square)
Even if you had to gang one or more sheets of plwood together with a spline joint or scarf joint, I would opt for that along with the dado joint vs. the rabbet joint. (Again... of course IMHO)

IMHO=In My Humble Opinion (I guess it could also mean In My Horrible Opinion )

I just feel that a dado joint is a good structural joint. It is stronger than the glue and or screws that hold it together. The rabbet joint, on the other hand... I just don't feel that it is any better than a butt joint. I just don't see any structural properties to this joint, when compareed to the dado joint. Take away the glue and screws, it will fall apart. (You guessed it...IMHO)

Ive used a rabbet joint in cabinet making on the back side of cabinets as a way to be sure that everything is square on the cabinet.

I don't mean to disuade you from using a rabbet joint. I just feel that a dado joint at this location makes better sense.
Hey, It's your project, so do it the way you want to do it. Talk can be cheap, but there is some excellent wisdom here on this board.

[Dee Bee]

This is a great topic. It is raising guestions I had not considered before.

But can someone reply to how fasten a stick and skin "sandsich wall" to the floor frame? The replys so far seem to be using 3/4 or 1" ply.

I am planning on extending the floor frame out over the frame of the trailer to gain a little bit more rom for sleeping. Now I see that in doing this I lose the strength of having the walls sit on the trailer frame. I was planning on gluing and screwing the bottom framing member of the wall to the side of the desk framing. But this will mean all the shear stress will be carried only by scews and adhesives.

I need a better plan. But I am not that skilled in contruction so send me some ideas!

Thanks for the help

DEE

[Guest]

Hey Dee Bee,
I think this drawing might help. (Although the frame rail isn't where you want it)


If the frame rail is going to be repositioned with the wall and floor cantilevered beyond the frame rail... The floor must be ridgid enough as to not want to flex. There has been some discussion in previous threads about this and as I recall, most posters were not too giglish about this cantilevered idea. I feel that if your floor is ridgid enough, I don't see why you couldn't cantilever the floor a bit past the frame rail. (IMHO)

[kennyrayandersen]

How about this. If you want to cover the frame like I do, weld on a lip the same width as the thickness of your plywood onto the bottom of the frame. Do it so that it supports the edge of the plywood so that you can screw the plywood into both the frame AND floor without the shear loading issues.

In this case, the floor would be attached by both shear fasteners in the vertical (side fasteners) and horizontal directions (fasteners that go through the floor into the top of the frame). There is no better load path than shear (compression maybe, but there are times when the compression becomes tension as during a pitching condition etc.). The critical load for a tear-to-frame attachment is probably the deceleration during abrupt braking, or a crash condition (if you hit something, you wouldn’t want the tear coming off the frame and whacking the back of your car to add insult to injury!). In that case, all of the fasteners take shear, but especially the sidewall to frame fasteners.

My plan for the floor will be a sandwich with a 1x2 (minimum) around the perimeter. The sidewall will over hang much like the figure above, only it will just overhang the floor. The 1x2 will be biscuited, screwed, and glued into the sidewall – there will be no frame. Which brings up an interesting point: if you don’t need a frame, how much load could be going from the frame to the body? Not so much. The only failure I’m read about in this area seemed to be between the sidewall and the body, which I think is a more critical joint. Too few screws were used in the joint to the sidewall. If I remember the fix was to install an aluminum angle which attached the wall and floor together, but dowels or biscuits with screws and glue would eliminate the need for this angle (which was a retrofit anyway).

[Mikedaub]

I'm glad I keep coming back to this forum because of all of the help.

Finally my summer is starting to calm down a bit and I am able to start back on building this guy. Rain all season in New England has me building everything in my basement, and piecing it together. Well, the rain has stopped, and its time.

When I thought about putting the walls on, I never thought about load weight of the build and after reading some of this post, I am concerned. Here is the way I was planning on doing it, Sorry for the bad photoshop skills.



So, I have the floor down, then was going to put the wall even with the bottom of the frame so it covered it and secured them together with the 1x2 strapping that is glued and screwed. For extra measures, I was also going to bolt the walls to the frame in about 3-4 different spots. Hopefully that makes sense.

With the strapping and bolts, think that will be strong enough?? For the most part, I used 15/32 pine ply and 1x2 pine straps.

Thanks in advance..

[kennyrayandersen]

I'm glad I keep coming back to this forum because of all of the help.

Finally my summer is starting to calm down a bit and I am able to start back on building this guy. Rain all season in New England has me building everything in my basement, and piecing it together. Well, the rain has stopped, and its time.

When I thought about putting the walls on, I never thought about load weight of the build and after reading some of this post, I am concerned. Here is the way I was planning on doing it, Sorry for the bad photoshop skills.



So, I have the floor down, then was going to put the wall even with the bottom of the frame so it covered it and secured them together with the 1x2 strapping that is glued and screwed. For extra measures, I was also going to bolt the walls to the frame in about 3-4 different spots. Hopefully that makes sense.

With the strapping and bolts, think that will be strong enough?? For the most part, I used 15/32 pine ply and 1x2 pine straps.


Thanks in advance..

Why don't you just biscuit or dowel the floor (biscuits would be blind) to the sides and forget the strip. You could put biscuits or dowels every foot or so, and it would be very strong. Additionally, if you put bolts from side to frame, as you said you were going to do, it removes any loads that would want to separate the wall from the floor in the side-to-side direction. You could liquid shim the floor to the trailer with liquid nails or something (just to make sure the load from the flour goes into the frame). That way, you wouldn't have the strapping protruding into the cabin.