What’s your favorite wood for the bottom and how to seal it

[lacofdfireman]

Just wondering what the go to wood is for the base of a teardrop style trailer. I’m going 3/4” Baltic Birch for my sides and probably 1/2 for my top but what about the base of my project. This piece will be bolted to the frame so I need something sturdy. Should I do 3/4” Baltic Birch for the bottom also”. What thickness and type of wood would you use? And I need wood that can be bought locally not some crazy exotic wood.


Also what’s the best way to seal the wood on the bottom. Seems like on my last build I used some type of roofing tar stuff from Lowe’s. What’s another option? Also need something that can be bought locally.


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[noseoil]

I made a light frame out of 3/4" X 1 1/2" poplar & skinned it with 1/8" baltic birch top & bottom. Used 3/4" foam in the openings, then coated top & bottom with 2 coats of urethane. On the bottom I rolled it with 2 coats of white roofing, still looks good. Hard points are where the solid blocking is, hollow portions are just foam inserts. No problems with it this way.

[working on it]

• My TTT started out with a 1/2" thick 4x8 sheet of Birch plywood, that we bought for another project. It had been sitting in a wood rack in one of our sheds for 15-20 years, and had aged well, was weather-stabilized, and was as flat as Kansas, so I stole it (my wife had saved it for ??? reason), and used it for my trailer's sub-floor, bolted to the frame cross-members with eight 3/8" carriage bolts (the heads of which were countersunk 1/4" into the deck). I laid down a thick bead of PL Premium adhesive on the frame before placing the Birch plywood on top, for weather sealing below, following by using spray-on automotive undercoating (non-asphaltic, rattle-can stuff, that goes on dry).
• I wasn't sure if I trusted using only 1/2" thick plywood as a floor (I've always used heavier/thicker wood than others do), so I added another 1/4" on top. Using Titebond 2 to glue a 1/4" thick Luan 4x8 sheet onto the plywood, aI then secured it all with 38 Tek screws around the frame perimeter, into the tubular steel. As a finishing touch, the top of the floor received 3 coats of polyurethane on the Luan (the Birch plywood previously got edge-treatment with the poly/thinner "mix"), which made it pretty bulletproof. I later completely covered it with a rubber-backed carpet/mat. With all those bolts, screws, & glues holding it together, and thoroughly sealing the wood, my floor may outlast the steel frame!
• I was indecisive about using 1/2"-or-3/4" plywood for walls and roof, and just happened upon an impromptu "overstock" display of about 15-20? sheets of pre-sanded ABX 3/4" ply, for $25 each. I quickly snapped up 6 or 7 sheets, as the others were snatched up by two other guys. I couldn't bypass the deal. So, I used 3/4" for the rest of my trailer, as fate had decided the matter for me.

[tony.latham]

I'm building #4 in my head. I'll "break ground" on it this winter.

The floor will be 1/4" subfloor plywood, 3/4" pine and plywood frame, hard foam in between and topped off with another layer of 1/4" subfloor. The bottom will be sealed with epoxy. You'd have a hard time catching me sealing with the black goo that still holds some favor. That might have been the go-to stuff in the '40s but times have changed.



You can pour a lot of un-needed weight into a teardrop floor.

Tony

[KTM_Guy]

1" thick Baltic Birch frame and 1/8" Baltic Birch top and bottom. 1" rigid foam, epoxy coated top and bottom.

[friz]

Mine is 3/4 marine ply with glass and epoxy

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[Tomterrific]

Will your tear be stored outside? I'll suggest using pressure treated 1x boards over the frame and 3/4" simple exterior ply for the floor. 1/2" is even lighter and extra 1x's can be used as stiffeners. The 1x boards are to lift the floor to keep water from intruding into the edge of the ply from underneath. The foil faced butyl flashing tape between the trailer rails will also be good if raising the floor 3/4" is too much. I feel an insulated floor is not needed since the sun is not shining on it and any foam sleeping mattress is insulation.

3/4" walls are not needed in my opinion. Too heavy for no benefit. Traditional 1/2" ply walls are heavy enough that many builders, including myself, go 1/4" with 1x battens running top to bottom for a ridged wall. 1x battens frame the windows and doors for a solid 1" screwing base.

Tt
Once again, these are just my opinions. I am not a wood worker, more engineer type.

[noseoil]

Tony, you might think about 1/8" for the bottom of the #4 build, instead of 1/4". I don't have any pock-marks on mine from rocks or dirt roads & it's still looking good after nearly 20,000 miles in the last few years. The 1/8" is holding up well so far, as is the white roof coating. Easy to see underneath when working with the white bottom, since it's so bright.

In general, 1/2" plywood is still the building standard for new home construction for a typical roof load. That's generally 1/2" (actually 7/16") OSB with 2x roof joists at 24" on center. That includes a lot of snow loads as well, so going to smaller centers & shorter spans allows us to make a thinner roof panel.

Floors are different, but a floor load is just the mattress & two people sleeping on it, so with a 65# mattress & say 400# of people (people can vary in weight considerably, so I'm using a 200# person as the standard in this instance), that's still just 15# per square foot of loading for a 5' wide full size mattress. If the mattress & people load is just 370#, the load for a 5' wide floor is down to 12# per square foot. If the trailer frame is built with a cross-member under the door opening, & an extra stick or two is placed there as well for the "backside load" in the floor frame prior to skinning, a light frame & skin floor is plenty stout for the butt-loading it will take when entry into the bed is made. A hard point for the bolts (small hardwood block) is all that's required for fastening to the frame.

I'm just saying that 3/4" plywood is really overkill, unless there aren't but 2 cross-members supporting it on the frame. 1/2" is really plenty & 1/4" with proper stick-framing is really good enough.

Here's mine with the 3/4" poplar & 1/8" skin on the bottom. You can see some added blocking in the second picture where bolts were needed for attachment. It's beefed up in the galley area on the right for the "battery load" of 65# in one small spot in the middle. Light can still be strong, it just takes a bit of thinking to make it work...

[working on it]

I'm just saying that 3/4" plywood is really overkill, unless there aren't but 2 cross-members supporting it on the frame. 1/2" is really plenty & 1/4" with proper stick-framing is really good enough.

• 

  floor support.jpg (327.06 KiB) Viewed 3170 times

• As illustrated above, my decision to add 1/4" on top of my base 1/2" birch plywood floor, was because the large 60" x 46" spot (total area inside the perimeter frame, minus the two cross-members at front & rear), inside the cabin area, that was only supported by the center spine of the frame. The cabin area had two inches resting over the rear cross-member, and the front was well-supported with 2 supports for 12 inches of flooring. On each side of the frame, only 1" of plywood contacted the steel, so I used the 38 Tek screws primarily to assure full perimeter contact there, though both front & rear floor-ends have 1.5" of frame underneath.
• That large area in the cabin, with roughly 1335 square inches on each side of the center spine being unsupported, would be under my mattress, so if I slept or kneeled on one side, it would've had to support up to 285 lbs (myself, clothing & gear, 1/2 mattress, etc.). So, I treated the floor as a shelf, so I could use the "Sagulator" https://www.woodbin.com/calcs/sagulator/ to calculate the permissible loading.

• 

  my floor, treated as a shelf, on the sagulator.jpg (182.47 KiB) Viewed 3170 times

• This calculator convinced me to use the additional 1/4" sheet, just to be safe. We have a large shed where our contractor used too thin a floor, and it sags, so I didn't want the same condition to befall my otherwise-toughened trailer. More is better. I'm sure that the center spine, and the other half of the flooring, spreads the loads, but I wanted to be sure.

[halfdome, Danny]

I always use 3/4" Pacific Birch Light plywood (48 lbs) for the floor and contact cement a full sheet of plam (Formica or Wilsonart) on top and bottom. This way it's completely sealed from the elements.
Danny

[lacofdfireman]

So here is a photo of my frame I built. Do you think I’m better off just just bolting the 1/2” ply straight to the frame or building a wood frame out of some 1x2or 3’s and glueing a 1/4” sheet on top of the frame first then bolting it down? Is there enough cross support on my frame to do it this way?




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[RonS]

We'll just toss this into the category of "most of ya'll are over-building and putting weight into floors that could be better saved for more ballast (beer)"

I have an aluminum cargo trailer. The frame looks similar to your frame above, except there are 3 cross supports "inside the box" where you only have 2. Mine's a 5x8 and has what appears to be 5/8 ply floor. It's rated for 2400 pounds, and has hauled several loads of gravel, the lightest being about 1200 pounds and the heaviest just over 2000 pounds. I doubt many teardrops see that much weight on their floors, 3/4 is certainly overkill.