[PhilBa]

I have a project where I need to build 50 planter boxes to go in a green roof we are building. They are of a simple design (see image below) to make it easy to bang out. The plan is to use 3/4", 5.5" width cedar. The appearance isn't important as they will be covered up by plants. We will fit landscape fabric in the bottom to prevent soil loss - the center drainage gap is 1/2" wide and the side ones are 1/4". I've got a jig worked up to make it easy to build the boxes.

I'm not 100% sure the best way to build the boxes. This is where I could use some advice. Are staples the right fastener - will work better than nails? I know that the acid in cedar will react with iron to make dark stains but they won't be visible so that's ok. I think galvanized is the way to go though maybe copper will last longer? Not 100% sure. Also, are 18 gauge staples reasonable? I think any thinner won't be strong enough. Thinking 1 1/2" length.

Also, looking at pneumatic staple guns. Any suggestions as to brands and or models? Probably don't need a beast to drive 1 1/2" staples into cedar.

 

[Nickp]

Nice project, Phil...

I would think the box will be big enough so that the dirt will want to push the sides out a bit. And if you need to carry it at all with dirt in it, it will no doubt rack on you a bit.

With that, my suggestion would be coated deck screws...You're gonna need 800 of them considering two for each board end...

15 or 16 gage nailer would probably do the trick...thinking 5 per board end...

Bostitch makes a good gun in that size...

 

[Bstrom]

Under such conditions, how long will Cedar last in the open? Especially the bottom?

Regarding the build, would it be a lot trouble to cut a locking miter for the corners to get the most strength with no extra effort? Uses just one bit and is just as easy as a butt joint to assemble...I would think the same staple size as a hardwood floor nailer uses would pretty beefy.

This is an interesting project logistically...

 

[Herb Stoops]

A HF staple gun ought to work fine for a one time projrct like this,with 1 1/", or 2" staples.
HErb

 

[PhilBa]

Wow, that was fast!

Nick, Yes, I expect a bit of movement. They will be placed side by side on the roof. The plan is to plant the starts in them and carry them up to the roof area - 2 flights of stairs. So soil and plants but not watered. Probably 20 lbs range. I'm going to think about maybe shortening the boxes a bit to minimize bowing. Especially if I can't find cost-effective 3/4" cedar. I dunno, screws add a huge amount of labor - I'd need to drill pilots and would worry about splitting the cedar. Definitely a better way to go in general, though. If there were planters that sit on a deck and get admired for the design and construct, there would be no question of using better joinery.

Brian, The boxes will sit on a drainage layer - pumice covered with landscape fabric (well, something a bit upmarket from that). They won't be standing in water though still fairly wet. We are putting low water plants in so we will let the boxes dry out a bit. Still, I expect at least a 5 year lifespan or so. The commercial units are plastic but they only warrant them for 3 years. Lock miters - for anything indoor, I'm totally there. The goal is to get this done with some low skilled help (aka family) in a reasonably short amount of time. Banging out the rough-cuts first - 300+ cuts. Pretty easy with a stop on my SCMS. Then 8 miter cuts for each box - 200. The butt joint starts to look like a good idea.

Herb. Yeah, looked at the HF 29.95 stapler. It get's ok reviews on the HF site so probably worth trying. if it doesn't work well, I can always get a better one and I'm not out a lot.

 

[Stick486]

Narrow crown SS staples will work fine provide you change the corner joints from butt joints to rebated rabbets for the reasons Nick gave...
you will have to staple into both the long and short sides...
deck screws will split the wood because you are at the ends of the boards and the shape of the head acts as a wedge...
grove the bottoms of the sides to accept the bottom slats... do this joint as a rebate also...
when you assemble let the bottom reveal show..
when you do your glue ups treat the wood as an oily tropical wood...
size the end grain..
I strongly suggest you use Weldbond instead of TB... Weldbond is waterproof...


Use synthetic, non-water-based glues.

Since water is repelled by the wood’s oils, using water-based glues like Titebond® can pose problems—though Titebond® II or III are usually better at gluing oily woods than Titebond® Original. Instead, use glues that aren’t water based, and/or glues that can bond a wider variety of materials like plastics and other non-porous surfaces (since that’s practically what we’re doing with these exotic woods anyways). Weldbond will do a way better job since it will meet the mentioned criteria...

Wipe the wood surface with a solvent prior to gluing.

Since the primary problem that tropical woods present in gluing is their oiliness, (with density probably being the second biggest problem), any of these natural oils and resins that you can remove from the wood surface will help the glue adhere that much better.
While it’s not a cure-all, wiping the wood with a solvent first goes a long way. But you have to be sure of two things: first, you should try to glue the pieces of wood to be joined as soon as possible after the solvent has evaporated from the wood surface. This is because the wood’s oils will tend to migrate back to the surface of the wood where you removed some of the oils. Secondly, you have to be sure that the solvent you’re using is actually dissolving and removing the wood’s oils. A good way to gauge this is by checking the towel that you’re using to wipe the solvent to see if it’s changed to the wood’s color.

Note:
If you’re initially testing a solvent, make sure that the wood is clear of any small particles of sawdust that might make it appear as though the towel is being discolored. Try a cloth with water first as a baseline: it should basically stay white since the water does not dissolve the wood’s heartwood extractives. Some common solvents that you can try are: acetone, denatured alcohol, lacquer thinner, mineral spirits, and naphtha.

.

 

[Bstrom]

Wow, that was fast!

Brian, The boxes will sit on a drainage layer - pumice covered with landscape fabric (well, something a bit upmarket from that). They won't be standing in water though still fairly wet. We are putting low water plants in so we will let the boxes dry out a bit. Still, I expect at least a 5 year lifespan or so. The commercial units are plastic but they only warrant them for 3 years. Lock miters - for anything indoor, I'm totally there. The goal is to get this done with some low skilled help (aka family) in a reasonably short amount of time. Banging out the rough-cuts first - 300+ cuts. Pretty easy with a stop on my SCMS. Then 8 miter cuts for each box - 200. The butt joint starts to look like a good idea.
.

Would a simple stretcher 1X1 across the top edge after you have done the planting help keep the side panels under control?

I sincerely wish you well with the carrying chore - you have your work cut out for you!

 

[JOAT]

A HF staple gun ought to work fine for a one time projrct like this,with 1 1/", or 2" staples.
HErb

Likely would. However, I have not been able to log onto the HF site for at least a couple of weeks. I would like to order 2 or 3 things from them, I had assumed they would at least have the mail order side still going, but possibly not.

 

[Herb Stoops]

Look in the wooden fence section at HD or Lowes for the cedar boards, they are usually good quality, the last time I did a project I used them for some planters,the boards are planed one side to 5/8" thick, 6' an 8' long. They might have some full roughsawn 2 sides for 3/4" tho. Don't use treated, might effect plant growth.
Herb

 

[Cherryville Chuck]

The deck screws would hold it together better but you'd need to predrill pilot holes and be a bit careful about over torquing the heads. It's such a soft wood that it will tolerate a bit of crushing without splitting usually but going into the sides without the pilot will split some of the boards. I've used untreated cedar for fence pots and fence rails and your lifespan is a max of about 8 years. Oiling it would help. \

I don't know if I'd bother with any glue. I've tried all kinds, including resourcinol and PL400 and NOTHING holds for long. Some of the stainless fasteners I've used were very slick and pulled apart easily. Galvanized tends to grip better and will probably last about as long as the boxes will. The strongest corners using just small air driven fasteners would be cross nailed miters.

 

[DaninVan]

Never, ever use copper fasteners with Cedar! The aciidic nature of Cedar will eat copper for breakfast!
I remember years ago, an Architect up here specified copper nails for a Cedar shake roof; long story short, the whole roof had to be redone after a couple of years.

 

[DaninVan]

Phil; carry the boxes up completely empty. bring the soil up separately, and start your plants in nursery pots. Anything up to but not over 1 gal. I do this every year, twice a year actually; Spring and Fall.
I've already either over Wintered some plants in 1 gal. pots, and/or bought bedding plants in 2 1/2" pots...growing them on for planting into large planters once the danger of night frosts is past.
Trying to carry those fully loaded boxes is a recipe for disaster. Just do your final setting out of plants in place.
At the risk of sounding like a **** don't try moving those boxes loaded up!

 

[DaninVan]

Further to that Copper and cedar thing, remember those Revere Copper adverts for Copper gutters, back in the 50's and early 60's? Same thing happened; folks with too much money tried Copper gutters with Cedar roofs....real bad idea.

 

[1fizgig]

I was going to suggest something other than staples, only because my experience with stapled wood "joints" has been that they're rather temporary for anything outside.
But perhaps with a decent glue (or maybe without glue at all) and a good joint as previously suggested you've got a better chance of having a longer-life product. Glad to her they won't be sitting in water as such.
I guess from what I've read the plan is to be as cost-conscious as possible as well as managing the skills of those involved assisting?

How hard a wood is the cedar? I don't have any experience with it, so just thinking about the ability to fire the staples home, and this may dictate the stapler needed.

 

[Stick486]

How hard a wood is the cedar? I don't have any experience with it, so just thinking about the ability to fire the staples home, and this may dictate the stapler needed.

hard doesn't enter into the equation, it just isn't...
it is the softest or just about of the pines... (Janka 350)...
install staples 90° to each other and they won't so easily pull...

screws, as in deck, w/ a few MC changes/cycles and the screws will split the wood...
a truss headed screw will treat the wood better and be less likely to split it...
hold the best of all the fastening options...
the top board will need a clearance hole and the bottom board needs a pilot hole...
dip the screws in glue to strengthen the wood fibers..
a tapered point drill bit works best for the clearance/pilot hole...

Common Name(s): Western Redcedar, Western Red Cedar
Scientific Name: Thuja plicata
Distribution: Pacific Northwest United States/Canada
Tree Size: 165-200 ft (50-60 m) tall, 7-13 ft (2-4 m) trunk diameter
Average Dried Weight: 23 lbs/ft3 (370 kg/m3)
Specific Gravity (Basic, 12% MC): .31, .37
Janka Hardness: 350 lbf (1,560 N)
Modulus of Rupture: 7,500 lbf/in2 (51.7 MPa)
Elastic Modulus: 1,110,000 lbf/in2 (7.66 GPa)
Crushing Strength: 4,560 lbf/in2 (31.4 MPa)
Shrinkage: Radial: 2.4%, Tangential: 5.0%, Volumetric: 6.8%, T/R Ratio: 2.1

Here's a comparison to give you some idea....

.

 

[Stick486]

Some of the stainless fasteners I've used were very slick and pulled apart easily.
Galvanized tends to grip better and will probably last about as long as the boxes will.

The strongest corners using just small air driven fasteners would be cross nailed miters.

size the end grain 1st...
WRC needs to treated as an oily tropical wood...
the rebated rabbet would relieve the stress on the staple...
I drawers routinely w/ rebates, Weldbond and a 23GA pinner...
they don't split nor come apart...

get the SS staples w/ serrations and hot glue on them

https://www.fastenerusa.com/staples/stainless-steel-staples/1-4-crown-l-series/

exactly on thee cross nailed corners...

 

[DaninVan]

Re your drawing, Phil; I like that you've got the bottom boards literally on the bottom, but I'd build it so that all four side bottoms are in full contact with the bottom edges of the side boards. Nailing/screwing up into them all the way around will add tremendous strength where it needs it most. It'll prevent the sides and ends from blowing out; most of the force is at the bottom~sides.
Hopefully that made sense...

 

[Cherryville Chuck]

size the end grain 1st...
WRC needs to treated as an oily tropical wood...
the rebated rabbet would relieve the stress on the staple...
I drawers routinely w/ rebates, Weldbond and a 23GA pinner...
they don't split nor come apart...

get the SS staples w/ serrations and hot glue on them

https://www.fastenerusa.com/staples/stainless-steel-staples/1-4-crown-l-series/

exactly on thee cross nailed corners...

I've had no problem with glued edges or joints inside, it's outside that's that has been the problem. The wood is oily but it is also porous. Water gets in beside the joints and the wood next to the glue line fails. I topped the uprights on a couple of cedar benches I made and I blind doweled them so that the holes didn't go right through to the top of the boards and they even let go.

Cedar is really common here and I have a few growing on the property so I've used quite a bit over the years. Mechanical fasteners work the best. I made dozens of squares of cedar roof shakes when I was young and installed a few of them. Phosphorus coated box nails worked well putting those on and last just about forever, even the ones on the ridge caps where they are exposed to the weather. There were some old shake roofs around when I first moved here that were getting close to 100 years old and were still shedding rain. They were getting so thin you could see light through them. Some of the fence posts and rail fences are around 50 years old but those had to come from fire killed trees to last that long.

As soft as cedar is the knots are notoriously hard and chip grade 4 carbide bits easily. You are better off to use a bit with grade 3 carbide when routing cedar.

 

[DaninVan]

For all its faults I love working with WR Cedar.
Carrying a few wet WR Cedar boards home from the mill leaves my van scented with that that rich pungent perfume for several days.

 

[sreilly]

Well my thought earlier in the spring for building some plant stands for the deck has been reinvigorated and answers to questions I didn't even know I had have already been answered. No flat roof here but if I did I would have done just this some tears ago after our first trip to Alaska (we embarked at Vancouver). I saw many flat roof buildings in Vancouver that had planted roofs including trees and really liked the look and idea. Seemed like a very progressive area. For my roof I will likely have solar panels before long. Thanks for starting this thread Phil and thanks to rest of you for the education on cedar and its outdoor use methods. Seriously good thread.