# Building: How to build an outdoor climbing cube part 2 — the climbing surface

Thing practiced: building the holiest wall

(This is the second part of 3 — part 1 covers design, foundation, and framing; and part 3 will cover flooring, finishing touches, and routesetting.)

## So far

There’s a frame, but no surface to mount climbing holds to. What next?

Tools used for climbing surface (utility rating out of 5):

• Stanley yellow panel carry handle (★★★★½)
• putty knife (★★★★)
• hand sanding block (★★)
• rubber mallet (★★★)
• 500 golf tees (★★★½)
• paint rollers and tray (★★★★)
• paint can opener (★★★★★)
• paint stirrer (★★★½)
• two Wal-Board Tools 8" taping knives (★★★★)
• Wal-Board Tools 14" mud pan (★★★★)
• a sacrificial sheet of 1" x 4' x 8' foam insulation (★★★★)
• Makita 7.25" circular saw with Diablo 40-tooth blade (★★★★½)
• tape measure (★★★★½)
• regular Sharpies (★★★★)
• metallic Sharpies (★★★★)
• 2' level (★★★½)
• Bosch 12V drill (★★★★½)
• Black and Decker drill (★★)
• Black and Decker 20V impact driver (★★★★½)
• Fisch 7/16" Forstner bit (★★★★★)
• standard drill bit and impact bit set (★★★★)
• reciprocating saw
• hammer (★★★)

Other tools used:

• whiteboard
• 8x11 paper
• several cameras
• JBL Charge 3 (★★★★★)

Parts list (climbing surface):

• about 800 2-hole T-nuts from Escape Climbing with accompanying mounting screws
• 11 sheets 3/4" x 4' x 8' marine-grade CDX plywood
• 3 Simpson Strong-Tie galvanized heavy angles
• 6 1/2" bolts/nuts/washers
• 400 Deckmate #9 x 3" screws
• 300 GRK #9 x 2.5" R4 screws
• 40 GRK 5/16" x 4" RSS structural screws
• 40 GRK 1/4" x 2.5" RSS structural screws
• 2 gallons KILZ 2 interior/exterior primer
• 2 gallons Behr porch and patio paint (silver gray low-lustre enamel)
• 7 gallons drywall mud
• 15 pounds play sand
• 3 lbs DAP Plastic Wood-X wood filler

## Planning

### 1. Deciding on the plywood to use

Based mainly on the perceived safety of obtaining sheets mid-pandemic, we decided to go with 3/4"-thick marine-grade, pressure-treated plywood from Economy Lumber Oakland. Each sheet was a standard 4' x 8', and we decided to get 11 sheets to cover all our surfaces and leave some extra for adding volumes later.

### 2. Choosing the T-nut layout

Climbing holds are mounted to a climbing surface (whether made of wood or not) with 3/8"-16 bolts threaded into 3/8"-16 T-nuts that are attached firmly to the climbing surface.

Before getting started with preparing our climbing surface, we needed to decide how we would lay out our T-nuts. To do this, we looked around at other people’s builds, and drew alternatives out on sheets of 8.5” x 11” paper, and settled on a grid with holes sqrt(32) == 5.66” apart, diagonally (equivalent to rows of holes 8" apart horizontally, spaced 4" apart vertically, and offset horizontally by 4" per row).

### 3. Setting up the workspace

Four feet by eight feet of plywood turn out to be way more cumbersome to handle in practice than they are in theory, so we needed to amass a few tools and clean out some space to make it possible to work with our plywood sheets.

First, we needed to figure out a way to cut our sheets, without snagging our saw blade (i.e. if the sheets collapse in from two sawhorses supporting each short end) or wasting too much wood cutting into our supports (i.e. if we used long 2x6s to support the sheet along its length). After trying to come up with cleverer options, we decided to just get a cheap piece of 4' x 8' foam insulation from Home Depot to place under an entire sheet of plywood as we cut it, and be okay with shredding the insulation over the course of the project. This worked pretty well.

Then, learning from the failures of the stubborn approach to post digging last time, we decided to purchase a sheet-goods lifter. This is a \$5 plastic handle-type thing that you use to make it possible to get both arms around a wide sheet to carry it safely. This, disappointingly, also worked pretty well.

Then we spent some time moving lumber/other stuff around our home until there was a large-enough space to have three flat-sheet-of-plywood-size spaces: one for resting, one for marking and drilling, and one for one of: cutting, T-nut mounting, priming, texturing, or painting.

## Plywood

### 4. Cutting to size and filling in the surface with wood putty

We tried to design the shape of our wall to use an intact sheet of plywood where possible, to minimize excess cutting. The whole climbing cube is pretty small, though, so there were only three sections that were 4' x 8' or larger flat — so there were only three sheets of plywood we could keep whole.

For the rest of the climbing surface, we tried to close-pack our sections as tightly as possible to minimize material waste:

To make the cuts, we placed the foam insulation directly underneath the sheet being cut, marked our cuts, then just ran the circular saw across the plywood — leaving cuts in the foam but a neat and unburred plywood cut, and no cut-up sawhorses.

Because we were using CDX plywood (which has faces of quality C and D — not good), there were significant flaws and gouges in most of the sheets. We tried our best to fill these with wood filler, then sand the surface down to be reasonably flat (but not perfect — we knew that we’d still be texturing and painting on top).

### 5. Marking and drilling

After each sheet was cut to size and roughly-flat, we marked and drilled holes for our T-nuts. We tried to stick to the 5.66" grid described in 2., with some holes offset to avoid hitting the framing members that would sit behind them.

To make the holes the T-nuts would fit into, we drilled using a 7/16" Forstner bit, which was the perfect size to have the T-nuts sit snugly. (Forstner bits are expensive but make fantastically precise, crisp-edged holes — if we’d used standard bits, the holes would likely be too ragged to fit our T-nuts perfectly.)

We thought it’d be important to make the T-nut holes as perfectly perpendicular to the surface as possible, to make sure the holds would mount securely. To try to achieve this without too much tooling, we used a block of wood with a hole drilled through it as a guide. This was imprecise enough (but I was lazy enough to not make a proper jig) that we ended up abandoning this partway through and just doing this by eye. So far this has turned out to be workable.

### 6. Mounting the T-nuts

We chose 2-hole T-nuts from Escape Climbing, which hit a sweet spot in optimizing for barrel length, corrosion-resistance, and availability during the pandemic. (In an ideal world these would be stainless and I would’ve gotten to order them from the McMaster-Carr catalog, but that option was prohibitively more expensive.)

To mount the T-nuts into the plywood, we hammered them in with a big mallet, predrilled pilot holes in each screw hole, and attached with two (provided) screws.

### 7. Teeing

Now, with the sheets cut to size and full of T-nuts, we were ready to add the surface finish to the plywood. To avoid getting any primer/texture/paint into our arduously-mounted T-nut threads, we stole an idea we saw on YouTube and plugged them with golf tees.

### 8. Priming

To improve adhesion of our texture to the plywood, we started with a latex primer layer. We used KILZ 2 interior/exterior primer, which seemed to be reasonably priced for the quality.

### 9. Surface texturing

We were originally going to skip this step and just use paint with some sand in it directly on top of the primer. We tried this on one sheet, though, and found the wood texture was too pronounced to allow for smearing, and gave us a headache.

We thought we’d be consigned to misery forever, but our friend Kris suggested that we look into rock texture, and instead of giving up we figured out how to mix up something nicely-thick that would still stick well to the plywood: about 2:3:8 by volume of sand, primer, and drywall mud. We applied this with drywall taping tools instead of a paint roller, although in retrospect it might’ve been easier to thin it with water and apply with a paint roller.

### 10. Painting

By this point we were really bored of doing this. But, painting is fun? We chose Behr porch and patio paint because their display at Home Depot was appealing and because climbing walls, porches, and patios are all walked on with feet.

## Putting it all together

### 11. Mounting the wall G plywood to frame G

We had decided (when framing) to use our existing fence posts (which were already concreted down 16") as our main frame, with 2x6s added horizontally to carry load to the posts. Because these 2x6s were placed with their 5.5" face flush to the fence, in order to place the plywood flush against them, we needed to drill out holes where the T-nut backs and hold bolts would intersect with the girts.

After preparing the framing members, mounting the sheets was straightforward: we used a handful of large structural screws and several handfuls of wood/decking screws per sheet to attach the plywood both directly into the fenceposts and to the girts.

### 12. Mounting the wall F plywood to frame F

Mounting the surface for the right half of wall F was even more straightforward: because the 2x6 framing stringers were mounted in a standard balloon-frame configuration, we had been able to drill our T-nut holes to avoid hitting the stringers. We mounted the sheets using structural screws and wood/decking screws both directly to the posts and to the stringers across the sheet.

### 13. Mounting the WALL·E plywood to FRAME·E

For the cave wall (WALL·E) (and the corner of wall F above), we again begged for help from our friend S, who agreed to help us make this work. This was trickier than the other walls for a few reasons:

• the sections were overhung at different angles, so we couldn’t rest them on each other while drilling, and attaching the plywood sheets while holding them in place was physically taxing;
• the wall was taller, so we needed to do this work on a ladder;
• I had dug an asymmetric and partial hole in the ground to get started on the flooring, so using the ladder was a fun and dangerous activity; and
• senioritis.

Eventually, with the help of S’s reciprocating saw, we got this up.

### 14. Finishing: covering fastener holes and filling in cracks and edges

We wanted the sheets to feel like one continuous surface (and for climbers not to be hurt by protruding edges), so we filled the holes and the sub-millimeter gaps between plywood sheets with wood putty, drywall mud, and paint.

Now we have a cube! Can we resist climbing on it until we have proper safety matting in place?

### P.S.: references

Thanks to the Vancouver Carpenter for being very handsome and teaching us about drywall.

# Building: How to build an outdoor climbing cube part 1 — design, foundation, framing

Thing practiced: building the tiniest and most-exposed of houses

(This is the first part of 3 — part 2 covers how we built the climbing surface; and part 3 will cover flooring, finishing touches, and routesetting.)

As a staying-inside project this pandemic, V, some friends, and I built this miniature climbing gym. Its name is minicube:

Tools used for foundation and framing (utility rating out of 5):

• Makita 7.25" circular saw (★★★★½)
• Rockwell 4.5" compact circular saw (★★½)
• 2 Swanson Tool speed squares (★★★★★)
• Bosch 12V drill (★★★★½)
• Black and Decker 20V impact driver (★★★★½)
• 16-inch-long 3/8" and 1/2" spade bits
• standard drill bit and impact bit set
• tape measure (★★★★½)
• 2' level (★★★½)
• post level (★★½)
• shovel (★★★)
• hammer (★★★)
• regular Sharpies (★★★½)
• metallic Sharpies (★★★★)
• no. 2 pencils (★★★)
• T-bevel (★★)
• some string (★★★½)

Information tools used:

• whiteboard (★★★★½)
• 8x11 paper (★★★★)
• 4x6 and 5x8 index cards (★★★★)
• blue painters/leftover skeleton tape (★★★★)
• Jira (★★★)
• SketchUp trial (★★★)

Other tools used:

• several cameras
• JBL Charge 3

Parts list (foundation and framing only):

• 750 lbs Quikrete quick-setting concrete
• 2 pcs 6x6 x 16' pressure-treated lumber for primary posts
• 2 pcs 4x4 x 12' pressure-treated lumber for secondary posts
• 4 pcs 2x6 x 10' pressure-treated lumber for bottom cross-bracing
• 50 pcs 2x6 x 12' douglas fir framing lumber for the rest of the framing
• 1/2" carriage bolts/nuts/washers
• 3/8" carriage bolts/nuts/washers
• Simpson Strong-Tie LUS25Z 2x6 face-mount joist hangers
• Simpson Strong-Tie 12 A21, 26 A23Z, 22 A34Z, 4 A35Z angles, 4 H2.5Z hurricane ties, and 1 TP15 tie plate
• 600 Simpson Strong-Tie #9 x 1.5" SD connector screws
• 300 Simpson Strong-Tie #9 x 2.5" SD connector screws
• 12 GRK 5/16" x 4" RSS structural screws
• 12 GRK 1/4" x 2.5" RSS structural screws
• 20 GRK #9 x 2.5" R4 screws
• a handful of nails
• Rustoleum gray paint

## Why

We saw Stacey’s, and it created a sense of wonder in our hearts. The dream: of a place of refuge a few steps away from one’s usual cares; a place where the outlines of the self could be more distinct. A place that would let us dream in peace; to try on alternate futures and feel how they fit. Something uncomplicated and fun.

## Design

### 1. Exploration, goals, and constraints

Our goals were (1) to have a climbing area where people can recreate, (2) with a cave, (3) and a few corners for stemmy climbs; (4) without being annoying to the neighbors.

Constraints: it all had to fit in a 110" x 110" footprint, without anchoring to the existing building. Figuring out how to preserve the existing sunlight was also important — building the walls too high would block too much light, but too-short walls aren’t climbable.

After a few experiments, we decided on a three-sided configuration with one taller (but still short) wall with 10° and 65° overhangs, close to the existing building (marked as WALL·E), and two shorter vertical walls on the other two sides (walls F and G). WALL·E would be about 10' high, while walls F and G would be about 6' high.

## Design

### 2. Engineering design

After we had a rough idea of what we wanted to build, it was time to engineer it. This was fun: I got to revisit beam theory, read about/measure West Oakland soil densities, read and reread the Oakland building code; and a bunch of other desk work.

After we finished all the load calculations (love a cantilever), we chose our materials and drew it up in SketchUp:

## Design

### 3. Getting ready for fabrication

Fabrication seemed straightforward: we just needed to sink the footings, build the structure, then clad it with a climbing surface.

We assembled the materials:

Then warmed up and tested our tools by building some watching V build some sawhorses.

## Foundation

### 4. Digging

First, we called before we dug.

Next we had to kill all the plants that were previously growing in that space (RIP wisteria), and take a few inches of surface soil off to maximize available height.

Then, in an excruciatingly tedious process, we dug our post holes 42" deep (note to diggers: please don’t be stubborn, just borrow/rent/buy a post hole digger).

## Foundation

### 5. Setting posts for WALL·E

We used pressure-treated lumber from Economy Lumber Oakland for our posts. For WALL·E proper, we used one 6x6 for the leftmost post, and two 4x4s for the center and right posts.

Because the posts would be holding up about 1,500 lbs of dead weight and potentially several times that in (dynamic) live loads, we needed to make sure the foundation was sound.

To set each one, we filled the bottom 4" of each post hole with gravel, put a few nails in the post to get extra grip for the concrete, poured concrete for the remaining 3+' to ground level, then smoothed the top of the concrete away from the post to try to direct any rainwater runoff away from the post.

## Framing

### 6. Doing the rest of the framing for WALL·E

There were two parts to our framing: horizontal girts to tie the posts together and serve as the main load-bearing structure, and a standard-ish balloon frame to carry load from the climbing surfaces back to the posts. We used pressure-treated 2x6s for the parts of the frame that would touch the ground, and standard 2x6 douglas fir, painted with RUST-OLEUM silver gray, for the rest.

We framed everything using 2x6s at about 16" on-center, with slight deviances depending on hole placement for the climbing-hold holes (more on that in the next post).

First, we put up WALL·E’s horizontal girts. We attached these to the posts with 1/2" and 3/8" carriage bolts because the girts would be part of the critical load path from our climbers to the ground, and these would be critical joints. (This meant that we got to use these absurdly-long drill bits.)

For the 10° and 65° overhanging walls, we used joist hangers to carry load from the framing members to the post/girt structure. Joist hangers are the fasteners used to attach floor/ceiling boards to the vertical frames in a standard wood-framed house. In our climbing cube, the overhanging walls carry load more like a ceiling/floor than like a vertical wall in a house.

The first section of wall framing we put up was the 10° section. We cut, painted, and beveled the wood stringers, then attached them to the girts, posts, and themselves with joist hangers, 1/2" bolts, various other Simpson Strong-Ties, and structural and wood screws:

After that, we put up the framing for the 65° section. This was basically the same as for the 10° section, except that the forces here would be larger, so we sized up the structural elements and fasteners commensurately:

We put up a minimal vertical frame at the bottom of WALL·E for mounting the kicker board:

That was as far as we wanted to get with framing before putting in our last two support posts.

## Foundation

### 7. Setting the last two posts (in wall F)

The last two posts were one pressure-treated 6x6 (our longest post: 112" above ground, 42" below ground) to support WALL·E from the top and wall F, and one pressure-treated 4x4 for the right side of wall F. We used the same process as for the earlier three posts, but this time with some video:

## Framing

### 8. Doing the framing for walls F and G

Framing up walls F and G was much more straightforward than WALL·E — these would be vertical walls, going up only to our fence line (about 6'). For wall G, we planned to use our existing fence posts (which were already concreted down 16") as our posts, adding only horizontal girts for bracing and mounting the climbing surface to.

First we had to remeasure and replan, to see if our original plan still made sense. On a second pass, we decided to cut the height of these two walls, to (1) block less sunlight, (2) not be such an eyesore for the neighbors, and (3) avoid digging any more post holes.

For wall F (the vertical wall adjoining the cave wall), we put up a straightforward balloon frame in place using 2x6s, Simpson Strong-Ties, and some screws — a relief after WALL·E.

For wall G (a totally-vertical 16'-wide traverse wall), we cross-braced our 4x4 fenceposts with horizontal 2x6 girts attached with structural screws.

### 9. Back to WALL·E: framing the topmost section

To put up the framing for the 0° vertical section at the top of WALL·E, we procrastinated for two weeks, decided we might never complete the project, then called in help from pro contractor team S and C. With them on the team it was a breeze and a joy.

Phew. Framing complete. Next post: okay but what about the climbing part? (===, what’s the fastest way to mount 800 T-nuts?)

### P.S.: references

Special thanks to jennsends and MattBangsWood for information, dispelling our distrust of YouTube (a little), and inspiration.