Thursday, June 9, 2011

Bench Planter III: Seating

I had intended to buy bluestone (sandstone), basalt, or some other nice masonry product for the top seating surface of the wall, but Jackie was intent on using some sort of composite decking material, like we used on our back steps.  Stone would have been much easier in some ways.  Mix up some mortar and plop it down...  But since the surface was going to be about 12" wide on top of a 6" wall, there would be some cantilever forces to deal with, and mortar isn't the greatest for that.

After several evenings of head scratching, here's what I came up with.  It's simple, strong, and removable if we change our mind or damage it.  First off, I mixed up a small batch of mortar and put a smooth coat on the top of the wall, pitching it very slightly so water wouldn't pool and (especially) have cracks to freeze in and damage the masonry.

We had to drive to Tualatin to pick up three 16' lengths of gray composite decking, because stupid Home Depot quit stocking the stuff I bought from them for the back steps.  I cut them down to 12'-3" and saved the offcuts to build the sides.  The front bench was made from three pieces, two 5" and one 2-1/2" in the center.  I ripped 1-3/8" off either side of the 5-3/8" stock for the center piece, and ripped a little 3/8" ribbon off one side of the other two to get the 5" pieces, because I wanted to get rid of the rounded edges in the middle of the seat.  Ripping them was a challenge I solved by building an oversized plywood sub-base for my circular saw and clamping a scrap fence to that.

Then I cut 11" sleepers from pressure treated 2x4, fastening them at the ends and every 16" along the front of the wall with 1/4" x 2-3/4" flat-head Tapcon screws.  Some sleepers got two fasteners to resist the cantilever forces.  I've never been a fan of Tapcons.  They seem like they're made more for the contractor who wants to get it done in a hurry than for people like me, but they do work and I'm installing a lot of fasteners so if one fails it's no big deal.  I've also got more experience working with concrete anchors and have learned the importance of drilling a little deeper and especially of cleaning out the anchor hole.  Concrete dust isn't like wood dust.  It doesn't compact past a certain point, and if you leave any in the bottom of a hole, it can cause the fastener to seize up, so brush & blow out big holes with an air gun, or at least run the drill bit in and out a few times to extract most of the excess.  The 3/16" holes go pretty fast with my big Bosch rotary hammer.  I also am now the proud owner of a small impact driver (I got a Milwaukie drill / impact driver set last year), which makes driving these puppies a piece of cake.  Install a #3 phillips bit into the driver and put on your hearing protection!  Bbbbbbbbbbbbbt.  Done.

Use a mason line to get them all lined up
The decking was fastened to the sleepers with #7 x 2-1/2" stainless steel finish screws, pre-drilled and countersunk, of course.  I left a minimal 3/32" gap between the decking, to keep the appearance neat and easy to clean.
Shorter sleepers on the sides
The sides were built in a similar way, but with a narrower surface made from 5" wide and 2-1/4" wide pieces.  Three 6" sleepers were installed on each side, and one of the 3'-9" offcuts was ripped in half to make the narrow strip.  I used the long 1-3/8" strips to trim around the lower edge of the seat, hiding the sleepers.  It doesn't look perfect from all directions, because the ends of the decking show the ribbed bottom, but it's very solid and should hold up well to the elements.
the finished seating surface
I think an idea that would have been more fun would have been to cast our own concrete pieces, like building a concrete kitchen countertop.  With the right reinforcing and some cast-in attachment hardware, it would have been strong and stable, and we could have stained it whatever color we liked, or put a cast or embedded design in it.  Maybe next time!