make a Concrete and Wood Garden Bench

Hi everybody this is Kent from MAN about TOOLS
and today we’re making this wood and concrete garden bench. I’ve been wanting to make some benches to
go along with the concrete garden boxes I’ve been casting. I like the blend of concrete and wood with
simple, clean lines. This design has square concrete legs and a
flat planked wooden seat. Here’s how the bench goes together. The concrete legs have three protruding seat
bolts at the top and one bolt on the inside to attach a stretcher. Three planks make up the seat. Nuts with washers are threaded on the stretcher
bolts through a hole in the side. The seat planks are also secured with washers
and a nut. And two ties are screwed to the bottom of
the planks. I wanted to make strong connections between
the concrete and the wood. I know there’s a number of ways of doing this
with drilled anchors and brackets. But, for this first bench in this series I
wanted to try casting anchor bolts in the form during the pour. In the similar fashion as a house foundation
with anchor bolts for the sill plate. And so nothing else would be needed once you
stripped the form from the casting. Now I know this would mean a bit more work
in the construction of the form, but building the bench in the end should be faster and
should make it very sturdy. So here’s the form for casting the legs. The form has a 3/4″ plywood base with an angled
inset attached, just like the the garden boxes. A two part block holds the seat bolts in place
and can be taken apart after casting. The end wall and side walls are made of plywood. The anchors are 3/8th’s galvanized carriage
bolts 3 1/2″ long. The form has a bridge that holds the stretcher
bolt in place. This stretcher helps to prevent side to side
racking, as the seat boards have only a single attachment point on each end. The bolt block and bridge are made from standard
framing lumber. When assembled, concrete is poured in to fill
the form. I’ll start by cutting plywood on the table
saw and checking that it’s square. For these forms I used plywood as it’s what
I already had around the shop. The legs are identical so one form is enough
but, as I was filming and prototyping, I built two. One from recycled fir plywood, and one from
birch. You don’t need a lot of power tools to built
the forms or the bench. You can get by just fine with a circular saw,
drill, and driver. You could use a circular saw, a home-made
guide, and clamps for these cuts as well. If you’ve built the garden box forms then
this should be pretty straightforward. Like the base, the inset is plywood but beveled
at 30 degrees. I make one inset from birch, and the other
from fir. I lay out and mark the corner locations on
the base and drill pilot holes for the screws that will attach the inset. I apply a little glue then attach the inset
with screws from the underside of the base. I have a complete set of plans available for
download on my website:, with dimensions in inches and millimetres. Next I’ll cut the three plywood sides for
the form. I rip them to width then cut them to length
with a mitre saw. You could use a speed square and circular
saw to make these cuts instead of a miter saw. The bolt block is made from two pieces of
framing lumber. I rip the upper and lower pieces from a 2×6. I rough cut these an inch longer than needed
as I will trim it to final length after the pieces are screwed together. It’s easier to align this way. I mark the location for the three bolt holes
and mark the screw locations between them. I use four screws to attach these two pieces
together. I clamp them, drill pilot holes, then run
the screws in. I’ll trim it to it’s final length then take
this bolt block to the drill press to cut three counterbores on the outside face. I swap bits and drill three holes on the inside
face to hold the bolts. I’ll talk more about the reason for the counterbore
later. The thru hole is 3/8’s diameter and the bolts
fit snug with little or no play. I want the bolts to be held firmly and to
not move once they are set in place. I mark and drill pilot holes for the screws
that will hold the bolt block to the base and sides. I use the drill press for this but you can
freehand these. The bridge is made from a 2×4 and holds the
bolt for the stretcher. I cut the span and two supports to length
and mark the center for the bolt. I counterbore and drill on the drill press. All holes and counterbores could also be done
using a drill guide instead of a drill press. I mark and drill pilot holes in the supports. Then assemble the bridge with 3″ screws. With all the parts done I’ll do a test assembly
of the form to see if everything fits together as planned. I’ll use self drilling, washer head style
cabinet screws for most of this. Along with some two inch and three inch wood
screws. The pilot holes really help speed this up. Now I’ll check the fit of the bridge and attach
it to the walls of the form with 2″ screws. It doesn’t always go this well but everything
fit the first time for both forms. I mark each part with a sharpie, so I can
reassemble it the same way. I take the forms apart before I coat them
with oil. I also disassemble the bolt block to get oil
on all surfaces and seams. I had some mineral oil left over from making
the garden box forms. This oil is sold as Butcher’s Block or Cutting
Board Oil. It’s fast and easy to apply and seems to work
well. Mineral oil can be bough from Animal Feed
suppliers or in drug stores or pharmacies. I apply it to all faces then leave overnight
to soak in and dry to the touch. I reassemble the main box of the form and
run a bead of latex caulk on the inside edges. This makes the form watertight, gives a small
radius on the outside corners, and it’s easy to remove after casting. Latex works well as it’s not overly strong
and will allow you to disassemble the mold once the concrete sets up. When the caulking is dry I spray the inside
of the form with vegetable cooking oil to keep the concrete from sticking. Now I’ll insert the three bolts. I line them up with the outside face of the
bolt block. I don’t want the ends to stick out past the
outside edge as this will make the bolts stick up on the bench seat. I add a nut to the ends of these bolts and
snug it finger tight. The counterbore allows room for my fingers
or a socket. As this is a prototype, I wasn’t sure how
well the bolt block would hold the bolts in place during assembly, pouring, and vibrating
the form. The nut is just a bit of added insurance. Now I secure the bolt to the bridge with a
washer and nut then set the bridge in place and screw the supports to the form walls. The form is now ready for concrete. I set out saw horses and use some shim strips
to level them front to back and side to side. This is an important step as the form has
to be level. So here’s the ingredients for the concrete. CSA Mortar Mix, glass fibre, plasticizer,
colour, and Citric Acid powder. I use 55 lbs of CSA Mortar Mix to 5 quarts
of cold water, a packet of plasticizer, 1.3 ounces of citric acid, and 4 and a half ounces
of colour. I also will add a bit of glass fibre for extra
strength. I measure the water then add it to a pail. I then add the other ingredients and dissolve
them in the water. I have an egg beater style mixer on my drill
that works well for mixing this concrete. I use a plasticizer to make the concrete flow
and pour like water. And I add the citric acid to give more working
time. I
then slowly add the mortar mix, about a quarter of a bag at a time. In North America, the Rapid Set brand can
be found at Home Depot. I add a third of an ounce of glass fibre for
more strength. This is the manufacturers recommended amount. I have a full blog post for this project at that lists details for the concrete mix I used, and all the tools and
hardware. The CSA mortar mix has a light beige colour. And that’s fine but I wanted to make the legs
grey so I added black concrete dye to the mix. I was thinking that it would blend better
if I added it to the water first. I’ve been asked a lot about colour additives
for concrete so I added some for these castings and will try other colours in the future. I used a length of wooden dowel to stir the
mix to check for any clumps on the sides or the bottom of the pail. When it’s blended smooth I pour it into the
form, filling it right to the top. I really like this CSA mortar mix and I used
it in Part 4 of the garden box series so I decided to use it again for these forms. It’s really easy to mix, pours like water,
sets up fast, and requires little or no troweling. After about 10 minutes I vibrated the form
to bring any bubbles to the surface. For this I use a reciprocating saw without
the blade. While the first pour was setting up I mixed
another bucket of concrete. And filled the second form. Then vibrated it after about 10 minutes. In about 45 minutes the concrete began to
solidify. Then shortly after that it began to dry and
show a white haze. I sprinkled water on the surface every 10
minutes or so for about an hour to keep it wet and allow it to cure. After an hour of this, the concrete can be
removed from the forms. It was the end of the day so I covered the
forms with plastic and left them overnight. Now for what I think is the best part of all
of this: stripping the forms to reveal the casting. I wasn’t sure how well the split bolt block
would work or if it would be difficult to remove but it went just fine. The newly cast legs should now be at around
half their full strength. They will reach their full strength if you
keep wet to cure for four weeks. For this project I’m not going to worry about
that here and I’m going to build the bench right away. For safety, I put a few wraps of tape around
the exposed bolts while I was handling the leg castings. I used a small block of concrete from a previous
pour to round off any sharp corners on the casting while it was still relatively soft. I’ll make the seat for the bench from red cedar
2×6’s. I’ll cut them to length on the mitre saw then
lay out the hole locations on each end. I’ll use the drill guide to first counterbore
for the nut and washers, then drill through for the bolt. I use a square as a gauge to get a consistent
bore depth. The stretcher is made from a 2×4. I had some cedar 2×6 left from the seat planks
so I ripped it down on the table saw. I lay out and mark the location for the holes
on each end and drill them from both sides with a forstner bit. I drilled a pilot hole first to help guide
the larger bit. And this worked pretty well. To make drilling into end grain for the stretcher
bolt easier I first make a drill guide from a scrap piece of 2×2. Then I clamp the stretcher and guide to my
bench. The drill will follow the guide and give a
centered and true hole. I’ll attach ties under the seat to connect
the planks and prevent any side to side racking . These are made from a 1×4. And they have a 45 degree bevel on each end. I’ll drill pilot holes now to make assembly
of the bench easier. I sand the ends of the planks to round over
the corners. And sand off any rough spots on the other
parts. Then apply two coats of oil-based stain and
leave everything to dry overnight. To help with assembling the bench I mark the
corner locations of the legs on a flat surface. I use a long straight edge and framing square
for this. I set the legs in place while I slide the
stretcher onto the bolts. Then add the seat planks and check everything
for square. I add washers and nuts to the seat bolts just
finger tight for now. I slide the flat washer and lock washer on
the stretcher bolts. Then thread the nut on the bolt and tighten
with a wrench. Not too tight, just enough to pull the end
of the stretcher against the concrete leg. And I do the same on the other end. I can now tighten the nuts on the seat planks
with a socket wrench . The ties are screwed to the seat planks from
underneath. I use a scrap strip of wood and clamps to
hold it in place while I run in screws. With the seat planks having only two attachment
points, the ties are required to counter any twisting forces. I realized that my center two pilot holes
should have been offset as the driver was blocked by the stretcher. So I just drilled two more holes. I forgot to add rubber gaskets to keep any
wood from contact with concrete. Wood will wick moisture from concrete and
cause rot. So a rubber gasket will help prevent this. I used an old tire inner tube and cut the
gaskets with scissors. When I move this bench out to the garden I’ll
add the rubber gaskets then. Thank you so much for watching. If you like what you see on our channel then
give us a thumbs up and hit subscribe if you haven’t done so already. We’ll see ya next time.

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