How to make a concrete seat

Cover

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Preface

ConcreteA mixture of sand, gravel, water and cement which hardens to a stone like condition when dry. furniture for the garden certainly takes a lot of beating.
It pretty much fits in with any type of landscape design. This concrete seat is a little beaut. It is easy to make and inexpensive. In fact, most of the work and cost is in the making of the form (mold), however you only need to make the form once in order to make as many seats as you like.
Once you are setHow much the teeth are angled out on a circular saw blade. up and have made one seat, chances are you’re bound to make another.
And of course, a concrete seat is going to last a long, long time.

Introduction

This concrete seat is 32″ (800mm) long, 14″ (350mm) wide, and stands 14″ (350mm) high.
It is reinforced with wire mesh and weighs around 117 lb (53 kg).

Designing and writing about such a project is a lot more involved than simply making it for one’s self.
A lot of thought has to go into the design and the method of making, so it can be explained in a way that readers are able to understand.
Thought has to go into the easy availability of materials, along with terminology.
Also taken into consideration is the type of tools that the average DIYer is likely to own.

This particular project took four takes before it was ready to put to paper.

Maybe make a few to sell!

There is more expense and time in the making of the form (mold) for the concrete seat, than in making the actual concrete seat itself,
however you only need to make the form once in order to make multiple seats.

It makes good economical sense to make more than one seat after taking the trouble to make the form.

Not including the form, the cost of making each seat is inexpensive in relation to a similar type of seat made from woodTimber, lumber. The hard fibrous lignified substance under the bark of trees.

You basically only need a wheelbarrow of concrete mix, some reinforcing mesh, and some release agent, all of which can be obtained quite cheaply – and even more so in bulk. Each seat takes but a couple of hours to make and gets easier with practice.

Maybe there could be a couple of bucks in making and selling the odd seat or two….just a thought.

This complete project (all the pages together in one handy PDF ad-free file) can be purchased online and downloaded immediately to your computer for only $5.  Grab here.

About the measurements, Materials you will need and Informative notes

This project is in four parts

Part 1. Making the form (mold)

Part 2. Preparing the reinforcing mesh

Part 3. Making the concrete

Part 4. Casting the concrete

The four parts will guide you step-by-step through all the stages of making the form (mold), preparing the reinforcing, making the release agent, applying the release agent, making the concrete, pouring the concrete, settling the concrete, removing the form, and cleaning-up.

There is also a page giving easier options, albeit for a less exciting seat.

* Note 1:  2½” (62mm) thick wood is less common than ¾” (20mm) thick wood, and harder to cut the shape with a jig-saw (although it can be done). The ¾” (20mm) thick wood is more readily available and of course a lot easier to cut, but you will need three times as many pieces, as you will need to glue and screw three pieces together to make up for every one piece of the thicker wood. The thicker option is the best way to go if you can manage to acquire the wood (or close to it) and have the tools to cut it.

• 8ft (2400mm) of ½” (12mm) angle fillet, allowing for a little bit of waste. * see Note 2

* Note 2:   Angle fillet is a triangular shaped strip of wood. Its purpose is to make a beveled-type edge around the top of the seat. You can use a different profiled piece of wood if you want something a bit more fanciful, or you can disregard it altogether for a plainer look.

• Half a standard sheetAny broad, thin surface. of ⅝” (15mm) thick plywoodA piece of wood made of three or more layers of wood veneer laminated together with glue.. A standard sheet is 4ft x 8ft (1200mm x 2400mm) so you will need half of that, allowing for a little bit of waste.

• I piece of ⅛” (3mm) thick plastic sheet, 40″ x 22″ (1000mm x 550mm). * see Note 3

* Note 4:   The angle brackets are to hold the leg form to the seat form. They make for easy alignment when it comes to assembling the form for casting. The bracket size given above is not absolute. Anything similar will do as long as it does the trick. You may have to make your own by cutting, bending, and drilling a piece of sheet metal. On the other hand, you can do away with them altogether and use clamps to hold the leg forms to the seat form. This latter method will require a bit of extra measuring and aligning when it comes to assembling the forms for casting.

• 5 sq ft (0.5 sq m) of 5/32″ (4mm) or slightly thicker reinforcing wire mesh. * see Note 5

* Note 5:   Home-mixed concrete is not always as strong as it could be, so reinforcing steel or mesh is necessary. The mesh and method used in this project is but one way of adding adequate reinforcing. You can even make up your own grid using the same size or a thicker rod, and join the intersections with tie wire. The most important point is that the reinforcing covers the area of the seat and is also tied to other reinforcing that bends into the leg area.

• About three-quarters of the average heavy-duty wheelbarrow full of concrete mix (gravel, sand, and cementA powdery type substance made from a mixture of earths materials such as limestone and shale, which is sintered (cause to become solid mass by heating without melting), ground, and mixed with small amounts of calcium sulphate and calcium carbonate. Cement is activated by water and when mixed with gravel and sand, forms concrete.).

• And… some release agent so the concrete doesn’t stick to the form. * see Note 6

* Note 6:   A release agent is a substance that is applied to surfaces to prevent them from sticking, in this case so that the concrete does not stick to the form. You can purchase form release agents from some building supply stores, often in handy little spray bottles. You can also make your own for a fraction of the price out of an even mixture of used car oil and diesel, and apply it with a paintbrush or a rag. That’s what we do.

The cutting list for the form

Plywood

LumberAny of the framing wood./wood

Then, on a flat even surface, glue and nailA short nail with a large flat head used for securing roofing felt, plasterboard, sheet metal to wood etc. or screw the (c) pieces and the (d) pieces together in picture-frame fashion.

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Step 1.2   Cutting the plywood, the plastic, and assembling the seat form

Cut a rectangular piece of ⅝” (15mm) thick plywood, 40″ long x 22″ wide (1000mm long x 550mm wide).

Also cut a rectangular piece of ⅛” (3mm) thick *plastic sheet, 40″ long x 22″ wide (1000mm long x 550mm wide).

*Note:   The plastic sheet is to make a smooth finish on the top of the seat. The end product of a concrete cast will be as smooth as the form. The plastic sheet can be any thickness, or you can disregard it altogether, in which case the finished product will be as smooth as the plywood form – which can still be an acceptable finish.

Lay the piece of plywood on a flat even surface.

Then lay the plastic sheet on top of the plywood sheet and the ‘picture frame’ on top of that.

Temporarily hold everything in place with clamps while you screw the all the pieces together.

FixTo secure with nails or screws. (glue and nail) strips of ½” (12mm) *angle fillet (f) around the inside perimeter of the seat form against the frame and the plastic sheet.

*Note:   Angle fillet is a triangular shaped strip of wood. Its purpose is to make a beveled-type edge around the top of the seat. You can use a different profiled piece of wood if you want something a bit more fanciful, or you can disregard it altogether, for a plainer look.

Step 1.3   Cutting the form pieces for the legs

Cut 4 pieces (e) of *2½” x 5½” (140mm x 62mm) wood, at 12″ (300mm) long.

Each piece will need to be shaped.

Cut a piece of cardboard 5 ½” (140mm) wide x 12″ (300mm) long.
Draw a grid onto the cardboard with line spacings 1″ (25mm).
Then copy (draw) the shape as shown in the grid plan, onto the cardboard using the grid lines as reference points.
Cut out the shape on the cardboard and use that as a pattern to mark all the (e) pieces. They can then be cut using a jigsaw or other suitable tool.

This complete project (all the pages together in one handy PDF ad-free file) can be purchased online and downloaded immediately to your computer for only $5.  Grab here.

*Note:   2½” (62mm) thick wood is less common than ¾” (20mm) thick wood and harder to cut the shape with a jigsaw, although it can be done. ¾” (20mm) thick wood is more readily available and of course a lot easier to cut, but you will need three times as many pieces, as you will need to glue and screw three pieces together to make up for every one piece of the thicker wood. The thicker option is the best way to go if you can somehow acquire the wood (or close to it) and have the tools to cut it.

Next cut 4 pieces of ⅝” (15mm) thick plywood, 17⅝” long x 12″ wide (440mm long x 300mm wide).

Mark six hole positions on each piece. Refer to the drawing for hole positions.

Step 1.4   Assembling the forms for the legs

Sandwich the (e) pieces between the plywood (b) pieces.
Position the pieces in place (refer to the drawings on the previous page) and hold them there with clamps.
In all, there will be two leg forms, each consisting of two (e) pieces and two plywood (b) pieces.

The plywood (b) pieces are already marked for drilling. That was done in Step 1.3.
Drill through the leg forms on each drill mark.
Use a ½” (12mm) diameter drill-bit to drill the holes. The bolts are ⅜” (10mm) diameter. The bigger hole enables the bolts to be easily inserted and removed.

It is important to make the holes approximately ⅛” (2mm) bigger in diameter than the bolts to ensure that they (the bolts) can be removed easily when it’s time to release the form-work.

When the holes are drilled, you can then insert the galvanized ⅜” (10mm) hex bolts into the holes, add the washers, screw on the wing-nuts, and tighten.

Next screw a 4″ x 2″ x 2″wide (100mm x 50mm x 50mm wide) *galvanized angle bracket (or similar) to each end of each leg form. Four brackets in all.

Use only three screws to hold each bracket, as they will have to be unscrewed when it’s time to release the form-work.

*Note:   The angle brackets are to hold the leg form to the seat form. They make for easy alignment when it comes to assembling the form for casting. The bracket size given above is not absolute. Anything similar will do as long as it does the trick. You may have to make your own by cutting, bending, and drilling a piece of sheet metal. On the other hand, you can do away with them altogether and use clamps to hold the leg forms to the seat form. The latter method however, will require a bit of extra measuring and aligning when it comes to assembling the forms for casting.

This complete project (all the pages together in one handy PDF ad-free file) can be purchased online and downloaded immediately to your computer for only $5.  Grab here.

Step 1.5   Aligning and bolting the leg forms to the seat form

The purpose of this step is to allow for easy alignment of the leg forms over the seat form during the casting process.
The casting process involves half-filling up the seat form with concrete, placing in the reinforcing, filling the seat form with concrete, and fixing the leg forms in place ready for more concrete.
It is the latter stage that is made easier and quicker with the addition of the angle brackets.

Do this step in the following order:

Measure 4⅜” (110mm) along pieces (c) from the inside corners of the seat form and mark across pieces (c). See fig.1.

Place the leg forms against the mark. Ensure that the leg forms are equal distance from the sides. Mark the drill holes on pieces (c) through the holes in the angle brackets. (See fig.2.) Then remove the leg forms.

Drill down into pieces (c) to a depth of ½” (12mm) with a 1⅛” (28mm) diameter drill bit, and then continue the rest of the way through with a ½” (12mm) drill bit. (See fig.3.) There will be four holes in all.

Insert a ⅜” (10mm) coach/carriage boltA metal rod that has a head on one end and threads on the other and is used to fasten together lumber. The most common bolts used or referred to in projects within this website are coach/carriage bolts and hex bolts. into each hole from underneath and secure each bolt with a washer and nut. The nuts will finish below the surface of the wood. See fig.3.

*Note:   The angle brackets are to hold the leg form to the seat form. They make for easy alignment when it comes to assembling the form for casting. The bracket size given above is not absolute. Anything similar will do as long as it does the trick. You may have to make your own by cutting, bending, and drilling a piece of sheet metal. On the other hand, you can do away with them altogether and use clamps to hold the leg forms to the seat form. The latter method however, will require a bit of extra measuring and aligning when it comes to assembling the forms for casting.

Part 2. Preparing the reinforcing mesh

Steps 2.1 to 2.3   Cutting, shaping and tying the mesh

The reinforcing used in this project is *welded wire mesh. It is a grid of 5/32″ (4mm) thick wire with spacings at 6″ (150mm).
This reinforcing mesh and method is not the only way. Other material and methods can be applied. See the note at the bottom of this page.

Step 2.1   Cutting the mesh

Cut the mesh to the sizes given in fig.1. Cut one A piece and two B pieces.
The B pieces will have to be trimmed, bent, and shaped to suit.

 Part 4. Casting the concrete

Steps 4.1 to 4.3   Applying the release agent, half filling the seat form and placing the reinforcing

Lay all the form pieces out on a flat work surface.

Step 4.1   Applying the release agent

Apply ample *release agent to all the form pieces on all sides with a paint brush.
Wipe off any excess with a rag.

*Note:   A release agent is a substance that is applied to surfaces to prevent them from sticking, in this case so that the concrete does not stick to the form. You can purchase form release agents from some building supply stores, often in handy little spray bottles. You can also make your own for a fraction of the cost out of an even mixture of used car oil and diesel, and apply it with a paintbrush or a rag. That’s what we do.

Step 4.2   Half filling the seat form

Pack the seat form an inch or two up off the work surface so that you are able to get a hand under the ends. This is so you can lift an end up slightly and drop it multiple times in quick succession to vibrate and settle the concrete to help eliminate air pockets and make a smooth surface.

A little under half-fill the seat form with concrete and vibrate the form to settle the concrete. Do this by tamping and poking the concrete with a broad thin stick, say ⅛” (3mm) thick x 1½” (38mm) wide, also by using the rapid drop method as mentioned above, and also by tapping around the edge of the form with a hammer. The more vibrating the better.

Step 4.3   Placing the reinforcing

Step 4.5   Attach the leg forms to the seat form

Partially assemble each leg form, with one side panel (b) only, and place them in position on the seat form around the reinforcing wire.

Slipping the angle brackets over the bolts in the seat form will automatically place the leg forms in the right position.

Then add the second panel (b) to each leg form and fasten them in place with the wing-nuts.
Likewise, tighten the angle brackets to the seat form with wing-nuts.

Step 4.6   Topping up the leg forms

Start shoveling concrete into the leg forms.

But as you go….

More rapity tapity tap
As you go, tamp, poke, prod, with a broad stick – say a piece of plastic, steel, or wood about ⅛” (3mm) thick x 1½” (38mm) wide.
Do a lot of rapity tapity tap around the sides of the leg forms.
It would spoil an otherwise good job if the end product was full of air-pocket holes and gaps for the lack of a bit of rapity tapity tap

Once filled and settled, remove the excess concrete.

Have a bit of a clean-up

The next morning you can clean up a bit more.
All the splashed and spilled concrete should scrape off from the form easily enough if the form work was adequately coated with the release agent.

That’s pretty much it for a while.

Let it sit there for three or four days.

Let the concrete set (cure) slowly
The longer concrete takes to set (cure), the stronger it will be.
Keep the concrete shaded during the curingThe hardening of concrete. The process of becoming hard or solid by cooling or drying or crystallization. In concrete application, the process in which mortar and concrete harden. The length of time is dependent upon the type of cement, mix proportion, required strength, size and shape of the concrete section, weather and future exposure conditions. The period may be 3 weeks or longer for lean concrete mixtures used in structures such as dams or it may be only a few days for richer mixes. Favorable curing temperatures range from 50 to 70 degrees F. Design strength is achieved in 28 days. period.
Keep the concrete moist for at least a day or so by hosing with a fine mist every now and then. This is more crucial in warmer conditions.
The release agent, apart from just being a release agent, also serves another purpose. It prevents the moisture in the concrete from soaking into the form, thus helping to prevent the concrete from drying out too fast.

Step 4.7   Releasing the leg forms

Undo all the wing-nuts off the bolts on the sides of the leg forms.

Take out all the bolts.
The bolts should slip out easily, simply because the diameter of the bolt holes are bigger than the diameter of the bolts. The holes are ½” (12mm), the bolts are ⅜” (10mm). You did make the holes bigger, didn’t you?

The sides of the leg forms should come away quite easily.
This is when you get the first look at your handiwork, and you will find out if you did enough rapity tapity tap.

Remove only the first angle bracket. Do one at a time, so as not to get them mixed up (for possible future castings).

Once you have taken off the first angle bracket, you can then remove the respective piece (e), by nudging or tapping it out from the top.

When that piece (e) is off, immediately screw the angle bracket back to it.
By doing one at a time, i.e. taking off one angle bracket, removing the respective piece (e), and screwing back the angle bracket to the same piece it came off, then you are not going to get all the bits and pieces mixed up should you decide to make another seat.
Now remove the other three angle brackets and (e) pieces in the same manner, one set at a time.

This complete project (all the pages together in one handy PDF ad-free file) can be purchased online and downloaded immediately to your computer for only $5.  Grab here.

Step 4.8   Releasing the seat form

Slip a piece of board under the middle of the seat form.

Of course, you will need someone to tilt the seat back while you do that.

The board can be 1″ (25mm) thick more or less, it doesn’t really matter, and 20″ (500mm) long x 6″ (150mm) wide.

Stand on the two sides of the seat form and give a little bounce up and down.
This will break the seal between the concrete and the form. You will visibly see the seal breaking – a slight parting between the concrete and the form.
The seal will be more of a suction seal, rather than an adhesive seal, because of the release agent. Standing on the form and giving a little bounce will break that seal.

Now stand on the two ends (as opposed to the two sides) and do the same thing.

Now the concrete seat should easily lift out of the form.

If by any chance it does not, then turn the whole unit upright and knock one end of the seat form up by hitting it from underneath with a hammer.

You only need a little bit of air in to break any suction hold.

Mmmmmmm. Looks pretty good to me.

Appendage: Easier options

Easier options albeit for a less exciting seat.

Discard the angle fillets

You can do-away with the angle fillets for a plainer look around the top of the seat.
If you do-away with the angle fillets you must run the bevel cut on pieces (c) and (d) through the full thickness of the wood.

Discard the angle brackets

Use clamps instead of the brackets to hold the leg forms to the seat form.
You will save sourcing or making the brackets and fitting them, and also save from having to fix the connecting bolts to the seat form.
The downside is that without the brackets and by using clamps, you will have to manually measure and position the units as you go. Okay for a one of, but probably not much chop if you intend to make a few.
The brackets on the leg forms and the connecting bolts in the seat form make for a quick and accurate alignment when bringing them together during the casting process

This complete project (all the pages together in one handy PDF ad-free file) can be purchased online and downloaded immediately to your computer for only $5.  Grab here.

Discard the fancy shaped (e) pieces

You can replace the fancy curved (e) pieces with straight pieces, say 2 ½” x 2 ½” (62mm x 62mm) stock or bigger.
This will save the time and effort of making the curved (e) pieces.
It will also save a little time during the casting process, as you will not have to dismantle the leg forms when positioning them around the reinforcing.

The downside is that the legs of the finished product will be straight, and pretty much characterless.

Discard the plastic sheet

The plastic sheet is to give a smooth finish to the top of the seat. You can do away with it and just use the plywood.
If the plywood surface is smooth, then so too will be the finish on the concrete (although probably not as smooth as with the plastic).
Concrete will take on the same finish as the form itself.