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Designed to accommodate up to eight guests, this outdoor table is not likely to fly or tilt. Its base is indeed cast in a concrete base that ensures stability to any test.

Making a wooden table on a concrete base

Necessary material

  • Solid chestnut trays (54 and 35 mm thick)
  • Panel falls
  • Medium (4 mm thick)
  • Threaded rod Ø 8 mm
  • Lag screw (10 x 160 mm) with nuts and washers
  • Wood screws (5 x 80 mm)
  • Vinyl adhesive for outdoor
  • Concrete iron (Ø 8 mm)
  • Wire
  • Concrete ready to use
  • Hydraulic lime
  • Polyurethane or acrylic varnish for outdoor

Difficulty: 3/4
Cost: 350 €
Time: 1 week
Equipment: stapler, squeezes, trowel, pipe wrenches, reciprocating saw, hand planer, screwdriver, eccentric sander, jigsaw, wood combi, radial saw, drill press, 10 mm square chisel mortiser, circular saw on guide rail...
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When making a solid wood table for outdoor use, the essential is to provide the removal and swelling of the material according to the degree of ambient humidity. For this reason, the crosspieces of the tray are not glued together. The uprights are sealed in a concrete base by means of lag bolts, for a perfect stability, despite the size of the plate (135 x 125 cm).

A wood that resists outside

If the base weighs considerably the table, it also has an advantage: it is not likely to be reversed by the wind. In addition, concrete insulates wood from soil moisture. The essence chosen here for the uprights of the legs and the sleepers of the plateau is the chestnut tree. Economical, it offers excellent resistance in the outdoor environment. Oak, acacia or Douglas pine are also suitable, as well as many exotic woods.

Three different assemblies

For its implementation, a wood machine, combined type, is perfect.
But we can also provide planed wood section 50 x 50 mm and 27 x 66 mm and replace the various assemblies (here mortise and tenon, burring, groove and tongue) by simpler solutions, pigeon type (domino, lamella or pin).
The tray is composed of twelve cross members assembled with double mortise and tenon in two sockets. Its two side rails and the sockets are joined by double interlocking. Thirteen intermediate crosspieces fill the gap of 50 mm between the cross members; assembled by tongue and groove, they do not have tenons.
The base consists of eighteen equally spaced amounts of 50 mm, which form two perforated pillars, connected to the plate by means of support rails.

Make the tannins react

On chestnut, as on oak, the rain water causes the appearance of dark spots because of the tannins contained in the wood. To prevent this inevitable effect, the tannins are "reacted" with a alkaline product (like lime) to evenly darken the color of the wood. Over time, it will tend to lighten under the effect of UV. This particular tinting does not exempt from protecting the wood, either with a hard oil, or with a varnish for outside.

An alternative to tenons and mortises

The mortise and tenon joints are complex to make. By pigeons, they simplify the work and make it accessible to all.
Three main processes are commonly used.

  • False tenons (Dominos type) that avoid having to place two trunnions, but which require investing in a specific tool (Festool) quite expensive.
  • The trunnions, preferably passable with a double stitcher, failing with a simple drill.
  • Slats that are suitable for solid wood provided that there are pieces of sufficient width (at least 65 mm).

Preparation of wooden pieces

Debit the wood with a radial saw

  • The different pieces are cut into chestnut trays of 54 and 35 mm thick.
  • Cut long with the radial saw leaving a margin of about 3 cm.

Line the trays

  • Line the trays to obtain the desired sections, leaving a margin of about 5 mm.
  • Use a circular saw on a guide rail or a band saw.

To reconcile the pieces of wood

  • Cut and rough plan the sawing pieces to obtain sections of 50 x 50 mm (base and top) and 24 x 66 mm (intermediate pieces of the board).

Creation of double tenons and mortises

Create mortises

  • Dig double mortises (10 x 34 mm) at the chisel mortiser in the 50 x 50 mm section sockets.
  • Connected to the sleepers, they form the skeleton of the plateau.

How to make a wooden table on a concrete base: make

  • The double studs on the cross-members of the framework can be machined with three tenoning trays superimposed on a router with a sliding plate.

Clamp the pieces

  • The parts must be firmly clamped against a splinterguard.
  • We can also dig the space between the two tenons mortise if we have two trays tenon only.

Finish the arches with a radial saw

  • If the tenoning trays are not thick enough, finish the sawing with the radial saw or adjust the distance between the tenoning trays again for a second pass.

Using a milling cutter

  • The double studs have shoulders to adjust to the width of the mortises and allow to place lateral grooves.
  • Use a bur to be calibrated or grooved.

Intermediate sleepers

  • The intermediate cross members have two shoulders, the sideways have a single groove on the inner side and longer tenons to form a double interlocking.

Check assemblies

  • Check the interlocking of the joints before machining the lateral grooves on the frame cross members, and the 10 x 10 mm tabs on the intermediate crosspieces (section 24 x 66 mm, without studs).

Machine grooves and tongues

  • Work on the router equipped with a special milling cutter for machining grooves and tongues.

Assembly of the wooden table top

Assemble the sleepers

  • Assemble the cross members into the mortises before threading the intermediate cross members into the grooves.
  • The operation must be carried out without forcing.

Leave a game allowing the wood to inflate

  • The table is intended to stay outside, a certain clearance is necessary to allow the wood to inflate a little under the effect of moisture without causing tension

Bridle the wooden table top

  • Clamp the tray with clamps (the dormant clamps are well adapted).
  • Only the struts of the angles are glued (vinyl glue for outside).

Araser the ends

  • After drying the glue, sharpen the ends of the joints by double bending if necessary.

Chamfer and sand the edges and bottom of the board

  • With a hand plane and sandpaper, chamfer all sharp edges, then sand the underside of the table top.

Handyman's tip

Fastening by wooden dowels

  • If it is possible to glue all assemblies by tenons and mortises (choose a glue for outdoor slow grip), we can prefer a fixation by wooden dowels.
  • Placed from underneath, they will be cut with a saw.

Assembly of the base

Drill the cross ties on one side

  • Using the drill press drill the Ø 5 mm connecting links on one side.
  • On the adjacent side, drill Ø 24 mm on 10 mm of prof. then 8 mm for the passage of the threaded rods.

Drill the amounts

  • The uprights have a single hole (Ø 8 mm), centered on the thickness of the pieces and 50 mm from the upper ends.
  • Place stops on the table of the drill.

Assemble the uprights and sleepers

  • Thread the threaded rods (Ø 8 mm) into the holes made to assemble uprights and crosspieces.
  • Place nuts and washers in the cuvettes (Ø 24 mm) and tighten with a pipe wrench.

Center the footing

  • Center the legs under the table top.
  • The ends of the uprights protrude slightly to be placed between the cross members of the tray.

Screwing the legs under the tray

  • Screw the base under the table top through the Ø 5 mm holes after milling the hole entries.
  • Use wood screws 5 x 80 mm.

Drill the amounts in the axis

  • With the drill, drill in the axis of the uprights (Ø 8 mm) before placing lag screws of 10 x 160 mm, without forcing the risk of splitting the wood.

Install spacer blocks

  • Place spacers (section 50 x 50 mm) to ensure the parallelism of the studs, then connect the lag bolts with reinforcing bars, tied with wire.

Manufacture of the base of the table

Build a rectangular crate with falling wood

  • With the panel drops and the cleats screwed together, build a rectangular box of 120 mm high and internal dimension of 620 x 860 mm.

Screw the cleats

  • Staple a 4mm medium strip inside the crate to form an ellipse.
  • Screw cleats into the corners to hold the pressure of the concrete.

Chamfer the edges

  • Cut with a jigsaw a slightly smaller ellipse that will serve to stabilize the base.
  • Chamfer the edges for easy stripping.

Screw the panel into the bottom of the formwork

  • Center and screw the cut panel at the bottom of the formwork.

Adjust the height of the formwork

  • Lay the table on trestles.
  • Adjust the height of the formwork: the top of the concrete base must be at the same level as the base of the studs.
  • Adjust the levels of the table and the formwork.

Check the connection between the rebars and the feet

  • Center the formwork in relation to the table.
  • Ensure that rebars and lag bolts and concrete reinforcing bars do not touch the edges and bottom of the formwork.

Pour concrete

  • Pour a classically dosed concrete at 350 kg / m3.

Formwork and finishes

Sand the table with an orbital sander

  • Wait at least 48 hours before disposing.
  • Meanwhile, sand the wooden parts with an orbital sander (sandpaper # 80, then 120).

Color the chestnut table to react the tannins

  • Induce a uniform coloring of the chestnut by applying a mixture of water and lime (a handful of lime in a bucket of water), in order to react the tannins.

Sand with sandpaper

  • Rinse off the traces of lime, then sand by hand (extra fine sandpaper # 180 to 320) before applying an exterior varnish (polyurethane or acrylic).

Disassemble the base of the base

  • Disassemble the base of the base by dismantling the crate containing its elliptical shape.

Wooden table with a concrete base

  • The concrete does not need to be treated, but you can apply a colored coating or paint.

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