Laying a Wooden Terrace on Exposed Aggregate Concrete Slabs: This Is How It Works

Laying a Wooden Terrace on Exposed Aggregate Concrete Slabs: This Is How It Works

Laying a wooden terrace on exposed aggregate concrete is also easily possible for laypeople, provided the correct procedure is known. Our instructions and tips will help.


The preparation for laying the terrace beams consists of four steps. It refers to:

1. Dismantle

If there are already beams or slabs on the concrete, they must first be removed. As well as old beams and fixings.

2. Cleaning

The exposed aggregate concrete must be cleaned thoroughly. A broom can first be used to remove coarse, dry dirt. A more thorough cleaning can then be carried out with a high-pressure cleaner such as a Kärcher.

3. Repair damage

Once the concrete has dried, it should be carefully checked. If there are cracks or holes, loose pieces of concrete and impurities must be removed and repaired. Repair filler is usually sufficient for this. However, cracks or holes must be large enough to be filled with them. If necessary, they have to be widened or enlarged for this. Even then, they should be thoroughly cleaned again so that the filler can reliably bond with the hardened concrete.

4. Check the slope

So that rainwater can drain off well, the terrace has to slope down slightly away from the house. A gradient of two percent is sufficient. For a length of one meter that means one difference of only two centimeters. However, this slight difference ensures a safe drainage of the water.

5. Measure the terrace and calculate the material requirements

Before the girder beams and wooden planks can be installed on the exposed aggregate concrete, the material requirements must first be known.

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Calculate material requirements – examples

So that you don’t have to spend an unnecessarily large amount of money or make additional efforts to procure the material, the material requirements for the wooden terrace should be measured and calculated as precisely as possible. All that is required is the length and width, which means that the area can be calculated in square meters.

For a terrace five meters long and four meters wide, the calculation is as follows:

4 mx 5 m = 20 square meters

Because cutting off the planks can lead to a loss, an additional ten percent should be planned for them.

20 qm: 10 = 2 qm
20 qm + 2 qm = 22 qm

The total material requirement for the boards is therefore 22 square meters. The calculation for the support beams is similarly simple. The required length corresponds to the length of the terrace. The necessary number depends on the width. As a rule, one girder every 50 centimeters is sufficient. This results in the calculation:

4 m: 0.5m = 8 support beams
8 support beams x 4 m = 32 running meters (running meters)

In addition, a waste of five percent must be planned for the bars. At 32 running meters, the calculation is as follows:

32 running meters: 20 = 1.6 running meters
32 running meters + 1.6 running meters = 33.6 running meters

Assemble support beams – instructions

When the preparations have been completed and the required amount of material is available, assembly can begin. To do this, the girder beams are first aligned parallel to the house at a distance of 50 centimeters from each other. In addition to the bars themselves, you need:

  • Cordless screwdriver
  • drilling machine
  • Spirit level
  • pencil
  • Folding rule
  • Wood flakes
  • hammer
  • Dowels
  • Screws
  •  two bricks

If these necessary utensils are also available, proceed as follows:

  1. The first support beam is then placed exactly on the house wall. A spirit level is used to check whether the bar is straight. If this is not the case, pieces of wood can be pushed underneath to align it horizontally.

  2. Use a folding rule to mark crosses for drill holes in the middle of the bar, 20 centimeters from the outer edges. Markings should also be placed in between. Regular distances between 50 and 80 centimeters are ideal.

  3. The bar is placed on a brick at each end and the markings are completely pierced.

  4. The support beam is again aligned exactly with the house wall. Now the pre-drilled holes are used as a template to drill holes through them in the exposed aggregate concrete.

  5. The bar is removed again so that dowels can be inserted into the holes. Each dowel is lightly hammered into the ground with a hammer.

  6. After aligning and checking with the spirit level for the last time, the first support beam is now fixed with screws.

  7. At a distance of 50 centimeters, all other beams are now installed in the same way.

Tip: So that the distances between the support beams do not have to be measured with a folding rule every time, two slats can be sawn to the length of the respective desired spaces. These are placed between the bars and serve as spacers and orientation.

Floorboards assemble

As soon as the support beams are fixed on the exposed aggregate concrete, the decking can be installed. The procedure is as follows:

  1. Appearance: If the length of the boards is not sufficient for the length of the wooden terrace, the wooden boards should first be placed loosely on the beam structure. Here you can quickly determine which distribution and which cuts result in an appealing pattern.

  2. Measure, mark, saw: Once the laying pattern has been determined, the respective lengths are measured and marked. The markings on each bar are then connected to each other in order to draw a cutting line. The beam is sawn off along this line. Since only a small percentage was taken into account for the waste, so that the costs remain as low as possible, you should measure and work very precisely.

  3. The first board is aligned on the edge and checked for the desired slope with a spirit level. If this is not the case, wooden plates can be pushed between the plank and the beam to create the slope.

  4. Two screws are set per support beam and screwed in with the cordless screwdriver. If the wood is very hard, you should first drill a pilot hole for each hole with the drill. To ensure a harmonious overall picture, it is advisable to mark the holes beforehand.

  5. First the board is fixed with two screws at each end, then it is also screwed to all other beams. The procedure is repeated for each board.
    In order to keep the same distances between all decking boards, it is recommended to use a piece of wood. A thickness of five millimeters is usually sufficient as an expansion joint, but is still comparatively inconspicuous. 

Tip: Both the joists and the boards should be installed with at least one helper. Otherwise, the work will not only take much longer, but errors will also occur more quickly. This is because the beams and planks can slide relatively easily if they are not held and aligned at both ends at the same time. This is especially true during drilling and screwing.