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Water damage to ground spots because of rising groundwater

Ground spotOutdoor lighting has to endure cold, rain, wind, but also groundwater which rises to the surface occasionally. This is mainly a threat for ground spots of course.

The groundwater level differs from one area to another and changes throughout the year. Still, it’s best to always make your ground spot connection watertight.

What is groundwater?

Groundwater is all the water in the subsoil. The water is situated in the pores between the solid soil particles, such as sand, peat and clay.

Groundwater level

The subsoil is saturated with water from a certain depth. This depth is called the groundwater level. The water that’s situated above this groundwater level, is normally called soil water or soil moisture.

Mainly rainfall

Groundwater mainly comes from rainfall. After the water has hit the surface, it finds its way through the soil. When this water goes down further and reaches the groundwater, it’s called percolation.

Flow through pressure differences

Groundwater doesn’t always go from high to low. The flow is caused by pressure differences. In some cases, groundwater rises because of capillary attraction. That’s when it becomes a threat to your ground spots.

Water damage to ground spots because of capillary attraction

When the groundwater level is high enough to flood the junction boxes of your ground spots, there’s a chance water’s been sucked into your ground spots through the cable. This happens under the influence of ‘capillary ascension’ or ‘capillary attraction’. You can avoid this by filling your junction boxes with resin.

What is capillary ascension?

When groundwater runs upward through the pores in the soil, that’s called capillary ascension. This originates from the cohesion of the water and adhesion between the water and the pores.

Comparable with the behavior of water in tubes

capillary attractionThe best way to illustrate capillary ascension is by using different tubes, which represent the pores. The image on the right illustrates how capillary ascension happens.

Tube 1:

In the first and widest tube, you’ll see the water creep up against the edges. This is caused by the attraction between the water and the edge (adhesion). The formation of these hollow rims in the water is called undulation.

Tube 2:

The second tube is smaller, causing the intersection points of the undulations with the water level to be very close to each other. The water surface now looks like a dimple.

Tube 3:

The third tube is the narrowest and shows signs of capillary attraction. The same force (adhesion), which caused the undulations, now causes the water to rise. The adhesion between the tube and the water in this case is stronger than the cohesion between the water molecules.

Water through cable to ground spot

The narrower the tubes, the higher the water can rise. An electricity cable, which can have a miniscule opening, therefore is perfect for capillary ascension. This capillary ascension makes it possible that water gets sucked from the junction box into the ground spot through the cable.

Prevention by casting resin in junction box

To prevent this from happening, it’s best to cast resin in your junction box. This way water can’t reach your connection and water won’t get to your ground spot. Furthermore, it’s best to put a 30cm layer of gravel underneath your ground spots. Gravel has larger pores than normal sand and lets water pass easier. The larger pores also prevent the rise of groundwater through capillary attraction.

The exact way to do this and a few extra tips and tricks can be found on our help page on installing outdoor ground spots.

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