drainage gravels

Drainage Gravels behind Reatining Block Wall

Drainage gravels are generally used to facilitate the movement of water around your property or more to the point away from it altogether! The most common usage is behind retaining walls where having a drainage system is extremely important but in other cases trenches can be dug under lawns or gardens and filled with drainage gravels to ensure these areas don’t become waterlogged.

Every landscape project is different and may require different amounts of drainage and to that end you can source drainage gravels in a number of different sizes and in any quantity that you need…..be it a few shovels full, a trailer or ute load or a full truck load. The sizes available are: 5mm, 10mm, 20mm and 40mm and some helpful hints would be: As the size increases, the larger the air spaces so the greater the flow of water through the drainage gravels. Unfortunately and importantly, as the size increases so it becomes harder to shovel! The most common sizes used are the 10mm and 20mm (a compromise between the above two points). Some sizes are now available, not only in drainage gravels form but also in a manufactured form … from recycled concrete. Both are just as effective but the recycled products are generally a little cheaper and are lighter. If you need help in calculating the amount you need, just ring the office and we will confirm the quantity required.

How important are drainage and drainage gravels?

The short and simple answer is …. EXTREMELY IMPORTANT!

Whenever we build a wall, be it retaining a stable “cut” in the land or holding back fill, the effort we put into the drainage behind the wall is crucial to the success of the wall itself. By erecting a vertical or near vertical structure at a point where the land changes in height, there is the potential for it to become a “Dam Wall”. If this occurs, water will be trapped behind the wall where it builds up pressure and in some cases result in the wall failing and falling over.

In any DIY video or guide produced, there will always be a strong emphasis on the drainage material used behind the wall being built. The whole reason for the drainage and drainage gravels are so that during heavy rain or extended wet periods, that water does NOT collect behind the wall and has a way to “escape” This is done by placing an Ag Pipe at the base of the wall (behind it) and then covering this with Drainage Gravels. The quantity of drainage gravels used will vary depending on the height of the wall and the amount of water runoff expected but as a general rule, the more drainage gravels used the better.

One thing to avoid at all costs, is lining the back of the retaining wall with plastic as this will indeed result in water being held behind the wall. If you are concerned about dirt seeping through the joints in the wall, then you can line the wall with a filter cloth called Geofabric (Bidim) as this will let the clean water drain through and hold back the dirt.

When designing your wall, check the manufacturers’ brochures or the DIY videos and guides on our website to get the full story on the importance of drainage, drainage gravels, and how to do it.

Again, when designing your wall, check the manufacturers’ brochures or the DIY videos & guides on our website to get the full story on the importance of drainage, drainage gravels, and how to do it.