How to build a raised garden bed using Besser blocks?

Rohit.sharma29

Hi Community,

I am a newcomer here and love to perform DIY tasks around the house. Since all this is pretty new to me I want your advice to understand how to build a raised garden bed using besser blocks.

Current Situation: I have a front yard with a slope of around 500mm, I want to build a raised garden and garden bed and don't want to use wood for the retaining walls instead want to use pavers or besser block to create something that would look good.

Questions:

1. How do I cater for the slope in my front yard so that the garden bed is almost level with the base of the house?
2. would I have to use cement to join the besser blocks together or a very good quality construction adhesive would be equally good to hold the block together?
3. How would I backfill, do I need to back the cavities in the besser blocks as well?
4. If I use Construction adhesive would the retaining wall be able to withstand the soil pressure pushing the blocks?

MitchellMc

Welcome to the Bunnings Workshop community @Rohit.sharma29. It's wonderful to have you join us and many thanks for your question on building a raised garden bed.

Because you’re retaining up to 500mm of soil, this moves beyond a simple garden edging project and into structural retaining wall territory.

If you want to use Besser blocks to retain soil, they must:

• Be built on a proper concrete strip footing or slab foundation
• Be reinforced with vertical reo bar (starter bars set into the footing)
• Have the cores filled with concrete (core-filled)
• Ideally include horizontal reinforcement depending on height and length

Simply stacking blocks and using construction adhesive will not be sufficient to retain soil pressure. Even at 500mm high, soil becomes very heavy once saturated, and adhesive alone will not withstand that lateral load over time.

In most cases, a Besser block retaining wall is laid with mortar, reinforced with reo, and then core-filled. Drainage behind the wall is also critical. You would typically:

• Install ag pipe (with fall to a legal discharge point) behind the wall
• Backfill with free-draining gravel
• Wrap drainage gravel in geotextile fabric
• Install weep holes if required

Regarding your specific questions:

Catering for the slope
You would step the footing down the slope in sections or excavate and create a level footing at the lowest point. The footing must be level for the blocks to sit correctly.

Adhesive vs cement
For a retaining wall, mortar, reinforcement and core filling are required. Adhesive alone is not appropriate for a structural retaining wall.

Backfilling
Yes, the block cores must be filled with concrete if the wall is retaining soil. Behind the wall, you backfill with drainage gravel, not soil directly against the blocks.

Can adhesive withstand soil pressure?
No. It is not designed to resist sustained lateral earth pressure, especially when soil becomes wet.

Because this wall will be retaining soil and is near your house, I would strongly recommend engaging a qualified landscaper or retaining wall contractor. They can ensure the footing depth, reinforcement and drainage are appropriate for your soil type and local regulations. In many areas, retaining walls over a certain height also require council approval. I would be certainly contacting you local council, since this retaining wall will be right next to the footpath.

Please let me know if you have any questions.

Mitchell