How to build a concrete block raised garden bed?

[MamaCass]

Me again! 

I wanted to build some raised garden beds from concrete block and render them. But I have heard that cinder blocks and besser blocks can contain FLY ASH which is very carcinogenic and harmful to humans can leach from the blocks into the soil. 

can you tell me if the concrete blocks sold at Bunnings contains FLY ASH? Or if you have any masonry blocks or the like that don’t contain fly ash and is safe to use in food growing garden beds. 

thank you. 

 

[EricL]

Hello @MamaCass 

Yes, both cinder blocks and Besser blocks contain fly ash which is a component of these materials. As an alternative, I propose using 200 x 50mm Sleeper H4 Sienna MicroPro 2.4m. They are used in landscaping and retaining wall applications. They also have termite resistant treatment and are suitable for use in vegetable beds and Children’s play areas.

For extra protection, I suggest painting the bottom and inside face of the sleeper with Gripset Betta 1L Waterproofing Membrane Bitumen Rubber. It is still possible to get that rendered look you are after. Once you've built the raised garden bed you can cover it with cement sheeting and render over the cement sheeting to give it that solid concrete look. 

Here is a handy step-by-step guide: How to build a raised garden bed by @Adam_W 

Let me call on our experienced members @Dave-1, @Nailbag and @AlanM52 for their recommendations.

If you have any other questions we can help with, please let us know.

Eric

[AlanM52]

Hi @MamaCass,

 I agree with @EricL's suggestions but personally I would be OK to use Besser blocks rendered on the outside and sealed on the inside.

The percentage is small like 5% and when I stand back and look at the big picture I figure it's likely all the other stuff we use including potting mix adds up to be a greater threat to our health.

Cheers

[Dave-1]

Good Evening @MamaCass 

My mind is nodding with both @EricL and @AlanM52 's statements I would actually go the route of using the bessa blocks and then seal the inside (which you would want to do so the water dosnt seep through the masonary blocks staining the outside) You could also use the pool liner for inside the garden bed if you were still concerned

As a side note, I have headed away from raised beds, maybe edged garden bed areas instead?. Mostly because we fill the beds with material that really wont be used efficently. It saves your back yes and also looks great but growing wise "wiggles hands" I have had one sleeper high raised beds for years and only just removed them (they rotted out) But always felt that they really didnt help with evaporation or protection. My next effort will be a bed level with the lawn, maybe a sharp edge. Tho it will need more maitenance to keep weed free.

Dave