Expert: Bruce E. Johnson - 3/27/2009

Question
Hi Bruce,
        I am building my first retaining wall & it is about 20m long with inside & outside curves. It will be made of small blocks 150mm deep by 150mm wide by 90mm high. It will be 3 blocks high (so as you can see, fairly low). Should I use a concrete footing or gravel footing & should I back it with soil directly or gravel? Thank you for your time.

Answer
Hi Jai,  a wall this tall probably can do without a poured concrete footing especially since you have some inside and outside curves to help brace it.  Not sure if your footing needs to be gravel.  It might be better off if you just compact the natural soil well.  I would put some gravel or small diameter rock behind the wall to help the moisture flow around the wall.  It would also behoove you to put some weep holes along the bottom to help eleviate water that tends to build up from irrigation and weather.  If you are just laying the stones dry without mortar I recommend a Liquid Nail (or equivalent) landscaping stone glue to hold the work together.   I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com