Raised beds - rendered breeze blocks?

Hello all,

Trying to create raised beds similar to those shown here http://www.mylandscapes.co.uk/patio_garden.htm . It has been suggested that this could be accomplished by cutting breeze blocks in half lengthways then rendered.

Is this sensible or is there a better idea?

Many thanks,
Richard

Not sure what you mean by "cutting breeze blocks in half lengthways"
You could build the wall from normal or hollow concrete blocks and then render them. If you want them to look thin from the top just build a normal thickness retaining wall and then just do a thin top course lined up with the front of the wall. The soil will cover the step in the back of the wall.

What do you mean by a thin top course?

Forget that, I was being slow. Thanks for the advice, sounds logical.

In terms of drainage, I'm only planning on building the front and side walls, the back is onto a fence. Do you think the gaps in the bottom of the fence and between planks will be sufficient for drainage?

I realise the fence will rot over time, but it will be over a timescale that doesn't concern me.

I meant not so deep from front to back so once the soil is there it gives the impression that the whole wall is much thinner than it really is. So most of the wall might be 225mm thick but the top course only 100mm or whatever you decide. But the top course would be lined up at the front with the lower courses so it looks like one wall.

Hi Richard,

richwsmith said:

I realise the fence will rot over time, but it will be over a timescale that doesn't concern me.

Click to expand...

Unless it is a brand new and substantial pressure treated closeboard fence, it will rot in about a year with wet soil piled against it. If it is the aforementioned new fence it might last two years before the wet rot starts causing problems. By that time most of the plant roots would have found their way between the panels and have started ripping it apart anyway.

I'm assuming it must be your fence, but if the fence is along a boundary and it rots/collapses causing the contents of your planter to be washed onto neighbouring land then a liability for damages can arrise.

If you are going to build three sides, build the fourth as well and leave drainage holes at the bottom. You don't have to render the back so long as you use blocks that won't blow. Or, if it really must be timber use pressure treated decking boards at least 30mm thick to line inside the fence, leaving a ventilated gap. At least then in 10 years when that rots through you can replace it without rebulding the fence. Why skimp on a few extra £'s now when you can do it properly in the first place?

Firstly, many thanks for the advice.

It is new and pressure treated, I'd assumed I might get 7 or 8 years before rot posed a problem but the assumption was only based on an uneducated guess.

If the best I can expect is 2 years, then I'll take your advice and create a divide between the back of the bed and the fence as it is a boundary fence like you say.

My motivation for not building the back wall was this will make up almost half of the materials and time required (it's going to be 15m x 0.5m).

I will be taking up old flagstones elsewhere in the garden, could these be stacked against the fence to create a barrier without being bound together and actually forming a wall or do you still feel this is a shortcut not worth taking?

Personally I wouldn't let it touch the fence, and would leave a small space for air circulation. You will need to keep any gap clear of leaves and so on once a year but that would be it.

Fences - even the modern 100% absorption pressure treated panels will have a short life in contact with wet soil which is why timber gravel/kick boards are always a minimum of 20mm thick, and when they do go they don't affect the stability or service life of the fence. As you have just paid for a nice new fence it would seem silly to shorten the life of it by a) piling wet soil against it and b) putting a fairly substantial loading on the bottom of the panels. If it is a good quality and properly capped you should get at least 30 years out of an average fence. (I recently replaced a cheap 45 year old lapped panel fence that was still structurally sound, and treatments nowadays are a lot better and penetrate deeper.)

As your run is 15m it would likely be cheaper and quicker for you to use quality PT decking boards for the back wall, screwed to quality PT posts set in at 800mm centres with coated/stainless screws. Run a strip of DPC vertically beween the posts and the boards before fixing and cap the whole run. That should last at least 10 years, or even longer if the timber is good quality. Line it with those spare paving stones set off slighlty at the base and it will make a big difference - possibly even outliving the fence. When the boards do eventually rot through it will still take a few years of use because the posts will hold them in place.

When using PT timber check on each cut that the treatment extends at least half way through the timber, and ideally all the way through. If it only penetrates the first few mm then it will not last very long. If you buy from a decent timber merchant or any of the large commercial fencing companies you should get a good quality.

Whatever you make the back wall out of, ensure you still allow for drainage along one of the long sides.

If your flags are thick enough and uniform in size then you might be able to hammer in some angle steel and slide them between these. Or even consider gabion baskets or a sleeper wall.

Thanks all. Went for brick walls in the end, one at the front and the one at the back with a 2” gap at the back between the wall and the fence panels/posts.

For some of the front wall I was able to utilise an existing 4 courses of brick (hence sticking to bricks throughout) and raise this to 6 courses. I’ve left out mortar on the bottom course (vertical joins) for drainage on the new walls, is it best to use a masonry drill bit and drill out the bottom of the vertical joins for drainage on the existing?

If so, I’ll be doing this after I lay the new patio as I’m not sure what level on the wall the new flags will come up to due to the fact I plan to raise the level slightly as the gradient of the garden is steeper than it needs be. Am I safe to butt the new flags directly against the brick wall as long as the drill holes are at this height and run downwards into the beds?