Back in March, we created the base for the Greenhouse. The size was largely dictated by both cost and available space. In the end, I went with a 2m by 4.8m base, which will allow me to site a 6ft x 14ft greenhouse, with space left for water butts. Coincidentally, this size also perfectly suited a ‘project pack’ of brick pavers, which are typically around 9.5sqm.
Why Brick Pavers for a Greenhouse Base?
When it comes to greenhouses, some models are suited to soft ground and others need a firm foundation. A concrete slab or paving slabs are the most common. Laying a concrete slab does require a degree of skill to ensure it’s level – a skill that I don’t have. Paving slabs are cumbersome and heavy.
I chose to use brick pavers for three reasons. Firstly, because they’re small and manageable. I could relatively easily move a dozen at a time. As my plot is furthest away from the entrance gate where the delivery would be made, this was fairly important. Secondly, the end product is more attractive. Finally, the cost versus the paving slabs was surprisingly insignificant. It cost me only £15 more using brick pavers than it would have done using basic ‘utility’ slabs.
For my 2 x 4.8m base I needed the following;
- Two tonnes of MOT hardcore – I paid £42 per tonne (‘jumbo bag’) for this.
- Two tonnes of sharp sand, which again came in at £42 per bag.
- Six 25Kg bags of general purpose cement – £4.50 each
- 488 (a full pallet) Brick Pavers – these were 30p each, bringing the total to £146.40
The total cost of the base came in at £341.40, roughly £35 per square metre. The timber ‘frame’ was already in place, but would otherwise have only cost a few pounds.
New vs Old
When it comes to allotments, buying ‘new’ isn’t something that happens often. Even sheds and greenhouses are frequently, if not usually, acquired second hand. If you have the transport, and time, to source materials then a significant saving can be made. Paving slabs, especially, are often easy enough to source in small quantities. Hardcore and Sand is a little harder to come by – and certainly harder to transport safely.
My physical limitations meant buying new and having it delivered to site, was only ever going to be my option.
Framing the Greenhouse Base
There are two ways this can be done. You could mark out the corners with string, then dig out soil within, thus giving you a ‘pan’ to place the materials in. Alternatively, and the approach I took, create a timber frame. Measuring and ensuring it’s ‘square’ is critical here – a mistake I made and would later have to be rectified.
My frame was part of adjoining beds, so not quite deep enough for the greenhouse base itself. Therefore, we use both approaches to a degree – digging out some soil within the frame too.
Adding the MOT
All two tonnes of MOT were then wheelbarrowed and tipped into the frame. This was done in stages – spreading it out with a rake every few loads, then tamping down.
Ensuring the MOT is firm is critical, so using either a tamper or ‘whacker plate‘ is essential. We used a tamper, to save the cost of hiring or buying a whacker. If laying pavers for other use such as driveways, a whacker would be essential.
Once all two tonnes of MOT had been tipped, spread and tamped the first bag of sand was then wheelbarrowed and tipped into mounds.
Levelling with Sand
A perfectly level base starts with the sand. Once the sand has been piled on top of the MOT, it’s then spread out and made level. To ensure it’s level, we start with the highest point and build up from there. Tamping also continues throughout this process.
Laying the Brick Pavers
We start with the edges – front, back and side, of the base. These are laid with a mix of sand and cement. No water is needed as the atmospheric moisture is sufficient to harden this mix. As each brick is laid, it’s gently firmed down using a rubber mallet. A spirit level is essential and used as each brick is added to ensure they are level.
Once the edges are in place and level, the remaining sand and cement are dry-mixed and added. This should be compacted too – we used a hand tamper, but a vib plate/whacker would usually be recommended. A piece of timber, as wide as the base but with the height of the pavers cut at each end, is used to ensure this mix is level. It’s worth noting that we added cement to this mix as the ground below was very soft – if your ground is firm, sand alone would suffice here.
The remaining bricks can then be laid in your chosen pattern. I chose a ‘basketweave’ pattern as it’s one of the quickest and easiest to lay. If you’re feeling adventurous, patterns such as 45-degree herringbone are very attractive.
Finishing the Greenhouse Base
With the brick pavers all in place, the final step is to fill in the gaps between them. For this, we used ‘Play Sand’, which is finer than sharp sand. I used two 10kg bags for this, which was plenty. I tipped each bag on top of the base and brushed it around. This can be a time-consuming process, but there’s no harm in doing it a little at a time, as I did. I added the first bag, spread this around so most gaps had some coverage, and then ‘topped it up’ over the coming days. Once complete, each brick paver will be firmly in place with a little of the sand visible between the gaps.
You may find, as I did, that after some rain you’ll need to top this up further as the rain settles the sand further. You could, of course, add water yourself if you wish. Further tamping of the base at this stage can also help the sand settle quicker.
An alternative to play sand is silica sand, which is similar to play sand but kiln dried and reaches the gaps more efficiently. In my case, play sand was simply easier and cheaper to obtain.
The finished greenhouse base looks attractive, is functional – and cost little more than using paving slabs.
Huge thanks to Steve from SJS for giving up his time to complete this project for me.