DIY Sandpit: Building a Garden Sandbox

Post length: 1,249 words, about 5 and a half minutes.

Our son is now 19 months old and as my parents were staying with us for Easter this year, and the weather was so nice, my dad and I decided to set to work building a DIY sandpit in the garden.

DIY Garden Sandpit.
The finished sandpit.

We initially spent some time looking at off-the-shelf sandpit options such as this square one and this large octagonal one but didn’t find anything which quite met our requirements. The commercial offerings were often too small and generally quite expensive for what, in effect, is a wooden box. So we decided to build our own.

Measuring & Materials

The first step was to measure the area and work out what we were going to use. We chosen a spot in the garden near to the patio and next to one of our existing raised beds. It seemed to make sense to make the side of the sandpit match the size of the existing bed. We didn’t want the other dimension to be too much different, but decided that could depend on the materials available.

My first thought was to use sleepers for the frame of the sandpit — this is what the existing beds are made with — but that seemed wasteful. Not only would it push the price of the project up, but it would also be a waste of space. We wanted to maximise playing space and the walls didn’t need to have a huge amount of strength. Sleepers seemed like overkill. The obvious choice was to use decking board.

Decking is easy to work with, strong enough, treated for use outside, cheap and abundant in DIY shops, especially at the start of summer. It also has the advantage of coming in exactly the length we wanted it for the long edge: 1.8m. The shorter edge was then a simple decision. The other standard length of decking seems to be 2.4m. Therefore it followed that the shorter edge of our sandpit should be 1.2m.

Depth was also important. The decking boards we had chosen were only 25mm wide and we wanted to make the pit deeper than that. The solution was obvious: make the frame two layers high.

I sketched up a quick diagram on the back of a notepad, made a list and popped over to our nearest DIY store.


Trolley full of materials.
A trolley full (mostly of sand).

The first stop was for the decking itself. Wickes have a ‘value’ range of deck board which seemed ideal for this job. We used two 1.8m boards for each of the long sides and one 2.4m board for each of the short sides. That came to £25 for the wood.

We also needed some fixings. Angle brackets for the corners and four flat plates to hold the boards together in the middle of each side. My plan was to use two angle brackets on each corner, but once in store found some 4-hole angle brackets. Using these helped to fix the boards vertically as well as at right-angles, and meant using four rather than eight. I ended up with four corners and four straight “jointing plates” meaning the fixing hardware cost just £5.64.

In order to make this all go together we needed some screws. Fortunately we inherited some decking screws when we bought the house so were able to reuse those. I also already had some 20mm screws from a previous job which were ideal for fixing the brackets. Had we needed to buy these it would have come to around £7.59.

The final piece for the frame was the base of the pit, to stop weeds and insects finding a new home. The pond liner we ended up using was possibly overkill for the job but was left over from another project. A weed control fabric would have been fine, as would a damp proof membrane. This would have cost us an extra £20-ish had we needed to buy it. We picked up a tarpaulin as a temporary cover for just £5.

All in all the cost of the materials to build the box would have come to just under £59 had we needed to buy it all. Easily cheaper than any of the flat-pack versions.

Groundwork & Construction

Building the pit was quick and easy. We just needed was a saw (we used a cicular saw to speed the whole process up), an electric screwdriver, and a staple-gun which was borrowed from my dad.

Building the Frame

The first step was to cut the longer pieces of decking in half to use for the shorter sides of the pit. With that done it was a matter of screwing it all together.

Diagram of reinforced corners.
Diagram of overlapping boards with decking screws.

We fixed the boards which made up each wall one on top of another using the jointing plates. We then screwed the angle joints in place to form the final box. At the corners we over-lapped the long and short edges as shown in the diagram on the left. We strengthened the corners by driving some spare long decking screws through at the top and bottom of the overlaps. Using the combination of the two fixings not only makes the corners strong, but help to retain the sand by pulling the top and bottom edges together more tightly.

Next we roughly cut the liner to size and stretched it over the outside edge of the frame. Making the corners as neat as possible we we stapled it in place all the way around. Once fixed in place we trimmed off any excess with a stanley knife to leave about 6 or 7cm above the base of the frame.

Preparing the Site

In order to hide the liner, help hold the frame in place and to make the sides a bit easier for little legs to step over, we wanted to sink the box into the lawn by a couple of centimetres. This was the most physically demanding bit of work so while the sun shone and everyone else sipped cocktails, I marked out the frame and dug down about 10cm.

Laying bed of sand below the frame.
Laying a bed of builders sand with the fame in the background.

Similarly to lining a hole for a pond we dug out more than we intended to sink the frame. This was to allow us to lay a bed of builders sand between the earth and the liner to protect it from anything sharp in the ground below. A good money saving tip, if you don’t want buy the sand: use a piece of old carpet to line the hole. Just make sure you remove any carpet tacks before you do, or you’re defeating the object of the exercise!

With the hole prepared, it was simply a matter of lifting the frame into place. Once in the hole the majority of the liner is hidden below the edge. As the area around the sandpit grows back the liner will become almost invisible behind the grass.

Finishing Touches

Sand castles.
Castles in the sand.

Of course no sandpit is complete without sand. Play sand is remarkably hard to come by in any great quantity in DIY shops, but we managed to find this one at Wickes. We currently have 15 of these 25KG bags in the sandpit, and it could easily take another 5 or 10. That comes to £60 — a cost which would of course exist for the pre-made pits too!

With the frame in place and filled with sand, there was only two things left to do: add some toys and have some fun!

Posted on Tuesday 18th June, 2019 at 1:33 pm in DIY, Parenting.
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