Mini Concrete Blocks - All Weather Building!

This is going to sound like a variant of the 3-Little Pigs / Big Bad Wolf fable...
You've played with plastic Duplo Bricks (but you're supposed to keep them indoors);
You're played with wooden Building Blocks (but these don't like getting soaked in water/mud);
And now you crave the full outdoor, all-weather, bespoke experience!
Now you need to level-up to mini-concrete Blocks (for the aspiring Bob The Builder in your or your child!).

Perhaps a tad over-dramatic, but in all honesty, this was where I found necessity to be the mother of invention: I spent forever washing the mud off Duplo Brick my son played with outside in the dirt, picking the bits from the crevices, and of course the wooden blocks if not dried properly actually go mouldy. Even when you put them in the washing machine, it's ok, but not ideal.

We had played with 'full size' building bricks, but this required considerable supervision, as my Son was able to stack them high enough to potentially fall over and hurt himself! So I hit upon the idea of making them smaller, but with all the outdoor durability of real bricks, and also as a 'rugged' play experience, it is fun to give kids an atypical material or product to engage with. Kids seem endlessly fascinated to emulate 'grown-up' things, and from my time working in the Toy Industry, I've come to believe that the trick is to 'scale it down', and to make affordances so they can interact, (rather than to 'dumb it down'), whenever it is possible (safety, cost, etc.).

In this guide, I go through the steps to making some nice little concrete bricks by making your own moulds. I especially like the notion that you can create your own designs and shapes, and that with a little engineering knowledge of the material, you'll be able to get more confident and ambitious!

For the Teachers out there, I know the physics of 'keystones' and arches still seem to be on the curriculum for many schools, and this would be a great classroom project to trial variations to find the perfect keystone angles/geometry.

Essentials:
Cement: https://amzn.to/3eklmWd (though I'd get from a DIY store!), along with Sand & Gravel.
Plastic Adhesive (UHU or SuperGlue).
ABS Plastic (or you can use card): https://amzn.to/3uvo3Ji
Bucket, Stick for Mixing, Gloves and Goggles (when mixing and pouring).

Optional:
Wire Mesh: https://amzn.to/3tv4zEg
Snips: https://amzn.to/3o5xcqn

The back-story of this project came from days out playing by a riverbed. Between the litter, and fly-tipping, there was some great adventures to be had - one being making clay (from riverbed silt), and this in term lead to making a 'Mud House', as shown in the first picture.

I was reminded of how much I enjoyed doing this when I was a kid, and so much of the fun is the rhythm and process, of mixing, spreading, laying stones/bricks, repeat....

...and of course, the tension of not knowing when it might fall over. Did you build too fast, too wet/dry, could the shapes tesselate better, does it need more binder (grass), or more sand for internal friction?

All these things seem to happen, without needing to say a word. As kids, we seem to 'absorb' this tacit awareness of the world around us, simply by doing.

As it happens, this came full-circle, and we used mud and the fabricated concrete blocks to make some really robust buildings....more on that later, but for now - on with the Instructable!

I use 2mm ABS Sheet, as it is easy to cut using a knife and a ruler. You do not even need a saw or rotary tool - and it gives a clean finish...

Start by marking out the 'side' of the dimension of the brick you want to make.

(I've always tried to make life easy, and avoid copious measurements, so here I just used the width of the metal ruler (about 25mm/1"). I scored a series of lines in the sheet.). I suggest about 2-3 scores per line.

Then I scored perpendicular to this, this time about 75mm / 3" long (these I did mark), and others 40mm / 1.5". From this 'grid', you will find you can simply bend and snap the plastic into the required sides.

This should give you batches of 2x 40x25mm and 2x 75x40mm pieces.

If you want more detail on this, I have guides here (LINK).

And also a video showing how to do it (LINK).

I wanted to show how after all the scalpel-work is done, even a 4 year-old can snap the plastic.

If it's too difficult, I suggest pre-scoring a little deeper, but this can be done, once you have the hang of it.

A bit like a 'cookie cutter', you need to create the perimeter for the brick-moulds. I did this by using sticky tape. This is a surprisingly good material, as it has a little elasticity, and holds the shape in tension.

Stick the sides and ends together as shown, ready for the bases...

I applied the same 'score and snap' technique, and used this to create a series of rectangles to fit the base...(ie 75+2+2mm by 40+2+2mm), so a 79x44mm section. If you don't want to be this accurate, you can simply cut them 'oversize', and this is fine also (you'll see I've done this with some later on!)

I then applied Superglue to the corners, and left to dry fully.

All ready to go with the glue thoroughly dry.

If you want to also play with curved shapes, you can do forms like this, either by bending by hand, or if you like you can warm the plastic with a heat-gun, or a hot hairdryer. Again, another reason I find this material very fast to work with. More here (LINK).

As mentioned in the pre-amble/intro - if you wanted to experiment with these shapes, this was a nice trick, and also shows a more efficient way to mould even the 'straight' bricks, as it uses both sides for moulding!

I began by folding a sheet of A4 paper some 4 times, and then cutting out a basic keystone shape from the stack of paper to get 16 identical shapes.

I was then able to 'test' how big the arch would be (see second picture), and this seemed a good form. (If you're not happy with it, regroup the templates, and cut a more acute angle on each side.

I then took these paper templates, and laid them head-to-toe, as shown in the third image, and marked the positions, before arranging as shown. Safe to say, the top and bottom sides are from one long strip of plastic.

It's worth noting that the vertical joins are not glued, and are left free. This is to allow the mould to 'flex', so as to release the bricks when dry. (If you glue all sides, this will make it hard to remove). However, do glue the 'bottom' edges to the base.

Note these are done in single 'strips', so as to allow easy flexing to release the bricks.

In all honesty, this was me getting slightly carried away. It's true this certainly makes some of the long bricks much stronger, but it's not critical for the 'normal' 75x40mm bricks!

I happened to have some left over from another project, so this was not an 'expense', but you can use any other wire placed laterally on long bricks. Though I'd suggest adding kinks to it to give the concrete more to 'grab'.

I confess, I was too 'hands full' with concrete, and kiddo, to also take pictures, but the trick is to pour in half full, drop in a piece of mesh, and top up. Job done!

So this is just huge fun for kids! All the play of sandcastles - but with a 'cooking' aspect to measuring out quantities, and mixing to a given consistency.

I used 1 part Portland Fast Dry Cement, 3 Parts Sand, and 4 Parts Aggregate - as this was what was on the pack, but you should follow what your supplier advises on the pack. I used a plantpot as the 'unit' / part, as this was easy to for my son to handle, despite the holes!

I'm not going to write a blow-by-blow guide on this, as firstly, it's hard to do it whilst holding a phone, covered in dirt, and watching kiddo, but also because Instructables wrote the guide I was using anyway!

>> Concrete Class: https://www.instructables.com/Concrete-Class/

Safe to say you want a consistency which is not so liquid it's sloppy, but no thick it does not 'tamp' down and flow. If you're unsure - mix up a mini batch first.

Here's the filled 'Keystone' bricks.

They look 'shiny' / wet on top, because firstly I smoothed them out with the trowel, but secondly I 'tamped' them on the table to release air, and excess water rises to the top.

Once dry, depending on the weather and the type of cement you have, they can be released when 'set', but still moist to touch. This is fine, but be aware that they are weaker, and benefit from more time to dry. But if you're confident not to break them, it means you can speed up production. I found after some 2 repeats, I was able to de-mould after 1 hour on a warm day.

NOTE: As much as you might think heat helps - drying too rapidly is not good for concrete, so oddly if it's really hot, place in shade.

My description perhaps makes sense now - as you can see here, the mould can 'flex' and allow the Bricks to be easily removed, for both the rectangular bricks, and the keystone variety.

It depends how gentle you are, and how much glue you applied, but if the sides snap off, it's totally fine, and you just tape/glue them back again for the next moulding session.

I got easily 6-7 repetitions out of each mould (I have loads of bricks now!), and they would have kept on going too. Highly re-usable. I kept them for any future projects, but you can also recycle ABS.

I placed the 'wet' bricks to finish curing / drying, on a well ventilated table.

As can be seen, the bricks took on quite a lot of the detail, even the glue over-spill in places, so in hindsight, I think I should have made a 3D printed (inverted) logo or name on these! Hope you can do this. Perhaps even Blu-tak, Clay or Plasticine will work fine?? Please share if you do!

This was a really fun project, to do with my Son, but also to then step-back and allow him to build some crazy creations of his own.

True to expectation / design - it has rained, snowed, and had sun on for some time now, and the bricks have held up well to all the elements, as well as wear and tear from paying with friends too!

As mentioned, the keystone bricks worked very nicely - both functioning as good stacking bricks for walls, but also providing a tricky but fun challenge to assemble (with only two hands).

I have not tried painting the bricks yet, but this strikes me as an easy thing to do, and will probably be quite fun. You can also buy pigments for concrete, but I found these unreasonably expensive for a project this small and casual, but if you can get a mini quantity, perhaps you can try adding colours too!

You may also see I used toilet tubes and yoghurt pots to also make unusual bricks - so have fun, and try out different shapes and materials...

Hope you like it, and thanks for sharing any variations you make!

The great thing about concrete is that it 'sucks' moisture up, so much that mud can be used like 'mortar' to glue bricks together, and they can even support their own weight!

And make precarious leaning towers.

Safe to say, they come clean through soaking / scrubbing in a bucket of water (or a puddle!!).

They can be combined with offcuts of wood, to make a bridge as shown here - to span a puddle, in games or with plastic toys!

This was when our local park football field was flooded...sometimes you find unusual games in the mot unlikely of situations!

Other kids in the park also wanted to join in, and created homes, games, and all sorts of other things using the bricks. This is what some play specialists call a 'play starter', in that [a brick] is not in and of itself that special, but it becomes something simple enough to get ideas started, and then once going, it recedes, and more and more novel elements some into play.

I love how this brick house, had grown beyond the obvious, to have 'trees', and even a 'bath' (made from a plastic bag) were 'invented' by the kids, as well as many stories and role play games.

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Please share what you enjoy making with these mini building bricks.