DIY breeze blocks

[sda]

I'd like to make some hollow concrete breeze blocks, the ones with the two square holes in. Is there an easy way to produce a mould that doesn't require cutting wood, etc? They won't be for building work.

[Skippy]

Not really , a wooden mould or shutter is probably the best choice and can be used over and over again.
That said you could take four blocks that you wish to copy and place them so they enclose a space the same size as a block , that'll mean the edge corners are just touching. Then line with thin plastic to stop the concrete sticking and use something like recycled polystyrene packaging to form the "holes" in the blocks and fill in the rest with concrete.

Problem of course is that you would be using plastic and polystyrene on a pretty much single use basis whereas a wooden shutter will be far more fitting for a green building forum

[diggernotdreamer]

don't they cost like 50p each to buy, probably cheaper and easier to buy them ready made

[Skippy]

I think they are a bit dearer than that but as you say not hugely expensive , and even cheaper if you ask on free cycle .

[dave45]

£2.97 here http://www.buildingmaterials.co.uk/concrete-blocks.html

I built two garden walls with them, and can inform you that they are not precision-manufactured.... i.e. its a challenge to lay them accurately if you assume they are

[Skippy]

Didn't think they were that expensive . I was thinking the regular 4" blocks were about a quid each. To be honest I have a large pile of blocks that haven't cost me anything as I generally keep an eye on builders skips ( clue in my username ) where it's common to find a few at a time left over , new and just dumped. Sometimes they are used but clean up really easy. Granted though the hollow blocks are rarer to find.
We never asked sad what the blocks were to be used for , perhaps there are alternatives.

[Odsox]

£2.97 here http://www.buildingmaterials.co.uk/concrete-blocks.html

...and I thought things were expensive here !

Standard 4" concrete blocks here are about 50p and 8" hollow blocks about £1.00.
I've got through lots of blocks since moving here, oh and that price is delivery as well.
It's notoriously difficult to find Irish prices online, but I found this one ..... https://www.build4less.ie/bricksblocks-c-8_10.html

[diggernotdreamer]

WHAT!!!!!! you found an Irish price online, I don't believe it. We went to Quinns and bought the double cavity blocks and they cost us 75 cent each, I think we are lucky here as building materials are very cheap, unlike everything else which is expensive

[doofaloofa]

@ sda

What are you using the blocks for?

[sda]

I want to make an enclosure as a slightly raised bed and use the holes to pot flowers in. I thought I might use a large plastic tub of some sort and put a couple of boxes or jars in to make the holes, put the concrete in and tip the form out and leave it to dry. A 20kg bag of concrete mix is only six or seven pounds.

[doofaloofa]

How many blocks can you buy for £7?

Hate to be a dick, but precast concrete products are very often better value for money than poured

Economy of scale or something

[Skippy]

Next question would I suppose be how many blocks you need. A tonne sack of sand and gravel will lower the costs per block and a reusable mould would be the way to go , however , that would then need to be equated with the time spent if that time could be used more productively.

[doofaloofa]

@6:1 (aggregate:cement) you will get approx 0.1m3 per sack, that's about 11 standard 9" blocks

That will be about 36 shovels of aggregate, or 2 barrow loads