Turfstone formwork / concrete advice

[Boobah]

Hi

I would like to use forms to make turfstone paving.

The 1st batch, I released after 24hr (time constraint), they were solid enough, but it would of benefitted from release agent; (the slabs broke upon removal from mold).

What release agent is recommend for plastic molds? Most products cite metal/ wood use-case. I am considering a silicone aerosol spray…

Another question pertains to finish, of the surface to be walked on.

Consider that council slabs are poured in a form and 10mm basalt is rolled in the top to give an exposed agg finish.
However this is not possible with these forms because the walking surface is at the bottom of mold/form (upside down).

The first batch were smoother than desired. See attachment.
When preparing the cement, Instructions re: water volume were followed, but it seemed too dry to pour into the molds (& for level finish) so i added watrr (maybe too much).

Is it just a question of water volume in a given mix, to attain a finish like that seen on e.g. breeze blocks? (Is there a name for it)?


Thanks

 

[Ivor Windybottom]

They look promising.

All new concrete is normally smooth looking, e.g. look at concrete fence posts or lintels in B&Q. The fairly soft sand-cement paste will weather away over the years, exposing the pebbles beneath.

You probably need a vibrating table to shake the air out. Also multiple moulds so you can make a reasonable number at once, because they'll need to sit in the mould for a while. Probably a few days.

You could possibly experiment with putting a cosmetic surface into the mould first, perhaps with a bit of sand and cement to tack it into place.

But, honestly... this is unlikely to make sense to DIY. Add up the material and tool costs together with your time and it's probably cheaper and a whole lot less back-breaking to just buy the things.

 

[^woody^]

Search for " release oil " or " strike release oil "

For a rough surface you need to reduce the fines (finer sand) as they fill the gaps to make the surface smooth. You may also need to alter the bigger aggregate to smaller and maybe courser (less round) aggregates.

Or, perhaps spread a 5mm or so level layer of screed sand in the mould first, and wash this off after block has set

You can vibrate the moulds with a SDS drill

Water ratio affects the final strength (more = weaker) but also helps the mix to flow and compact (more water better compaction). So its wise to get this just right.

Let the blocks cure for 3-4 weeks. Keep them damp during the curing process.

 

[Boobah]

Perfect answers thankyou both
I completely agree buying them would be less bother but it ought to be highlighted blocks are typically made to 80mm depth to withstand heavy vehicles.
For paving in a garden you could theoretically shave off 30mm and save on materials that way.

I thought i would try it. I have 10 molds (ebay).

Theyre also not always locally available.

Shall look at the oil mentioned and also try experimenting putting screed at the bottom

Thank you again

 

[Ivor Windybottom]

80mm sounds about right to drive a car over.

They could easily end up spanning gaps, rocking about, sitting on stones etc.

They need to be thicker than slabs due to the blooming great hole in the middle.