For 6mm scale, I use beach sand.

I just take a cup full home whenever I visit a beach with suitably fine sand.

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Currently doing a plastic scenery kickstarter

I use EXO TERRA DESERT SAND

Fine aquarium sand is also pretty good. Get a bag of that and you're set for life, basing-wise. And you have enough for your friends to mooch off you, as Dave found out.

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Let us playtest like the Greeks of old... You know the ones I mean

I use play sand myself.

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SG

Ghost's Paint Blog, where everything goes that isn't something else.

Builder's sand would be fairly coarse. Try play sand, as suggested, as it's also pretty fine.

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Currently doing a plastic scenery kickstarter

Budgie grit.

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You can usually find various grades of sand in aquarium/animal shops. The coarse grain one (like builder sands generally) is fine for small rocks, but you can also find very fine beach sand. I bought a 3Kg bag of each a few years back for something like 3€ per bag, and that's enough for several war gamer lives.

Actually builders sand is what I use and it's very fine and I got it free from a building site A 60ml container has lasted me about 10 years or more!

If you go to any builders yard, purchase fine sand or sharp sand i think its called, I have used on when i did my patio, its the sand you brush in afterwards to fill the little gaps in between the slabs! its the same consistancy as the sand in an egg timer!

Have not used it on minature bases though, but would think it would be spot on, about £4 a bag off the top of my head,
I will try some soon as im planning on finally basing my pre heresy marines. Im trying to get away with just the sand on a black base on my horus marines as it takes to long to paint the bases

Will let you know how i get on

I pinched some builders sand out of a sandbag (presumeably as rough as it comes). The panting isn't top notch but you can get an idea of scale below, I dont think it's terrible.

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You see a mouse trap? I see free cheese and a f*cking challenge! - Scroobius Pip

Beach sand or Woodland Scenics fine ballast. 18 cu. bags would be enough for several Epic armies.