Hypertufa is very brittle for up to a week after you mix it, depending on temperature. You must be very careful handling it or removing moulds during this time. It should also be kept continually moist or wet, most people wrap it in plastic. You can also cure it underwater. It is best to leave it overnight before placing underwater to achieve an initial cure. After it is strong enough to handle, you should leave it for several weeks, still kept wet, to fully cure.

Your mix will be quite weak, but should set to something usable if you cure it properly. For more strength, you can use slightly more cement (not too much!), a fibre mesh in the mix, a reinforcing structure like chicken wire, special admixes (also make it cure faster), or some sand (sand makes the whole thing heavier). You don't have to crush the perlite because it is mainly there to create air pockets that make the piece lighter. If you do crush it into smaller pieces, you will get a stronger result but it will weight more.

Irish Moss Peat sounds like the right stuff. It is a brown powdery material when dry. Remove or crush any lumps because they will make the mix weaker and can leave big holes in the surface when the weather out.

thanks for your help, shrubs_n_bulbs, most helpful.
So, a few more questions here :))

how much more cement d'you reckon I should use?
I was planning to build troughs buy using a large box as the outside mold and a smaller box as the inside mold..d'you think I should build a chicken wire frame instead?
where would I get fibre mesh from (I'm in UK!)?
where would I get admixes from and what sort should I get???
LAst, but not least ... if I do all the above, would the trough I produced look like the one on the forum home Page?? at least in colour??

so many questions ... thanks for looking though

Hypertufa recipes are a many-splendoured thing! Maybe 3:3:2 peat, perlite, and cement. Check the FAQ for some recipes. You can make good hypertufa with your recipe but you do need to cure it properly. Patience might be the best thing to learn first :)

Building large troughs around chicken wire is a good idea. Bit messy though, get the chicken wire completely flat before you build around it or it will keep poking through the wet hypertufa.

I've linked to one source if you want to try fibres. You might want to check out builders supplies and hobby shops locally because you only need a tiny amount. They are handy for stopping cracks and can help to reduce freeze/thaw weathering.

Admixes are easy to find, try B&Q, a builders supply, or similar. They can increase strength, but the main uses are to increase workability and decrease setting time. There are also admixes to improve water sealing.

The square planter is described by Michele as hypertufa made with white portland cement, but I don't know the exact recipe used. Ordinary portland cement is grey and produces a darker result. In my experience hypertufa is usually browner than that because of the peat and that might actually be a concrete with no peat at all. That type of surface is quite smooth for hypertufa and is typical of the result against a mould.

Here is a link that might be useful: Concrete fibres