This is a great spot but the response times are in a day as compared to some websites where responses come in 15 minutes.
There is diffinetly enough expertise here to help you and I am not the one qualified as I did my first Tufa last sat. I have now done 5 projects all using different molds. Only one tufa put on the outside. I have however done lots of tile jobs and over 10 tons of stone on walls both inside and outside with no rocks ever falling off.
Can you provide more information to help folks answer you?
On your mold shape. IT is a confusing description.. rectangle with 6 sides??? 1" bolts" wow that is big.
You say 12 x8? how long??
Do you plan on going inside your mold or outside?
Do you want smooth walls or what?
Do you want this container waterproof?
How much colorant did you use per bag of quickrete?
Do you know thee is a maximum amount. did you put in to much latex?
do you have any idea why you project cracked? did you use mold release or plastic liner?

Now to answer some of your questions until the pros respond.
#1 yes I think tufa would be good. I believe its main advantages over cement are that is is lighter and has a more porous natural stone look. That is not to say you cant get a smooth look just most folks are trying to imitate Natural tufa stone. My first pot was an inside the mold casting and had rather smooth walls. I used a brush to rough it up and get rid of the shiny cement look. This exposes the perlite beads and air bubbles and such. I also distressed it with a chisel. I guess trying to age it and make it look like a medieval house water trough???
#2 1/1/1/1 1 pt portland cement not quickrete. to 1 part peat moss to 1 part sand to 1 part perlite. I have used 2/0/1/5 and 2/0/3/3 so far and not much difference. So far I have not read what the peat does for you except lighter and decomposes maybe weakening the project over time??
#3 I think you can end up with a smooth side against the mold with ease and the exposed edges if you spend some time with tools.
#4 they make both liquid and powder colorants.. the dry powders I got said 1 # to aa bag of cement maximum.. Not sure exactly what ratio that is.

#5 90% strength in 7 days 100% in 21 days..
Some folks report 1 week times to planting.. You might have to soak in a water or slight acid bath to neutralize the basic nature of the lime. I figure 5 days cure 3 days soaking in acid water and then a few days in regular water bath and I will be good to plant in about 10 days.
Depending on how long your pots are you might want to get some cement fibers to add strength to things. Available at the cement plant for free if you ask the right guy. Usually a worker and not the boss.

Could you recommend other websites where i can post this question.

ok so my mould has 6 sides,
four for four walls, one for the base and one of top that protrudes into the base(when i unmould this is where the dirt would go)
the screws are a inch long with bolts to hold sides together.

the mould is also 12" long
i would prefer if the mould can withstand outdoor temps, but not very picky about it.

yes i would like to smooth the walls, prefer if i don't see the perlite granules.

yes i would like it tobe waterproof too

1/4 cup of colorant + 1/4 cup of latex for 7 pounds of quikrete,

i coated the mould with vegetable oil before filling it with quikrete.

hope i answered all your questions,
thanks again

Not sure where else to post this.. this is a good spot.
So it sounds like you have a totally closed mold?? so
How do you fill the piece? Did you just fill it up and then put the top on to make the insides.
How stiff is your mold? I don't see how you put the mud in and then put he top on. I cant imagine with a thick cookie dough mix that you could get it to squish or have the right amount to begin with.
As for waterproofing, there are sealers made for concrete that you can put on after it is made. What was the consistency of your mixture? Normally concrete is like oatmeal.
TRy a mixture of 1/1/1/1 portland/sand/peat moss/perlite and 1 part water and then add more slowly till it is very thick but not wet looking. It should be able to form into hamburger patties in your hand with 3-4 pats without getting much of wet surface. You should be able to form this on the inside of your mold 1 1/2" thick and maybe just leave the top off. let sit 18-24 hours before trying to get out.
Might be a little hard to get it to go up 12" without slumping back down unless it is quite dry. It might look a little porous on the inside but he outside will be smoother. IT will be more smooth if you are able to pat it alot. but it needs to be dry to do this without slumping. Can you describe the curve on the sides?

also email billie as she is an expert they say.
https://auth.gardenweb.com/members/billie_ann

ann, I'm going to assume that the "5/6" near your name in your first post is your zone. Hypertufa can remain outdoors in your zone....if it's potted up with a tree or shrub (I've got sedums in some that stay out all Winter) or you tie a piece of plastic over the top so moisture can't get in and if it's on soil, place a board underneath to break contact with the ground or if it's empty, roll it over so the bottoms facing up and place under a deck or cover with plastic. That's the same way that you would treat a concrete planter. Did you do a search on this forum or look at the FAQ page?
1) whatever you did to the concrete to make it crumble could happen to your hypertufa. I would guess too much dye and too much liquid.
2) strong hypertufa recipe===equal parts portland cement, sand and peat moss. Bash the peat moss around to smooth out the lumps and remove any sticks. I sift mine.
3) if the sides of the mold are smooth and you pack the hypertufa mix tight, the sides should be smooth.
4) I don't add colorant to the mix. I paint or stain or leave natural.
5) The size planter you are making should cure in 24 hours.
6) You'd have to check with your mould manufacturer but the hypertufa can stay outdoors in your zone.
7) You don't want to see perlite granules, then don't use perlite. The only way you won't see perlite or peat moss or vermiculite is not to use them because all of them will show through. You'd have to make the planters out of mortar or get a vibrator to vibrate the molds to bring out the cream and that doesn't always work.
8) It's a planter, why would you want it waterproof?
9) Too much colorant!

10. You did right, coat with vegetable oil. I use the spray cans of oil to coat my molds.
    Elkski, Concrete will cure 90% in 7 days but it never completely cures.
    You can plant in week. Most plants aren't that sensitive to the lime and from watering the plant the lime will leach out. I do use a water bath (just water) to leach out the lime because until it's leached out, someone that's sensitive to the lime can get a nasty burn.
    "the dry powders I got said 1 # to aa bag of cement maximum" Most common bag of cement weights 94 lbs.
    You do NOT need fibers for these little planters! Billie