Hi everyone, I am a artificial rock contractor (pool and spa) and an expert with specialty concrete mixes - specifically vermiculite which is also commonly known as "pool base". I have read through this thread and there are a few things I wanted to offer some clarity for: 1) The reason that you should pre-water the vermiculite is becasue vermiculite is incredibly absorbant. If you do not pre-water it will leech water from your concrete depriving it of moisture and likely leading to hairline cracking and crazing if the surface layers. The mix itself can still be "dry" as someone eluded above that concrete that is too wet becomes weak. This is extremely true. Pre-watered vermiculite is much easier to proportion and regulate the water in the mix. 2) Soap in concrete mixes is an "air entrainer" as discussed in a post above however soap has long since been used as an ingredient in vermiculite concrete mixes for different reasons. Vemiculite concrete is very sticky and can be difficult to trowel. Adding a tiny bit of soap, like dish soap, makes the concrete smoother and less inclined to cling to the tools. 3) It was posted above that concrete for construction does not get adjusted for water content. This is not true. Concrete is and can be adjusted on the fly in almost every mixing condition to account for changing conditions, heat, direct sunlight, concrete consistency, slump etc. There is a point past which you should not hydrate the mix but before that it is no problem at all to adjust slump. Every single mix through a mixer gets individually watered. Ready mix concrete will ask you if you are happy with the slump of the mix when they arrive to your site and will wet it up if you want them to. 4) Use water reducer to achieve desired placement slump without compromising the strength of the concrete. A tiny bit too much water equals a substantial loss of finished strength. 5) The best release agent for silicone is wax based release agents. In most cases if you are not sure what to use you should use wax based. I hope this info helps some of you out. If you want more information on lightweight concrete mixes check out the link below Here is a link that might be useful: Lightweight Concrete Mixes

Nik, go read al's advice to you in the container forum. He uses his mix, of course, but he states that he has hypertufa pots, and he does NOT put drainage holes because they are so porous, they self drain. Not sure how accurate that is, but Al's mix is much different than the dirt the majority of folks use, and if you do have drainage holes, maybe you might need a heavier soil? I'd still put holes, but not big ones! The thing that attracted me to hypertufa in the first place was how lightweight it is, and the fact that it allows air to get to the roots. I BELIEVE in air pruning roots so that they don't circle and get root bound, like in a regular plastic pot. I'm not sure if hypertufa pots prevent roots from going root-bound, so I'd be tempted to stick a thousand bamboo skewers in the sides and bottom of mine for light and air holes. When a root meets light and air, it stops, prunes it's self, and forms many root branches. It then can take advantage of all the nutrients in the soil, and any branches that meet your air/light holes, will do the same and branch more. I'm not sure on a big 3" thick pot if the thing would be porous enough without dozens of tiny holes. If you have not heard of that concept, google "air pruning," or "root pruning," and you will understand. A farmer's view (orchard growers) of a container, is different than a gardener's view for sure! Good luck with this project! I'm watching every step! Also, feet on the bottom will lift the container and the roots will prune themselves and not stick out of the drain holes. Suzi

I once had a sewing business, I understand that need, what did was get the ones that hang on the door and fold up flat against the door and out of the way. I had one conviently located in the sewing room and one in the laundry room. Since they are out of the way and don't require dragging out and hauling around it is a big win. They have held up great through the moves, got rid of all the other irioning boards. different models some have iron holder and place to hang clothes. Here is a link that might be useful: over the door

Having done some further research since posting, I've found what I likely need is intensive roof soil. Not only is this lighter, but also suppliers can provide the unsaturated and saturated weight. For example: http://www.rooflitesoil.com/uploads/documentation/Technical%20Documents/SPECIFICATIONS/PDF%20Versions/rooflite-extensive-mcl.pdf They give a saturated weight of 1.15 g/cm3. Which equates to 1150 kg/m3. So given a fill height of 600mm, I get: Imposed load of saturated soil in planter: 1150kg * 0.6 = 690 kg/m2 or ~ 6.9 KN/m2. The roof suppliers assumption of 7.5 KN/m2 would give about 10% overhead. I imagine even if I find a structural engineer to do the calcs, they will want to know the soil used. So I guess my next port of call is to call a few suppliers of roof soils and confirm the specifications. Perhaps they can also confirm the drainage design required.