May 13, 20197 yr Building on the comments from this thread, the good weather forecast, and the current low level of the water table , we're planning to 'sink' our poo tank this coming weekend. Using dry mix concrete. (Thanks J for the advice, we'll do exactly what you did) In recent weeks I've been reading a lot about concrete - and more specifically dry mix concrete. @Bitpipe talks about using up spare cement and and sand: this search provided some very interesting reading. It seems a very versatile mixture, which until recently, i would not have given it any thought. The search above points to all sorts of uses. But without water - how does it go off? Does it just take the water out of the atmosphere? And so that means you can't guarantee when and how fast it sets? Is there a rule of thumb about when to use dry mix instead of wet mix?
May 13, 20197 yr from my experience using it for bedding pavoirs it goes off pretty quick the nature of cement pulls the moisture out of the the sand you mix it with + ground surrounding it , so next day its not like sand anymore only worry would it will not flow like wet cement ,so any voids ,especially under tank will not self compact like wet stuff and whats to stop you giving it a hand when you have finished by wetting it down from the top a bit if its a large amount? sure someone may give you a more technical view on it Edited May 13, 20197 yr by scottishjohn
May 13, 20197 yr Author 7 minutes ago, scottishjohn said: [...] whats to stop you giving it a hand when you have finished by wetting it down from the top a bit if its a large amount? sure someone may give you a more technical view on it Nothing. There is a 'puddle' of water at the bottom, about 2 meters down. I asked about how dry is dry because at the moment, my sharp sand is very dry indeed. It's 'crusted' - I need to break it up before i can shovel it. Whereas the same pile of sand was easy to use a month ago.....
May 13, 20197 yr The term should be semi dry Its dry compared to normal concrete but still has water mixed in I normally ask for a curb mix I put two cube in ours to sit the tank in Dont forget to fill your tank to the top with I just left a hose running all night As it was quite late when I finished
May 13, 20197 yr You should fill the tank with water to just above your concrete level, not necesarilly "full" Some manufacturers don't want you to fill it completely until ALL the backfilling is done. Why do you want to pour it dry? We did ours wet so we could be sure it settled and used a long stick as a poker to work it into all the nooks and cranies.
May 13, 20197 yr an old builder mate said to me years ago his dry mix was basically enough water so it just clumps together when you squeeze it in your hand
May 13, 20197 yr Author 9 minutes ago, nod said: The term should be semi dry Its dry compared to normal concrete but still has water mixed in I normally ask for a curb mix I put two cube in ours to sit the tank in Dont forget to fill your tank to the top with I just left a hose running all night As it was quite late when I finished A curb mix.... I live and learn every day .... 1 minute ago, ProDave said: You should fill the tank with water to just above your concrete level, not necesarilly "full" Some manufacturers don't want you to fill it completely until ALL the backfilling is done. Why do you want to pour it dry? We did ours wet so we could be sure it settled and used a long stick as a poker to work it into all the nooks and crannies. Exactamento. Why dry? Laziness, and curiosity, and cos J's lot did it with a dry mix ; but now I know its a curb-mix, and isn't completely dry. Fascinating stuff concrete. 3 minutes ago, Vijay said: [...] enough water so it just clumps together when you squeeze it in your hand There ya go, simple, practicable easy.
May 13, 20197 yr The advantage of dry mix is mainly that it's easier to shovel, it clumps up on the shovel and so you can shift more of it. The annular gap around the suspended tank isn't that easy to get concrete into, either, so being able to shovel the stuff where it's needed is useful. Concrete used for anchoring a tank doesn't need to be particularly strong, as it's only really there to stop the tank floating up whenever it's emptied. As long as it's a good enough mix to cure to one solid lump, and key to the projections that poke out of the lower area of the tank, then that should be good enough.
May 13, 20197 yr Aren't there mixing issues with dry mix with one sort of cement mixer being better? Something to with "paddles"? Seem to recall this when discussing whether I went for screed or wet concrete for my floor.
May 13, 20197 yr Author 5 minutes ago, Onoff said: .... Something to with "paddles"?. .... We're not that far up that particular creek... yet
May 13, 20197 yr When they installed my treatment plant they used “dry” mix, it was just damp, wet enough to be concrete but not to flow like the slab they laid. Also they filled the tank level with the concrete as it was being backfilled. Yes “curb” mix makes sense, dry enough to be built up around curbs stones.
May 13, 20197 yr 1 hour ago, joe90 said: When they installed my treatment plant they used “dry” mix, it was just damp, wet enough to be concrete but not to flow like the slab they laid. Also they filled the tank level with the concrete as it was being backfilled. Yes “curb” mix makes sense, dry enough to be built up around curbs stones. Sounds just like curb mix ?
May 13, 20197 yr When mixing remember it's easier to add more water. Don't be tempted to put too much in until mixed through. Surprising how little water can take a mix from semi dry to wet
May 13, 20197 yr My requirements were very low tech, mainly to use up a few jumbo bags of sand on site (as they're in the way) and to backfill the driveway pillars with something vaguely solid inbetween teh steel core and the block outer. Sand was damp but not wet, had sat out in all weathers for a year. Cement was obv. bone dry from new bags. 6:1 ratio on advice from the landscaper we used, mixed on a sheet of 12x8 ply using child labour - £5 / hour - he wanted a set of AirPods so I made him sweat for them We managed 3 1.2 of the pillars over Easter - will knock the rest out now it's dry again. it did need a bit of compacting - i just used a broom handle to pack it down a bit. After the rain of the last few weeks it's now hard as rock so job done from my pov.
May 13, 20197 yr terminolgy a dry mix to me ,was just the sand with what ever moisture it has +cement for laying slabs or paviors -tumble in mixer and lay pavoirs . water will not drain through once its set ,so not suitable for some places -need proper edge drains leave 24 hrs --its gone hard and don,t need it that thick if its a good base your laying on ,I had driven 20 t flat bed over it more than once never moved and no weeds -bit of moss ,but never weeds ,
May 13, 20197 yr 10 hours ago, Bitpipe said: mixed on a sheet of 12x8 ply using child labour - £5 / hour - he wanted a set of AirPods so I made him sweat for them Send him round - I’ve got 2 tonne of kerb mix that needs doing ..!!
May 14, 20197 yr 18 hours ago, PeterW said: Send him round - I’ve got 2 tonne of kerb mix that needs doing ..!! You can have him for a few months if you like - just make sure the WiFi is good...
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