Building Foundations

[Andrew*]

I didn't manage to get the concrete for my astro station done last thursday, in part because our hobby group was cancelled. In the meantime, I've got to the bottom of the situation.

I've dug down 3 feet, and am still not onto hard ground. The ground is soft sandy soil with big rocks in, and my hunch is that building on that is not going to do any favours for the stability of the station. Unfortunately, with the actual hole being quite small, I'm literally digging under my feet, which is not very easy and progress is slow. I've decided to stop there and compensate for the soft soil like this:

What I've done is got a 2" trampoline pole, hammered it down a further 2-3feet into the ground. Around it, I've thrown in some big rocks. Next I'm going to level it off with sand to minimise shifting. I've got a short length of drainpipe, which is going to go around the trampoline pole and be filled with concrete. I'll fill the hole up to 1' beneath the surface with smaller rocks and sand, hammer it down to compact it, throw in a separater (tarp or similar) and finally fill the station with concrete as planned. Don't get it? Here's a diagram:

My reasoning?

Trampoline pole connects the whole shebang to harder ground.

The concrete in the drain pipe holds it there.

The rocks don't shift, like soft soil would.

The sand keeps the rocks in check. Concrete would mean it can't be removed so it can be a garden again.

The tarp separates the top half from the ground so it can be (re)moved when no longer needed

Since I have absolutely no experience in building, what do you think of this idea?

Please give me lots of criticism/suggestions here as I want this thing to work first time!

Cheers

Andrew

[radioactive]

Andrew its a good idea to make the hole bell shaped when you have unstable ground to work with and why not just use what may seem like a weakish mix for back filling it that's 9 parts ballast 1 part Portland cement this is the standard building trade mix for underground posts and so on and dont make it wet you only need just over 1 percent saturation to make cent go off just make sure its compacted well when backfilling the pole is a sound idea I used one of those washing line umbrella things as reinforcing my actual pier if making the actual pier from concrete then the mix ratio is 6 parts ballast to one part cement again this is the building trade norm for mixes above ground this wants to be slightly wetter but not too wet again make sure also you mix the composition thoroughly at all times for stability if you need instruction on how to mix then just ask

hope this helps a bit

[Andrew*]

it does, thanks.

is the 9:1 mix relatively easy to break up for when it gets moved?

I also have a question about the actual using of a cement mixer. I won't be able to make all my concrete in one load, so would you suggest doing it in batches (filling it, mixing it, and then emptying, filling, mixing, emptying etc.) or just keep on chucking the stuff in, making sure you keep to the right mix?

I only know one trick for this, which is use a bucket, not a shovel to get an accurate mix. Any other tips to make the job simpler?

Cheers a lot

Andrew

[blinky]

I am watching this thread with interest. I too have never operated a cement mixer or even hand mixed cement so am concerned I get it all correct!

[Kaptain Klevtsov]

One thing I learned, is if you load it with a shovel, it'll grab the shovel, rip it out of your hands and throw it at you. Bit dangerous those mixer jobbies. I'd chip in with how to use one properly but I guessed when I used one last.

Kaptain Klevtsov - author of "When Mixers Attack!!"

[Sam]

I'm watching this thread with interest as well, good warning KK - I'll keep that one in mind.

[Andrew*]

I'd heard that one :shock: Getting a bit worried!

my main question is: how much do they hold? I don't want to go putting too much cement in there and then find it's spilling out before I've got enough ballast in for a good mix, or even that it can't handle the weight! I have use of an ordinary commercial mixer - not sure of its capacity...

so for emptying it, is it best to unload it into a wheelbarrow rather than switch it off and shovel it out?

I can't believe I'm getting stagefright from a operating a concrete mixer :shock: :D

Andrew

[Black Shuck]

One thing I learned, is if you load it with a shovel, it'll grab the shovel, rip it out of your hands and throw it at you. Bit dangerous those mixer jobbies. I'd chip in with how to use one properly but I guessed when I used one last.

Kaptain Klevtsov - author of "When Mixers Attack!!"

Another tip!! Don't walk past the mixer and look at it! It gets upset and has the nasty habit of spitting cement/hard core mix into your face/eyes (been there, done that, didn't listen my Dad, etc, etc ).

Good to see you are progressing Andrew. Hope to hear more soon.

All the best.

Bill£

[Kaptain Klevtsov]

Tip it into a wheelbarrow while its still turning. If you try to shovel it out you'll struggle because of the internal flights getting in the way.

Oh, and to load it, use the shovel to throw stuff in, don't do it like feeding a baby, more like when a child has a go itself first time.

Kaptain Klevtsov

[radioactive]

mixers come in various sizes if you are going to hire one then get what is termed by the hire company as a barrow mixer and yes of course they can be dangerous they are not a toy after all they do serious work they need to be powerful its okay to be Wary of them but never be afraid that's only tempting fate what I tend to do is whilst it is not switched on I put the first mix ratio into it have the ballast say five measures then 1/2 a measure of water then switch on for 4 revolutions or so then switch off and put in the 1 measure of cement then the other 4 measures of ballast then switch on again (I am presuming the mixer is powered by electric not liquid fuels

at this stage determine how full the mixer is what you want is for it to mix without spilling any out over the front rim as this could make it tip over

remember 9 - 1 ratio means you can divide it up say 4 1/2 - 1/2 is still the same ratio it will not take long to mix 2-3 minuets is all it needs as kk says tip into into a barrow this is better with two people if available one to hold the barrow and don't tip the bulk to fast or it may make the barrow tip over! remember it does not need to be wet the mix is all the more stronger the less water it has in it for the average I would say one whole measure of water per mix as a guide the resulting concrete should clump together and not just spread out before you this is a good indicator you have it about correct slump value you can make your very last mix just a touch wetter if you have to trowel finish it but please dont go mad with the water as the last bit is the bit the weather will get at so maybe make your last mix a 6.-1. ratio

hope this helps

ps dont forget to clean out the mixer the cleaner its kept the better it is to mix with + if you want to travel to Leeds un back you can use mine

[Andrew*]

thanks a lot chaps.

Started the work this afternoon and it's going really well. Didn't read your posts until after we'd filled the hole from 3ft. I decided to use a 9:1 mix (and half a measure of water) and hopefully it won't be too difficult to take out later on....

I inadvertantly took all the advice you gave, although I never read it... so everything's going really well. No tipped barrows, no sloppy weak concrete, nicely compacted after every barrow, no stones in the eyes, no mangled shovels. All good

I've just put in a thin layer of ballast between the foundation and the station instead of using a tarp- I hope this will not mix with the concrete and glue the whole lot in. Also I hope it doesn't detriment the sturdiness... any thoughts?

Didn't get any pics though. Will do when we fill up the actual station with a 6:1 mix tonight.

Cheers

Andrew

[radioactive]

would rather you put some newspaper down first but I guess its not bad well done mate so we now have concrete evidence that you are getting on with the job