JamesF's observatory build

[JamesF]

Mind you, having to lift 160kg of concrete over 1.3m high to pour it, now that's hard work.

James

[Astrokev]

5 minutes ago, JamesF said:

A 280mm diameter tube 1.3m tall, Kev?  I reckon that's only about 160kg

James

Speaking metaphorically of course ?

[JamesF]

Been thinking a bit more about the drilling of the holes, particularly in the bottom block...

A wise man would probably mark up the intended positions of the holes, possibly from a template, then drill them in each block and make up a new template for any that did wander, using the second template to place the threaded rod in the concrete for the pier foundation.

James

[JamesF]

1 minute ago, Astrokev said:

Speaking metaphorically of course ?

You never can be sure with observatory concreting ?

I'd hazard a rough guess that our cement mixer does about 100kg per load and I've done twelve loads so far and perhaps have ten more to do, though it depends how much other stuff I can find to throw into the pier bases.  Today I discovered some offcuts of reinforced concrete beam about 500mm long, left over from another project, so they'll be going in.  I'd only have to take them to the tip otherwise.

James

[Peter Drew]

Drill a pilot hole with a small masory bit first.   ?

[JamesF]

Yes, I was thinking that starting small and then enlarging the hole would be a good plan.

James

[JamesF]

Little progress this weekend thanks to having quite a few things to do on Saturday and coaching at a swimming meet on Sunday.  I did however manage to drill holes (in both ends) of the lower blocks for each pier:

I've labelled them so I know where they belong once I make up the jigs for placing the threaded rod in the foundations, just in case the holes wandered a bit and they aren't completely identical.

I started with a 5mm pilot hole and opened it up to the required size afterwards.  Initially I just used my corded hammer drill in "non-hammer" mode, but there was a casualty:

That drill had a hardened tip once

Actually, there was another casualty and almost a third, as I had "help" from my father-in-law.  He insisted on getting straight in there with the SDS drill with the bit for the full-size hole in hammer mode, failed to drill the hole anywhere near straight and blew a huge piece of the block off the inside as the bit went through making it impossible to bolt down with a nut and washer   Just as well I bought enough that there are spares after all.

Once I'd stopped reaching for nearby heavy blunt objects I retrieved the SDS drill, turned off the hammer mode and went back to drilling pilot holes and opening them out again.  That worked nicely and my SDS drill bits remain unscathed (as does my father-in-law, but only just).

This evening I took the shuttering off the pads in the middle of the long sides of the floor and sorted through what I need so I can re-use it for the three pier foundations.  I'd really like to pour all three in one hit if I can, so I'm hoping I can get the new shuttering made up and in place and the jigs and threaded rod for fastening down the lower blocks sorted for Saturday morning.  The best-laid schemes o' mice an' men gang aft agley as the saying goes however, so I'll just have to see how it works out.

James

[Peter Drew]

I use just single holes on my "Tod" piers but I do use large "washers" made from 8mm aluminium x 75mm diameter to spread the load. The piers are also free standing.

[Alan White]

^^^^^^^^^^^^^ There speaks the Concrete Block Pier Master ^^^^^^^^^^^^^^^^^^

[JamesF]

I did give some thought to the number of bolts/threaded rods to use.  In this particular case where I'm working off sloping ground and have a suspended floor the concrete block foundation seemed most sensible, especially if I want the option to change to steel piers in the future (though I do believe this is unlikely), "just in case"   Having them freestanding would have been awkward in terms of ensuring there was no movement at the base and they'd probably need to be four blocks high which brings more stability issues.  Basically the cost of getting this bit wrong is high, so overdoing things in an attempt to reduce the chances of being wrong is less of a problem, particularly when the cost of doing so is relatively low.

Had I gone for a single rod I'd probably have used something like a 16mm or 18mm diameter (I think I even have some 22mm hanging around), but smaller has some advantages (especially if I need to cut them out at a later point) so I chose to go with multiple 10mm rods.  Two seemed insufficient as there is perhaps potential for rocking.  I can't recall why I decided not to go with three, which would have been sufficient.  I ended up at four, anyhow.

In a different situation I'd quite possibly take exactly the same approach as Peter, though if we had one available for guests if the council ever gets around to granting our planning application then I'd probably have it fixed to something hefty at the bottom so there was no chance of it falling on a small child or something equally unpleasant.

James

[Peter Drew]

On 10/06/2018 at 18:50, Gina said:

How deep is the concrete block with the gravel round it?

50mm.

[JamesF]

I'd be happy with that sort of depth myself in a free-standing environment.  It's going to be exceptionally hard to budge that.

James

[Peter Drew]

@JamesF. I'm just describing what has worked for my purposes, extra development is worthwhile. I have a 3 1/2 block pier for a 5" F15 APO the base has 5 600x600x50 concrete slabs, 4 in a square with the 5th bolted to the others through its corners but it is still freestanding. 

[Gina]

That sounds a good idea ??

[Gina]

Why oh why did I go for a 800mm cube for the base of my pier????  Over engineering in the extreme - but that was what was recommended at the time!

[JamesF]

Mine should work out about 700mm x 500mm x 500mm, but that's mostly to get the required height and then not wanting too narrow a base for that height.  A flat site would have been far easier.

James

[JamesF]

Managed to remake most of the shuttering this evening.  The weather forecast looks good in the run-up to this weekend so I might take Friday off to make sure I have everything organised, get the shuttering in place and all levelled up, make up the jigs for the threaded rods and then I can just start shovelling stuff into the mixer on Saturday morning.  Might go and pick up another bag of cement, too.  I'm worrying that I may not have quite enough.

James

[Astrokev]

In my experience you always need more cement and ballast than you think!

[JamesF]

I have to admit to being a bit "old school" when it comes to mixing mortar or concrete.  I know pretty much how many shovels of sand/aggregate will give me a full mixer load and half a bag of cement (ie slice the bag in half and tip one half in) gives the right proportions for concrete.  I know some people do measure out bucketfuls or whatever to get exactly the right proportions, but it's always been close enough for me.

James

Edited June 20, 2018 by JamesF

[JamesF]

Well, I managed to get the shuttering in place for the three pier foundations today, but that was it, largely because although I'd taken the day off I still ended up working until gone 11am.  I was really hoping to get the threaded rod sorted as well, but just ran out of time.  I've also back-filled the holes that the shuttering is sitting in so the soil will support most of the outside when the inside is full of wet concrete.  I had to get the digger out again to enlarge one hole.

So tomorrow I need to cut and bend the threaded rod, make up the jigs to hold it in place in the concrete, possibly nip down to the builder's merchant and get another bag of cement and then I can get cracking.

I'm quite looking forward to this bit being finished as after that there's a lot of timber work that can be done piecemeal, so I can make progress in any spare 15 minutes or so.

James

[JamesF]

Horseflies were out mob-handed today, too.  Tricky blighters, but they get a bit over-excited when they think they're about to get a decent meal and drop their defences.  Allowing them to land on me and then swatting them immediately seems to work well.  Around a dozen have now been sacrificed to the success of my pier foundations.  They're not having my blood whilst I'm still using it.

James

[Astrokev]

1 hour ago, JamesF said:

I'm quite looking forward to this bit being finished as after that there's a lot of timber work that can be done piecemeal, so I can make progress in any spare 15 minutes or so.

James

Yeah, it was a great feeling when I'd finished the concrete work. Too much like hard work! Much more at home with cutting up bits of wood ? 

[Gina]

Same here!!  A long hard day's work even with an electric mixer, pouring my block and pier!!  I shall never forget that! ?  The six support blocks for the building were a lot easier and could be done one at a time.  I rather like working with wood.

[JamesF]

Well, my pier foundations are now done.  Photos later.  For the moment I'm still replacing fluids and allowing my sore hands to recover.  I reckon I've shovelled over a tonne of materials three times today -- once from dumpy bags into the trailer to get it all down to the site, once into the mixer and once from the barrow into the shuttering.  I'm quite relieved it's all over.  As things worked out I didn't need the extra two bags of cement that I bought this morning, but they'll get used anyway when the builder returns to finish making the steps that will lead from the house down towards the observatory.

The horsefly score for the day is about 9.5 to 0.5 in my favour (I got bitten once, but swatted the fly almost immediately so I've classed that as a score draw).  I have never known them be this bad before.

James

[Dr_Ju_ju]

I'm allergic to the little blighters & blow up like a balloon, so hopefully you have fended them all off.....