Garden Pier..

[NickK]

So I have a 24"x24" paving slab in the centre of the garden. Originally this had a small barrel to prevent herons from landing - curtesy of the previous owners.

My thinking is an exposed pier with a base block 24x24" but with a bit deeper to provide stability then a 40"x10" pier - enough for a refractor with imaging kit on the back, but also easy to use with a visual setup. 

The top of the pier will be locked level with alignment - then the base of the removable EQ6 will then simply slot in and lock - fully aligned to polaris. When not in use - a sun-dial and small wooden table will also be sotted on.

I'll run an armoured cable for power/data to a external box. 

My calculation will be about ~16 x 25Kg bags of concrete then additional ballast. I'll put rebar/mesh into the structure.

[DaveS]

Good luck! I'll be following this with regard to my own project, which is somewhat similar but at an earlier stage.

[MikeP]

Something like that might suit me too, so I'll be following along.

Mike

[NickK]

So I have been looking at the quantities required - http://www.diydoctor.org.uk/projects/mixing_concrete.htm - for a C20 mix.

For a H/W/D of 0.60 x 0.60 x 0.80 m or 0.3 m^3 volume, it's giving me:

Concrete - 96 Kg

Sharp sand 180 Kg

Gravel 360 Kg

Water 53 Litres 

With 25 Kg bags from Wickes, the current rough estimate is (not including the pier volume):

4x Concrete (http://www.wickes.co.uk/Lafarge-Mastercrete-Cement-25kg/p/154100)

8x S Shand (http://www.wickes.co.uk/Wickes-Sharp-Sand-Major-Bag/p/220112)

14x Gravel  - but I'm looking for a cheaper source than 5.99 per 25kg

Then add about £22 for a mixer for the weekend. Add cost for re-bar to reinforce and 6mm ply for the pier walls (hex shapes).

Still working out more details .. but that's giving me a ballpark figure..

[NickK]

Also looking at 36" from the ground top of the pier.

Also I'm looking at these brake discs (60mm central hole): http://www.eurocarparts.com/ecp/c/Vauxhall_Corsa_1.0_2012/p/car-parts/car-service-parts/regular-service/brake-discs/?104580709&1&271f1618daa91d5499109b993ca47e7d8d2d0ea8&000027 for £16 for two.

These are vented hence provide additional stability.

[laser_jock99]

I made my garden pier just over 1m tall- as Newtonian user I wanted to keep the overall height low. In the observatory the pier height is maxed out so a scope can peep over the walls!!

[red dwalf]

i did a simular build using a 8" water / waste pipe, it`s solid as a rock and apart from the Altair puck on the to fasten my mount, it was don`t too expensive.

these can be painted as i have done.

build thread here.

http://www.robslack1.webspace.virginmedia.com/Pier%20Build.htm

[NickK]

Decided that pea shingle would be a better bet for the gravel at £2.38 or 10 for £1.83 each.

http://www.wickes.co.uk/Wickes-Pea-Shingle-Major-Bag/p/220128

Now I have to work our a quick release/always aligned mechanism..

[NickK]

Ok, so volumes:

Base is 0.61x0.61x0.80 m = 0.3 m^3

Pier as 10"x36" = 0.0463 m^3

Total = 0.3465 m^2 (a little additional)

The resulting quantities:

Cement: 111 kgs

Sharp sand: 208 kgs

Gravel: 416 kgs

Water: 61 ltrs

111/25 = 4.44 = 5 bags concrete, 5 for £4.82, 5x4.82 = £24.10

208/25 = 8.32 = 9 bags sharp sand, £1.82, 9x1.82 =  £16.38 but .. just checking the 10 for 1.40 is £14..

416/25 = 16.64 = 17 bags pea shingle, 10 for £1.83, 17x1.83 = £31.11

Total 735 Kg.. (£69.21)

So given the focus can cope with a good 200 Kg (i.e. just me inside)..  that's a few car loads over the next few weeks... 

[JamesF]

If you can cope with having a bit left over (or make a slightly bigger hole there's always this to replace both the sand and gravel:

http://www.wickes.co.uk/Wickes-Ballast-Jumbo-Bag/p/220082

Unfortunately it looks like Wickes hit you with a fairly hefty delivery charge.  Our local builders merchant would charge about £10 more for the bag and deliver for free, so it might be worth looking around a bit.  Get the cement delivered at the same time and save a lot of faffing about (not to mention mess) in the car?

James

[NickK]

Hmm my concern with large aggregate is a limited about of sand and I'm assuming that it would give a rougher finish than pea shingle..

Problem I have is that there's 238 Kg left over.. that's a little more than I'd want

[Skywatcher 200]

 Hi NickK,

                 Just a word of warning  Re: vented Disks

Also I'm looking at these brake discs (60mm central hole): http://www.eurocarpa...8d2d0ea8 for £16 for two.

These are vented hence provide additional stability.

The internal structure can make them difficult to drill, my first attempt resulted in a shattered drill,  having caught one of the internal webs !

I ended up using solid disks, even though they are thinner !

Andy

[JamesF]

If you tamp the mix down as you go you'll end up with some finer particles at the top that give a reasonably smooth finish, and if you want better than that then a float will do the job.  You'd probably want to do that whether you use ballast or pea shingle, to be honest.  You shouldn't end up with that lumpy a surface either way.  I'd quite happily walk in bare feet on the slab I've just laid.

I like the ballast because the mix of particle sizes makes good concrete and it saves having to split bags into odd fractions to maintain the right mix.  Quarter of a tonne left over does present a few problems for disposal though, I'll grant you

James

[NickK]

 Hi NickK,

                 Just a word of warning  Re: vented Disks

The internal structure can make them difficult to drill, my first attempt resulted in a shattered drill,  having caught one of the internal webs !

I ended up using solid disks, even though they are thinner !

Andy

Interesting - I'd not thought about that - I'll have a look for a single disc version. Also still trying to think of a way todo a quick release that maintains a good alignment..

[NickK]

If you tamp the mix down as you go you'll end up with some finer particles at the top that give a reasonably smooth finish, and if you want better than that then a float will do the job.  You'd probably want to do that whether you use ballast or pea shingle, to be honest.  You shouldn't end up with that lumpy a surface either way.  I'd quite happily walk in bare feet on the slab I've just laid.

I like the ballast because the mix of particle sizes makes good concrete and it saves having to split bags into odd fractions to maintain the right mix.  Quarter of a tonne left over does present a few problems for disposal though, I'll grant you

James

Hmm I think the pea shingle for effect on the pier too.. have to keep someone happy..

[unger61]

i did a simular build using a 8" water / waste pipe, it`s solid as a rock and apart from the Altair puck on the to fasten my mount, it was don`t too expensive.

these can be painted as i have done.

build thread here.

http://www.robslack1.webspace.virginmedia.com/Pier%20Build.htm

I had a look at your site and the build sequence. Very well done... gives me some ideas. Thanks for that.

[NickK]

Has anyone used a concrete sealant? From all the research it seems to be the thing todo - give a coating to prevent ingress of moisture.

[NickK]

Has anyone used a concrete sealant? From all the research it seems to be the thing todo - give a coating to prevent ingress of moisture.

Ok, it seems that it's worth waiting for 6 weeks for the concrete to weather. This allows any salts etc to come to the surface and be washed off (preventing white stripes etc) before the sealant is applied dry.

The reason I'm asking is that if the water gets into cracks on an exposed pier and winter freeze hits.. the pier isn't going to last long!

[NickK]

For the concrete former I'm thinking a sheet of OSB (http://www.wickes.co.uk/Products/Building-Materials/Sheet-Materials/OSB/c/1000194) then cut to form an octagonal tube with a flat sheet at the base (and hole) then make some octagonal rings around it. It's not moisture resistant so a quick inner coating of external varnish should make it water proof enough for making the pier.

Whilst at Wickes I had a look at the concrete and bags of gravel/sand. They look smaller than I was expecting (for 25Kg) but they're the right size.

I have a free(ish) weekend coming up.. so I may decide to get the former done..

[red dwalf]

if your looking to concrete the pier base and a pier then a mix of 9 ballast to 1 cement mix would be ok, re bar inserts is a good idea as concrete for structure is week or can be and the re bar will reinforce it, concrete does get harder over time but should be ok to use after 2 or 3 days drying, don`t mix it too wet and tamp it down to get rid of air bubbles and it will give a smooth texture to the faces once the former is removed.

then can be painted with masonary paint and it`ll be fine.  

[NickK]

I have permission to dig

I've just looked up the frost level - 450mm under the soil, but I note that the guide on regulations (just for clay movement) is about 1m for maximum movement..

Next task this weekend is to build the former which I'll make out of OSB board. I'll start picking up the raw materials.. target is to do the pour first week of November. 

[AllanJ]

Hi Nick, I put an Altair pier in last year, hole was 2x2' by almost 3' deep. A digging bar was very handy, as was a narrow spade I also used for cable trench. I made a wooden form for the top few inches although open around its supporting timbers. The form was levelled at the correct height to be flush with existing patio slabs. I also hammered in some rebar, plus a few lumps of rock encountered in digging as hard core. I put in 450kg of aggregate and cement at 5:1  (borrowed my neighbour's mixer and the mix / filling started about 0830, finished and relaxing with beer in hand by 1130). I put a cable up through the middle of the pier, so plastic plumbing and a strong cord for pull through was good, and I made a rough "bridge" to hold the pipe central for the hole in the base of the Altair pier. Cable is run through garage wall and just plugged in when in use. The pier is bolted to L-shaped bolts embedded in wet concrete using a plywood template fitted over the former(needed extra care making  and positioning this).

Hopefully some photos on Flickr:

Allan

[NickK]

Quick trip - 4 bags of sharp sand, 4 bags of pea shingle .. so 200Kg down... the suspension could take 150Kg more (assuming I leave S at home - a bag and a bit ).

Still to get.. 5 bags concrete,  5/9 bags sharp sand and 13/17 bags pea shingle (575Kg) - so I think that's two car loads..

 

Also got a post-hole digger which will prove useful for two fence posts I will need to redo at a later date..

[mhard26339]

Hi Nick, I made my pier using discs from the same company on EBay (New obsey in Norfolk UK) and I used sold discs, the biggest I could find were from a Mazda 5 rear. The end result has been superb with a good solid pier as the result.

By the way, you will probably use more concrete than you think you will.

Regards

Mike

[NickK]

So I picked up a sheet of OSB2 - I had B&Q cut it down into sections that will fit into the car..

The interference lines are because I use a HPS lamp in the garage - but you can see the 10" octagonal pier markings. The little rule with a digital display is £15 from axminster - really good for things like this as it reads out the angle 135 degrees for the corners for an octagon. 

His Dark Materials - second car load today.. that's all the pea-shingle (17x25kg) now just need a bit of sand and concrete. I also picked up some meter long zinc threaded M12 for the through bolts. Need to find a source of rebar and hire the mixer..

Having fun doing the carpentry

I have some leftover sandolin exterior varnish that I will use on the OSB on the inside and base to ensure that the concrete does not weaken the structure. I'll also make some hoops that bolt together to hold the pier former together.