Pier construction (Tordmorden)

[FrenchyArnaud]

Hi guys, 

so, following the thread here: 

I have begun the construction of the pier. I am opening this thread to document the progression; as I have been reading countless threads and watched countless videos before begining, I assume this will, at some point, be of interest to someone (and allow me to keep track as well)

So, for starters, the quick photoshop of what the GF agreed to: 

I understand it's a classic design called a Tordmorden Pier. 

That was the original plan but it went south from the get-go. My idea was to screw/glue the bottom brick to the tile, which is solid and encased on a concrete slate, avoiding the need to build a foundation. However! Just for peace of mind I probed, pried the tile with a crowbar... And it popped right out without any resistance. The material underneath felt and sounded like concrete indeed, but I was able to mark it with the crowbar, and it turned out to be some sort of hard, but brittle grout. So I drilled into it to have a better feel of what I was facing and the drill went rigt through it in seconds. 

 

Totally unsuitable to rest the pier... So, plan B. I need a foundation and for that, no two ways about it, I need to cut away this slate of whatever it is and dig underneath it. Brittle but pretty sturdy and a good 3" thick, I tried brute force but no way. So I did the obvious: drilled all around to cut it..

.

From there I was able to fracture it with the crow bar and pry this part of the slate open without disturbing the other tiles. (GF would NOT have been impressed!) 

 

From there is has been much more straight forward but back breaking: break the ground with the crow bar, dig out, rince, repeat. I am now left with a neat 1.5ft * 1.5ft * 1.5ft deep hole where there once was the tile. I cannot go deeper as I have hit what looks like either the bed rock or a massive boulder. Either ways, I am confident this will be ok. 

The plan is to fill it with concrete with one of the hollow bricks 3/4 submerged in it, exposing only the side surface (21cm*21cm) about 1" above the level of the adjacent tiles. And this, will be my foundation... 
Half way through digging:

Next stage : pouring concrete and inserting the underground block to create the leveled anchor plane the rest will be glued on
To be followed! 
 

Edited January 29, 2023 by FrenchyArnaud

[Graeme]

Looks like a good start. 

Are you going to isolate your underground block from the surrounding slabs?

Regards

Graeme

[FrenchyArnaud]

I tell you what, I have spent 2hours asking myself exactly that when I realized I needed a new plan. It is actually 2 questions: is it needed? How to do it? 

I could not decide if it was needed but i sure as **** was not able to come up with  simple way to do it, so I decided that no there will be no dampener. The downside is, I will need to avoid walking there during sessions but I usually don't anyway. I just wonder if the temperature change will make the tiles oscillate 😞

[Graeme]

11 hours ago, FrenchyArnaud said:

is it needed? How to do it? 

No, but it's one more thing to aid image quality. You could shutter around the top 6" of concrete and take it out after curing. Or you could build a raised timber frame.  

[ollypenrice]

I shouldn't worry. There is no need to be near the pier when you launch the imaging run.

Olly

[M40]

A great start 👌 and as for a dampener, how about installing some wood around the existing slabs and slab base, pour your concrete, remove the wood when dry and then just back fill it with pea shingle.

[FrenchyArnaud]

Ok, Day 2! 
Went to Jewsons, bought all I needed : 5bags of quick concrete "postfix", 4 hollow blocks and masonery glue. Because my garden is accessible only from behind/around the house, I had to carry all of it around and that's no fun. Fortunately I was able to recruit my trusty assistant Mocha for help. Well, for moral support at least; well, he has a knack for being exactly where it is the most irritating but hey ho, he's trying. That must count for something. 

I threw a couple of liters of gravel stolen from the flower bed at the bottom to provide a support for the first block, which will act as my anchor. 

That allowed me to present this first block/anchor and set it stable and, after a lot of fiddling and jiggling, to get it nicely aligned and level.

This Postfix aka Blue Circle aka Postcrete does not require mixing. The way it works, you fill the hole 1/3 to 1/2 with clear water, pour the dry mix on top of it, paddle with a stick to eliminate bubbles (and in my case, make sure the mix gets inside the lower hollow), until the water surface is reached, and repeat until you are at the desired level, at which point you just cover the top of the mix, still dry, with more water. You have 5 to ten minutes for the whole operation so you really want to make sure you have everything at hand. After 15minutes it is mostly set and pretty much impossible to move. I dedicated 2 minutes half way through to making sure the block had not moved and was still perfectly level.

Once you reach top level you can, if you wish, smooth the surface - I did not bother. Here is the result. 

 

 Because I added tons of water, it took about 1 hour to really set, but right now, about 2 hours in, it is pretty much rock hard. I will not try to walk there or do more out of precaution but I am confident I could stand on the block and it would not break a sweat. 

Only I did. That's some serious exercise for old me. 

Next stage: glueing the 3 other blocks on the anchor - that at least in theory should be child's play as my support is dead level and rock solid. 

[FrenchyArnaud]

9 hours ago, M40 said:

A great start 👌 and as for a dampener, how about installing some wood around the existing slabs and slab base, pour your concrete, remove the wood when dry and then just back fill it with pea shingle.

Yes I could have done that but I read your idea AFTER  I poured, plus, it woukd have added too many steps for my taste (even though objectively that would have been better)

I keep the idea though because if it turns out I can detect foot steps on the guiding graph, I think I can dislodge the adjascent tiles, cut the slab base underneath the middle of the tiles and fill this fracture line with sand or sthg, in effect isolating the square where the pier is and the ones directly around it from the rest of the walking zone, while still having the benefit of a 3x3 tiles surface to fight gravity sinking of the foundation. 

I'll do it if it proves needed.

[FrenchyArnaud]

Ok, I can't help but share with you this preview...


The blocks are glued with CT1 (brand C-Tec) and the local jewson's reliably informs me that after 24H it will be easier to break the blocks than to unbond them. I hope it is true.

The mount is actually screwed on as I drilled the block BEFORE installing it (I was unsure how hard it would be) Drilling the main axis was not especially difficult but drilling at the right place was. So I drilled 3 times on 2 blocks before one of the centering was correct - this centering now sits on top of the column. Drilling the brake disc holders will be much easier because I will just clamp the disc in place and use it as a guide. Of course this is just a temporary fixing for the sake of the picture, the mount will be put on a proper adapter. 

So now I am only waiting for the brake disc to be delivered 😇

The GF is hunting for the correct colour of concrete paint to match the fences and is looking into hanging small flower pots to decorate the column; I will supervise the weight distribution but I am confident it should be ok. The thing is solid as a rock - litterally. 

[Macavity]

4 minutes ago, FrenchyArnaud said:

The blocks are glued with CT1 (brand C-Tec) and the local jewson's reliably informs me that after 24H it will be easier to break the blocks than to unbond them. I hope it is true.

You can always "jiggle it a bit"! (Or leave it well alone?) 😁
If it fails to bond, you can DRILL the blocks and add bolts?

It may "kill" a standard drill, but I was surprised how easy it
was to drill (at least) standard concrete blocks! 😉

[CraigT82]

Looking good, I wouldn’t worry about trying to dampen the pier from your footsteps, just don’t go near it once you’ve started the imaging run, or pause the run if you do need to go near it. Some longer cables to get the laptop a bit further from the mount will be good. 

[FrenchyArnaud]

Just now, CraigT82 said:

Looking good, I wouldn’t worry about trying to dampen the pier from your footsteps, just don’t go near it once you’ve started the imaging run, or pause the run if you do need to go near it. Some longer cables to get the laptop a bit further from the mount will be good. 

Actually it's all piloted from inside the house in the comfort of my office with multiple screens etc 😇 I love the geek feeling 😅

[FrenchyArnaud]

1 hour ago, Macavity said:

You can always "jiggle it a bit"! (Or leave it well alone?) 😁
If it fails to bond, you can DRILL the blocks and add bolts?

It may "kill" a standard drill, but I was surprised how easy it
was to drill (at least) standard concrete blocks! 😉

Yeps, that was my thought, metal plates on the sides and drill it essentially as a belt. It proved so easy to go through that I may do it just because. 

Edited February 1, 2023 by FrenchyArnaud

[FrenchyArnaud]

Ok, Day 3!

So after long discussions with the GF, we decided that it would be better to get rid of the tiles altogether and cover the whole area with gravel like the flower beds. To me this offers multiple advantages: it's economical, easy, and allows me to bury the cables which in turn avoids fiddling with pipes running all around the garden. Besides, I have hope that the 3" of gravel will be sufficient to dampen any vibration the occasional step there could produce. 

So, step one : ripping a line of tiles out, which involves a very high tech, scientifically approved method (brute force), an operation conducted with precision instruments (42" crowbar) The objective is to lead the cables (USB and electrics) to the hole in the outer wall where an unrelated cable is already present (red arrow)

Then I put the cables down and covered them with a pvc profile screwd directly into the grout that was the base of the tiles. 



After that I just had to dump the gravel. I did not take the pain to wash it, I count on the rain for that - hence the difference in colour with the flower bads. Later, (when the pier is operational) I will rip the other tiles and make the whole area covered in gravel. 

The next step is to

1) drill a wider access in the masonery (20mm) and pull the cable indoors. This cable will be powered by a 12V 8A unit which I already have. (more than enough to power all of the gear)

2) put the adapter plate in place (should be delivered very shortly) fix the cables along the pier and install the proper electric plugs etc at the top of the pier. 

Getting there! 

Edited February 6, 2023 by FrenchyArnaud

[Graeme]

Looking good Arnauld. The gravel was a good idea.

Regards

Graeme

[M40]

Superb 👌 very small footprint, perfect. We have gravel around the base of my pier which works really well....but... you become very aware of the noise it makes late at night. 

I am currently in discussion with management on various proposals on the way forward, so can I suggest that before you rip the rest of the slabs up, have a think in case it could be a concern for the neighbours. All the best.

[FrenchyArnaud]

34 minutes ago, M40 said:

Superb 👌can I suggest that before you rip the rest of the slabs up, have a think in case it could be a concern for the neighbours. All the best.

Thanks.

Yes, valid point that we discussed. That is already sorted 👍 In any case, objectively apart from the dog (and me to put the teleacope cover  on/off) noone will walk there at night. I am more concerned about the resident foxes and cats seeing this new expense as a litter tray / playing ground 🙄

[Ole Larsen]

You can se my setup and building a pier. http://www.mit-observatorie.dk  in Danish, but i think google can translate.

Edited February 7, 2023 by Ole Larsen

[FrenchyArnaud]

Day 4. Keep in mind, I work full time so I only have about one hour a day at most to work on that and a few hours at the week-end. 

So, after sleeping on it I decided my 5m USB cable was unsuitable, too short on the pier side and not giving enough play in the inside of the house. I think I will just make my own life miserable forever if I do not have enough room to play with. So I ordered a 10m USB3 with repeater, and I will exchange the cable as soon as it arrives. Fortunately, by conception it will be quite easy. 

In other news, I brought in an extra 150kg of gravel and laid it! So the gravel is now about half way through and it begins to give a good idea of what it will be like when finished. 

So now I am waiting for the delivery of the adapter plate AND the long extension... And as soon as they arrive I will be able to finish it all  and at long last, to see my OTA where it belongs! 

Edited February 7, 2023 by FrenchyArnaud

[FrenchyArnaud]

-ignore-

 

Edited February 7, 2023 by FrenchyArnaud

[FrenchyArnaud]

Thanks to @Graeme who took the pain to drill the disc to specs before shipping it (it was delivered this morning but I was working) the pier is now assembled and as luck would have it, will see first light tonight! The cabling is not done yet but of course,  I will simply use my usual cable set up. 

The disc is simply maintained by 2 expanding M10 bolts and the central axis of the mount; it is also glued with the rest of the CT1 to absorb any irregularity of the concrete and make sure there is no possible oscillation. There is no levelling system obviously but it is pretty much dead straight anyway.

The whole thing is solid as a rock and I am very, very pleased with myself! 

[CraigT82]

Nice work! Nothing more satisfying than when a bit of DIY turns out well.

[Graeme]

That's a fine looking pier Arnaud. And a very nice disc, it looks like the one I have!

Good luck with the first light.

Are you going to build a roll off roof shed around it?

 

Edited February 8, 2023 by Graeme

[Peter Drew]

As the originator of the "Todmorden" pier I'm always pleased to see another one take shape.  Also pleased to see the mount bolted or fixed through the top of the block rather than a rat's cage.       🙂     

[FrenchyArnaud]

2 hours ago, Graeme said:

That's a fine looking pier Arnaud. And a very nice disc, it looks like the one I have!

Good luck with the first light.

Are you going to build a roll off roof shed around it?

 

Thanks! Yes, fine disc 🤭

No roll off shed, there is just not the space.

I just realized that my azimuth bolts are dead (inner threads of the "nuts" are pretty much smooth) which means I need to do heavy repairs if possible or the mount is dead 😞 A bit gutted but trying to stay positive