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KyleStoke

Observatory Base Problem

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Hi All, I have taken the plunge and purchased an observatory.

The site I had chosen to put it currently has a concrete slab, I was going to remove it but this has proved harder than I first thought.

It is Thick and reinforced, I wanted advice if it was possible to leave it there and add more concrete as i need it, and also to somehow cut a hole out in the center for my pier plug.

I have added pictures of the site and would welcome any advice.

IMG_20160424_104737895.jpgIMG_20160424_104719763.jpgIMG_20160424_104725713.jpg

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Is the the existing concrete big enough to site your observatory on ?  If so, use it as the base and cut a hole through it for the pier foundations.

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My advice is to hire an electric demolition breaker. The biggest you can get and the low voltage supply for it from a tool hire shop. Break it all up into manageable pieces and reuse them to sink into new concrete that you lay. Leave a hole big enough for a new pier centrally situated. Or lay the pier support first then the observatory base around it.

Trying to break up a concrete base like that is a very hard job. Concrete gets harder with time as it matures. Using a pick axe is not recommended!

Starting from scratch is the simplest method in the long run. Trying to lay a new concrete screed on top of that will end in failure as your new concrete will most likely not adhere properly and also most likely crack after a while where the edges of the old concrete are. If you do try to concrete over the original base you will need at least 3-4 inches of  new mix. I have tried this in the past and had no success as it always cracked eventually.

Do it once and do it correctly!

 

Best of luck.

 Derek

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Agree with Derek, hire a big breaker and it will make mince meat of it, get a mask and ear defenders, might annoy the neighbours for a while but it will be worth it :)

Dave

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You may get water seepage into your observatory unless there's a false floor going on top of the concrete. If you were planning to use the concrete as your floor, you might consider using Wedi board as a floor lining. Wedi board is a Styrofoam  slab resin backed on both sides. It's easy to cut and you can board on top of it without the danger of waster ingress.

Mike

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Completly agree with using a big breaker with a couple of "points" use padded gloves as your hands will suffer from vibration after a while. Something that size will be gone within 30 mins.

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If you do hire a breaker. Don't bother with those giant electric ones. They are utter rubbish. I never hire those electric ones as they are never powerful enough, and are too huge, awkward and heavy to use for extended periods. Hire a hydraulic breaker instead. These are miles more powerful, smaller and easier to handle. The power pack is separate so you aren't lifting the engine each time you move it like you are with the electric garbage. The hydraulic breakers are far superior in every way. The hire cost is often almost the same and you are getting a much more powerful, better tool. ;) 

 


 

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I agree about the hydraulic breakers being better but they are  not always available in hire shops around the country!

 

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Everybody thank you for the advise, looks like its 100% for break it up and start fresh.

I will look to rent one next weekend and get it broken up.

I was hoping it was just a thin layer i could of broken by hand but never mind.

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Did you ever sort out your steel for a pier.

Dave

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28 minutes ago, Davey-T said:

Did you ever sort out your steel for a pier.

Dave

Hi Dave, I found a place through work that would let me know when they had a suitable off cut. Which I Could of had for pretty much nothing, 

But then i saw a piece of ventilation ducting that was 200mm in diameter and just short of 2m long so I was going to make a concrete one.

I brought that had the material to make the template for the owls nest type bit and then the boss(wife to be) canceled the roll off roof project because she didnt like the support legs for the roof runners. 

So then i got permission for the dome as it was out of the way up a corner, ordered that but when i sat down and thought about it I decided if i bodged the pier up it would all be pointless so i added one of the Pulsar ones to my order.

Sorry if thats too much detail.

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Wives eh, can't live with them, can't bury them under the obs'y :grin:

Dave

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On 24/04/2016 at 15:16, KyleStoke said:

Everybody thank you for the advise, looks like its 100% for break it up and start fresh.

I will look to rent one next weekend and get it broken up.

I was hoping it was just a thin layer i could of broken by hand but never mind.

I used an electric one to break up the old patio.  They are heavy and alot of hard work to move around.  If I had thought about it I would have got a hydraulic one.

http://www.hss.com/hire/p/hydraulic-breaker-petrol

--

Mark

Edited by MarkyD

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Who's got the biggest wheelbarrow and breaker !!!

Do you really want to break up this slab?   Just make use of it and extend as necessary for intended obsy. The final obsy floor should be above ground-level to avoid water ingress by min of 80mm  - sealants DON'T work longterm.   Bolt scope column to ex base and isolate from obey floor. AP may need remote operation - I just keep still during the brief subs!  Visual = no problems :-) 

Good luck

Nyte

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Be aware is the concrete base a extension of your garage base, is it connected to it, if not is it a cap on a old mine shaft or clay pit someone has gone to a lot of trouble to put rebar in there as well you never no you get a lot of them around stoke it could be goodbyyyyyeeeee.  

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6 hours ago, baldeliftman said:

Be aware is the concrete base a extension of your garage base, is it connected to it, if not is it a cap on a old mine shaft or clay pit someone has gone to a lot of trouble to put rebar in there as well you never no you get a lot of them around stoke it could be goodbyyyyyeeeee.  

If its a cap on a mine shaft I will end up with a very deep pier plug.

I was told that a previous owner had a hot tub there which I suppose would be heavy requiring the reinforcement.

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After 7 hours of very hard graft yesterday I removed the old slab, it was far harder work than I had expected. Quick question to those in the know, would it be ok to lay the new concrete on top of the gravel like base.

IMG_20160430_154331421.jpgIMG_20160430_154333733.jpg

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Wit is the best way but compact it as best you can first. Also when mixing the new concrete mix in a waterproofer additive such as Sika1. You can get it usually at Screwfix or a builders merchant outlet. 

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5 minutes ago, Physopto said:

Wit is the best way but compact it as best you can first. Also when mixing the new concrete mix in a waterproofer additive such as Sika1. You can get it usually at Screwfix or a builders merchant outlet. 

Thanks, I will add it to the list although im not sure if i will mix it or get some people to pump some ready mix in.

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If you plan out the base exactly size wise then it can be mixed and poured easily depending upon your fitness. But the lifting (continuously) of bags of sand and aggregate mix and cement can be a killer if you are not used to it. If you do try, count on about 1 ton per 1/2 cubic metre. So if you are pouring say 10 square metres  at 10 cm thick that's 2 tons of mix, before water is added. Mix at 4:3:2 sand:aggregate:cement. Will give a good strong mix. You can use less cement but does cause a bit of weakness at that small thickness. The Sika 1 used to cost about £30 per 5 litre container.

If you do not do a lot of lifting get a premix and ask for water proofer additive. No point in hurting your back for a few quid.

If the area is easily accessible they can pipe it in if not make sure that they will barrow it to your base area.  Be sure that every thing is ready as they do not like to be kept waiting and some will leave it in a heap on the path, or pavement, or worse still take it away and still charge you. 

Make sure you tell them the exact volume you need to fill and ask around for prices. If not reputable they might miss out on the waterproofer or use less or poor quality additive. As the saying goes "you pays your money......"

Best of luck.

Derek

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Thanks for the tips Derek, My brothers friend has a mixer so may well go down that root

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Hole finally dug, bit of shuttering to do and then concrete pour but that should the last major obstacle

IMG_20160507_120608136.jpg

It doesn't look that deep on the picture but once the shuttering is added its just under a meter deep.

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On 1 May 2016 at 11:19, Physopto said:

...

Make sure you tell them the exact volume you need to fill and ask around for prices. If not reputable they might miss out on the waterproofer or use less or poor quality additive. As the saying goes "you pays your money......"

Best of luck.

Derek

Also, don't get too much as (my builder tells me) that if they have to take any back they will charge you a lot (as I guess they have to dispose of it).  When I had my garage done they were looking/asking me about somewhere they could dump any excess as they didn't want to have to pay if it turned out to be too much. Or check with supplier before ordering what they do if you don't need all that was ordered.

Around me there are companies that specialise in smaller volumes of ready mix.

Ian

Edited by psamathe
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