Forum home› Tools and techniques
This Forum will close on Wednesday 27 March, 2024. Please refer to the announcement on the Discussions page for further detail.

Advice Please on Base for Greenhouse

TheveggardenerTheveggardener Posts: 1,057
in Tools and techniques
I'm looking for some advice please on a greenhouse base. We have a base there at the moment but it needs extending buy a foot on two sides the back and right hand side. The existing slab is about two bricks deep made up of bricks and slabs, we never laid it so don't know how it was laid. We will be using breeze blocks and infilling with rubble and will be cemented over on either side of the 4 center slabs then the GH will sit on top and be anchored to the base. There are 3, 90cm x 60cm slabs at the moment one more to be added  running from front to back and it will have cement either side between the gaps of the slabs we will cement  but will leave a gully and the same in the cement on either side so that any water can drain out. If you take away the three slabs from front to back that is what we found when we took the shed down.

Question
1) Do I need to dig down and make foundations to the extension.
2) If so how deep do I need to dig down. 
3) How long will it take to dry before we can put the GH onto it.

My son is off work in a weeks time and ideally we would like to get the base ready before then so we can put the GH up but we want to make sure we do it right. I will be rendering round the whole base once it is ready.

Hope all the above make sense and we would be grateful for any advice.


«1

Posts

  • TheveggardenerTheveggardener Posts: 1,057
    Bumping up for advice as I really need to get this sorted by the weekend.
  • hogweedhogweed Posts: 4,053
    Not sure why or where you will be using breezeblocks. Will the green house be sitting on top of the breeze blocks ie they will make a little dwarf wall? 
    Personally I would lift all the slabs, put shuttering up and fill the whole base with concrete if you don't intend to have soil beds in the greenhouse. 
    'Optimism is the faith that leads to achievement' - Helen Keller
  • Joy*Joy* Posts: 571
    I would agree with Hogweed as concrete would be easy to keep clean. Greenhouses need a good clean with Jeyes fluid in winter to keep nasties at bay. (What a lovely smell!!) 
  • NollieNollie Posts: 7,529
    I’m struggling to understand where the breeze blocks go as well, NannaBoo, are you running them around the outside of all the slabs, level with the centre paving slabs, to create a sort of raised bed, then filling that with concrete on top of the rubble to the same level as the slabs? That would kind of make sense as the breeze block rectangle forms a retaining structure for the poured concrete within. 

    The breeze block/extension bit needs to be dug down a bit and filled with compacted hardcore or gravel, with the breeze blocks cemented into that. How deep? Hmm, maybe around 15cm would do. 

    Concrete takes longer than you think to ‘go off’ (set and achieve full strength), ideally 30 days, but most builders would scoff at that. If you can’t wait that long, give it at least a week to ten days, and keep lightly hosing down the poured concrete so it doesn’t dry out too quickly and crack prematurely.

    The only issue you might find is subsequent cracking of the concrete between the rubble and the solid slab areas because you are joining two different materials, pre-cast slabs and loose-filled rubble topped with pouring concrete, with different tensile strengths. 
    Mountainous Northern Catalunya, Spain. Hot summers, cold winters.
  • TheveggardenerTheveggardener Posts: 1,057
    Sorry should have said the picture shows the existing slab that was there but it's not big enough for the new GH. It need to be extended it, I have enough breeze block to go round two side, (along the back and along the right hand side) of the picture. What I need to know is do I need to dig down and make a foundation for the extension which will be attached to the existing base. Looking at the picture to the left and right of the picture we will be infilling with rubble then we'll be cementing either side of the center row of slabs the other slabs will be centered over leaving the center slabs showing. Once we are left with the base the greenhouse will go on top. Who ever build this left lots of pockets which rodent have been living in, we did try to break up the concrete and lift the slabs but that won't move the are like to one's the corporations used before they started to use what they do now tarmack. These slabs are really heavy, my son put his back out after moving just three of them they measure 90 x 60 cm. I hope this give you some idea of what we have to do but really we need to know should we be digging down to make a foundation or just putting the breeze blacks on the soil and cementing them together.
  • hogweedhogweed Posts: 4,053
    NannaBoo - I can move 90cm x 60cm thick old fashioned slabs myself!  Fair enough I cannot lift them but can easily walk them away and then relay them successfully! They are not that heavy! 
    I still don't understand what the breeze blocks are for????? Is this what you are trying to do or please explain why you need breeze blocks?

    'Optimism is the faith that leads to achievement' - Helen Keller
  • TheveggardenerTheveggardener Posts: 1,057
    Hogweed the green is correct but the breeze block will only be at the top and right of your drawing. We had a 6 x 10 shed there when we moved in and have removed it, we found the base was either long or wide enough to put our 6 x 10 GH on. We need to extend it at the top by a foot and on the left hand side by a foot so the GH sit safely onto it. I propose to extend it using breeze blocks and then infill with rubble on the entire site and then put cement where the rubble and breeze blocks are to give and even floor but leave the center slabs exposed. Sorry I'm not very good at explaining but taking your sketch where you have indicated breeze blocks would I need to dig down and make a foundation for the breeze blocks to sit on or can the go straight onto the soil and once the cement has set lay the rest of the concrete on top
  • hogweedhogweed Posts: 4,053
    So is the ground lower at the top and the right and you are using breeze blocks to raise it to the same level as the rest of the ground??? 

    'Optimism is the faith that leads to achievement' - Helen Keller
  • hogweedhogweed Posts: 4,053
    Perhaps another few pictures would help us.

    'Optimism is the faith that leads to achievement' - Helen Keller
Sign In or Register to comment.