Allotment Gardening Advice Help Chat

Chatting => Design and Construction => Topic started by: tallulah on December 23, 2011, 09:47

Title: concrete floor in greenhouse
Post by: tallulah on December 23, 2011, 09:47
Hi all
I'd be very grateful for some advice. 

My greenhouse - 8x12' - has a concrete base.  I've been growing in pots, and have staging all down one side.  However, I really want to have soil borders a la polytunnel.  So, would it be feasible (regarding the stability of the frame) to pick-axe away a strip of concrete on each side so I can create soil beds.  Or, would I be able to build raised beds on top of the concrete, and if so, how high would these have to be, and would they need to be a kind of self-contained box?
Title: Re: concrete floor in greenhouse
Post by: JayG on December 23, 2011, 11:02
I think it would be extremely difficult to remove the concrete to make borders without cracking the areas supporting the greenhouse - if it's very thin (3" is the least it's likely to be unless you've had the cowboys in!) you might be able to cut through it with a serious angle grinder which would obviously help (still a hell of a job though!)

You could built planters on top of the concrete - considerations are obviously the soil depth you can achieve without reducing the headroom you have left for your plants by too much, and drainage - any structure would need to include arrangements for excess water to drain away at or very near the bottom of it (depending on whether it is sitting on the concrete or slightly raised.)

My greenhouse has a concrete base and I'm pretty much resigned to using large pots and growbags (I actually used whole bags of MP compost laid flat this year because they provide a good depth and are easy to get rid of at the end of the season.)
Title: Re: concrete floor in greenhouse
Post by: savbo on December 23, 2011, 11:04
second Jay's comments - the problem is knowing how deep your concrete is - even if it looks thin at the edges, it might get much deeper towards the middle, making breaking it out much harder ( as I found out on a project many years ago where a 1-day job became a 2-week one!)

and breaking it through while leaving a strip at the edge to support the frame will be very difficult - would probably need to try to cut through it?

So on balance I would go for a 1' deep raised bed...if you line the bottom of an open box with weed control fabric the soil won't wash out but water will be able to drain away
Title: Re: concrete floor in greenhouse
Post by: sunshineband on December 23, 2011, 12:20


I agree with the comments about removing the concrete -- not good!

Have you thought of drilling drainage holes through the concrete
 with a wide drill bit, and then putting weed membrane over the area before building raised beds?

This will not affect the height of ehat you can grow if you have already been growing in pots, and stop water washing along the floor of the house from under the beds.
Title: Re: concrete floor in greenhouse
Post by: Axe on December 23, 2011, 12:57
i would just stillsaw 2 tracks from the front to back then break them up aslong as you cut about 4-6 inches infront of the frames the concrete should hold perfectly fine.
Title: Re: concrete floor in greenhouse
Post by: Willie_Eckerslike on December 23, 2011, 15:31
If your greenhouse is already in place, then I would think that ANY work on the concrete is likely to shock the glazing and you could end up with a large bill to replace it.
Growing in containers means it is easy to replace the growing medium each year. Digging out the beds is a big job, as is importing fresh soil.
Title: Re: concrete floor in greenhouse
Post by: tallulah on December 23, 2011, 19:02
Great answers, thank you.  I think I'll try and sit some raised beds on top, with the weed membrane lining them.  Now I just need to work out a really simply design as I'm not that handy with wood.  I also have a really big hard paved terrace area at the back of the house that in my opinion is totally wasted and I want to put some tall raised beds on this as well, so I need to get a really easy diy design going!
Title: Re: concrete floor in greenhouse
Post by: Tom_Good on December 30, 2011, 23:38
You can cut the shape you want to knock out with an angle grinder and then sledgehammer the cut out for a fairly neat edge (depending on the depth) make sure itís the right type of blade if you are going to use a grinder (assuming you have power there) and donít forget grinders and pavement cutters can kick like a mule and can kill quite quickly if they hit the right arteries.

Bolster chisel to define the edges (with goggles) if you have the time and arm power Ė get a good one for a job like this Ė it will save a lot of heartache.
Title: Re: concrete floor in greenhouse
Post by: tallulah on December 31, 2011, 17:48
You can cut the shape you want to knock out with an angle grinder and then sledgehammer the cut out for a fairly neat edge (depending on the depth) make sure itís the right type of blade if you are going to use a grinder (assuming you have power there) and donít forget grinders and pavement cutters can kick like a mule and can kill quite quickly if they hit the right arteries.

Bolster chisel to define the edges (with goggles) if you have the time and arm power Ė get a good one for a job like this Ė it will save a lot of heartache.

Good Grief!  Even more reason just to stick some raised beds on top - much safer!