New greenhouse on uneven stone slabs

djlacerate

Hi All. Long time lurker, first time poster!

We have just bought a shiny new 5x8 alluminum greenhouse from the greenhouse people, and yesterday I put together the alluminum base to check positioning and level. I knew that there would be some gaps at points under the base due to the stone slabs being slightly uneven, and was planning on filling those with morter, but unfortunately the two shorter sides of the greenhouse are not quite level (see pic), they are both out by the same amount according to the spirit level. The 2 long sides are perfectly level according to the sprirt level but am now unsure what to do about the slight slope.

I have attached a few pics showing the base position on the slabs, a gap under one of the base slats, and the spirit level reading on the slide that is not level.

I'm not sure what the best plan of action is to sort this out. Any suggestions?

Thank you!

Emptyheadtime

I wouldn't be too concerned about the slope as it will help water run off. I would be concerned about the gaps and the base not being flat. Is it glass or polycarbonate and are you planning on securing the base somehow to prevent it blowing away? 

djlacerate

Thanks @Emptyheadtime. Its a glass one (link). It does sit flat and level, one the long sides at least, but there are gaps along each of the sides between the aluminum base and the stone slabs due to the contours of the stone. I was planning on using a stiff morter mix to fill the gaps once built, and then anchoring to the stone slabs using bolts as recommended in the manual.

My worry was the slight slope, as I have read that a level base is important for the overall longevity of the greenhouse and also for easier assembly... 

Uff

I think you are right to be concerned but the problem isn't insurmountable. Could you level the base with thin pieces of slate and the seal with exterior sealant?

Pleased you've joined in and welcome.

djlacerate

Thanks @Uff. Do you mean try to fill the small gaps with slate and then seal, or lift the green house on the lower side to make the whole base level with slate?

If the latter, then one whole 8ft length of the base would be lifted and so not touching the stone slabs at all - it would probably need to be lifted 20mm or so.

JennyJ

The paved area will have been deliberately built on a slight slope so that water drains away from the wall. At least it's even in the direction of the short sides. I wonder if you can get a thin strip of something (hardwood?) to put under the lower long side to level it? @Uff's slates would do the same thing and would probably look more in-keeping with the surroundings.

You could lift, level and re-lay the slabs in that area but that would be a bigger job. Or lift slabs and lay a concrete footing or use the plastic grid stuff with gravel - that way you could have soil beds in the greenhouse. There was a thread recently where someone had used the plastic grid base for a shed https://forum.gardenersworld.com/discussion/1071108/plants-for-growing-through-gravel/p1

djlacerate

Thanks @JennyJ. If I lifted the low side with slates at each corner, and then packed in a stiff morter mix to fill the resulting gap along the entire length of the lefted base - along with the other small gaps around the base, do you think this would hold the weight of the greenhouse once I removed the slate?

I like the idea of hardwood but think it may deteriorate over time due to the abundance of rainwater we are blessed with in Sheffield! 

Pete.8

I had the same problem as you when I put up a Halls 6 x 2 lean-to greenhouse on my uneven patio many years ago.
My neighbour (a retired builder of 60+ years) advised finding a mix of small stones/gravel to fill the gaps then mortar it all in.
The stones/gravel will not crush or crumble under the weight and the mortar will hold them in place.
It worked out very well

Uff

Sounds as though you've solved the leveling problem now @djlacerate.
Unless it's in a very wind free spot I'd find a way of anchoring it down, a mobile greenhouse can cause a lot of damage costing a lot of money and heartache. 

JennyJ

djlacerate said:

Thanks @JennyJ. If I lifted the low side with slates at each corner, and then packed in a stiff morter mix to fill the resulting gap along the entire length of the lefted base - along with the other small gaps around the base, do you think this would hold the weight of the greenhouse once I removed the slate?

I like the idea of hardwood but think it may deteriorate over time due to the abundance of rainwater we are blessed with in Sheffield! 

@Pete.8 's idea of using stones with mortar (or bits of slate like @Uff suggested, with mortar, not removing them) would be stronger.

djlacerate

Great advice everyone! I like @""Pete.8"  's idea of using gravel in the morter mix to strengthen it - I may use this in addition to the slate.

When it comes to finally bolting the thing down to the slabs, which needs to be done after the glazing apparently, will I be able to drill through the morter/gravel mix without undoing all of the pointing work? My worry would be that it may break apart...