OT: Some concrete leads

[whiskychaser]

Have bought a new greenhouse for my lady. And before you ask, yes she did want one!:) Of course it has to be constructed on level ground. The site is concrete and slopes away from the property and to the right with odd lumps and bumps. Digging out the concrete isnt an option. I thought of putting timber batons on the ground but I dont fancy planing 32ft of timber into 8ft 'wedges'. So I'm looking for an easy way to make an uneven, sloping surface flat without touching whats there already. Anyone help?

[Ross]

Use "sleepers" of varying thickness parallel to the building. Lay your flooring across them.
If there is the slightest potential for water I'd keep a little pitch away from the structure.

[pingu]

No need to plane the wood - as long as it's high enough you can just lay the wood on what's already there (if it's really bumpy/uneven then maybe use expandable polyurethane foam to fill the gaps). So if you site slopes 6" and you want a minimum thickness of 6" (i.e. 6" deep concrete at one end, 12 " at the other end) then you just need 12" wide plywood laid on its side.

[Phatty5BMW]

What do you plan on growing in that GREENhouse eh? :P

[Ferret]

I wasnt really expecting anything so constructive:)
I like the idea of sleepers Ross but the ground really isnt even. Its a bit of an exaggeration but it would be a bit like having a barrel on its side and trying to balance a plank on top
Pingu I like the idea. But if I use a straight piece of 6" planking wont I just end up with a 6" deep bed of concrete on a slope? The tops of the planks need to be horizontal so I can tamp it down - and end up with a horitontal surface. But the foam idea to fill the gaps is great. Not sure it would hold the concrete back though?
Phatty5BMW, you will not believe this but somebody smashed the old greenhouse. They stole 3 tomato plants and a bag of compost. My guess is they thought what you may be thinking.
Thanks for the replies!!:)

Whynot get some plyboard up to the edges of the 'crete, create a perfect vertical and fill with some fresh concrete to level it off?

Sorta |/\| and fill in the gaps?

[whiskychaser]

I wasnt really expecting anything so constructive:)
I like the idea of sleepers Ross but the ground really isnt even. Its a bit of an exaggeration but it would be a bit like having a barrel on its side and trying to balance a plank on top
Pingu I like the idea. But if I use a straight piece of 6" planking wont I just end up with a 6" deep bed of concrete on a slope? The tops of the planks need to be horizontal so I can tamp it down - and end up with a horitontal surface. But the foam idea to fill the gaps is great. Not sure it would hold the concrete back though?
Phatty5BMW, you will not believe this but somebody smashed the old greenhouse. They stole 3 tomato plants and a bag of compost. My guess is they thought what you may be thinking.
Thanks for the replies!!:)

[Paul in NZ]

why dont you get some say 100x100 or 100 x 75 to act as bearers and cut wedges to pack them up level say every 900 mm.You can have a few of those and lay some sort of floor on them,or put some floor structure(say joists and ply on top of them

[whiskychaser]

Whynot get some plyboard up to the edges of the 'crete, create a perfect vertical and fill with some fresh concrete to level it off?

Sorta |/\| and fill in the gaps?
I dont have a concrete base as such at the moment-just a very wonky surface. The pro's would probably dig an 8ft square hole and start afresh but thats not an option for me:(

[AngryPopTart]

Can't you just place planks on all four sides, like a mold or form, and seal them at the bottom so there's no leaks, then fill the inside with fresh concrete until it's flat all the way across?

[Ross]

If the surface is that bad you have a couple of options. Scribe the sleepers to match the concrete under(Who poured this mess?) or form around the existing pad and pour a level layer on top.
If'n it were me I'd level the concrete.

[whiskychaser]

Can't you just place planks on all four sides, like a mold or form, and seal them at the bottom so there's no leaks, then fill the inside with fresh concrete until it's flat all the way across?
That would be the idea. The big problem is how you seal the bottom to stop the new concrete running out:)

[whiskychaser]

If the surface is that bad you have a couple of options. Scribe the sleepers to match the concrete under(Who poured this mess?) or form around the existing pad and pour a level layer on top.
If'n it were me I'd level the concrete.
Thanks Ross but there isnt an existing pad to form round. The mess was poured many years ago and foul water drains run shallow underneath. I've done them before but risking hitting one isnt something I need. So we come back to scribing sleepers as you suggest -or planing 32ft of timber into crazy wedges. Which is where I came in. To be honest I'd normally just get on with it but the glass wont fit in the frames if I get this wrong. All this cos she wants to grow her own vegetables:)

[Ross]

Did someone just pour the concret onto the ground?
If you are going to build a glass structure you will need a stable surface.

[AngryPopTart]

Then just build a form around the concrete, even if it's larger than the existing slab, with the boards in the ground and pour a completely new slab to cover over the old one.

[Tiger]

From reading all the replies you wrote, seems like your slope is quite alot over long span... That's such a large greenhouse. A couple of options...

1. Hire a concrete leveler specialist... What they will do is come to your site... drill a couple of holes and pump in grout or new type is polyurethane to lift up your concrete to almost level. Most likely grout in your case as you have to raise quite a bit. This is costly for big concrete as you describe. After this is done, you can pressure wash the concrete and lay a thin layer of concrete resurfacer to level out the rest of concrete.

2. Create a level form all around your existing concrete base, support it well so it doesn't blow out. Pressure wash the concrete and then put a layer of concrete conditioner so it will bond to new concrete well... and hire a truck to deliver and pump concrete into the form.

3. Pressure wash your concrete... Lay the perimeter where your new greenhouse will sit on... create a 8" perimeter level form all around it. Use concrete conditioner... then pour concrete into the form. If the bumpy surface bother you for your greenhouse floor, surface concrete leveler or sand and lots of patio blocks.

4. The right way is as you know... jack hammer all concrete out and relevel the ground, and form... but this is practically #2.

If the issue is you don't know how to level that concrete form or concrete over such a large span, use water level or transit... water level is much easier to use.

[Tiger]

Another thought... I think the concrete was level for your original greenhouse... the land settled as rain wash away soil so that's why you got a sloping concrete. To prevent this from happening again, you have to do the retaining wall around the slope, or your greenhouse will do the same thing over long time.

[pingu]

No, the concrete - if it's nice and runny (but not so runny that it runs past the foam) - should find its own level.

If you want a really nice job then you could first make a platform of concrete by relying on the concrete to find its level. Once it has set, take off the planking and attach fresh 4" high planking (or whatever, depending on high thick you want the second concrete layer to be) to the side of the concrete using Rawplugs etc.

Then pour a second layer of concrete over the first layer and tamp the second layer down, using the new planking as a guide, to get a nice flat surface. Job done.

[Tiger]

Similar to what I said... my way is safer and more true level. Remember... glass will crack under stress of unlevel foundation.

[leicesterboy15]

Have you got a picture of the location? Might be a bit easier to visualise then.

From what you describe I think we had something similar with my workshop shed, we built a brick border and concreted them in, then filled the hole with hardcore (well, stuff that was left from removing the fireplaces) and sand. We then leveled it off and flagged over it leaving the old concrete hidden and a nice level square base. If your greenhouse is normal shed size, you don't even need to flag it, you could run beams off the brick base under the greenhouse supports, that may be quicker.

But I would have thought the easiest way would be what has been suggested and make a wood border and fill it with concrete. As long as the consistency is correct and the wood is attached so it can take the weight it doesn't need to be completely tight, it won't run out of all the gaps unless they're large! If they do just run around it scooping up the excess until it starts to dry or hammer off the excess once its dry.

[Ross]

"No, the concrete - if it's nice and runny (but not so runny that it runs past the foam) - should find its own level."

It's this sort of method that likely got him the surface he has.
Either form it correctly, pour on top and finish, assuming it's clean and rough enough to stay put. Or sleepers, either scribed or shimmed as Paul says.
A glass(any) structure on a Mickey Mouse foundation is just asking for it.
If it is attatched to the existing structure it should also have some foundation below the frost line to prvent the addition from moving independantly of the house.
If you put it on a pad it shouldn't be attatched to the house as it will move around more than the house.

[whiskychaser]

Thanks for the replies and suggestions! I tried to take some pics but they dont show the levels clearly so there is no point posting them. Just to clear a couple of points though: The land that belongs to the house isnt very big and its all concreted over. The old greenhouse didnt sit on its own pad, it sat on a 'flat bit' of that. The new one is much bigger so wont fit on it.
My latest idea is to put down a bead of cement and lay the frame into it. I'd then make sure the frame is level and let it set. I could then fill the centre at one go and be able to tamp down and level it using a plank across the tops of the frame sides. Anyone want to shoot me down in flames?

[pingu]

Well the concrete that they were using on the Burj Dubai (or whatever it's called - the tallest building in the world) had that consistency so it can't be all bad!

[Ross]

I think what you are describing is forming atop the old pad which has been suggested. Someone else made the suggestion of sand and blocks for a floor which I like.

[whiskychaser]

I think what you are describing is forming atop the old pad which has been suggested. Someone else made the suggestion of sand and blocks for a floor which I like.
Because of how the threads get mixed up I'm not entirely sure what was said when. What I DO know is I got a tranny problem on the way home. My younger son tells me he's got fuel dripping from underneath his car. Am I going to be busy this weekend or what? :(

[Paul in NZ]

I am not a builder but have been involved in the coonstruction industry since my forst job..you have two options...both similar
1) form a timber floor using reasonably large timber beams packed of the concrete to create a level base...start from there...or as someone else suggested maybe a brick or block "ring foundation" and a timber floor on that..
2)same thing using concrete as just a ring(perimeter) foundation in concrete and continue on with timber or go over the top and fill the whole thing with concrete,but if the substrate concrete is thin the weight of the new concrete slab may be too much...I am pretty sure i would go with the timber option.If you use proper treatred timber and fix down well(avoiding drains) you should be sweet,and even be able to remove it easily if required.I can send you some sketches of what i mean if you want.

[632 Regal]

they have concrete grinders you can rent to take the bumpies out then as others suggested if you dont want it sliding off the hill into the vally below shim the ****er... Idonno what Im talking about but did se the concrete sanders, usually rented by amateurs that really fubar up a job.

[whiskychaser]

I am not a builder but have been involved in the coonstruction industry since my forst job..you have two options...both similar
1) form a timber floor using reasonably large timber beams packed of the concrete to create a level base...start from there...or as someone else suggested maybe a brick or block "ring foundation" and a timber floor on that..
2)same thing using concrete as just a ring(perimeter) foundation in concrete and continue on with timber or go over the top and fill the whole thing with concrete,but if the substrate concrete is thin the weight of the new concrete slab may be too much...I am pretty sure i would go with the timber option.If you use proper treatred timber and fix down well(avoiding drains) you should be sweet,and even be able to remove it easily if required.I can send you some sketches of what i mean if you want.
Thanks Paul. I was just on the way out of the door to get a pressure washer when I read this. I had more or less decided to lay a new slab on top of the existing surface. But I had never thought about the existing concrete not being strong enough to take the weight. If that went it could take out the drains underneath too:( And I like the idea of it being more portable. Be grateful if you could pm me any sketches:)