I have an old garage with a thin slab and would like to build a wider (on one long side) garage.
What is the appropriate/economical way to do it? Is it possible to cast a new slab that "swallows" the old slab, and if so, how thick does it need to be poured over the old slab?
What is the appropriate/economical way to do it? Is it possible to cast a new slab that "swallows" the old slab, and if so, how thick does it need to be poured over the old slab?
I believe you will have problems if you cast the new slab partially over the old one. The ground under the new part of the slab will settle somewhat, causing the slab to crack at the joint between the new/old slab. This can be solved by reinforcing the slab so that it becomes self-supporting. That reinforcement would involve both top and bottom reinforcement and a relatively thick slab of about 200mm.
200mm is more than I want to raise the old part of the garage. I have asphalt outside and already have enough difficulty driving in anything other than jeeps without a ramp.
A small crack is not the end of the world.
To make it trickier: The old slab is uneven today and needs to be leveled, while the previous owner tried to smooth it with a thin layer that has cracked and now lies loosely on top.
Is there any way I can combine new/expansion of the slab and fix it so the old floor becomes even? It doesn't need to be perfect since it's just a hobby garage, but you want to try to get it as good as you can while you're at it.
A small crack is not the end of the world.
To make it trickier: The old slab is uneven today and needs to be leveled, while the previous owner tried to smooth it with a thin layer that has cracked and now lies loosely on top.
Is there any way I can combine new/expansion of the slab and fix it so the old floor becomes even? It doesn't need to be perfect since it's just a hobby garage, but you want to try to get it as good as you can while you're at it.
I've started to realize that the garage needs to be quite high to be good.
My existing slab is 10 cm thick and uninsulated. I have read that I should have 200 mm insulation in the slab, does that apply also to slab on slab or can I skimp on the part that isn't a "new" slab? If I want 200 mm insulation, how thick do I need to cast?
How do you do it step-by-step when casting slab on slab? Do I need to treat the old slab? Drill in reinforcement?
edit: Can moderator move thread to small houses, garages, sheds?
My existing slab is 10 cm thick and uninsulated. I have read that I should have 200 mm insulation in the slab, does that apply also to slab on slab or can I skimp on the part that isn't a "new" slab? If I want 200 mm insulation, how thick do I need to cast?
How do you do it step-by-step when casting slab on slab? Do I need to treat the old slab? Drill in reinforcement?
edit: Can moderator move thread to small houses, garages, sheds?
I have cast a garage in two slabs. They are edge to edge with a 10mm cellplast in between. Then I filled the last 20mm of the joint with self-leveling compound. After one winter, there was a hairline crack that's hardly visible.
The old rough slab you could also self-level, one downside is that self-leveling compound is expensive. Maybe you can find a cheap brand during a sale, k-rauta sometimes has some cheap brands. Self-leveling compound requires a minimum of 10-20mm.
Adhesion (you prime the concrete beforehand) is nothing to worry about, it's rock solid.
The old rough slab you could also self-level, one downside is that self-leveling compound is expensive. Maybe you can find a cheap brand during a sale, k-rauta sometimes has some cheap brands. Self-leveling compound requires a minimum of 10-20mm.
Adhesion (you prime the concrete beforehand) is nothing to worry about, it's rock solid.
Thank you very much for your response. The idea of using cellplast in between sounds like a great tip. I am now considering casting on 200mm insulation + 100mm concrete on top of the old slab and bringing the new part up to the same level.
If you're going to have underfloor heating, you "must" have insulation underneath. Of course, you don't have to, but you'll be ruined otherwise.fulingbusen said:
If you insulate a little between the slabs (maybe those 10mm Benny wrote about could be enough), you might be able to have underfloor heating, at least if you don't crank up the temperature too much and perhaps settle for an 18-degree warm floor.
An uninsulated slab is obviously colder, but also more humid. There's usually a certain cold, damp concrete smell with a cold, uninsulated slab.
Alright, then it's time to cast 200mm insulation + 100mm concrete (with water-borne heating pipes) on both the new section and over the existing ones.
Is there any risk that the old slab won't fare well being "encased"?
Is there any risk that the old slab won't fare well being "encased"?
Thanks for the input, was the old slab insulated previously or did you find that 100mm insulation/cell plastic was sufficient there?
No, it wasn't insulated before. It was the ceiling height that determined the amount of insulation, if I remember correctly. We raised the house with three layers of leka but couldn't raise it more without it looking odd.
However, it has worked well in every way so far. We have tiles throughout the basement on the casting so any moisture can breathe out.
However, it has worked well in every way so far. We have tiles throughout the basement on the casting so any moisture can breathe out.
Ok, thanks. Then maybe I'll also be satisfied with 100mm cellplast.