We've bought a new property which has a 10m x 7.5m barn; the barn was originally a cowshed and milking parlour and has a concrete floor which is very uneven, has drainage channels and large holes in it. We will be using the barn as a garage and workshop; it needs the floor relaying and I will be incorporating insulation in the slab as the temperatures get down to -40C in winter! The slab needs breaking up and digging out and a new slab pouring; we have had quotes from local construction firms and the quotes were astronomical, so we plan to do this ourselves.

Presumably an excavator with a breaker attachment is the way to go, can anyone suggest how long we should hire it for (I've hired diggers, but never used a breaker attachment before)?

Do you really mean -40°C..??!!

 

75sqm of concrete - which is probably 150mm or more thick - will take a lot of work. You’ll need a 5 tonner with pecker on it and it will take 2-3 days of work to break that lot up and then the same to clear it. You’ve then got a lot of concrete to get rid of….

 

Your other issue may be that there is reinforcing mesh in the slab. That will be a problem for both breaking up and removing.
 

If it is a barn - and you have the height - then I wouldn’t be removing the current deck. I would be looking to fill the holes, edge with a row of blocks and then overlay with 100mm of insulation and then go with mesh on chairs and top with concrete.
 

You can easily build up a ramp to take the 200mm or so of the new slab and tbh it will be much cheaper than taking it out and the difference will be negligible. I would say though unless you’re going to sort walls and the roof then insulation in the floor is going to be an expensive folly !!

Yes, -40C (this is in Northern Finland); we don't believe there's any reinforcement in the slab. Pouring on top of the existing slab sounds attractive, I need to check that the current garage doors height will still be sufficient if we raise the floor level; that may also limit the machine I hire, a 5 tonner is quite high.

I suspect that the building contractors are covering their behinds by quoting for a completely new slab so they can be 100% certain of no future issues; I am not worried if a few cracks appear somewhere down the road!

Yes, we are (heavily) insulating the barn and installing heating, after all my new man-cave needs to be cosy!

We pulled up around 500m² of agricultural slab in just over a week with a 5T excavator, pecker and a 1T dumper.  We were slowed down by a reinforced perimeter ring-beam that had 30 - 40mm rebar in it and had to cut the rebar into manageable lengths.

 

 

Ours was also a cowshed, so had a significant rake on the slab for slurry drainage. We'd have lost a lot of height to have mass infilled over the top and then insulated.

 

The 5T machine broke it up quickly. I did other channels through hard-standing areas with a 1T, and that was hard going.

The garage doors are 1800mm high, adding 200mm to the slab may cause us a problem with clearance; it's probably a toss up whether we increase the slab height by 200mm and raise the aperture for the door by the same amount, or go with plan 1 and break up the original slab and re-pour it.