Hello,
I couldn’t find a section for civil engineering work, so I hope this is the right place.
We plan to install a garage in October, which requires pouring a concrete slab and building a foundation with excavation to a depth of 0.5m (20 inches) and placing and compacting gravel to 0.3m (12 inches). The area is 7 x 9m (23 x 30 feet). In addition, all the soil from the house excavation needs to be removed.
Today, a local civil contractor visited. The cost per truckload (10 tons) is 180 euros. The total excavation cost is about 150 euros. Bringing in lava rock and compacting it costs 35 euros per m³ (cubic meter). All prices are exclusive of VAT.
The transport costs seem reasonable. However, I find the price of 35 euros for placing the lava rock quite high.
Is there a general rule of thumb for this? We asked for a fixed price, but that wasn’t possible. He can’t estimate the amount of soil currently on our field. But shouldn’t he be the expert? I obviously can’t do this, but I simply calculated the volume of the slab and multiplied it by a loosening factor of 1.3. Can’t he do that?
So:
Is 35 euros for lava rock including compaction reasonable?
Is it normal that you can’t demand a fixed price? Do civil contractors usually not agree to that?
Thanks and best regards,
Stephan
I couldn’t find a section for civil engineering work, so I hope this is the right place.
We plan to install a garage in October, which requires pouring a concrete slab and building a foundation with excavation to a depth of 0.5m (20 inches) and placing and compacting gravel to 0.3m (12 inches). The area is 7 x 9m (23 x 30 feet). In addition, all the soil from the house excavation needs to be removed.
Today, a local civil contractor visited. The cost per truckload (10 tons) is 180 euros. The total excavation cost is about 150 euros. Bringing in lava rock and compacting it costs 35 euros per m³ (cubic meter). All prices are exclusive of VAT.
The transport costs seem reasonable. However, I find the price of 35 euros for placing the lava rock quite high.
Is there a general rule of thumb for this? We asked for a fixed price, but that wasn’t possible. He can’t estimate the amount of soil currently on our field. But shouldn’t he be the expert? I obviously can’t do this, but I simply calculated the volume of the slab and multiplied it by a loosening factor of 1.3. Can’t he do that?
So:
Is 35 euros for lava rock including compaction reasonable?
Is it normal that you can’t demand a fixed price? Do civil contractors usually not agree to that?
Thanks and best regards,
Stephan
A
AallRounder1 Oct 2013 06:52Hello,
for soil replacement, as with all other underground materials, it is common to use whatever is locally available—that is, what local suppliers have in stock. To the best of my knowledge, lava gravel is generally approved for foundation sub-bases, but the material should be quality-controlled (which ensures the correct grain size distribution) and the grading should be appropriate. For creating a frost-protected sub-base, a grain size of 0/32 mm (0/1.25 inches) is usually used and recommended—what does your groundworker plan to use? It would also be useful to ask about the water retention capacity of the "lava." After all, you don’t want to create an underground pond, but rather allow water to drain cleanly and quickly into deeper layers, meaning it should be solid, dense rock—not loose granules.
Frost protection is also key for determining the depth of soil replacement: 50 cm (20 inches) seems too shallow to me because, despite severe climate warming, the so-called frost penetration depth in Germany still ranges between 60 cm (24 inches) in the north and 120 cm (47 inches). If you’re going to the effort of soil replacement, sufficient depth would be advisable—unless there is already a frost-resistant layer at 50 cm depth at your site (what does your soil report say?).
If you want to reduce costs, you could use recycled concrete with a grain size of 0/32 mm (0/1.25 inches) instead of natural material. This is generally cheaper material-wise than natural stone. Your price apparently includes labor, so material costs are only a part of the total. You might be able to reduce this part to around 5–10 € per ton (approximate cost for recycled concrete here, including taxes). Consider asking for an alternative quote.
Regards,
AallRounder
for soil replacement, as with all other underground materials, it is common to use whatever is locally available—that is, what local suppliers have in stock. To the best of my knowledge, lava gravel is generally approved for foundation sub-bases, but the material should be quality-controlled (which ensures the correct grain size distribution) and the grading should be appropriate. For creating a frost-protected sub-base, a grain size of 0/32 mm (0/1.25 inches) is usually used and recommended—what does your groundworker plan to use? It would also be useful to ask about the water retention capacity of the "lava." After all, you don’t want to create an underground pond, but rather allow water to drain cleanly and quickly into deeper layers, meaning it should be solid, dense rock—not loose granules.
Frost protection is also key for determining the depth of soil replacement: 50 cm (20 inches) seems too shallow to me because, despite severe climate warming, the so-called frost penetration depth in Germany still ranges between 60 cm (24 inches) in the north and 120 cm (47 inches). If you’re going to the effort of soil replacement, sufficient depth would be advisable—unless there is already a frost-resistant layer at 50 cm depth at your site (what does your soil report say?).
If you want to reduce costs, you could use recycled concrete with a grain size of 0/32 mm (0/1.25 inches) instead of natural material. This is generally cheaper material-wise than natural stone. Your price apparently includes labor, so material costs are only a part of the total. You might be able to reduce this part to around 5–10 € per ton (approximate cost for recycled concrete here, including taxes). Consider asking for an alternative quote.
Regards,
AallRounder
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