Sorry I couldnt guess at the concrete costs since you seem to use a builder, you'd need to work out the volume needed and check how the supplied volume compared with the set volume. I am a diy'er and mixed my concrete in a borrowed mixer that I ended up buying. Personally I'd regard it as a fairly cheap material. I also laid my own blockwork.
2 years ago stone and sand where about £17 a ton here and I think std blue circle cement was about £5 a cwt, £100 a ton. Block was, I think, about 45p per 18x9x4 block. I suppose my concrete worked out about £20 a ton. Working on concrete weighs about 2.5 times water and water weighs 62.3lb per cubic ft I think that works out that my concrete cost about £1.4 per cubic ft
Between gravel infill in quite long pipe trenches and the concrete I think I used 7 ton of stone, most of which will have been for concrete, so a diy'er can make fairly large quantities of concrete
Re the cost of fibreglass verses the cost of G4 it may be worth getting actual quotes, my recollection is G4 is expensive.
Maintenance is an issue I have seen raised with pressurised filters.
Is your son old enough to mix concrete and lay block, sorry I dont know your gender. Also a pond is a long term thing so his wants should be less significant than yours as I would guess he will move out at some point.
Posted on Aug 26, 2006, 11:40 PM from IP address 84.65.75.138