On several posts here the responses when people have queried what stone to use in soakaways etc., has been to use Type B Filter material .. but NOT Limestone.
Why? all my local suppliers only offer limestone, and when I mentioned I can't use this they counter with .. 40mm clean limestone is what is used, and they supply it for soakaways and drainage all the time.
As my job is imminent I called Building Regs, and they also advised that there is no problem with Limestone, and they would advise 30-40mm clean stone rather.
The job is a 1.5m wall with a gap behind it of 300mm .. I intend putting in pipe bedding layer to level off, a 110mm perforated flexy french drain (60m of it) and surround that with drainage material - to a depth of 300 - 400mm, all this wrapped in Terram.
On top of this will be about 800mm of sub soil, and on top of that about 300 of top soil.
I will leave the ends of the pipe open, water egress is expected to be minimal but this will keep pressure off the wall.
Stone for drainage - Why 'not' limestone
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Rick
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Rick Hughes[br]UK SelfBuild: http://uk.groups.yahoo.com/group/UK_Selfbuild/
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Rick
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OK I have read that ... after trying all stone suppliers and quarries in may area, they all advise that Limestone (40mm clean) is what is used for land drains, soak aways etc.Stuarty wrote:Read the 4th paragraph here
Even called my local building Control dept. and they sayu that Limestone is perfectly OK, they have no problems or restrictions when used for drains that are not intended to be permanently wet.
They did add that if the drain is expected to be handling hundreds of gallons of water a day then there is a remote possibility of leeching, but no problem other than that.
Looks like I don't have an option as all the quarries are quoting in region of £11.50 /tonne delivered (Limestone) the only way I could get anything else is bulk bag and that is well over double the price.
Be interested in Limestone is that much of a problem.
Rick Hughes[br]UK SelfBuild: http://uk.groups.yahoo.com/group/UK_Selfbuild/
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Rick
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The local Building Control dept. were even more helpful, one of their inspectors called out this morning (had an inspection at another build on site) ... he confirmed that in the authority area that Limestone is used for all pipe bedding, land drains, soakaways .... I showed him the section referred to above, and he agreed that this is an issue for permananetly wet stone .. i.e river banks etc. but in all normal house/commercial building this has no problems ... he added that with respect to calcium carbonate precipitation, blockage of 40mm by this will not happen in my life time or that of my kids, and is more akin to the time it takes to form stalagmites.Rick wrote:Stuarty wrote:Read the 4th paragraph here
Even called my local building Control dept. and they sayu that Limestone is perfectly OK, they have no problems or restrictions when used for drains that are not intended to be permanently wet.
So looks like 40mm Limestone is the way forward for me. (at least on cost and geographic area)
Rick Hughes[br]UK SelfBuild: http://uk.groups.yahoo.com/group/UK_Selfbuild/
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danensis
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If I recall my chemistry correctly rain passing through carbon dioxide in the atmosphere becomes carbonic acid, which will dissolve the limestone. As CO2 levels increase and acid rain gets worse, the rate of dissolving will increase. You soakaway will end up as calcium hydroxide, which will block the outflow.
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Tony McC
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Giving the nod to "limestone" for use with drainage projects is fraught with problems because there is so much variation in the limestones we have available in these islands. The hard, dark Kilkenny bluestone seems a million miles from the soft, oolitic chalks of Southern England, but technically, they are both limestone.
In many parts of N. England, in Scotland, and in much of Ireland, limestone is not used for drainage projects because we have better materials readily available. This is not always the case, and I know that a hard magnesian limestone gravel is used in parts of Derbyshire and over in Teeside.
For my part, I've seen at first hand how limestone can degrade, and within my own lifetime. I've seen land drains installed in the 1970s that are blocked to buggery by degraded lime. Thankfully, my geology background helped me identify just why such a high degree of degradation had occurred in such a relatively short period, and I have to admit it was a reasonably exceptional situation, but the point remains: limestone degrades, and if there is an inert alternative available, then that would be my first choice.
My preferences and my advice is based on personal experience and "best practice". Many BCOs in NW England will not permit limestone to be used as a pipe bedding, and most drainage engineers would never recommend limestone as a land drain material.
The world won't come to an end if someone ignores this advice, especially those unfortunate enough to live in the more petrologically challenged parts of the islands, but my policy remains: I'll never recommend nor advocate the use of limestone for any drainage project.
In many parts of N. England, in Scotland, and in much of Ireland, limestone is not used for drainage projects because we have better materials readily available. This is not always the case, and I know that a hard magnesian limestone gravel is used in parts of Derbyshire and over in Teeside.
For my part, I've seen at first hand how limestone can degrade, and within my own lifetime. I've seen land drains installed in the 1970s that are blocked to buggery by degraded lime. Thankfully, my geology background helped me identify just why such a high degree of degradation had occurred in such a relatively short period, and I have to admit it was a reasonably exceptional situation, but the point remains: limestone degrades, and if there is an inert alternative available, then that would be my first choice.
My preferences and my advice is based on personal experience and "best practice". Many BCOs in NW England will not permit limestone to be used as a pipe bedding, and most drainage engineers would never recommend limestone as a land drain material.
The world won't come to an end if someone ignores this advice, especially those unfortunate enough to live in the more petrologically challenged parts of the islands, but my policy remains: I'll never recommend nor advocate the use of limestone for any drainage project.
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