Njug 4

[Woodcut33]

Hi

 

Can anyone tell my why NJUG 4 does not recommend using builders sand around roots when resurfacing?

 

Is it because of the possibility of contaminants (lime/salt) or because it has less pore space than sharp sand and would therefore defeat the object of creating an oxygenated layer beneath a compacted surface?

[sloth]

It can, I believe, contain salts toxic to roots

[Pedroski]

I doubt salts are the problem - builders sand is 'washed' these days (has been for many years), and any builder worth his salt will know that salt in a mortar mix reduces its strength. The problem is likely to be be more to do with the fact that it's not free draining (as you say, small pore space), whereas sharp sand helps drainage. Sharp sand also helps to loosen up clay type soil, while builders sand will create a solid lump when mixed with clay soil.

[sloth]

Good points, however I am pretty certain the presence of toxic salts in builders sand is mentioned in BS5837: 2005, can't recall if it is mentioned in the new document though...

[Mark Cattell]

Would a builder recommend builders sand when resurfacing? All the resurfacing works i have been involved in sharp sand was the only sand used as a base layer, Builders sand shifts and is prone to localised compaction so will not form a stable base, whereas sharp sand form a uniform stable base when compacted with a wacker plate. I also still think that the builders sand does wash out when wet, but not sure if this contains harmful salts that are detrimental to trees.

[Pedroski]

Just found some info on the Leicester gov web site Highways, transportation and development - Appendix F - Highway, Transportation And Development

 

You should take particular care when backfilling excavations within a tree protection zone. Tree roots are particularly affected when soil is compacted and they can also be damaged by the mechanical action of tamping down. Backfill material around exposed roots should consist of a fine granular material which provides a high proportion of air space. You should not use builders’ sand as it is toxic to tree roots. The material should be compacted using hand-tamping methods which maintain a degree of aeration and enable tree roots to survive.

 

I notice here that it mentions builders sand being toxic to tree roots - however I am convinced the problem is more due to lack of aeration and drainage, which will definitely be damaging, than it is to salt toxicity. I am now going to find out more wearing my scientist hat

[sloth]

I look forward to what you discover, do keep us informed please :thumbup:

[sloth]

Any advance on this?