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Mixing
A conventional cement mixer can be used, although for larger
projects a roller-pan or paddle-mixer is preferable. Lime
mortars mixed in drum mixers are prone to balling. However, the
following mixing procedure can reduce this problem. It is vital
to ensure that when measuring materials this is done by volume.
A gauging box or bucket will be necessary for this task.
Measuring by shovel is not acceptable since quantities will be
inconsistent:
1 Start with an empty mixer.
2 Add 1 part sand
3 Followed by 1 part lime
4 Followed by 2 parts sand
5 Mix dry for at least 5 minutes
6 After 5 minutes slowly add water until the desired
consistency is reached, it is very important not to drown the
mix by adding too much water.
7 Once the desired consistency is reached mix for a further
20 minutes
(The above example is based on a mix ratio of 1:3).
The mix, to begin with, will appear dry but as mixing time
increases the mortar will become much ‘fattier’. If too much
water is added the risk of shrinkage will increase and the final
strength reduced. Do not use any plasticisers.
Water Content
The addition of water should be considered carefully, as it
will directly affect the ultimate strength and durability of a
mortar. The more water introduced into the mortar mix, the
weaker will be the final result. However too little water will
prevent the chemical processes taking place and weaken the
material. Generally, water should be added sparingly, until a
useable consistency is achieved.
The masonry background may also affect mortar strength. Dry
backgrounds can quickly ‘suck’ moisture from newly applied
mortar. This should be controlled by dampening down the
background prior to mortar application.
Storage of Lime & Aggregate
Roundtower Natural Hydraulic Limes are supplied in
water-resistant paper bags. If the bags are allowed to get wet
they may be irreversibly damaged. Also, once opened the exposure
to air will start to weaken the hydraulic set. As a result any
opened part bags left at the end of the day should be carefully
folded over at the top and put into a dry store. In this state
the lime will remain useable for a further 2 or 3 days.
Thereafter it should be discarded. For larger orders Roundtower
Natural Hydraulic Limes are supplied in 1575kg (63 x 25kg bags)
plastic wrapped pallets.
Aggregate should also be covered since if left exposed fines
can be washed out and the material as a whole can gradually
separate.
[see health and
safety]
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The Building Lime Company | Tel: 01980 611950 | Fax: 0845 658
7788 |