Re-exploration of lime in masonry construction and plasters for the building is a work in progress. Documentation of traditional techniques, in Western India, testing of materials over a period of time and use of I.S codes for lime construction guide our current work. A deeper understanding of such materials, their chemistry and practices is essential. We believe that sharing such knowledge will lead to a better awareness about the choices we make as professionals.
Section 1: Common terminology in lime plaster/ mortar. Pre-mix ingredients/ proportions/ general specifications & special notes
a) Lapti: Is molasses obtained from sugar factories, also called ‘rasi no gud’ in Gujarati. It should be fluid and dark brown in color. Prepare a mixture of 15 lit Rasi no Gud + 200 lit waters. To be stored in a 200 lit drum with a lid.
b) Chuna(lime): Kali chuna - non-hydrated non-hydraulic lime. Bagged or loose non-hydrated lime from Jodhpur/Khimsar/ Degana region of Rajasthan is the preferred source especially from non-mechanized small lime kilns.
c) Slaking: Mixing gradually, non- hydraulic lime with water to form a paste/ putty in a slaking tank/pond and allowed to settle. To be periodically mixed with a spade and must always be stored below 6 inches of water to prevent oxidation.
d) Chuna Lapti: A wash of ‘slaked lime + Rasi Gud/molasses diluted’ mix is prepared for use before the first plaster coat. The proportions in this case are 10 liters of diluted molasses and 1 tagara kali chuna. (slaked lime). Lime and lapti when mixed to form chuna lapti should turn to a bright yellowish / ochre colour. This wash gives the necessary bonding for the wall before the first rough coat is applied. Also fills small cavities and holes on surface of masonry for better bond with the first coat of lime.
e) Ghani: Container or volume of lime mortar mixer/grinder.
f) Methi (fenugreek): Dry seeds to be used.
g) Guggal (Commiphora muku): vendor: LVG Ambawadi Ahmedabad or other reliable source.
Process: *Boil Methi & Guggal in desired proportions, which varies for summer/winter use. Method of making methi & guggal mix solution:
*Summer use: 2 liters water+ 200gms methi + 100gms guggal, boil well, cool and keep aside.
*Winter use: 2 liters water+200gms methi + 200gms guggal, boil well, cool and keep aside.
Note: The solution may have a foul smell after a few days but can be stored and used as per proportions below. This mix is for use in plasters only. To use in lime plaster, mix 2-lit concentrated solution in 20-lit water and use 1 liter per ghani during mixing and preparation of plaster mix.
h) Sand: Coarse river sand.
Use of coarse sand- 1st / 2nd coat for plaster.
Fine sieved sand- 2mm final finish coat.
i) Surkhi: 1” to 2” sized brickbat (from well fired bricks) to be used in 4mm/6mm first coat, 3mm sieved- 2nd coat and finer in final finishing coat as needed.
j) Masonry unit: 230mm x 110mm x75mm stabilized lime surkhi brick – Kesarjan.
k) Khhuni: Edging or plaster cornering tool -use metal khhuni- ½” dia edge + rt angle or wooden handmade tool to desired radius.
l) Muster / Planer: 2’ long planer tool used by masons.
Section 2: Mortar / masonry work
a) Hot masonry mortar mix proportions in lime mixer/grinder and process, for lime surkhi brick masonry work
b) Mortar Mix Proportions
Lime: 6 parts
Sand: 8 parts
Surkhi: 7 parts: (made from brick bats crushed in grinder)
Lapti: 1 liter per ‘Ghani’ (Mortar mixer container as 1unit)
NO METHI GUGGAL MIX IN MASONRY MORTAR
c) Method: Grind the above in lime mortar mixer with adequate amount of water to facilitate hydration in the mixer ideally for 15 minutes or until correct batter like consistency is achieved and lime is well slaked. Coarse mortar is ideal for masonry work.
d) Mortar consistency test: It must be such that it forms a sticky lump. This must stick when slapped against a wall. (*Optional gauged mortar: 1 part 43 grade OPC + 9 parts prepared lime under special situations but with the consent of the structural engineers as needed.) This may be needed in extreme conditions of wind and rain for 230 mm masonry walls for faster setting and safety of masonry work.
e) Cube testing: 75mmx75mm Cube tests can be done to ensure that the strength achieved is correct. Mortar strength tests for 7/14/28 days and compare results as per I.S specification for structural approval.
Section 3: Starting masonry work
Step 1: Wet and soak bricks thoroughly prior to start of work. Spread mortar evenly across the brick. Allow excess mortar to press out of masonry unit. This excess mortar should be raked out with a trowel to create a good seat for the first coat of plaster. Vertical joints to be packed with mortar and checked each time. No voids shall be left between brick joints.
Step 2: Curing: The masonry wall is to be covered with a wet jute cloth immediately to prevent quick drying. Curing by spraying the jute cover 3 times a day in summer and twice a day in winter is important. Curing must be done until initial strength for at least seven days is achieved. During rains, the top of wall or plastered wall must be protected with a layer of temporary mortar or sheet of plastic.
Section 4: Starting Plasterwork: For exterior surfaces – Surface preparation
Step 1: A wash of ‘lime –Rasi Gud / molasses diluted’ mix is prepared for use before the first plaster coat. The proportions in this case are 10 liters of diluted molasses and 1 tagara kali chuna. (hydrated lime). Lime and lapti when mixed to form chuna lapti should turn to a bright yellowish / ochre colour. This wash gives the necessary bonding for the wall before the first rough coat is applied. The surface to be plastered should be thoroughly wet with water first and then with chuna lapti. Allow the surface to dry a little and plastering of first can begin.
Note: Exterior plaster thickness: Overall plaster thickness to be achieved shall be 35mm including the final jiki finish as under.
1st coat: 12 mm max total with 6mm per layer to be done in two stages as base foundation coat)
2nd coat: 10mm max
3rd coat: 8mm pre-final coat.
4th coat: 5 mm finish jiki coat by jiki finishing agency.
Section 5: Exterior plaster mix proportions for 1st coat- exterior plaster
Lime: 6 parts
Sand: 8 parts (coarse graded sand)
Surkhi: 7 parts: (made from 30 mm brick bats crushed in grinder)
Jute sutli: 50 gm or 1 fistful per ‘Ghani’ shredded
Lapti: 1.0 lit per ‘Ghani’
Methi & Guggal sol: 1.0 lit per ‘Ghani’
Mortar mix must be of good workable consistency and should be coarse and granular in the first coat for better adhesion with the wall.
Step 1: First coat (foundation coat of 12mm in two layers of 6mm each)
Throw plaster mix with trowel onto wet wall. Use wood planer (2’ wooden muster) to spread where needed and leave coarse. Ensure even thickness of 6mm (usual normal first coat application practice to be followed as in cement plasters) surface will appear coarse with spikes and undulations. Surface should be in level but not flattened. Allow to set. The second layer of 6mm plaster may be done on the earlier coat after a minimum of 4 days. Each coat must not be more than 6mm thickness at any time.
Step 2: Curing
The setting time is recommended to be 24 hours after which curing should begin (water to be sprayed thrice a day in summer Morning/noon/evening), twice in winter(morning/evening) over a jute cover on plaster, not directly). Use a small fine shower nozzle. The curing should be carried out for a minimum period of 3 days / or until adequate strength is seen in the surface.
** (Simple test for strength- Try to score lines onto the surface with the edge of a trowel. The surface must be hard. This must be done before the second coat is started)
Step 3: First coat - layer 2 of foundation coat of 6mm
The application of the second coat should not be earlier than 5 days after the first coat is applied. Same procedure as in first coat to be followed including curing.
Step 4: Second coat - 10mm maximum – follow mix composition as before.
Plaster mix shall be a little finer than the first coat. Mix proportions same as first coat except for the exclusion of jute fiber. Line & level to be checked and finalized in this coat including rounding of edges as directed using a corner tool(khunni). Make small diagonal strokes/ lines or indentations across the surface using a wood planer to roughen surface lightly to prepare base for the next coat.
Step 5: Third coat - 8mm maximum – follow mix composition as before. Plaster mix shall be a little finer in consistency than the first coat. This is the final leveling coat. Line & level to be checked and finalized in this coat including rounding of edges as directed using a corner tool (khunni). Total thickness achieved shall be 30 mm to 32mm max. Make small diagonal strokes/ lines or indentations across the surface using a wood planer to roughen surface lightly to prepare base for the next coat.
Step 6: Curing : The setting time is recommended to be 24 hours after which curing should begin (water to be sprayed thrice a day in summer, twice in winter over a jute cover on plaster, not directly) Last curing of day to be done in the evening.
The curing should be carried out for a minimum period of 4 days. The application of the final coat should not be earlier than 4 days after the first coat is applied. The final coat can be done even after a month, but not without proper wetting of the wall surface.
Step 7: 4thcoat / final finish coat- 4 mm to 5mm Jiki dolomite finish.
Exterior plaster thickness: 6mm+6mm+10mm+8mm+5mm(jiki) = 35mm max.
Section 6: Plaster work for interior surfaces
Process: All procedures remain identical to the exterior plaster process.
Section 7: Finishing work for interior/exterior surfaces
Interior surface: Jikki or dolomite finish forms the final coat for the internal walls with lime plaster. No further painting or finishing is needed.
Exterior Surface: Lime finish plaster with natural pigments.
