I feel knackered; Wren is excited about taking things she's learned today and applying them to her work in Mali.
Here are the notes I took over the course of the day -- should any of you need some tips for your plastering projects ;)
GENERAL COMMENTS --
LIME
- lime plaster in bathroom in Japan, and lime wash in kitchens every year in UK -- lime has anti-bacterial quality. Is also caustic, so don't put your hands in it (use gloves and goggles). French sell hydrated lime, like putty - burns on contact.
- Use 'float' to spread lime plaster. Nice to have one straight edge and one rounded edge. Apply lime by scooping with trowel (flexible, if follow bumps of bale, or rigid trowel if want flatter look) off of hawk / hod (board with handle underneath). Want good base coat and second coat, timing very important.
- Scots use 'hurling' technique to throw lime slip onto walls and ceiling. Mexicans use special trowel with bent end, to slap lime on, then spread with float-like tool (heavier than UK float).
PLASTER
- grit size varies by thickness of plaster -- fine grain (eg ratio of 2:1) for thin, coarser for thicker wall...question of compressing correctly, otherwise cracks...test it and see shrinkage, then add more sand, or fiber, or water...nobody has the same clay...
- slip first (before base coat): dirt/soil from garden/earth (used as synonyms -- combo of clay and sand) sifted with 1/4 " + water...china or kalin clay is smooth and creamy, brown is chunkier
- add in straw and slap on
- Base coat of earth or lime plaster: use 1/2 inch sifter, and put 1/2 inch layer on wall...S uses clay and straw only, build it up quick (some ppl add sand); add design at this phase, coz if add later will break off
- second coat: 1 inch
- finish coat: fine mix using marble dust or fine silica (eg 90 -- higher number is finer)...if sift very fine, don't need to add pigment...
- sand: here, use 'washed plaster sand', is a clean sand...otherwise has clay and silt in it, so would have to adjust your ratios...Silica Sands are very clean (sold in pottery stores or swimming pool stores), good coz sharp edged and hence compress better
- pigment: mix sand and clay and add a bit of pigment (cheaper); contractors buy clay paint off the shelf and mix with water (but expensive)
THE MIXES WE WORKED WITH --
MIX 1: base coat
- ratio 1 clay : 3 sand -- for base plaster coat (just rough ratio)
- about 1/4 "
- first wet the wall (use detergent bottle if need to be careful indoors)
- scoop rectangle of mix on hawk, then take from back, and flip up (like flipping an omelet almost), and spread in wave motion on wall. Put hawk against wall to catch scraps. Spread across horizontal after, first with smaller then larger trowel, even float. Cover panel's worth of wall. press stick across in X shape to check if level.
MIX 2: plaster, works for exterior and interior both, about 1/4"
Recipe:
- 2 1/2 Kingston clay
- 1 1/4 sand
- 1 1/2 water
- 2 straw (1/2" sifted)...md by hammer mill, can buy good choppers now for USD 150
- always put water in first, put 1 for now (coz sand is wet...harder to add dry to wet than to add water later)
- (can mix dry goods in separate tub)
- add clay and let it soak up water thru capillary action (rather than actively mixing)...go have a cigarette...(See it turn a darker brown)
- put sand on top of that, let stand
- mix together -- is like chocolate cake mix
- add straw (the more straw, the less cracking...cracking comes from wet stuff drying, so if mix dry to start with, risk less cracking -- tho is harder to mix)
- ratio with too much sand looks nice at first coz is hard, but when starts to deteriorate is like little rocks have fallen out, and water gets in, doesn't weather well...straw/fiber is better, gets soft and melts together with clay...if leave it too long starts to ferment and smells bad but is good mix
- take flattish handful and smush against wall, spread it on with trowel or float, use barber u-shape motion to get snub corners, finesse corners with piece of plastic in smile-shape (from yogurt bucket, or cd even use saran wrap)
LUNCH
MIX 3 - lime clay for prep work for lime plaster
- lime plaster: ratio of 1 lime to 3 (clean) sand (washed sand, or silica)...think about how thick you're putting it on...fine mix for thin layer, coarser mix for thicker layer...have to polish it at the right time, all in the timing. Lime plaster likes to hang onto smthg really rough, so...
- lime clay: add 10% of lime plaster or to pH 12.4 (hydrated/slaked S lime, mix to consistency of sour cream, then add 2" water to top and let it age for 3 months, the longer the better...tho S has polished overnight slaked lime) lime to MIX 2 (add a bit of water too, so easier to spread)...lime makes clay mix really heavy and sticky
- once applied, scratch it -- then have mechanical as well as chemical attachment.
- for color: if mix with lime plaster, get pastels coz mixing with white; for strong colors, mix pigment with lime water and 'paint' it on wall before it dries, bonds to the plaster and have vivid color.
- to polish: base coat must be flat, lime plaster must be very smooth, timing right
- always keep white vinegar handy in case you get lime on you
MIX 4 - GLUE for natural clay paint ALIZ or ALIS (easy and fun)
- glue + clay + sand (or chalk powder, marble dust) + fiber (fine straw, hemp, paper, maybe) + mica (maybe)
- ratio 1 flour: 4 (5 or 6) water...make sure no dry flour lumps by passing thru sieve... then dilute it by 100% (ie add mix to another 4 HOT water)...mix to consistency of gravy...want it to cook slowly else bottom burns...keep stirring...
- then add sand, clay...and fiber...and mica...(to taste)
- dilute again by 100% -- 1 of glue to 1 of water
- pigments: iron oxide, goldenrod, or colors from pottery store...or earth or kalin sifted really fine (eg window screen doubled up twice....use glasses and face mask if finer than 40, known to cause cancer...)
- 4" wide brushes good,
- SIDEBAR: to sand-paint or sand-plaster on drywall: use 'sand paint' as primer - paint on coat of glue, then dilute 1C glue w 1C water and add to some sand (2-3C) till consistency of mushy sandpit and apply to board with trowel...let it dry completely...then next layer goes on very thin
- SIDEBAR on plastering around window. Plaster tends to shrink back, and you see gap tween wall and wood. Sol'n is to bevel future gap w 1:4 sand:clay mix over base coat (no more than 1 1/2" wide), taper down so thick edge is against wood and tapers to thin edge against wall.
- old Japanese method was to use fiber mesh (likw burlap), diminished shrinkage, would have thin base layer next to window -- the thinner, the less shrinkage
- for other joins tween diff materials: soak burlap in slip and leave to dry well
MIX 5 - lime plaster, ratio 1 lime:3 washed sand (watch your skin when scooping lime!)...if too dry, can add a little water from lime bucket
- want lime plaster to dry slowly...so UK good, coz damp...in SW, mist constantly while plastering...or add prickly pear coz adds sliminess (slows drying)
- S typically adds very fine fibers (cat tail, hemp fiber, cement fiber)...to hold plaster together, prevent cracking...
- now plaster the wall with it
- smooth over with stiff trowel (smoothness is just cream coming to surface, not compression), then use wooden float (looks like it roughs it up) and compress it, then go ober with flexible metal trowel to smooth it again.
- can use sponge to remove cream and reveal texture
BACK TO BASE COAT
- smooth with trowel
- fill holes with slip using 4" brush
- go over again with trowel
- go over with damp sponge -- takes dirt film off, shows pretty straw
SIDEBAR ON FLOORS
- ratio 1 clay to 4 sand (quite coarse)
- seal with linseed oil (heat in double boiler OUTSIDE coz of fumes)...S usually does 2 coats w 4" brush
ALIZ continued:
BASE COAT
- dilute (coz thickened) by ratio 1 glue: 1 water
- add 1 kalin (don't add pigment yet for base coat) and mix well
- add 2 filler...could be sand 40, for eg (use white sand if you want to add color later and don't want to worry about figuring out what end color will be)... Mica (could use different grades)... Straw...
NEXT LAYER (finer)
- dilute in ratio 1 glue: 1 water
- 1 kalin (or other pretty color clay)
- mix well
- 2 silica sand 60 (finer sand)
MIX 6 - another finishing PLASTER
- kalin + water + 2 kinds of sand
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