A Morning of Drilling, Then Eleven Months
The injection takes a morning. Twelve millimetre holes, a hand's width apart, along one bed joint at ankle height, and one person with a 400 mm SDS bit and a skeleton gun can treat the whole ground floor of a terrace before lunch. Almost nothing about whether the job worked is decided in that morning. It is decided by the plaster that goes back on afterwards, by what is left of the old plaster behind the skirting, and by whether anybody hung wallpaper in month three.
What the cream does is narrow and worth stating plainly, because a lot of disappointed customers were sold something wider. Silane and siloxane creams are carried into the mortar in a thixotropic emulsion, migrate out of the hole into the pore structure around it, and react to line those pores with a water-repellent layer. They do not fill the wall, do not block it, and do not stop vapour leaving it. A treated course still has open pores; water simply no longer wets their walls, so capillary rise loses its ladder.
The plaster is the difficult half. Ground water arrives carrying chlorides and nitrates, and those salts are left behind at the evaporation front as the water leaves into the room as vapour, concentrating there for as long as the wall has been wet. Both are hygroscopic: they pull moisture out of room air on their own account. A wall whose capillary rise has been stopped perfectly still shows a damp band if the salt-loaded plaster is left on it, and that is the callback that gets blamed on the injection.
The wall after treatment, cut through the injected course
- Finish skim — two or three millimetres of gypsum finish, isolated from the wall by everything beneath it and carrying no damp duty of its own Gypsum Plaster Finish Coat Volume Calculator
- Renovating undercoat — the coat that is actually specified against the salts, and the one that carries almost all of the thickness and the material Gypsum Plaster Brown Coat Volume Calculator
- Thrown key coat — a coarse open spatterdash giving the undercoat mechanical grip on a background that is still damp Gypsum Plaster Scratch Coat Volume Calculator
- Cementitious slurry — used only where the inner face sits below outside ground, where an injected course has no bearing on lateral water Basement Wall Waterproofing Coating Coverage Calculator
- Masonry and injected joint — the bed joint that took the cream, and the drill holes in it that have to be filled again before the render goes on Tuckpointing Mortar Repair Volume Calculator
What the Injection Cannot Be Asked To Do
This guide assumes the diagnosis is finished and rising damp is what you actually have. If a meter reading and a tide mark are the whole of the evidence, stop here and go and settle that first, because every remaining decision on this page is expensive and none of them helps a condensation problem or a leaking gutter.
Injection also has masonry it does not suit, and BS 6576 is written around walls with a continuous horizontal mortar bed to inject into. Random rubble with a loose core, wide voids, and bedding that runs in and out of the wall thickness give the cream nowhere continuous to go, and a barrier with gaps in it is not a barrier. Very dense units at the treatment course are the opposite problem: too little pore structure for the active to migrate into. Both are reasons to price a different remedy rather than to inject and hope.
The third limit is geometric, and it catches more jobs than the first two combined. An injected course stops water rising past it. It does nothing about water arriving sideways, so a wall whose internal floor sits below the outside ground, an external render carried down over the original DPC, a raised path, mortar droppings bridging a cavity, or a flower bed banked against the brickwork will all keep the wall wet after a perfectly installed injection. Walk the outside of the building and fix the bridges before booking the drilling, not after.
Choosing the Course, Then Setting Out Along It
Pick the bed joint, not a height. The target is the lowest sound continuous joint that still sits above the outside ground, and Approved Document C sets 150 mm above finished ground level as the figure for a damp-proof course in new work — on a remedial job you take the nearest joint that achieves it. Where the original DPC is visible in the external face, injecting the joint at or immediately above that line keeps the new barrier in the plane the building was designed around.
The internal floor decides whether one course is enough. If a solid floor slab and its membrane sit above the injected joint, the wall between the joint and the floor is still free to wet the plaster from below, and the treatment needs either a second course above floor level or a vertical link across to the membrane. On suspended timber floors, look at where the wall plate and joist ends sit relative to the joint before you commit, because a course injected above bearing timbers leaves those timbers on the wet side of the barrier.
Drill each leaf from its own side. A cavity wall is two walls and takes two treatments, and the holes stop short of the far face of the leaf being drilled so the cream is not pushed out into the cavity; a solid wall thicker than one drill pass is treated from both faces instead, each row stopped at the depth the literature states so the two overlap in the middle rather than leaving an untreated core. Holes go into the mortar rather than the units unless the system is written for unit injection, and they are cleared of dust before the nozzle goes in — cream extruded into a hole half full of drilling dust migrates into the dust, not the wall.
The drilling is a respirable crystalline silica job and falls under COSHH: on-tool extraction or water suppression, not a mask and an open window. Set out with a spacing gauge or a chalked rule, because eyeballing 120 mm across fifteen metres of wall drifts, and a wide pair of holes is a gap in the barrier at precisely the point nobody will remember.
How Much Cream a Wall Actually Takes
Cream is sold by volume and used by geometry, so the quantity is arithmetic rather than judgement. A 12 mm hole has a cross-section of about 113 mm², so a hole of a given depth holds that area times the depth, and holes at 120 mm centres come to 8.3 per metre of wall. Everything else follows.
Those figures are the fill volume of the holes and nothing more. Declared coverage on the product literature governs the order, because systems differ on hole diameter, on centres and on whether a second row is specified in thick masonry, and because a wall with open perpends will take noticeably more than its geometry suggests. Use the table to sanity-check the order, and buy the cartridges in one go: a wall injected in two visits from two batches is a guarantee claim waiting for an argument.
| Wall as drilled | Hole depth | Per hole | Per metre of wall | Metres per litre |
|---|---|---|---|---|
| 100 mm leaf, one side | 90 mm | about 10 ml | about 85 ml | roughly 12 |
| 215 mm solid, one side | 190 mm | about 21 ml | about 180 ml | roughly 5.5 |
| 330 mm solid, both sides | 180 mm each side | about 20 ml | about 340 ml | roughly 3 |
| Cartridge check | 380 ml cartridge | — | — | about 2.1 m of 215 mm wall |
Plugging What You Drilled, and the Pointing Outside
The holes are filled once the cream has been given the time the literature asks for. A perforated bed joint left open is a route for driven rain into the exact course you have just spent money treating, and on an exposed elevation it will find it. Fill with a mortar matched to the existing joint rather than with whatever is in the mixer: a hard cement plug in a soft lime bed concentrates stress into the arris of the brick either side of it and spalls the face off within a few frosts.
While the hop-up is there, deal with the pointing along that elevation. Rising damp and defective pointing are separate mechanisms with overlapping symptoms, and a wall barriered at the bottom will still stain at 1.5 m if driven rain runs into eroded joints above. Rake out to roughly two to two and a half times the joint width so the new mortar has something to hold onto, brush and damp the joint, and fill in two passes rather than one deep smear.
Volume for that work is joint length times width times raked depth, and the length is the item people underestimate — perpends add up to a surprising share of the total on a stretcher bond wall, and a repair described as fifteen metres of wall is rarely fifteen metres of joint.
Run the drilled bed joint and any raked-out pointing above it through together, so the make-good mortar is one batch mixed to one specification rather than two visits with two colours.
The combined length of all deteriorated joints being repaired.
The width of the mortar joint.
How deep the old mortar is raked out before repointing.
Repair mortar needed
2.507 gal
- Equivalent in cubic meters
- 0.01 m³
They open the calculator with your figures already in it
Tuckpointing Mortar Repair Volume Calculator: 2.51 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The volume is a plain rectangular prism: one width and one depth applied to the whole run. Deteriorated joints are not uniform — washed-out beds, voids behind the face and open collar joints in rubble stonework can take several times this figure, and you only find them once you start raking.
- It assumes you achieve the entered rake depth along the entire length. Where the existing mortar is still sound the rake stops shallower; around soft or friable units it runs deeper. Neither is reflected in the result.
- This is the mortar sitting in the finished joint, not the material you buy. It does not convert to bags of premix or to sand, lime and cement quantities — yield depends on the mix, sand bulking and what is lost to the board, the mixer and the scaffold — and it carries no waste allowance.
- Nothing here says what mortar to use. Binder type, strength and compatibility with the existing masonry decide whether the repair lasts or spalls the brick or stone, and on historic or lime-bound work that calls for mortar analysis and a conservation specification. A volume figure is not a mix specification.
- This is not a condition assessment. Cracking, bulging, displaced units, failed lintels, corroded wall ties and water getting in behind the face are not measured by joint volume, and repointing over a structural problem conceals it rather than repairing it.
The Strip Below the Outside Ground
Plenty of ground floors sit below the path outside them, and on those walls a horizontal barrier is answering the wrong question. Water is arriving through the thickness of the masonry under a head, not climbing it, and injection has no bearing on that at all. BS 8102 is the document that governs, and it separates the options into a barrier applied to the structure, a structure that is integrally watertight, and a drained cavity that collects and removes water rather than resisting it.
Where the retained strip is shallow and the water is seepage rather than a standing head, a cementitious slurry applied internally is a defensible barrier under that code, and it goes on before the key coat rather than instead of it. It is not a renovating render and it will not manage salts; the render over it still has to do the salt job described further down this page. Where the retained height is real, or the ground drains badly, a drained system is the honest answer and the slurry is a way of losing the argument slowly.
Quantity is coverage rate times coats, and both come off the data sheet rather than from habit. Two coats is the usual minimum for a continuous pinhole-free film, the second brushed at right angles to the first, and a rough or open background eats materially more than the nominal rate — fill the voids before coating, not with it.
Take the coverage rate off the product data sheet rather than a generic figure, because the difference between a sound rendered face and open brickwork is most of the order.
The total basement wall area to be coated.
The area one unit of coating covers in a single coat, per the manufacturer's data sheet.
The total number of coats specified for the application.
Waterproofing coating needed
32.5 gal
A coating on a basement wall is one part of a system whose other parts — drainage, a drainage board, and somewhere for water to go — do most of the work. Applied alone against real hydrostatic pressure, a coating is being asked to do something it cannot.
They open the calculator with your figures already in it
Basement Wall Waterproofing Coating Coverage Calculator: 32.5 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Excludes the drainage board, protection layer, perimeter drain and the sump or outfall the drain discharges to.
- Coverage rates assume a sound, prepared substrate. A rough or porous wall consumes considerably more, and voids must be filled before coating rather than by it.
- Positive-side and negative-side applications are different products for different situations; a coating designed to be applied externally will not necessarily work applied internally.
Hacking Off to the Salt Line
The old plaster comes off because it is contaminated, not because it is loose, and that distinction sets the height. Sound plaster above a tide mark is still salt-loaded for some distance above the last visible evidence, so the specification is normally to remove to at least 300 mm above the highest sign of salting or staining — on a typical 900 mm band, a line at about 1.2 m. Confirm the figure against the system holder's written specification first, because that document is what the guarantee is written against and a line drawn by eye is one the guarantor can disown.
Take it off the returns too. Salts do not respect the end of a wall, and a run stopped neatly at an internal corner leaves a contaminated strip on the adjoining wall that will bloom through the new work within a year. The same applies behind the skirting, which is where the worst of the contamination usually sits and where it is easiest to leave in place — remove the skirting first, hack the wall behind it, and set the new board back on packers afterwards rather than tight to fresh plaster.
Then clean up properly, which here means more than sweeping. Salt-laden debris left in the room, or one bucket used for rubble and then for gauging water, reintroduces exactly what you removed. Gypsum is a separate waste stream from general construction waste because it generates hydrogen sulphide under anaerobic conditions in landfill, so segregate it as it comes off the wall rather than sorting a skip later.
- Lift the skirting, architraves and any floor covering along the wall before starting, and keep them out of the debris.
- Mark the removal line 300 mm above the highest visible salt or stain, or to the height the written specification states, whichever is higher.
- Hack off to that line and carry the same height around every return and reveal the wall meets.
- Rake the exposed bed and perpend joints back a few millimetres so the new render has a mechanical key rather than a flush face.
- Brush the wall down dry, then remove the debris from the room entirely rather than piling it against the base of the wall.
- Photograph the bare wall, the injected course and the hole spacing before anything covers them.
What Everybody Means by the Wait
There are two waits on this job and they are routinely confused, which is why homeowners are told to leave a room empty for a year and builders are told they can plaster on Tuesday. Both are right about different things.
The wall itself dries slowly. The planning figure the trade works to is roughly a month per 25 mm of wall thickness once the source is cut off, putting a 215 mm solid wall close to nine months and a 330 mm wall well over a year. That is a planning figure and not a specification: real drying depends on thickness, on how much of the wall meets moving air, on heating, and on the season. If a decision hangs on it, measure rather than count months — drill samples from depth and have the moisture content determined gravimetrically to BS EN ISO 12570, or use a calcium carbide test on site. A pin meter pressed against a salted surface is measuring the salt.
The render does not wait for any of that. Renovating systems exist precisely so that a wall can be replastered while it is still drying: the undercoat holds the salts and lets vapour through, and the wall dries behind it. Delaying the plaster for a year to protect the plaster is a misunderstanding of what it is for, and it leaves the occupier living in a room with no walls for no benefit.
What genuinely does have to wait is the decoration, and this is where guarantees are lost. Vinyl paper, oil-based paint and anything else of low vapour permeability applied in the first months traps the moisture the render is designed to release; the finish blisters and gets reported as a failure of the damp-proof course. That is where the month-per-25-mm figure earns its keep — as the programme estimate for when the impermeable finishes are allowed.
Lath Where the Background Changes
Most of this wall is one material and takes render directly. The exceptions are predictable: a filled-in opening, a concrete lintel, a chase where a cable or pipe was buried, a timber bond course exposed by the hacking off, and the junction between the old plaster above the line and the new work below it. Each is a plane where two backgrounds of different suction and different movement meet under one continuous coat, and that is where the crack appears.
Expanded metal lath fixed across the junction carries the render over the change instead of letting it bridge one. Fix it to both backgrounds so the lap is real rather than decorative, with the cups facing upward so the mesh catches mortar, and press the key coat hard enough that material is continuous behind the wire rather than sitting on it. BS EN 13658-1 covers metal laths and beads for internal plastering, and it is the reference to quote when specifying.
One material decision matters more here than on ordinary plastering. This wall is full of chlorides and nitrates, and galvanised lath in that environment corrodes, expands and rust-stains straight through the finish — usually as a grid of brown lines that no amount of stain-block will hold back. Austenitic stainless lath and stainless fixings are the specification, and the cost difference across the few square metres a remedial job needs is trivial against the cost of finding out.
Lath on a job like this is measured in patches rather than elevations, so add the strips over lintels, chases and the old-to-new junction together before ordering — sheets come whole either way.
The total exterior wall area to be stuccoed.
Lath sheets needed
27 sheets
- Area to cover (with overlap allowance)
- 473 sq ft
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Stucco Lath Calculator: 27 sheets — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- The overlap allowance is a flat ten per cent applied to the area before any sheet is laid out, so it stands in for laps instead of deriving them from the 27 by 96 inch (686 by 2,438 mm) sheet — a wall broken up by openings, bays or a stepped foundation throws off far more cut sheets and unusable offcuts than one multiplier can cover.
- Rounding to whole sheets happens once, on the single combined area you enter, which quietly assumes offcuts travel from one elevation to the next; price each elevation separately and the same building normally lands a sheet or two higher.
- Sheet size is fixed in the code at 18 square feet (1.7 m²) and cannot be changed, so lath supplied in other panel sizes, in rolls, or as a paper-backed product with a different useful width will not divide into the count shown.
- Only area feeds the division, so a heavy self-furring diamond mesh and the lightest flat mesh return exactly the same number of sheets — the figure says how much wall gets covered, never whether the lath chosen suits the substrate, the exposure or the coats going over it.
- Nothing beyond the sheets is counted: the nails, staples or tie wire that fix lath at every support, the furring that holds unfurred mesh off the sheathing, and the terminations it runs into — weep screed, casing beads, corner aid, control joints — are all separate orders this number does not reach.
- The area is taken exactly as typed, so whether jambs, soffits and returns are inside it was decided before the page saw the number, and the arithmetic has no way to add back lath wrapped into a reveal or carried past an external angle.
The Key Coat, Thrown Not Trowelled
A background that is damp, salt-loaded and freshly hacked gives chemical adhesion very little to work with, which is why the first coat is thrown rather than laid. A coarse cement and sharp sand slurry flicked hard at the wall and left rough gives the undercoat several thousand mechanical undercuts, and it does not care that the wall is wet. Some renovating systems specify this coat as an open scatter over roughly half the face rather than a closed layer, so the wall keeps breathing through the gaps; others want full coverage. That choice belongs to the system holder, and mixing the two produces neither.
Let it set hard before the undercoat follows. A key coat still green when the next coat lands is dragged off by the trowel, and one left to dry out for a fortnight in a warm room pulls water out of the undercoat at the interface and leaves a dusty plane you can open with a fingernail. Take the volume from the thickness the system states rather than from ordinary work — a scatter coat and a full scratch coat are very different quantities of the same product.
Set the thickness to what the renovating system specifies for its key coat, not to the ten millimetres a three-coat plastering job would use, or the order comes back at twice what the wall needs.
The total area to receive the scratch coat.
The applied thickness of the scratch coat.
Scratch coat plaster volume
77.8 gal
- Equivalent volume
- 0.39 yd³
They open the calculator with your figures already in it
Gypsum Plaster Scratch Coat Volume Calculator: 77.8 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Gives the volume on the wall, and plaster is bought in bags. Turning one into the other needs the product's yield: gypsum basecoat is mixed with sand at a ratio the manufacturer sets, commonly somewhere around 2:1 to 3:1 by volume for a scratch coat, and one bag of neat plaster covers a very different area depending on which ratio is used and how the sand is graded. Read the yield off the bag and divide - a bare volume cannot be ordered.
- Says nothing about how much never reaches the wall. Hand-applied basecoat is lost off the hawk, off the trowel, onto the boards, and in whatever is left in the bath when the mix goes off - and gypsum basecoat sets on a clock that cannot be extended, so any batch mixed larger than the plasterer can hang inside that window is thrown away. Batch to the working time rather than to the total, and expect the practical figure for droppings and part-batches to sit well above the clean number this sum returns.
- One coat out of a system that is specified as a total. Interior gypsum plaster over metal lath is normally required to reach a nominal total thickness, commonly quoted at 5/8 in (16 mm) measured from the face of the lath across scratch, brown and finish - and where the wall or ceiling carries a fire rating, that full thickness and that lath are part of what was tested. Trimming the scratch coat here only pushes material into the brown coat; taking it out of the total is a different assembly.
The Undercoat Is the Specification
This is the coat that does the work, and it is where the argument in the trade lives. There are two coherent families of answer and one very common wrong one.
The wrong one is gypsum. BS EN 13279-1 covers gypsum binders and plasters, and every manufacturer working to it excludes their undercoats from permanently damp or salt-contaminated backgrounds, for two reasons: gypsum is soluble enough to be attacked where water keeps arriving, and it gives a hygroscopic salt a comfortable home to bloom back through. A bonding coat on this wall is not a shortcut, it is the same job again in eighteen months.
The first defensible family is the dense route, which is what the replastering guidance annexed to BS 6576 describes: a lean cement and sharp sand render incorporating a water-resisting and salt-inhibiting additive, applied in two passes to hold back both the residual moisture and the salts, finished with a thin gypsum skim that never touches the masonry. It works and it is cheap. Its weakness is that it is a barrier — the wall then dries through its external face or not at all, and the build-up is unforgiving of any bridge that survives at floor or ceiling level.
The second family is the porous route: a renovation mortar, class R in BS EN 998-1, or a system built to WTA Merkblatt 2-9. These are deliberately high-porosity, low-capillarity, high vapour permeability mortars. They do not resist the salts, they store them — crystallisation happens inside the render's own pore volume, well behind the surface, while vapour continues to leave through it. The thresholds for porosity, capillary uptake and vapour resistance sit in the standard and the declared values sit on the bag; ask for both rather than accepting renovating render as a description. The trade-off is cost, thickness, and the fact that a finite storage capacity is one that can eventually be filled.
Whichever family the job uses, thickness is a specification input and not a means of making the wall flat. BS EN 13914-2 covers the design and application of internal plastering and is the reference for build-up and tolerance. Get the plane in this coat, ruled off between screeds and floated once, because the finish above is far too thin to correct anything. And stop the undercoat short of the floor — ten to fifteen millimetres behind the skirting line, so the new render is not standing in a wet screed and wicking around everything you just installed.
| Dense water-resisting render | Renovation mortar, class R or WTA | |
|---|---|---|
| Mechanism | Resists moisture and salt reaching the surface | Stores salt in its own pore volume |
| Vapour | Low permeability — the wall dries outward or slowly | High permeability — the wall dries through the render |
| Named in | The replastering guidance annexed to BS 6576 | BS EN 998-1 class R, WTA Merkblatt 2-9 |
| Fails by | Bridging at floor or ceiling, or a bridge left outside | Exhausting its storage capacity after many years |
| Cost and thickness | Low cost, ordinary render thickness | Higher cost, usually greater built thickness |
Use the thickness from the system data sheet rather than a nominal figure, then add for the plane separately — an old wall that is fifteen millimetres out over its height absorbs that deviation in this coat and nowhere else.
The total area to receive the brown coat.
The applied thickness of the brown coat.
Brown coat plaster volume
49.87 gal
The brown coat is the coat that makes the wall flat and plumb, and it carries most of the thickness. It is where the material goes, and its cure is what governs when the finish can follow.
- Equivalent volume
- 0.25 yd³
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Gypsum Plaster Brown Coat Volume Calculator: 49.87 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- THE BROWN COAT IS THE LEVELLING COAT, so its thickness is set by how far out the background is rather than by a specification. A wall straight to within a few millimetres takes the nominal thickness; a wall out by 15 mm (0.59 in) over its height takes whatever it takes, and the average is the only figure that matters to the order.
- Material lost to the floor is real and is not a percentage. Plaster that falls off the hawk or the trowel on a scratch-and-brown job is gone, and on a rough background it is a substantial share of a bag.
- Suction governs how much stays on. An unprimed, highly absorbent background pulls water out of the mix and changes both the working time and the thickness that can be hung in one pass.
- Excludes the scratch coat below and the finish coat above, which have different thicknesses and different coverage rates.
- Does not allow for over-thickness where the substrate is out of plane, which on an uneven background can add substantially to the quantity.
- Cure time before the finish coat is a programme item, and rushing it is a recognised cause of finish-coat crazing.
Two Millimetres of Finish, and the Paint That Would Undo It
The skim on this wall is doing no damp work at all. It is a decorative closure over a coat that has already dealt with the salts, and its whole job is to be flat, thin and consistent — which makes it the layer most sensitive to what is under it. A suction difference across the undercoat prints through as shading under raking light, and a finish built up locally to fill a hollow dries at a different rate and shows as a shadow for the life of the wall.
Keep it off the masonry and off the floor. Carried past the top of the undercoat onto the old plaster above, or run down into the floor junction, the skim becomes exactly the bridge the whole build-up exists to avoid — a thin, soluble, hygroscopic path from wet material to the finished surface. It stops where the undercoat stops.
Then the decoration, which is the last chance to lose the job. Ask for the vapour permeability class rather than the marketing description: BS EN 1062-1 classifies coating materials by water vapour transmission and by liquid water permeability, and although it is written for exterior masonry, those V and W classes are the language a permeable finish gets specified in and most manufacturers declare them either way. A permeable mineral or silicate emulsion first, no vinyl, no oil-based undercoat, and no wallpaper until the wall behind has genuinely dried. Warn the occupier in writing, because the coating that fails the system is usually applied a year later by somebody who was never told.
Small as this quantity is, mix it against the whole area rather than bay by bay — a wall finished from two gauges at two consistencies reads as two walls under a window for good.
The total area to receive the finish coat.
The applied thickness of the finish coat.
Finish coat plaster volume
23.56 gal
The finish coat is thin, and its quantity is small relative to the coats beneath. What it is not is forgiving — it reveals whatever the brown coat left behind rather than correcting it.
- Equivalent volume
- 0.12 yd³
They open the calculator with your figures already in it
Gypsum Plaster Finish Coat Volume Calculator: 23.56 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- A FINISH COAT IS A THICKNESS OF 2-3 MM AND A QUESTION OF FLATNESS, not a quantity to be stretched. Applying it thicker to bury a background that was never levelled is the commonest cause of a finish that crazes or delaminates, and no material figure prevents it.
- Set is time, not quantity. A bag mixed and not used inside its working time is waste regardless of the area it would have covered, so the order is governed by how much can be laid in one working period as much as by the wall.
- Says nothing about the background it is going on to. Finish plaster over new board, over a brown coat and over painted plaster are three different preparations with three different suction conditions.
- Excludes the scratch and brown coats, which together account for most of a rendered wall's material.
- Coverage varies markedly with the texture being achieved; a smooth trowelled finish and a heavy float finish consume different amounts of the same product.
- Does not include the first coat new plaster takes before it is decorated, a mist coat or a primer made for new plaster, nor the paint that goes over it.
What All of It Weighs Going Up the Stairs
Take a room four metres by two and a half, replastered to 1.2 m all round, call it 14.4 m² net of the door. A five millimetre key coat is 72 litres, a ten millimetre undercoat is 144 litres, and a three millimetre finish is another 43 — about 260 litres of wet material, or eighteen buckets, on a wall that looked like a morning's work.
Mixed plaster and render weigh roughly 1.6 short tons per cubic yard, which turns that 260 litres into close to half a tonne carried in by hand and applied batch by batch. Gypsum cannot be retempered once it has begun to set, so batch size is set by what the gang can apply; a comparable weight leaves again as debris when the old plaster comes off; and on an upper floor or a working platform it is a real load standing in one place.
Add the coat volumes from the three calculators above, convert the total, and you have the number that decides how many people are carrying and how many mixes the day is split into.
The volume of wet plaster in cubic yards.
Approximate weight
16 short tons
About 1.6 short tons per cubic yard for mixed gypsum plaster; the dry powder is considerably lighter. A planning figure, not a specification. Confirm the figure with your supplier or waste contractor before relying on it.
- Conversion factor applied
- 1.6 short tons per cu yd
They open the calculator with your figures already in it
Wet Plaster Cubic Yards to Tons Calculator: 16 short tons — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
What this calculation does not cover
- Mixed plaster only travels between the mixer and the wall. With the mixer on the working floor, what climbs the stair is bags and a hose; with it at ground level, the wet weight goes up as well.
- Scaffolds and old suspended floors care what stands in one place, not what a day totals. Plastering concentrates it — bagged stock, filled baths, water and the plasterer at the same end of the platform. What that will take comes from whoever designed, hired or owns it.
- A background takes its coat at the coat's heaviest. The board or lath and its fixings carry the wet weight, and drying sheds only the surplus water — the rest is chemically combined into the set and stays in the wall.
Plaster volume follows from wall area and coat thickness, and the weight matters mainly for handling and for loading on suspended work. Mixed plaster is far heavier than the powder it came from, since the mix water is a substantial part of it, and that difference catches people out when estimating what has to be carried upstairs. Coverage is normally quoted by the manufacturer per bag at a stated thickness, which is a more reliable basis for ordering than a volume calculation.
The Second Winter
Most remedial DPC arguments happen between twelve and twenty-four months after the work, once the first heating season has passed. Almost every one turns on evidence that could have been photographed in an afternoon and was not: the bare wall, the injected course, the hole spacing, the removal line, the product batch, and the written specification the render was bought against.
When something does show, work the list below before touching the injection. The failures that present as damp on new plaster are mostly not failures of the barrier, and a second course drilled above the first is the most expensive way of finding that out.
Keep the paperwork with the guarantee, and hand the occupier a short written note of what may and may not go on the wall and when. A guarantee that survives the work and dies at the decorator is the commonest ending this job has.
| What appears | Most likely cause | Where to look first |
|---|---|---|
| A damp band at the same height as before | Contaminated plaster left above the removal line, or on a return | The old-to-new junction, and the adjoining wall at the corner |
| White fluffy bloom on new plaster | Salts migrating through, or a gypsum coat used as the undercoat | The specification the render was bought against |
| Blistered or peeling paint, plaster sound | An impermeable coating applied before the wall dried | The decorating date and the paint tin |
| Damp at floor level only | The render bridging into the screed, or a floor above the injected course | The skirting line and the gap behind it |
| Patchy damp above the treated band | Penetrating damp through defective pointing or a bridge outside | The external elevation, path levels and rainwater goods |
| Brown grid lines through the finish | Galvanised rather than stainless lath in a salt-loaded wall | The lintel and chase patches |
The order sheet for one room, in the sequence it is used
Two deliveries, not one: the injection kit and the make-good mortar go in first, and the render is bought against the system data sheet after the wall is open and the removal line is known.
- Injection cream, by metres of wall and wall thickness — Fill volume is hole area times depth times 8.3 holes per metre at 120 mm centres — check the order against the product's declared coverage and buy the whole wall in one batch.
- Make-good and repointing mortar — Drilled bed joint plus any raked-out pointing on the same elevation, matched to the existing joint rather than to the mixer.
- Removal line, measured not assumed — At least 300 mm above the highest visible salting, carried around every return; the render area follows from this line and so does the debris volume.
- Render system, by coat and by declared property — Key coat, undercoat and finish at the thicknesses the system states, with the porosity and vapour figures asked for by name rather than by the words on the front of the bag.
- Stainless lath and beads for the patches — Lintels, chases, filled openings and the old-to-new junction — austenitic stainless in a wall carrying chlorides and nitrates, never galvanised.
- Handling and waste — Wet material weight in, gypsum debris out as a segregated stream, and a batch size the gang can apply before the mix goes off.
Opens the calculators above on one screen with the dimensions from this article already filled in. Quantities only — this site publishes no price list, because local prices vary too much to publish honestly.