A Schedule of Sawn Limestone and a Merchant Quoting Brick
The stone schedule reads 450 by 225 sawn limestone, 350 thick, 8 mm joints, coursed. The merchant's estimating sheet offers bags per thousand brick. There is no arithmetic that gets you from one to the other, because the two numbers are not measuring the same thing: one is a property of a wall and the other is a property of a very particular unit that this job is not using. An estimator who divides anyway will order roughly a sixth of the mortar the wall needs, and will find out on the second lift.
Every bags-per-thousand figure in circulation is a coverage rate with three constants welded inside it that nobody writes down: the face module of the unit, the joint thickness it assumes, and the depth of bed the mortar is spread across. Change the unit from 215 by 65 to 600 by 250 and the first constant moves by a factor of ten. Change the joint from 10 mm to 2 mm and the second moves by five. Change a half-brick leaf into a 350 mm solid stone wall and the third moves by three and a half. The rule survives none of that, and it fails silently, which is worse than failing loudly.
The repair is not a better rule of thumb. It is to stop treating mortar as a consumable that comes with the units and start treating it as what it physically is on the drawing: a solid of known dimensions, whose volume you can compute from the same three numbers the setting-out already gave you. Every unusual unit on this page — autoclaved aerated concrete, dressed stone, adhered veneer, a wall that is already built and needs raking out — is the same computation with different values pushed into it.
The Joint Is a Solid, and You Can Measure It
Take one unit with its share of mortar attached: the bed under it and one head joint at its end. Its footprint is the nominal module, face length plus joint by face height plus joint. Subtract the unit's actual face and what remains is the mortar seen face-on, which for a face of length L, height H and a joint of width j is exactly j × (L + H + j). Multiply that by the depth the bed is spread across and you have the mortar volume that belongs to one unit. Divide one square metre by the nominal module and you have how many of those units stand in a square metre of elevation. Multiply the two together and the unit count cancels out completely, leaving mortar per square metre of wall equal to the joint's fraction of the face, times the bedded depth. Two numbers. Nothing else in the calculation is doing any work.
That cancellation is the whole reason a per-square-metre figure survives a change of unit and a per-thousand figure does not, and the limestone wall demonstrates it neatly. Its joints occupy 5.1 per cent of the face against standard brickwork's 17.2 — a third as much — but its bed is 350 mm deep instead of 102.5, which is three and a half times more. The two errors very nearly cancel, and the stone wall wants 17.9 litres of mortar per square metre against the brick wall's 17.6. Per thousand units, the same two walls are 1.91 m³ and 0.30 m³, a factor of six and a half apart. The estimator who works per square metre is within two per cent by accident; the estimator who works per thousand is wrong by more than the whole order.
- Read the actual unit face size off the supplier's schedule, not the nominal or trade size — for dressed stone this is a cutting list, and for AAC it is a manufacturing tolerance rather than a nominal module.
- Take the specified joint width from the drawing or the conservation specification, not from what the last gang laid.
- Establish the bedded depth separately: the full wall thickness for solid work, the stone bed only where a facing sits against a separate backing, the face shells only where the specification beds face shells.
- Compute the joint's fraction of the face — one minus the actual face area divided by the nominal module — and multiply it by the bedded depth to get volume per square metre of elevation.
- Deduct any head joints the unit system does not mortar, which on tongue-and-groove AAC is all of them.
- Keep the geometric volume and the waste allowance on two separate lines from here to the order, so the next job can calibrate the second one against what actually got used.
| Unit and joint | Bedded depth | Joint as a fraction of the face | Mortar per m² of elevation | Mortar per 1,000 units |
|---|---|---|---|---|
| Clay brick 215 x 65 mm, 10 mm joint | 102.5 mm half-brick leaf | 17.2% | 17.6 L (5.8 ft³ per 100 ft²) | 0.30 m³ (10.5 ft³) |
| Modular clay brick 7-5/8 x 2-1/4 in, 3/8 in joint | 3-5/8 in veneer | 18.3% | 16.9 L (5.5 ft³ per 100 ft²) | 0.23 m³ (8.1 ft³) |
| Dense concrete block 440 x 215 mm, 10 mm joint | 100 mm, fully bedded | 6.6% | 6.6 L (2.2 ft³ per 100 ft²) | 0.67 m³ (23.5 ft³) |
| AAC block 600 x 250 mm, 2 mm thin-bed joint | 200 mm, fully bedded | 1.1% | 2.2 L (0.7 ft³ per 100 ft²) | 0.34 m³ (12.0 ft³) |
| Sawn ashlar 450 x 225 mm, 8 mm joint | 350 mm solid wall | 5.1% | 17.9 L (5.9 ft³ per 100 ft²) | 1.91 m³ (67.5 ft³) |
Dressed Stone: A Small Fraction Across a Deep Bed
The first thing to settle on an ashlar job is what the bed actually is, because the wall thickness on the section drawing is frequently not it. A solid coursed wall in 350 mm stone is bedded across the full 350. A 100 mm ashlar facing tied back to a blockwork inner leaf is bedded across 100, and the blockwork behind it is a separate take-off with its own joint fraction and its own bed. A stone with a sawn bed and a rock face is bedded across the sawn part only. Getting this wrong is a straight multiplier on the answer and it is the single most common error on a stone estimate, because the number is sitting right there on the drawing looking authoritative.
The second is that the joint width on dressed stone is a design decision that the material constrains rather than a habit. What the stone will hold depends on how it was finished and how consistently it was cut, and the dimension stone specifications are where the tolerance argument lives: ASTM C568 Standard Specification for Limestone Dimension Stone and ASTM C615 Standard Specification for Granite Dimension Stone for the material itself, BS EN 771-6 Specification for Masonry Units — Natural Stone Masonry Units in the European system, and the Natural Stone Institute Dimension Stone Design Manual and the Indiana Limestone Institute of America's Indiana Limestone Handbook for the practice around them. Anchored and non-loadbearing stone assemblies are a different animal again, addressed by ASTM C1242 Standard Guide for Selection, Design, and Installation of Dimension Stone Attachment Systems, where the bedding material may be carrying almost nothing and the anchor is carrying the stone.
Sensitivity runs almost entirely through the joint. For thin joints the fraction is very close to proportional to j, so specifying 6 mm instead of 8 takes a quarter off the bedding volume, while a stone cut 10 mm short on the face barely registers. That asymmetry is useful when a schedule arrives with mixed stone heights and a single joint: take the elevation off in course bands, average the heights inside each band, and hold the joint constant across all of them, because averaging the joint is the one approximation that actually moves the answer.
Finally, bedding mortar and pointing mortar are two orders, not one. Where the joint is raked back at the face and pointed afterwards — routinely, on stone, and almost always on historic work where the pointing is a lime mortar answering to BS EN 459-1 Building lime and the bedding may not be — the bedding volume is reduced by the rake and the pointing volume is a separate linear calculation. Ordering one figure and using it for both leaves you short on the bedding and holding a pallet of the wrong mix for the face.
Put the cutting-list face size, the specified joint and the bedded depth in and it returns both figures at once: the stone count from the module, and the mortar volume from the gap the module leaves behind.
The total wall face area to be covered.
The actual face length of a typical cut stone unit.
The actual face height of a typical cut stone unit.
The mortar joint thickness between stones.
The depth (thickness) of the stone wall.
Stone units needed
238 stone units
Ashlar stone units often vary in size more than manufactured brick or block — this uses a single representative size, so real stone counts may vary if your units aren't uniform.
- Coverage rate
- 1.08 units/ft²
- Mortar volume needed
- 0.56 yd³
They open the calculator with your figures already in it
Ashlar Stone Masonry Joint Volumetrics Calculator: 238 stone units — 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
- Mortar volume assumes every joint is filled solid across the full wall thickness you enter. A stone facing tied back to a blockwork inner leaf is bedded only across the stone, and a rock-faced unit with a sawn bed is bedded across the sawn part only. Enter the actual bed depth, not the wall thickness shown on the section drawing.
- No waste is added. The stone count is the bare geometric fit of one representative unit across the face area you enter: nothing for cutting at openings, quoins, jambs, reveals and cills, nothing for breakage in handling and setting, and no deduction for openings — the area you type is treated as solid stone face.
- One stone size covers the whole wall. Coursed ashlar with varying course heights, random ashlar, and the oversized units used for quoins, cills, lintels and copings are not counted separately, and no course-by-course layout is set out — part stones at course ends and wall ends are carried as fractions of the total and rounded once at the end.
- The mortar figure is the empty joint volume, not a mix quantity. It carries no allowance for mixing and board waste, does not convert to sand, cement and lime or to bag counts, and excludes any pointing or repointing mortar, which the joint face takes on top of the bedding mortar.
- This is a quantity take-off, not a design. It says nothing about wall stability, slenderness, lateral restraint, wall ties or bed-joint reinforcement, and nothing about the mortar specification — on stone the mix is chosen to suit the stone and the exposure rather than defaulted. Freestanding and retaining stone walls need design to the governing code.
AAC: You Are Buying a Coverage Rate, Not a Joint
Autoclaved aerated concrete breaks the method from the other end. The joint is 1 to 3 mm of adhesive applied with a notched trowel, the blocks are manufactured to a tolerance that makes that possible, and thin-bed mortar is not sold by volume at all. It is sold against a consumption rate the manufacturer publishes in kilograms per square metre per millimetre of joint thickness, which is a different kind of number from a mortar volume and has to be handled as one. The material is covered by ASTM C1660 Standard Specification for Thin-bed Mortar for Autoclaved Aerated Concrete (AAC) Masonry, the units by ASTM C1693 Standard Specification for Autoclaved Aerated Concrete (AAC) and ASTM C1386 Standard Specification for Precast Autoclaved Aerated Concrete (PAAC) Wall Construction Units, and in the European system by BS EN 771-4 Specification for Masonry Units — Autoclaved Aerated Concrete Masonry Units, with BS EN 998-2 Specification for mortar for masonry — Masonry mortar treating thin layer mortar as a declared category in its own right rather than a thinly applied general-purpose mix.
The trap in that rate is the square metre it is quoted against. A consumption figure per square metre of bedded surface is not a figure per square metre of elevation, and the ratio between them is the wall thickness divided by the course height. A 200 mm block on a 250 mm course gives 0.79 m² of bed for every square metre of elevation; a 100 mm partition block on a 225 mm course gives 0.44. Read a bedded-surface rate as an elevation rate on that partition and you order rather more than twice what the wall will take. Read an elevation rate as a bedded-surface rate on a thick external block and you come up short. The technical data sheet says which one it means; the merchant's counter usually does not.
Head joints are the second correction and they are frequently total. Many AAC systems use tongue-and-groove or profiled ends laid dry, so the only mortar in the wall is in the beds. On a 600 by 250 block at 200 thick, mortaring the full perimeter comes to 2.2 litres per square metre of elevation; bedding only comes to 1.6. Whether the vertical joints get mortared is a system question with structural and air-tightness consequences, so it is settled by the block manufacturer's own installation literature and by the design — TMS 402/602 Building Code Requirements and Specification for Masonry Structures covers AAC masonry design in the American system, BS EN 1996-1-1 Eurocode 6: Design of masonry structures in the European — and once it is settled, it changes the material order by about a quarter.
The notch matters more than the joint does. The published consumption rate is tied to a specific trowel notch, because on a 2 mm bed the ridge profile is most of the material. A gang that reaches for a deeper notch because the blocks feel dry will move the actual consumption well past anything the joint thickness on the drawing would predict, and the first sign of it is running out. If the site is using a different notch from the one on the data sheet, the rate on the data sheet is no longer the rate.
One honest limitation, because it shows up as soon as you switch this calculator to imperial: it reports the mortar as a mass rather than as a count of bags. Thin-bed mortar has a standard 25 kg sack in the metric markets where AAC is a mainstream system, and no comparably established North American bag size could be verified for this site, so rather than invent a package that no merchant stocks the imperial answer stays a quantity. Convert it to bags against whatever your actual supplier sells, which is the only place that number honestly exists.
Enter the joint thickness and the consumption rate off the product's own technical data sheet — and enter the bedded area rather than the elevation if that is the square metre the rate was quoted against.
The total AAC wall face area.
The thin-bed mortar joint thickness.
The specific thin-bed mortar product's consumption rate.
Thin-bed mortar needed
288 lb
Coverage rate varies by specific product formulation and trowel notch size — confirm against your chosen thin-bed mortar's technical data sheet.
- Wall area
- 540 ft²
They open the calculator with your figures already in it
AAC Block Thin-Bed Mortar Calculator: 288 lb — 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
- No waste allowance is applied. The figure is the calculated mortar only — nothing is added for material left in the bucket, mortar dropped off the trowel, the extra worked in at cut blocks and around openings, or a bag opened at the end of the job. The metric result rounds up to whole 25 kg (55 lb) bags, which is packaging arithmetic, not a wastage factor.
- Wall area is taken as a plain gross face area: openings are not deducted, and the calculation has no idea of your block height or wall thickness — the two things that actually set how much bed-joint surface exists per square metre of wall. Before trusting the number, check whether your product's published rate is quoted per square metre of wall face or per square metre of bedded surface, because this model treats them as the same thing.
- The coverage rate is whatever you type and nothing checks it. Trowel notch size, block face texture and absorbency, how heavily the applicator loads the sledge, and temperature all move real consumption away from a technical data sheet figure, and none of them are inputs here.
- In imperial the answer is a quantity of mortar, not a count of packages — no North American bag size is assumed, so you have to divide by whatever your supplier actually stocks. In metric it is rounded up to 25 kg (55 lb) bags specifically; a different sack size changes the count.
- This is a quantity take-off, not a specification. It does not cover the levelling bed of conventional mortar the first course is normally laid on, says nothing about reinforcement, adhesion, fire rating or structural performance, and does not decide whether thin-bed adhesive is the right product for your block system — that comes from the block manufacturer's installation instructions.
When the Bed Stops Being a Joint
Adhered veneer has no joint fraction to find, because it has no module. Manufactured and thin-cut stone units are irregular on the back, laid to a scratch coat and a setting bed, and the material that disappears behind them is governed by how deeply the profile is dished rather than by any dimension on a schedule. The only sane estimating variable is an average bed thickness across the area, which is why the calculation for veneer takes an area and a thickness and stops there. Push a joint width into it and you will be estimating something the wall does not contain.
Where the veneer pattern is jointed and grouted rather than laid tight, that grout is a third order on top of the scratch coat and the setting bed, taken off the joint length exactly as pointing is. Three separate quantities, three separate mixes on some jobs, and one number on the order sheet is how a veneer elevation ends up half-clad with the scaffold still up.
Area and an average bed thickness are the honest inputs here, because the back profile of the units — not any joint on a drawing — is what decides how much mortar the wall swallows.
The total wall area to receive manufactured stone veneer.
The average combined thickness of the scratch coat and setting bed.
Mortar volume needed
268.1 gal
They open the calculator with your figures already in it
Manufactured Stone Veneer Mortar Coverage Calculator: 268 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
- This is the bed under the stone, and on an adhered veneer that is not all the mortar. Most manufacturers require every unit to be back-buttered — a full coat troweled onto the back of the stone before it is pressed home, so no void is left behind it — which is a second application over the same wall area. Buy to the setting-bed figure alone and the order can be short by a third or more.
- Liters of placed mortar is not bags of product. A pre-blended veneer mortar yields roughly 12 to 15 liters (3.2 to 4 gal) of mixed material per 25 kg (55 lb) bag once gauged with water, and a site mix has to be converted through its cement-to-sand ratio, so this volume still needs the yield printed on the bag before anyone can count pallets.
Backwards Off a Wall That Is Already Built
Repointing inverts every input. The units are already laid, so you are not counting them and their size is only interesting for what it implies about joint length. What you need is metres of joint per square metre of elevation, and that comes straight out of the same module: one bed length plus one head-joint height per unit, times the units in a square metre. Standard 215 by 65 brickwork with 10 mm joints carries about 17.8 linear metres of joint in every square metre of face, or 5.4 feet per square foot. The 450 by 225 ashlar carries 6.5, a little over a third of that, which is why a stone elevation that looks like far more work than a brick one is often far less mortar.
Depth is then the variable that decides the order, and it is the one nobody measures. Raking out to a depth of roughly two to two and a half times the joint width is the working rule for a durable repoint, but on any listed or conservation job it is the specification and the appointed adviser who set it, not the rule. At 10 mm wide raked 25 mm deep, brickwork wants about 4.4 litres per square metre; the ashlar at 8 mm wide raked 20 mm wants about 1.0. Both are small numbers that get badly under-ordered because the eye reads the elevation and not the depth behind it.
One thing not to carry over from new work: a repointing mix is chosen for compatibility with what is already in the wall rather than for strength, and a mortar harder than the units will do its damage at the arris of the stone or brick rather than in the joint. That decision belongs upstream of the quantity, but it is worth writing on the same sheet, because a raked-out elevation with the wrong pallet delivered against it is a very expensive week.
Measured joint length, joint width and raked depth are the only three inputs a built wall will give you, and the depth is the one that decides whether the order is right.
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.
From Cubic Metres to What Turns Up on the Pallet
A volume of mortar is still not an order, because mortar arrives in at least three commercial forms and only one of them is sold by volume. Site-mixed material is bought as sand by mass or by the loose cubic metre plus cement by the bag; factory dry premix comes in sacks or in a silo, priced by mass against a yield the manufacturer publishes; ready-to-use retarded mortar comes in tubs by volume. Three different conversions from the same cubic metre, and the yield figure that closes the gap belongs to the supplier of the specific product rather than to any published constant, which is why this site will not print one.
For a site mix, the working assumption is that the finished mortar comes out at roughly the bulk volume of the damp sand, because the cement and the water largely occupy the voids between the sand grains rather than adding to them. It is a serviceable assumption and it is not a specification. What it hides is bulking: damp sand occupies noticeably more space than the same mass of it dry, so sand ordered against a loose volume and sand ordered against a mass are two different deliveries. ASTM C29/C29M Standard Test Method for Bulk Density (Unit Weight) and Voids in Aggregate is the document behind that difference, and gauge boxes filled by eye on a wet morning are where it turns into a shortfall.
The mortar designation does not change the volume. Whether the specification calls up a type under ASTM C270 Standard Specification for Mortar for Unit Masonry or a designation under BS EN 998-2, it is answering a question about strength, bond and durability, and the wall needs the same number of cubic metres either way. Estimators lose time re-running quantities after a mix change that only altered the proportions inside the same volume; the thing that actually needs re-running after a mix change is the sand and cement split, not the mortar.
Waste is the last line and it deserves to stay a separate one. Droppings on the boards and the scaffold, the tail of every mixer load, beds spread wider than the unit, and material that stiffens past use all consume mortar that no geometry predicts, and the honest allowance is whatever your own last three jobs of this type recorded. A published percentage would be a guess dressed as a figure. Take the wall off elevation by elevation, add your own allowance to each, and write both numbers down, because the only way an allowance ever gets better is by being compared afterwards against what was actually delivered.
Three Numbers, Written Down Before the Order
Whatever the unit is, the take-off comes down to the joint's fraction of the face, the depth the bed is spread across, and the unit the material is actually sold in. Get those three onto the sheet and any wall — aerated block at 2 mm, limestone at 8, brick at 10, or a Victorian elevation being raked out at whatever it was originally laid at — becomes the same short calculation, and the answer travels with the wall rather than with somebody else's brick.
The rule of thumb was never wrong, exactly. It was a correct answer to one specific wall, carried away from that wall by people who had stopped noticing which one it was.
The sheet to fill in before pricing bedding material
Work the geometry first and the commercial unit last, and keep them on separate lines so a change of supplier does not force a re-measure of the wall.
- Actual unit face size from the supplier's cutting list or data sheet — Not the nominal or trade size. On dressed stone this is a schedule of real dimensions; on AAC it is a tolerance, which is what makes the thin joint possible at all.
- Specified joint width, taken from the drawing — For thin joints the mortar volume is very nearly proportional to it, so this is the input worth arguing about before anything is ordered.
- Bedded depth, decided separately from the wall thickness — Full thickness for solid work, the stone bed only for a facing on a backing, face shells only where the specification says so.
- Head joints that the system does not mortar — Tongue-and-groove AAC ends are laid dry, and taking the full perimeter instead of the bed alone overstates a thin-bed order by about a quarter.
- The square metre the supplier's coverage rate refers to — Bedded surface or elevation. The ratio between them is wall thickness over course height, and it is well over two to one on a thin partition block.
- Waste allowance from your own site records, on its own line — Droppings, mixer tails, over-spread beds and stiffened material. Kept separate from the geometry so it can be checked against what was actually delivered.
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.