Working out silicone usage correctly
You calculate silicone consumption with the formula joint width (mm) × joint depth (mm) × joint length (m) = consumption in millilitres. A typical 5 × 5 mm joint in the shower needs 25 ml per running metre by calculation, so a 310 ml cartridge theoretically lasts for about 12.4 m. Add 15–25 % waste for start, end and rework.
Contents
What you need
Project template “Apply sealant from the cartridge”You work out silicone usage with the formula joint width (mm) × joint depth (mm) × joint length (m) = usage in millilitres. For a usual 5×5 mm joint in a shower that comes to 25 ml per linear metre – so a standard cartridge of 310 ml will in theory run about 12.4 lin. m. Allow an additional 15–25 % for waste at the start, the end and for reworking, so that the cartridge really does last and you do not have to reorder with a new colour batch.
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Why the calculation is worth it
Anyone who merely estimates the material needed goes off course in practice in one of two directions: either the cartridge does not quite reach the end of the joint, or so much is left over that money is left lying around unnecessarily. Both can be avoided with a short calculation before buying.
The colour batch no longer matches exactly
If a new cartridge is needed halfway along the joint, the reorder can differ minimally in colour – which shows up above all with pale and matt shades.
An interruption halfway along the joint
Silicone has to be tooled before a skin forms. If the material runs out midway, a visible mark often appears at the transition.
Waste underestimated
The initial squeeze, voids and cleaning the cartridge nozzle use up extra material – anyone who does not allow for that buys too little.
A surplus wastes money
Anyone who orders considerably too many cartridges to be safe ties up capital in material that dries out in storage instead of being used.
The formula: working out usage in three steps
Measure the width with calipers or a folding rule at several points along the joint. As a rule of thumb for joint depth: sealant joint depth t = 0.5 × joint width b. The thickness of the sealant d corresponds to about 2/3 of the joint width b (source: Industrieverband Dichtstoffe e.V.). With very narrow sanitary joints, practice often seals roughly square, 5×5 mm or 8×8 mm for instance.
Add up all the edges to be sealed in the area – in a shower typically the floor-to-wall junctions, the corner joints and the finish at the tap.
Usage (ml) = joint width (mm) × joint depth (mm) × joint length (m). Example: 5 mm × 5 mm × 3 m = 75 ml. As up to 25 % extra has to be reckoned with depending on technique, allow generously for one additional cartridge per 8–10 lin. m started.
| Joint width × depth | Usage, calculated | Usage with approx. 15 % waste | Coverage per 310 ml cartridge |
|---|---|---|---|
| 5 × 5 mm | 25 ml/m | ≈ 29 ml/m | ≈ 10.7 lin. m |
| 6 × 6 mm | 36 ml/m | ≈ 41 ml/m | ≈ 7.6 lin. m |
| 8 × 8 mm | 64 ml/m | ≈ 74 ml/m | ≈ 4.2 lin. m |
| 10 × 10 mm | 100 ml/m | ≈ 115 ml/m | ≈ 2.7 lin. m |
Approximate figures for rectangular joints. In reality usage depends on technique, how the joint runs and the corners – with a lot of tool changes, reckon rather with the upper 25 % of waste.
Calculating faster with the usage calculator
Instead of working it out by hand, enter joint width, depth and linear metres straight into our usage calculator for sealants and primers. The tool works out the quantity needed automatically and additionally shows the primer requirement for the bonding flanks as well as minimum joint widths by material.
Which pack suits your project?
Sanitary silicones such as OTTOSEAL S100 are sold as standard in the 310 ml cartridge – an acetoxy-curing 1K silicone sealant with fungicidal and bacteriostatic additives, complying with DIN 18545 part 2 group E, with an application temperature of +5 °C to +35 °C. For larger areas or projects with many linear metres it is worth looking at bigger packs: OTTOSEAL S105 is available in some shades in the 400 ml cartridge as well, which delivers around 30 % more joint length per cartridge change. Unopened packs keep for at least 18 months stored cool and dry – so a small material buffer does not spoil straight away.
Common mistakes when working out quantities
Joint depth taken wrongly
Joint depth is measured down to the backer rod, not to the visible edge – anyone who overlooks that regularly allows too little material.
No waste allowed for
Anyone who calculates exactly with the arithmetic figure often ends up with too little – the real extra can be up to 25 % depending on technique.
Batch changed halfway along the joint
On bigger projects buy a spare cartridge from the same batch from the outset, rather than reordering later with a deviating colour.
Corner joints and junctions forgotten
Besides the long edges, extra material goes into corners, taps and drains – do not overlook those metres when adding up the total length.
Frequently asked questions
How many linear metres of joint does one cartridge of silicone manage?
With a usual 5×5 mm joint and a 310 ml cartridge, around 12.4 lin. m are possible on paper, and with realistic waste rather 10–11 lin. m. With wider or deeper joints the coverage drops accordingly, see the table above.
How deep does a silicone joint have to be?
The rule of thumb is: joint depth t = 0.5 × joint width b, measured down to the backer rod. The thickness of the sealant should be about 2/3 of the joint width.
How much waste should I allow for with silicone?
Depending on technique – hand gun, pneumatic or cordless gun – the extra can be up to 25 %. For most projects an allowance of 15–25 % on the arithmetic figure is realistic.
Is one cartridge enough for a complete shower?
A standard shower with floor, corner and tap joints often comes to 3–5 lin. m at 5×5 mm – a 310 ml cartridge manages that with some to spare. With larger enclosures or wider joints a second cartridge may be needed.
How long does it take for the joint to cure right through?
Silicone usually cures through at about 2–3 mm per 24 hours. Before the joint gets wet it should be able to cure through according to its depth.
Can I have the usage worked out online as well?
Yes, enter joint width, depth, linear metres and pack volume into our usage calculator for sealants and primers – the tool takes over the arithmetic automatically.
You will find further help in the How to: replace sanitary silicone – step by step, in the Guide: Which silicone for the shower? and in the Guide: Silicone joint keeps cracking. You will find the complete range in the category sanitary silicone.
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