Short answer: Both are natural-stone-compatible, both cause no edge-zone staining, both have a fungicidal finish and are available in matt colour shades. The practical difference lies in the smell: S 80 is low-odour and therefore the choice for occupied or used rooms – flats, hotels, catering, projects where people are present during the work. S 70 is the premium natural stone silicone with the broader standards profile and the larger pack sizes, the first choice outdoors and on larger areas. Where smell does not matter, go for S 70; where it is a nuisance, for S 80.
Why natural stone needs its own silicone
An ordinary sanitary silicone on a marble slab is one of the most expensive mistakes in interior fit-out. The reason is called edge-zone staining.
Classic silicones contain components that do not stay permanently bound in the material – plasticisers and low-molecular-weight fractions. On a glazed tile this has no consequences: the surface is closed, nothing can penetrate. Natural stone, by contrast, is porous. Marble, limestone, sandstone, many granites and practically all agglomerate marbles absorb these components.
The result is dark, greasy-looking edges that draw into the stone to the left and right of the joint. They do not appear immediately but over weeks and months, they get wider over time, and they can no longer be removed. No cleaner gets them out, because the staining sits not on but in the stone. What remains is sanding and repolishing the surface – annoying on a window sill, really expensive on a kitchen worktop or a staircase.
A natural stone silicone is formulated so that this migration does not take place. That is exactly its purpose, and exactly what the extra cost pays for.
Important: “Sanitary silicone” and “natural stone silicone” are not marketing variants of the same product but different formulations. A product without express natural stone approval does not belong on natural stone – not even “just this one joint”.
Head to head
| Ottoseal S 70 | Ottoseal S 80 | |
|---|---|---|
| Classification | premium natural stone silicone | low-odour natural stone silicone |
| Natural-stone-compatible | yes | yes |
| Edge-zone staining | no | no |
| Smell during application | normal | low-odour |
| Fungicidal finish | yes | yes |
| Colour shades | matt | matt |
| Weathering, ageing, UV | very good | very good |
| Indoors | yes | yes |
| Outdoors | yes | yes |
| Pack size | 310 ml and 400 ml, also as a matt variant | 310 ml |
The table shows why the question is asked so often: on paper the products are largely identical. Both seal marble and natural stone without discolouring it, both last outdoors, both are finished against mould growth.
The standards profile of S 70
Anyone tendering for a project or needing proof will find a broad test profile for S 70 under EN 15651, the European standard for sealants for joints in building construction:
| Part | Field of application | Classification S 70 |
|---|---|---|
| Part 1 | facade elements | F EXT-INT 25 LM or F EXT-INT CC 20 LM |
| Part 3 | sanitary area | XS 1 |
| Part 4 | joints in pedestrian and traffic areas | PW EXT-INT 25 LM (matt colour shades only) |
Two details in this table are important in practice:
“LM” stands for “low modulus”, that is low modulus of elasticity. Such sealants absorb movement with low restoring force. With natural stone that is decisive: a hard joint pulls at the joint flanks on movement and, with soft stone, can break out edges.
The restriction in Part 4 is not small print but a real turning point. The classification PW EXT-INT 25 LM for pedestrian and traffic areas applies only to the matt colour shades; the others achieve PW INT 12.5 E. If you are sealing a joint in a surface that is walked on – stairs, landings, floor connections – the specific colour shade matters, not just the product.
When to use which product
Take S 80 when smell is an issue
That is the case more often than you think. Typical situations:
The occupied flat where the bathroom is being renovated and the residents come back in the evening. The hotel where individual rooms are refurbished during operation. The catering trade, where joints on natural stone counters and floors are done at night and business carries on in the morning. Interior fit-out in offices and practices where people are working next door.
It also matters for you personally: anyone who spends a day applying joints in a small, poorly ventilated bathroom notices the difference clearly.
Take S 70 when it goes outdoors or there is a lot of it
Outdoors, at facade connections, at natural stone plinths, at terrace and balcony connections, S 70 is the product with the broader proven profile.
On top of that comes a very practical point: it is also available in a 400 ml pack. With greater joint lengths that means fewer cartridge changes, fewer start points and less waste – on a building site with a hundred metres of joint that is no small thing.
And if both apply?
An occupied interior and at the same time a large joint length – then what counts for more decides. As a rule of thumb: as soon as people use the room during or immediately after the work, S 80 wins. The time saved by the larger pack is quickly eaten up if a room is unusable for one day longer.
Application: what also matters with natural stone
The right product is half the battle. The other half is the application, and with natural stone there are a few points that go beyond the standard.
Check the smoothing agent
The usual washing-up liquid and water mixture has no place on natural stone. Surfactants can soak into the open-pored stone and leave lighter or darker shadows there – of all places along the freshly applied joint. Use a smoothing agent that is expressly approved for natural stone, and use it sparingly.
Mask off and pull off immediately
On polished stone, silicone smears are laborious to remove. Mask off both joint flanks cleanly and pull the tape off immediately after smoothing, while the silicone has not yet skinned over – at an angle outwards, not upwards.
Avoid adhesion to the joint back
The joint may adhere only to two flanks, not to the joint back. Otherwise it tears at the first movement. A backer rod made of closed-cell PE foam ensures this. The right dimensions are in the guide to joint width and joint depth.
Test critical stones beforehand
Very absorbent and light-coloured stones – some limestones, sandstones, light marble – react more sensitively than others. A trial joint on an offcut or at a concealed spot, left for at least a week, costs little and answers the question conclusively.
The general rules for applying joints cleanly – substrate, cutting the nozzle, dispensing angle, smoothing in one pass – apply unchanged and are in the guide to working with silicone.
The colour shade
Both products are available in matt colour shades, and that is no coincidence. Natural stone – apart from polished marble and granite – is predominantly matt. A glossy silicone joint next to a matt stone surface stands out immediately because it throws the light back differently from everything around it. With matt joints this effect disappears.
For the colour choice itself the same applies as for any other silicone joint: the grout is the reference, not the stone colour, and it is judged only after curing. How to arrive systematically at the right shade is explained in the article on silicone colours.
A note specifically on S 70: if the joint lies in a surface that is walked on, the colour shade also decides the normative classification – there the matt version is the right choice.
Which stones are critical
Not every stone reacts equally sensitively. Roughly: the lighter and more absorbent, the greater the risk.
| Stone | Risk of edge-zone staining | Note |
|---|---|---|
| Marble, light | very high | the classic case of damage |
| Limestone, Jura | very high | absorbent and light |
| Travertine | high | open-pored, still absorbent even when filled |
| Sandstone | high | strongly absorbent |
| Agglomerate marble, artificial marble | high | binder reacts additionally sensitively |
| Granite, polished | medium | denser, but not impermeable |
| Slate | medium | dark, discolouration is less noticeable |
| Quartz composite | medium | observe manufacturer's information, synthetic resin content |
| Ceramic, porcelain stoneware | low | closed surface |
“Low” does not mean “irrelevant”: even with polished granite and dark slate a natural stone silicone is the safe choice, because the polish does not close the pores completely and because open surfaces always arise at cut edges.
A special case is stones that have already been impregnated. A stain-protection impregnation reduces the risk but does not replace the right product – it wears off at the joint flank and is removed during cleaning. The decision for the natural stone silicone is made independently of it.
What neither of them can do
A natural stone silicone is a joint sealant, not an all-rounder. Four distinctions that are regularly overlooked in practice:
Silicone seals and absorbs movement, it does not carry loads. Gluing a natural stone slab to the wall is therefore not possible – there are adhesives matched to natural stone for that.
Where components move, the joint has to be planned in position and width. An elastic sealant in a joint that is too narrow tears anyway – only after two years instead of after two months.
Like all silicones, S 70 and S 80 do not accept paint. Where painting over is necessary – for example at connections to painted components – a different sealant comes into question, which must then be natural-stone-compatible.
Practically no sealant adheres to PE, PP and PTFE. Where a natural stone joint meets such components, adhesion must be clarified beforehand – if necessary with a test on an offcut.
Calculating consumption
The calculation is simple and avoids the annoyance of standing in the middle of a joint with no material:
Joint width (mm) × joint depth (mm) = consumption in millilitres per running metre.
| Joint | per running metre | 310 ml cartridge covers | 400 ml pack covers |
|---|---|---|---|
| 6 × 6 mm | 36 ml | approx. 8.6 m | approx. 11.1 m |
| 8 × 8 mm | 64 ml | approx. 4.8 m | approx. 6.3 m |
| 10 × 10 mm | 100 ml | approx. 3.1 m | approx. 4.0 m |
| 15 × 10 mm | 150 ml | approx. 2.1 m | approx. 2.7 m |
Allow 10 to 15 percent extra for waste, start-up losses and the residue in the cartridge. And note: with wide joints the depth is not made equal to the width, but shallower – the specific dimensions are in the linked guide to joint width and joint depth.
This is where the practical value of the 400 ml pack of S 70 shows: with an 8 × 8 mm joint, one unit covers a good metre and a half more. On a building site with many running metres that saves a noticeable number of changes – and every change avoided is a start point avoided.
Frequently asked questions
What is the difference between Ottoseal S 70 and S 80?
Both are natural-stone-compatible, cause no edge-zone staining, have a fungicidal finish and are available in matt colours. S 80 is additionally low-odour and therefore the more pleasant choice for occupied rooms. S 70 is the premium product with the broader test profile under EN 15651 and is additionally available in a 400 ml pack.
Can I use ordinary sanitary silicone on natural stone?
No. Plasticisers and low-molecular-weight fractions migrate into the porous stone and produce dark edges along the joint. The staining sits in the stone, not on it, and can only be removed by sanding and repolishing.
Which silicone do I use for marble?
A designated natural stone silicone – S 70 or S 80. Marble is among the most sensitive stones of all when it comes to edge-zone staining. With very light marble, a trial joint on an offcut is also worthwhile.
Are S 70 and S 80 also suitable for outdoor use?
Both are resistant to weathering, ageing and UV and are rated for indoor and outdoor use. For facade and floor connections with proof of standards compliance, S 70 is the product with the broader test profile.
What exactly does edge-zone staining mean?
The discolouration that arises when components from the sealant migrate into the adjoining porous stone. It becomes visible as a dark, greasy-looking strip on both sides of the joint, which grows wider over weeks. It is irreversible.
Can I also use S 70 or S 80 to joint ordinary tiles?
Technically yes – a natural stone silicone also works on ceramics. Economically it usually makes no sense, because an ordinary sanitary silicone does the same there and is cheaper. Where natural stone and ceramic adjoin, use the natural stone product throughout.
Why are natural stone silicones matt?
Because natural stone is predominantly matt. A glossy joint next to a matt surface reflects differently and therefore stands out. With S 70 the matt colour shade also has normative significance: only the matt shades achieve the classification for pedestrian and traffic areas.
How long does a natural stone joint last?
With clean application – correct joint dimensions, backer rod, no joint-back contact – five to ten years indoors is realistic. Outdoors and in heavily used areas, rather at the lower end of this range. For care and cleaning there is a separate article on cleaning silicone joints.
What does “LM” mean in the standard designation?
“Low modulus”, that is low modulus of elasticity: the sealant absorbs movement with low restoring force and therefore pulls less at the joint flanks. With soft and fracture-sensitive stones this is important, because a hard joint can cause edges to break out.
How many cartridges do I need?
Joint width in mm times joint depth in mm gives the consumption in millilitres per running metre. An 8 × 8 mm joint needs 64 ml per metre, so a 310 ml cartridge covers just under 5 metres, the 400 ml pack a good 6. Allow 10 to 15 percent extra.
Do I need a primer on natural stone?
With strongly absorbent and open-pored stones, a primer can improve adhesion considerably. Whether and which one depends on stone and product – this is in the technical data sheet. Where you are unsure, an adhesion test on an offcut decides, which you leave for a week and then pull off.
