Which silicone for stainless steel?
Stainless steel needs a neutral-curing silicone, not an acetate silicone, because acetate silicones release acetic acid as they cure. For metal construction, façades and window connections OTTOSEAL S 110 is the all-rounder; in commercial kitchens, food businesses and clean rooms OTTOSEAL S 69 is suitable, which is also available in the colour stainless steel.
Contents
- Two questions, one search term
- Why acetoxy silicone does not belong on stainless steel
- The two candidates compared
- Detailed comparison
- Which do you take for what?
- The colour "stainless steel" – where to get it
- Preparation: the step at which stainless steel joints fail
- Common mistakes with stainless steel joints
- Frequently asked questions
- Unsure about your application?
What you need
Quantities adjustableIn short: A neutral-curing silicone belongs on stainless steel – not an acetoxy silicone. Acetoxy silicones release acetic acid as they cure; neutral-curing products are, according to the manufacturer, "non-corrosive". For metal construction, facades and window connections the OTTOSEAL S 110 construction silicone is the all-rounder. In commercial kitchens, food-processing plants and cleanrooms, reach for the OTTOSEAL S 69, which expressly causes "no (rust) corrosion on unprotected metal surfaces" and is also available in the colour stainless steel.
Two questions, one search term
"Stainless steel silicone" in practice means two completely different things – and anyone who confuses them buys the wrong thing for their need:
1. The substrate is stainless steel
Sink, worktop, handrail, facade profile, ventilation duct. Here the curing system decides – neutral rather than acetoxy.
2. The colour is called "stainless steel"
A metallic-grey silicone that visually matches the stainless steel surface. Here the colour chart decides, not the chemistry.
Both can be combined – the products that carry the colour stainless steel are neutral-curing anyway. Further down you will find a separate section on the colour.
Why acetoxy silicone does not belong on stainless steel
Acetoxy-curing silicones – those are the classic sanitary silicones that smell of vinegar – give off acetic acid as they cure. In the product description of the OTTOSEAL S 105 sanitary silicone it says so literally: "As it cures, small amounts of acetic acid are gradually released."
On glazed tiles and sanitary ceramics that is unproblematic. On metal it is a risk: in the narrow, poorly ventilated joint the acid stays in contact with the material for hours. With high-quality, dense stainless steel nothing usually happens – with thin, ground, damaged or inferior grades, tarnish colours and pitting can occur. In addition: there is seldom only stainless steel in the joint. Galvanised screws, aluminium profiles, chrome-plated parts or fixings in the substructure react considerably more sensitively.
Neutral-curing silicones avoid the problem by design. The S 110 as well as S 69, S 67 and S 70 are declared in the manufacturer's information as non-corrosive.
Rule of thumb for the building site: If the fresh joint smells of vinegar, it is an acetoxy silicone. Neutral systems smell considerably milder. When the S 110 cures, according to the manufacturer small amounts of an oxime compound are released – ensure good ventilation during application and curing.
The two candidates compared
OTTOSEAL S 110 construction silicone
Neutral-curing premium construction silicone for connection joints on windows and doors made of wood, metal and plastic as well as for joints on facades, metal constructions, terraces and balconies.
- Non-corrosive, with fungicidal additives
- Very good weather, ageing and UV resistance
- Highly abrasion-resistant and streak-free
- Tested to DIN 18545 part 2, load group E
- Complies with DIN 18540-F and ISO 11600 G 25 LM
- Around 30 colours, incl. silver grey, anthracite, manhattan
OTTOSEAL S 69 cleanroom silicone
Cleanroom silicone for joints with high hygiene requirements – production rooms, food and pharmaceutical areas, ventilation systems. Exactly where stainless steel is the standard material.
- Causes no (rust) corrosion on unprotected metal surfaces
- Fungicidal additives, resistance to mould growth
- Tested for the cleanroom sector by the Hygiene-Institut Gelsenkirchen
- For HVAC systems in accordance with VDI 6022 sheet 1, tested to DIN EN ISO 846 (methods A, B and C)
- French VOC emission class A+
- Available in the colour stainless steel
Detailed comparison
| Feature | OTTOSEAL S 110 | OTTOSEAL S 69 |
|---|---|---|
| Curing | Neutral (1K silicone) | Neutral (1K silicone) |
| Corrosion behaviour | Non-corrosive | Non-corrosive – no (rust) corrosion on unprotected metal surfaces |
| Main application | Metal constructions, facades, windows / doors, terraces, balconies | Cleanrooms, production rooms, food and pharmaceutical areas, ventilation systems |
| Outdoors | Yes – very good weather, ageing and UV resistance | Yes – for long-lasting applications indoors and outdoors |
| Hygiene evidence | TOXPROOF building materials list TÜV Rheinland | Hygiene-Institut Gelsenkirchen, VDI 6022 sh. 1, DIN EN ISO 846 |
| Standards | DIN 18545 pt 2 group E, DIN 18540-F, ISO 11600 G 25 LM | IVD data sheet no. 31 + 35, VOC class A+ |
| Colour "stainless steel" | No (but silver grey, manhattan, anthracite) | Yes |
| Application temperature | +5 °C to +35 °C | +5 °C to +35 °C |
| Pack size | 310 ml cartridge, 400 ml and 580 ml foil bag | 310 ml PE cartridge |
| Shelf life | At least 24 months, cool and dry | 12 months from production date (+5 °C to +25 °C) |
Which do you take for what?
Stainless steel handrail, facade profile, metal construction outdoors
→ S 110. Declared for exactly this, UV-stable, easy to match in the facade colour range.
Ventilation duct, HVAC system
→ S 69. Expressly suitable for use in HVAC systems in accordance with VDI 6022 sheet 1.
Stainless steel connection to natural stone
→ S 70. Guaranteed to cause no edge-zone staining on the stone, is non-corrosive and can even bond natural stone to metal with movement compensation.
All construction and window silicones at a glance →
The colour "stainless steel" – where to get it
If it is not the substrate you care about but the appearance: the colour stainless steel is a metallic grey visually matched to brushed stainless steel. In the OTTOSEAL range it is carried by:
- S 69 and S 67 – besides RAL 7035, RAL 9001, RAL 9002, RAL 9007, RAL 9010, RAL 9016, grey, manhattan and transparent
- S 70 natural stone silicone – as colour number C197 stainless steel
Important: colour representations on screen are only an approximation. With visible joints on prestige surfaces it is worth looking at the applicator colour chart or a trial joint at an inconspicuous spot. More on this in the guide Silicone colours – which ones there are and how you find the right one.
Preparation: the step at which stainless steel joints fail
Stainless steel is a non-porous substrate – the silicone cannot key mechanically but adheres purely by adhesion. That is why cleaning here is not cosmetics but the step that decides adhesion.
This is how it goes according to the manufacturer's specification:
- Remove all contamination – release agents, preservatives, grease, oil, dust, water, old adhesives and sealants.
- Clean non-porous substrates such as stainless steel with OTTO Cleaner T, flash-off time approx. 1 minute, with a clean, lint-free cloth.
- Bonding faces must be clean, free of grease, dry and sound.
- Only then seal. Application temperature +5 °C to +35 °C.
Fingerprints on freshly cleaned stainless steel are already enough to disturb adhesion locally – after cleaning do not touch the joint flank again. Grease and silicone residue on stainless steel surfaces can be loosened beforehand with a stainless steel cleaner; but the final wipe of the bonding faces belongs to the Cleaner T, because care products can leave residue.
For applying and smoothing: hand-operated, pneumatic or cordless gun, smoothing with smoothing agent and smoothing spatula before a skin forms. The basics are in the guide Applying silicone – the complete instructions, the right joint geometry in the guide How wide may a silicone joint be?.
Common mistakes with stainless steel joints
| Mistake | Consequence | Better like this |
|---|---|---|
| Acetoxy silicone from the DIY store used | Acetic acid in the joint, corrosion risk on metal parts | Choose neutral-curing silicone |
| Only wiped dry | Grease and oil film remains, joint comes away after weeks | Clean with OTTO Cleaner T, flash off for 1 minute |
| Joint made with adhesion at the back of the joint as well | Silicone cracks when there is movement | Insert a round cord, let only two flanks adhere |
| Applied below +5 °C | Skin formation and curing disturbed | Keep to the application window +5 °C to +35 °C |
| Contact with EPDM, butyl or neoprene | Plasticiser migration, discolouration, loss of adhesion | Avoid contact with plasticiser-releasing materials |
Frequently asked questions
Can silicone really attack stainless steel?
High-quality, undamaged stainless steel is robust. The risk arises from the combination of acetic acid from an acetoxy silicone, a narrow, poorly ventilated joint and moisture – and it affects above all thin, ground or inferior grades as well as adjoining metals such as galvanising or aluminium. Neutral-curing silicones are declared by the manufacturer as non-corrosive and avoid the question completely.
Do I need a primer on stainless steel?
In many cases not, if it was prepared cleanly with OTTO Cleaner T. The manufacturer does point out, however, that good adhesion on many substrates is achieved "in part in conjunction with primer". With high loads – strong temperature fluctuations, expansion and shear forces, repeated contact with water – an adhesion test on an offcut is the safe variant.
What is the difference between S 67 and S 69?
Both are cleanroom silicones with an identical application profile, the same tests and the same colour range including the colour stainless steel. The differences lie in the detail – the separate guide OTTOSEAL S 67 or S 69 – which cleanroom silicone? works them out.
Which silicone for the stainless steel sink in the kitchen?
The sink-to-worktop connection is a classic sanitary joint on metal. Neutral-curing is the safe choice here – with natural stone worktops in addition compulsory, because acetoxy systems can cause edge-zone staining. The S 70 is tested for that (ISO 16938-1 and ASTM C 1248). Details in the guide Which silicone for natural stone?.
Does silicone hold on stainless steel permanently?
Yes – if the bonding face is free of grease and the joint was made adhering only at the flanks. If a joint comes away nevertheless, it is almost always down to residue on the metal surface or to a joint adhering at the back of the joint as well. The causes are broken down in the guide Silicone joint coming away – causes and solution.
Can I bond stainless steel with silicone?
No. According to the manufacturer, one-component silicones are "not suitable for bonding over a large area unless the special structural prerequisites for it are given". For bonding on metal there are separate products – see the guide Bonding with silicone – what holds and what does not.
Unsure about your application?
Give us a call – we will clarify with you which product suits your substrate and your load.
Baustoffheld
Lindenstrasse 56, 47623 Kevelaer
Telephone: +49 (0) 2831 – 916 77 03
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