Silicone Putty Recipe
Which Selleys silicone is a "100% clear silicone caulk that smells vinegary when curing"?
The smell is the identifier you are looking for. Silicones that give off a vinegar smell while curing are acetic curing silicones — they release acetic acid during the curing process, and that acid is what you can smell. In the Selleys range the clear acetic product is Selleys Glass Silicone Sealant, which is a 100% silicone sealant, supplied clear, and listed on its technical data sheet as acetic cure.
One important caveat comes with that recommendation, and it comes from Selleys directly: test the product and satisfy yourself that it is suitable for your particular application or purpose before you rely on it. Mould making is not an application Selleys publishes data for, and no Selleys technical data sheet covers mixing its sealants with other materials. Nothing on this page tells you a home-made putty recipe will work, cure predictably, or be safe to handle — that is entirely a matter for your own testing.
Acetic versus neutral cure, in plain terms
Every one-part silicone sealant has to give something off as it reacts with atmospheric moisture and turns from a paste into a rubber. What it gives off is how the two families are named.
- Acetic cure silicones release acetic acid. Strong vinegar smell for the first day or so. They bond well to glass, glazed ceramics and porcelain.
- Neutral cure silicones cure without releasing that acid. They are the choice wherever the acid could affect the substrate — mirror backings, stone, sensitive metals.
If a recipe or set of instructions specifies "the one that smells like vinegar", it is specifying an acetic cure product, and a neutral cure silicone is not a substitute for it.
Which Selleys silicones are acetic cure?
From their published technical data sheets:
- Glass Silicone Sealant — acetic cure, clear, 75 g tube or 310 g cartridge.
- No Mould Silicone Sealant — acetic cure, transparent or white.
- White For Life Silicone Sealant — acetic cure, white.
- Silicone 401 RTV — acid cure, clear, an industrial form-in-place gasket and electrical insulating product.
Of those, Glass Silicone is the one Selleys nominates in answer to this question, and it is the only one of the four that is both clear and a general consumer product.
Glass Silicone Sealant specifications
| Property | Typical result |
|---|---|
| Technology | Acetic cure silicone sealant, 100% silicone |
| Colour | Clear |
| Packaging | 75 g tube, 310 g cartridge |
| Skin time | 5–10 minutes (weather dependent) |
| Curing rate | 2 mm per day |
| Full cure | 72 hours |
| Elongation | Approx. 400% (ASTM D412) |
| Joint movement capability | ±25% |
| Service temperature | Permanent −60 °C to +150 °C |
Indicative data only, not intended for the preparation of specifications.
What the cure figures mean in practice
The two numbers that catch people out are the skin time and the cure rate, and they measure different things.
Skin time of 5 to 10 minutes is how long the surface stays workable. Past that, the outside has formed a film, and anything you do to it tears rather than smooths. It is weather dependent — warm, breezy conditions shorten it.
A cure rate of 2 mm per day is how fast the cure front travels inwards from that skin. It is the reason a thick section of silicone is not simply a slow version of a thin one: 2 mm cures in a day, 6 mm takes three days, and material sealed away from air does not cure at all. This is also why Selleys states that Silicone 401 should not be used in totally confined joints where the sealant is not exposed to atmospheric moisture. Any use that encloses uncured silicone inside a mass of material is working against the chemistry.
Where Glass Silicone is designed to be used
Its published uses are on or around windows and window frames, and in aquariums. It will bond to glass, glazed ceramics, porcelain, stainless steel, most woods, aluminium, many plastics, rubber and canvas.
For aquarium use specifically, Selleys' handy hints require you to allow it to cure for 7 days, then thoroughly wash out the tank with water, drain and refill it before introducing fish. It is described as suitable for constructing and repairing small aquariums; large tanks need specialist design.
Limitations
- Not recommended for use on concrete, cement products, zinc, or metals containing copper.
- Not recommended for below waterline applications, with glass aquariums the stated exception.
- Not for mirrors. The technical data sheet directs you to Liquid Nails Mirror & Metal instead.
- Not paintable. Complete any painting 7 days before applying the sealant.
- Storage. Store in a dry place below 30 °C, and use within 6 months of opening.
- Ventilation. Use in a well ventilated area and avoid contact with skin and eyes.
Reading the safety data sheet before you experiment
If you are considering any use outside the published directions — and mixing a sealant with another material is exactly that — read the product's safety data sheet first. Every Selleys safety data sheet is listed at Selleys Safety Data Sheets, and each is also linked from its own product page under Downloads. Technical data sheets are collected at technical documents. If you cannot find the sheet you need, Selleys' help and advice team can be reached through contact us.
Common questions
Why does some silicone smell like vinegar?
Because it is an acetic curing silicone, which releases acetic acid during the curing process.
Which Selleys product is a clear acetic cure silicone?
Glass Silicone Sealant. It is 100% silicone, acetic cure, and supplied clear in a 75 g tube or a 310 g cartridge.
Is a neutral cure silicone an acceptable substitute?
Not where the instructions call for the vinegary type. Neutral cure products cure by a different chemistry and do not release acetic acid.
Will Selleys confirm a silicone is suitable for mould making?
No. Selleys' advice on this question is to test and ensure the product is suitable for your particular application or purpose. There is no published data for that use.
How long does Glass Silicone take to cure?
It skins in 5–10 minutes and cures in 72 hours, at a rate of about 2 mm per day. Thicker sections take proportionally longer.
Can it be used in an aquarium?
Yes, for constructing and repairing small aquariums. Allow 7 days cure, then wash the tank out thoroughly with water, drain and refill before introducing fish. Large tanks require specialist design.
Can I paint over it?
No. Complete painting 7 days before applying the sealant.
How do I clean it up?
Uncured product with mineral turpentine. Cured product has to be removed with Selleys Sealant Remover or by cutting and scraping.
How long does an opened tube last?
Use within 6 months of opening, stored in a dry place below 30 °C.
Where do I find the safety data sheet?
On the product page under Downloads, or through the full safety data sheets listing.
What question was originally submitted to Selleys on this 'Ask an Expert' page?
A user asked about a silicone putty recipe for mould making that combines cornstarch and silicone as main ingredients. The recipe called for 100% clear silicone caulk that smells vinegary when curing, and specifically warned against using 'GE' or newer types of silicone. The user asked Selleys to suggest products they could try instead.
Does Selleys provide a recipe or formulation for making silicone putty from raw materials?
No. Selleys' available information focuses on finished, ready-to-use Selleys brand silicone sealant products rather than recipes or formulations for manufacturing silicone putty or sealants from raw materials like cornstarch and silicone caulk.
What type of silicone product was the user trying to avoid in their putty recipe?
The user's recipe specified not to use 'GE' silicone or newer types of silicone, and instead called for a 100% clear silicone caulk that smells vinegary (acetic/acid-cure) while curing.
What kind of Selleys products could be relevant to someone looking for a silicone caulk that smells vinegary when curing?
Selleys offers acid-cure silicone products such as Silicone 401 RTV, which is described as an acid-cure silicone adhesive sealant — a category that would produce the vinegary smell during curing referenced in the user's recipe.
What other finished silicone sealant products does Selleys offer besides acid-cure options?
Selleys also offers Wet Area Silicone (100% silicone sealant), Pro-Trade All Purpose Silicone (neutral cure), and No Mould Silicone Sealant, in addition to acid-cure products like Silicone 401 RTV.
Can Selleys provide technical formulation guidance for manufacturing sealants from raw materials?
No. For detailed technical recipes or formulation guidance for manufacturing sealants from raw materials, Selleys advises consulting with silicone chemistry specialists or material suppliers who specialize in sealant component formulations.
What topics can Selleys' expert information help with regarding silicone sealants?
Selleys' available information can help with ready-to-use silicone sealant products, application methods, surface preparation requirements, curing times and performance characteristics, storage and handling guidelines, and cleanup procedures for uncured and cured sealants.