Screw Caps

Right. So I have finally discovered why silicone sealant always ends up costing about three times what it says on the tube. It is not because the stuff is expensive, or because I apply it like I am icing a cake, or because I do DIY in the normal British way: 20 minutes of optimism followed by two days of swearing and a trip to Screwfix. 

It is because the moment you open a tube of silicone, you are no longer the owner of that sealant. You are merely the caretaker of a slow chemical process that is absolutely determined to turn your money into rubber.

And yes, before anyone starts, I did not just leave it sitting there with the nozzle open like a yoghurt pot in the sun. I did what every vaguely competent person does when they want to keep a cartridge usable. I jammed a nail in it, wrapped it in clingfilm, taped it, and generally performed the traditional rites of silicone preservation. It still set, because silicone does not respect folk remedies, no matter how confidently you apply them.

The key thing people miss is that silicone is not “drying” like paint. It is curing, which means a chemical reaction is taking place. Most household silicone is moisture curing, so it reacts with water vapour in the air and cross links into a solid rubber. That is literally the job. That is why it exists. Once you have squeezed out a bead and the sealant at the tip has met air, the reaction has started, and you have effectively lit the fuse. Blocking the opening afterwards is not the same as stopping the chemistry, especially if you have trapped a little pocket of moisture around the end.

In fact, a nail can make things worse, which is the sort of news that makes you want to sit down. The sealant cures from the outside in, so you get a plug forming at the tip. But if the nail does not seal perfectly, or if it leaves a tiny path for humid air to creep in, you have created a slow leak of moisture into a confined space. That is basically ideal conditions for curing, like a tiny damp greenhouse for polymers. Over weeks, the curing front can move deeper into the nozzle, and sometimes into the cartridge itself, until the whole thing turns into a rubber baton. You do not just lose the nozzle, you lose the tube, and you are left holding a perfectly cured product that is now only useful as a doorstop or an insult.

Clingfilm is not much better. It feels clever, because it is what you use to keep food fresh, and silicone is basically just a condiment for bathrooms. But clingfilm does not make an airtight seal on a nozzle that is already sticky, and it can trap moisture as well. So you come back a month later and unwrap a damp little parcel of disappointment, only to find the nozzle has become a solid plasticised fossil. You poke it with a nail, drill it out, cut it back, cut it back again, and eventually the hole is so wide that any “neat bead” becomes a kind of architectural extrusion.

I have tried those little caps that go on the nozzle too, and they are a lovely idea if you have never actually met silicone sealant in real life. In practice, they do not stop the nozzle curing, they simply help it cure neatly and efficiently. The nozzle still sets solid, because it is still full of sealant and still exposed to whatever air and moisture you have failed to exclude. It is like putting a hat on a man who is drowning. He looks slightly more presentable, but the outcome is unchanged.

So I assumed this was simply the way of things. Like printer ink, or washing machines that sound like a helicopter, or the fact that every “ten minute job” becomes a three hour saga involving blood. I assumed we were all meant to accept that half a tube of silicone will inevitably be sacrificed to the gods, and the only question is how quickly it happens.

And then I discovered these screw caps. Not the nozzle caps, not the little hats for the end of the applicator, but proper caps that screw onto the thread of the tube itself. Which means you can remove the nozzle entirely and seal the cartridge like a normal, civilised container, rather than a one shot dispenser designed to self destruct the moment you stop looking at it. It is such an obvious idea that it immediately raises the question: why have I never seen them before?

Because I have been to tool shops. I have bought more sealant than any household should ever need. I have watched tradesmen do this stuff in ten seconds flat while holding a coffee and a cigarette and somehow still get a perfect finish. I have never once seen someone casually whip out one of these caps and reseal a tube properly. Which suggests either it is a new invention, or it has been deliberately kept from the public by Big Sealant, who make a tidy living off the fact that we all accept waste as normal.

The funniest part is how I found out. I did not learn this from a builder, or from a DIY forum where the usual advice is to store it upside down and sacrifice a goat. I learned it by asking ChatGPT, because apparently we have reached the stage of civilisation where you ask a robot how to stop a tube of goo turning into a brick. And the robot, to its credit, did not recommend another nail. It did not recommend more clingfilm. It did not recommend prayer. It simply pointed out that there is a cap, a simple screw cap, that seals the tube properly. It has taken me 70 years to learn this.

So yes, I am buying a bag of them. I am putting them in the drawer. I will never again lose half a tube of silicone to the slow, inevitable chemistry of moisture curing cross linking, quietly turning my money into rubber while I am off making a cup of tea. If anyone asks why I am so pleased with a tiny orange plastic cap, I will tell them the truth. It is because I have finally won a long war against a tube of sealant, and that is as close to victory as British DIY ever gets.