Cistern - Hairline crack

Plus a wooden prop, presumably in view, a constant reminder to get a replacement.

Try and force it INTO the crack

If it were me, I'd slather the crack with rapid araldite, both inside and out, making sure the surfaces are completely dry of course.

Before doing anything else, I'd try and work some very thin, runny superglue (cyanoacrylate) into the crack.

Then anything waterproof over the top.

Any liklihood that the crack will propagate to somewhere more structural? Or is it just sealing required?

nib

You need Captain Tolley's - great stuff for exactly the problem you have:

Interesting product - never heard of that. Filed for later use.

Fracture mechanics has it that the stress at a crack tip is almost infinitely high. It's inversely proportional to the radius of the crack tip, which approaches zero.

But if the toilet is going to be replaced within a year, I wouldn't bother!

I think someone here recommended it when I asked about a similar problem

- maybe 5-6 years ago. I used it on a cracked cloakroom washbasin (we inherited the crack with the house) and the washbasin is still going strong and waiting for the decorating tuit for that room to reach the top of the list.

Thanks, before I read your post I had smeared some araldite on the inside only as I was reluctant to take the cistern off.

However I think I've made an error with trying to shortcut things and using the same seals, ie the one at the bottom of the syphon and the doughnut seal where the cistern sits on the bowl and I think water is seeping there.

So the good news is that the original problem: Subject: Toilet flush panic - visitors tomorrw Date: Fri, 11 Jul 2025 20:16:38 GMT

has been fixed. Just replaced the torn plastic "floor" to the lifting chamber with a similar thickness piece of plastic.

The bad news is the crack and the seeping. I guess I'm going to have to take it all apart again and get new seals unless anyone here has a clever answer.

What I don't know is how tight either joint should be fastened so I don't know whether I've gone too tight or not tight enough.

That was my thought. When the cistern is screwed back to the wall the crack may just propagate further. The usual way of stopping this is to drill a small hole at the end of the crack before filling.

Probably some silicone sealant on the inside will do. Fill the drill hole and a surface smear up the crack.

Unless you are 110% sure it isn’t going to ‘drop’ or otherwise move, causing the crack to spread, and cistern to fall apart, I’d replace it or fit a isolation valve with a lever and sign to remind people to close it.

Our neighbour had a failure in a toilet cistern while they were away. We saw water from the overflow but couldn’t contact them. I tried to turn off the outside stopcock, it was stuck. Eventually a plumber managed to do it. The water damage was unbelievable. They were living in a hotel for months while repairs were made.

A good trick is to use 'sanitary silicone sealer' and then while not set screw the fitting down till it squidges out everywhere, then leave to set and tighten down on the silicone gasket you have just created.

Seems to be just the fix I'm looking for an have ordered some, though I prefer to buy from Ebay.

I had used some araldite on the inside only but after seeing water on the floor I've taken the cistern off, put it over a sink, filled it up and observed best I can. The crack is more extensive than I though when I see it from the outside and hopefully Captain Tolley will come to the rescue.

Also having seen videos of the doughnut I think that trying to resuse the old one might be a mistake though of course if the toilet is not being flushed then that can't be the cause of any seepage.

Cheaper in larger amounts direct:

Indeed and already noted but I'm hoping 60ml will be sufficient for the one crack of a cistern that I'm intending will be my last such issue seeing as I've managed to my age without needing it before.