Why shouldn't you use Plumber's Mait with flush valves?

[SenileGit]

I've just installed a new flush valve and noticed after I finished that the instructions say "IMPORTANT: DO NOT use plumbing sealing compounds". This is written above the address of the company, not within the instructions themselves.
At this point I wasn't up to taking it all apart and trying to remove all the Plumber's Mait from the large rubber washer. Does anybody know the reason you shouldn't use 'plumbing sealing compounds'?
I used Plumber's Mait on the old flush valve too, and I suddenly remembered that the instructions back then also said the same thing, but this was only written as an afterthought, outside of the main instructions themselves, and I thought exactly the same thing - I'm not taking it all apart again! If they had any sense they would include the notice about plumbing compounds within the instructions, where it tells you to "ensure the 10mm internal seal washer is on the thread shank first".
The previous flush valve wasn't working well - it might not flush all the way down, or if it did flush all the way down, it would often stick and would continue to flush, until you fiddled with the handle. Could this be caused by an accumulation of Plumber's Mait residue in the water in the cistern? I don't know.

 

[johnny2007]

I never used any compound on a new cistern and never had a leak.
Usually washers and joints leak when they're disturbed.

 

[blup]

I doubt plumbers mait is going to be worse than the action of water with all its scale and other impurities.

Blup

 

[Madrab]

Absolutely no need for any sealing compound, a clean cistern with a new clean washer will very rarely leak. Adding compounds may either lubricate the washer where it ends up mis-shapen and doesn't sit properly or the medium used may not be chemically compatible.

Shouldn't get into the workings unless there was a ridiculous amount applied. Plumbers mate is terrible stuff IMO, gets everywhere when trying to disassemble stuff.

 

[SenileGit]

Madrab, I don't understand what you mean about it lubicrating the washer and making it mis-shapen - do you mean the washer can sort of slide out of position around the thread shank?
I would much rather not use Plumber's Mait - I won't use it from now on, I just didn't realise because the note on the instructions sheet was on the last place you look, which is daft in my opinion. I agree that it's a right pain to use, it sticks to my fingers and application is very difficult, and it's incredibly difficult to remove from rubber washers.

 

[fidom]

I would not use stuff like that unless you have a problem. These things don't tend to leak if assembled correctly with the washers provided. The only plumbing joints that worry me are PTFE taped threaded fittings. They date back to the days of iron pipe that needed a thread cut on each end. These days we have stuff like O rings, so I would like threaded fittings consigned to room 101!

 

[oldbuffer]

1. Plumbers Mait contains oil which can cause rubber to deteriorate.
2. I quite like Plumber's Mait, but only for sealing between waste flange and basin / bath top surface, rather than the rubbish foam type washers usually supplied. It can be cleaned off with white spirit.

 

[Madrab]

Madrab, I don't understand what you mean about it lubricating the washer and making it mis-shapen - do you mean the washer can sort of slide out of position around the thread shank?

Exactly, same things happens when too much silicone is uses - it lubricates the seal and it can be squeezed out rather than the surfaces grabbing it.

With a flush valve or fill valve - everything nice and clean and dry inside then hand tight the nut and a further half a turn should be all it needs

 

[Bod ...]

I never used any compound on a new cistern and never had a leak.
Usually washers and joints leak when they're disturbed.

That is dependent on the quality of the sanitary and the gubbins going into the cistern.

I always chuck the washers for basins and use a Dow Corning

 

[Bod ...]

Had two toilets today stuck together with silicone. I mean everything stuck. No screws just sticky stuff.

 

[johnny2007]

That is dependent on the quality of the sanitary and the gubbins going into the cistern.

I always chuck the washers for basins and use a Dow Corning

If I can, I use basin mate.
A brass nut for the waste is essential, I have a pot of them.
And yes, some washers are rubbish, but I prefer to replace with a better washer rather than silicone.
That's just me thinking about future maintenance.

 

[Bod ...]

If I can, I use basin mate.
A brass nut for the waste is essential, I have a pot of them.
And yes, some washers are rubbish, but I prefer to replace with a better washer rather than silicone.
That's just me thinking about future maintenance.

I don't paste the stuff as I'm with you on this. Its more than likely me who be fixing any future problems.

 

[Madrab]

I find it's all about using the right amount, as with anything. The trick I use with basins is just enough silicone applied into the gap around the shank of the waste and then a coated finger amount to just fill the threads where the nut will sit. I find plastic nut absolutely fine. They don't need racked up super tight, hand tight with just another 1/2 > full turn with a par of grips is all they should need.