Monobloc tap unable to tighten on ceramic sink

[foxhole]

Lower rubber washer locks the tap preventing movement while the nylon washer allow friction free tightening of the nut . The spacer is required for tops thinner than 35mm ( as instructions state.)

 

[johnbuckley]

Yeahaaa - 29 posts for fitting a tap lol

The hand nut with the brass thread should be able to go tight enough to allow the tap to be secured properly so it doesn't move. If it is moving then it can only be certain things. It's not tight enough, the o ring isn't large enough and isn't gripping properly or the surface or the o ring is slidy allowing the tap to move. Any tap on a ceramic sink shouldn't be overtightened, as it can damage/crack the ceramic.

I'd take the o ring out and clean it all up and the seals for underneath and underneath the sink itself and try again. If it still moves then time for a little silicone adhesive (not sealant).

Thank you for that. Yes I was thinking the same; a bit embarrasing really!
I have cleaned everything including the o ring. I was concerned a bit with regard to over tightening so, if I ever find a back nut I'll take care. I did tighten the supplied hand nut as far as I was able and I had a pretty good grip of it. The size of the o ring is a consideration and it's the one supplied with the tap although when looking at it fitted into the tap body, the protrusion is miniscule; just measured it and it protruded 0.4mm from the body of the tap; not sure if this would be enough when compressed; could this be the problem? I'll see if a thicker o ring is available at the plumbers merchants tomorrow.
Good call on the adhesive, I would have used plain silicone!

 

[johnbuckley]

Lower rubber washer locks the tap preventing movement while the nylon washer allow friction free tightening of the nut . The spacer is required for tops thinner than 35mm ( as instructions state.)

Thanks for that. I did use the plastic spacer initially until I realised, still didn't tighten with the spacer removed and the lower rubber washer and steel washer in place.

 

[johnbuckley]

Quick update. Tried 3 plumbers merchants for a back nut and all said not available as they are all bsp and my thread is a fine one. Out of time to keep searching for something that may not exist so I decided to go with advice above and use some CT1 under the base of the tap and O ring, got the supplied plastic nut as hand tight as I could and a little nip up with some water pump pliers; this morning all feels secure so job done.

Thanks for all replies to what has always been a straight forward job for me in the past.