Mapei Advise caulk or ptfe under their Silicon?

[tom1976]

Hi Folks,
Following a near disaster (using dispersant addy over Mapegum) I was not looking to repeat any mistakes so emailed and spoke with Mapei technical. Situation is two walls joining at 90 degrees, one over suspended floor, other masonry, hence need to use flexible joint, not just grout.

Looking into the gap between the walls 2-3mm you see mapegum over the mapei tape. I asked Mapei whether thier AC Silicon would be ok in contact with their Mapegum. They kinda scoffed- why would their Silicon be touching the mapegum in a wall joint?!!? I explained as above-wanting a flexible joint.

At this point he said to fill the gap with ptfe tape. Has anyone heard of this? He explained why, kind of, and also said that caulk could alternatively be used to largely fill the gap over which you can use the mapesil ac. I had visions of how many rolls of the plumbers white ptfe tape i'd need to fill all the vertical and horizontal gaps in the bathroom!!!

A little research lead me to 'backing rod'- a worm of spongy stuff that takes up voids and allows creation of the 'proper' Silicon seal. That is one that is no deeper than half it's width and not stuck rigidly to more than two sides. More wizardry. it does make sense now- that the material can behave best when given a form and scale that allows it to work best...

What do you people do.... I'd imagined that gunning all Silicon in there would work fine but now i am not sure at all..? Any thoughts?

 

[White Room]

Never used mapegum and never used ptfe tape either...strange one that.

 

[bugs183]

It depends on just how much movement you are anticipating will happen between the two walls. 99% of the time you would tile and put a silicon seal up the centre. But if you are anticipating lots of movement then you may need the above approach.
Have a look at: Movement Joints, Expansion Joints And Control Joint Profiles - Schlüter-Systems, there's bound to be a solution here for you.

 

[tom1976]

thanks Bugs!!