# Forum Home Renovation Waterproofing  bathroom wall joints and bond breaker

## inferno6688

Hi guys,
i have just finished sheeting my bathroom with villaboard, now i am deciding how best to seal the corners- wall/wall and wall/floor joints. 
The JH guide calls for a 6mm flexible sealant, so i am thinking of filling the gap with sikaflex 11fc, then afterwards a fillet of neutral cure silicon over the top to act as bond breaker.  
my reasoning is as follows
- i already have sikaflex 11fc, so i won't need to buy as much silicon for bond breaker if i just filled the entire gap with silicon.
- i read WP memebranes will stick to 11fc hence it can;t be used as a bond breaker
- i am planning to use eitherdavco K10 or Ardex WPM001 membrane, and they call for a neutral cure silicon as a bond breaker.  
Will the silicon stick the 11fc ok?
is my plan to use 11fc, then silicon on top going to be ok? 
thanks guys

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## Pulse

personally I used sika fc11 with k10 over the top, just looked at data sheets for both, sika fc11 has over 300% elongation to break and k10 plus has over 500%. Class three membranes allow a bond breaker cove sealant bead that is meant to take up the expected movement, I don't think it is a problem if they flex together since >300% is class 3. The silicone allows the membrane to seperate, I guess that allows 200% extra stretch but you don't want to test the membrane to its limits... 
in all I think your plan is fine 
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## METRIX

Yes silicon over the top of 11FC is fine this is the way it should be done if your not using a bondbreaking reinforcing bandage. 
Silicon will stick fine to the 11FC but not the other way around, also you should not use 11FC on it's own as this is an adhesive / sealant as all polyurethanes are, these are designed to stick to other surfaces, and for other stuff to stick to it including membrane. 
The membrane needs to be free to move wherever it wants in those critical corners, if it's stuck to a polyurethane, it negates the inherent flexibility of the membrane.
This exact scenario was demonstrated to us during training, it was amazing how much just the 11FC coated with membrane weakened the membrane, BTW 11FC is like sliced bread it's an amazing product.

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## Pulse

thanks metrix nothing beats a practical test  
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## METRIX

Yeah, that's why they showed us, so we didn't make that mistake as it's easily done.

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## inferno6688

thanks guys.  
do you bond break external corners? this is for the niches in my shower. i will bond break all the internal corners inside the box, but how about the external corner where it joins the wall? 
also how how about all the nail holes on the FC sheeting? 11FC or silicon? 
thanks

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## METRIX

External corners yes bond break, sheet penetrations smear some 11fc over thrm

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