# Forum Home Renovation Waterproofing  Waterproofing problem

## Relentless

Hi Guys, 
I am waterproofing an old rebated concrete shower base which has small mosaic type tiles very solidly attached. I will tile over the existing tiles. I ground the old tiles and have applied Prep 'n' Prime by CTA as a primer prior to applying a water based waterproofing membrane. 
Trouble is that after I primed it all I noticed that the instructions say that polyurethane membranes cannot be used over this primer. I was going to use PU Sikaflex to caulk all the gaps between the wall sheeting and the shower base. ( I primed the bottom 50mm of the wall sheeting too). So I'm thinking that if PU membranes can't be used then PU sealer is probably not suitable either. So what am I going to use? Neutral cure silicone? 
Hopefully someone who knows something about this can answer this because I need to seal it tomorrow so I can't get advice from the supplier until Monday.

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