Can You Silicone Over Expanding Foam

Can You Silicone Over Expanding Foam?

Silicone and the Expanding Foam don’t react with each other so there is no reason why you can’t silicone over expanding foam.

If you have a gap larger than 6mm it is actually recommended you fill it with expanding foam first, before applying a silicone seal.

It is standard practice to use Expanding Foam around Upvc window frames and then go over it with silicone to create a weather-tight seal between the window frame and the masonry.

Requirements to silicone over expanding foam

  • Gaps larger than 6mm should be filled with expanding foam before going over with silicone
  • The expanding foam must be fully set. Expanding foam can take around 30min to go off in warm dry conditions. In cold damp conditions, It can take a few hours.
  • Once cured the excess expanding foam should be cut back with an old hacksaw blade or Stanley knife
  • The area should be swept or vacuumed clean to get rid of any bits of expanding foam that might end up in the silicone.
Expanding Foam around Window Frame
Expanding Foam around the Window Frame

Warning: If you don’t fill larger gaps with expanding foam then you will lose all your silicone down the crack.

Problems going over Expanding Foam with silicone

If the expanding foam has not had sufficient time to cure before you apply the silicone, it can carry on expanding behind the silicone and cause bubbles to appear on the silicone surface.

If the expanding foam is wet you may struggle to get the silicone to stick.

You can also use expanding foam to fill joints in bathrooms, but you may need to go over it with a thick bead of silicone to create a good seal in areas that will get wet frequently.

Grey Silicone Wall Panelling
Grey Silicone Multi-Purpose Silicone

If you have any further information on how you can silicone on top of Expanding Foam let us know in the comments below.

Sam Wood

Wood by name, wood by nature. I am a fully qualified, time-served, award-winning joiner with an NVQ Level 3 in Carpentry and Joinery as well as an HNC in Construction. Beyond my joinery qualifications, I have also earned a degree in building surveying. I believe these qualifications make me perfectly positioned to provide expert advice on many different areas of DIY as well as share all of the tips I have picked up in over a decade working on building sites!

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