How to replace bottom window external rubber flashing?

[Rob001]

The bottom window's external rubber flashing has worn on most the windows in my home.

The images show one larger gap, but most windows have this strip torn to bits.

I've done some research to find that it likely can't be taken out and replaced, because it's slotted into the window frame, the whole frame likely needs to come out to fix it.

My questions are:

1. I've read not to 100% seal a window along the bottom as it can trap moisture in. Is this true, and if so, how do I seal along the gap without applying a 100% seal but also preventing water getting in?

2. Do I cut away the old rubber seal or silicone over it

3. What's the best silicon to use that will last the longest outdoors

4. Is there a self-stick adhesive strip that I can lay over the tip of the old, or cut off the old and place over the gap instead of using silicone

[EricL]

Hello @Rob001 

I had a similar question from another discussion and suggested using Moroday MDS2B Self-Adhesive Black Econo Door-Seal along the bottom of the window to replace the flashing. The door seal acts just like the window seal and prevents water from flowing inside but still allows air to pass through and circulate. I recommend wiping the aluminium surface with DIGGERS 125ml Isopropyl Alcohol - 125ml to make sure the surface is free of oil and grease. 

Another option is to use CAgroup 50mm x 3m Weatherproof Byute Flash Flashing Tape. Please note that the tape has a silver aluminium finish on its surface. However, if you were going to use silicone, I would have suggested looking at Sika 300ml Concrete Grey Sikaflex 11FC Purform.

If you have any other questions we can help with, please let us know.

Eric

[Rob001]

Thanks @EricL ,

If I use Silicone, do I need to do anything to allow air to pass through because it will be an air-tight seal along the bottom, which I heard is not good for the external of windows.

[JacobZ]

Hi @Rob001,

If you have a look at the mortar lines under the bricks that form the sill, do you see gaps in the mortar?

In a double brick installation, which I am pretty confident your house is, there should be a flashing that runs from the underside of the window frame into the mortar on the underside of the sill. There will usually be weep holes here for drainage.

There are also weep holes in your window frame here.

  

As long as sealing the underside of the window does not block these holes or the weep holes that are likely below the sill, then you won't have any problems.

Let me know what you find.

Jacob

[Rob001]

And if I choose to silicone, do I cut off that old rubber flashing or can I silicone over it?

There are weep holes in the brick under the windows. I think this is what you're referring to?

[EricL]

Hello @Rob001 

I suggest removing the old flashing as using silicone over it will not give you a dependable seal.

If you need further assistance, please let us know.

Eric