Is Compriband waterproof?

[Dunc]

As title, really. Is Compriband supposed to be 100% (for want of a better term) waterproof? Does it need anything like silicone in addition?

 

My windows are fitted with a ribbon of Compriband to seal against the reveal at the outside. This is in a timber frame, with the window set back 90mm back from the face of the kit. I dont have the timber cladding in place around all of them yet. After yesterday's fierce winds and pretty much 24hrs of rain I have water running in at one of the windows. The windward side Compriband is sopping wet; water can be squeezed out when puching it with a finger tip. I can't see the back of it as the airtightness membremane is already in place on the inside, but this makes me wonder if this is how the water got in. 

 

Rather concerned to have to rely on the cladding and reveal boards for waterproofness! 

 

 

[SimonD]

All of these tapes come in different thicknesses each of which has a specified compression measurement for water tightness, air tightness, wind tight etc. - e.g. thickness of 25mm, watertight to 12mm, air tight to 20mm. This means that even after expansion into the gap it should be fairly compressed to be water tight.

 

I don't suppose you have any way of knowing what the installers used?

[Mr Punter]

You can tell by giving it a prod with your finger.  If it is fairly stiff it is compressed.  Soft and squishy and they should have used a wider one.  Also, make sure it is proper Compriband, not a cheaper lookalike.

[Dunc]

Ah. 

No idea what brand or dimension was used.

Definitely soft and squishy

Sounds like it needs replacing.

 

[saveasteading]

Compriband is difficult to compress. It is used to seal bridges and dams,  and does not go squishy.

It sounds as if you have diy draughtstrip.

[Mike]

18 hours ago, Mr Punter said:

make sure it is proper Compriband, not a cheaper lookalike

+1. There are a lot of inferior competitors that perform much worse - it sounds like you may have one.

 

18 hours ago, Dunc said:

Is Compriband supposed to be 100% (for want of a better term) waterproof?

No; it's very good but, as mentioned by @SimonD, even genuine Compriband has limits. I recall calculating that their window strip is good for wind up to around 70mph. In an exposed position, it would therefore be a good idea to have a second line of protection. Either something to shelter it from the wind - your timber cladding might be enough do that - or vertical & horizontal 'cavity trays' behind it. For airtightness, add Ilbruck FM330 form (or similar) and/or an airtightness tape internally.

 

19 hours ago, Dunc said:

Does it need anything like silicone in addition?

Sealant would block Compriband's moisture vapour permeability, so if that property was one reason for choosing Compriband you'd loose it. If that's not a concern, then a suitable mastic is OK.

[saveasteading]

Compriband is a trade name but in a search brings up lots of copycat or simply squishy foam products.

 

I didn't realise Compriband, capital C, could breathe so there must be more products than I know of. Why does it need to breathe if it is non absorbent?

[Mike]

1 hour ago, saveasteading said:

I didn't realise Compriband, capital C, could breathe so there must be more products than I know of. Why does it need to breathe if it is non absorbent?

The advantage of moisture permeability is that, should any moisture get into the structure, it has an easy escape route - for example to reduce the risk of rot in timber windows. That's why I chose to use it on my current project - though I had to rip the cheap stuff out of the installers hands and give them the genuine product!

[Mr Punter]

My understanding of the Compriband system is that you have a vapour impermeable membrane - such as adhesive tape /EPDM - stuck between the frame and the structure before the plasterboard, insulation in the gap - like closed cell expanding foam, them Compriband on the outside.  This means no internal vapour should get between frame and structure, frame is not a cold bridge, window is sealed from outside weather and any moisture the gets in can escape externally.

[Dunc]

Problem is I have no way to know what they used and they have no inclination to be specific (unfortunately they've already been paid). "We've been doing this 19 years and never had a complaint" type of response.

The adhesive seems extremely strong so I'm concerned that ripping it out might not go well...

 

It was selected because I have a timber frame with cellulose fill so it would be advantageous to ensure any moisture that gets in can escape. Certainly the window is sealed inside with airtight tape and the void filled with foam so the cold bridge is dealt with and the internal vapour barrier is as good as anywhere else in the structure.

 

It does seem to have occured only with very strong wind-driven rain. There has been plenty of more "normal" rain which hasn't been a problem so perhaps addition of the cladding will suffice. I have added some temporary OSB "cladding" to see how that goes. Just need another Scottish Hoolie to try it out. Terrifying to think that if this had been done over summer the cellulose fill would already have been pumped in and I'd never have known until it rotted. Maybe being way behind schedule has some silver linings 🙄