Expanding Foam - an effective weather seal?

[Stones]

On site today, I was doing a bit of tidying up, picking up the odd bits of expanding foam that had been buffed off the surface of our EWI prior to rendering.  

Some of those bits had ended up in a small puddle and were merrily floating around.  Had me wondering just how effective a weathertight seal expanding foam would be a). exposed to the elements or b). protected from the elements  

 

Expanding foam impregnated tapes (e.g. Compriband) are routinely used for windows and doors, so presumably expanding foam would provide some benefit? 

[Onoff]

Seen a few basements in commercial buildings where they've tried to seal around pipe and cable entries with it. Water just pi$$es in. Might be a water table/pressure thing but it's failed every time. 

[IanR]

On my window install the gaps were sealed externally with silicon bead because the expanding foam is not water tight. 

[Construction Channel]

Probably would break down after a few frosts i fear, 

[Crofter]

Also not UV stable, will crumble eventually.

[Onoff]

And wasps & bees chew through as do birds.

[jamiehamy]

10 hours ago, Construction Channel said:

Probably would break down after a few frosts i fear, 

Not a chance... We did the ICF last year and there was lots of expanding foam here and there. Apart from discolour, there was no sign of deterioration.  It had been exposed to a good few frosts and all weather. When I cut into it,  under the surface was perfect.  That included stuff that had been immersed in water. 

 

It will be weatherproof,  as opposed to water proof - same as Compriband.  

Edited October 12, 2016 by jamiehamy
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[Construction Channel]

hmmm, interesting, a lot of OLD foam i have seen has often been very brittle, I assumed this was frost but could well have been UV deterioration. 

Did i hear somewhere that the recipe has changed in time? something about not being used around certain types of pipe? 

[Gimp]

I think Compriband type of tapes are different from what I understand as expanding foam, yes it is foam that expands, but I usually think of the spray version as expanding foam - the yellowish substance that expands in blobs. The door window tape to me doesn't act in the same way, it can be pushed back and does not harden once expanded.

 

I have some old expanding foam sprayed around the property where I live and although it goes lighter and perhaps more brittle when exposed to UV for many, many years, it still holds it place fine and none has ever come out.

 

Looking at its composition though, although for most general applications it seems pretty weather tight I think if it was needing to be weather tight under full on conditions say for sealing an area on a flat roof, somewhere rain might collect, etc then it might allow water to seep though after a time, either at the join or though its structure if it has been cut flush as it appears to be honeycombed. I'm not sure that it always quite fully expands into every crevice but rounds off a little. Just my opinion though from what I have noticed visually off the stuff. 

[TerryE]

IMO,  foam is a crap weather seal. However ,  it might be an effective scaffold to use to achieve a good weather seal.  Silicon and other competitive sealants have established a good track record for what you want,  but start to become impractical for gaps of more than a few mm.   Foam cut back to form a scaffold surface is an effective compliment. 

 

 

 

 

[Onoff]

Ref the use of foam as a scaffold I work closely on occasion with guys fitting commercial glazing. They will pack gaps with grey,  cylindrical foam strip - think pipe lagging without a hole up the middle. Comes in various diameters. It gets forced in then siliconed over the top. Some gaps are SO wide I've seen them simply cut the top of the mastic tube! They frequently use too, a torch on, embossed aluminium "felt" they call Solar Shield in gutter details etc.

[Ferdinand]

I would concur.

 

It is a filler not a seal. Unless there is a special sort.

 

Ferdinand

[Stones]

21 hours ago, jamiehamy said:

We did the ICF last year and there was lots of expanding foam here and there. Apart from discolour, there was no sign of deterioration.  It had been exposed to a good few frosts and all weather. When I cut into it,  under the surface was perfect.  That included stuff that had been immersed in water. 

 

Matches my own observations of our own ICF build.

 

21 hours ago, TerryE said:

IMO,  foam is a crap weather seal. However ,  it might be an effective scaffold to use to achieve a good weather seal.  Silicon and other competitive sealants have established a good track record for what you want,  but start to become impractical for gaps of more than a few mm.   Foam cut back to form a scaffold surface is an effective compliment. 

 

 

 

 

 

Very much the way in which my builder uses it externally - filling gaps in the ICF blockwork / EWI which aree then rendered over, or in the case of windows, as the scaffold onto which silicon sealant is then applied.