Re: Expanding foam and UV

[fred]

> It says on the side of Wickes expanding polyurethane foam that, if used

>> externally, it should be covered (with filler or mortar) within 7 days since >> it's not UV resistant. >> >> Anyone have any experience of exactly *what* happens to this foam if it's >> not covered within 7 days? >> >> I've just braved the elements for 3 days moving an external door - the new >> door is finally vaguely weatherproof (with a combination of expanding foam >> and frame sealant) but I really can't be arsed rendering & painting around >> it before the spring. Am I being foolish? If so, as a temporary measure, >> could I just paint the foam with some form oil-based primer? > > >The foam will initially darken in colour. In a few weeks, it will have >hardened considerably, losing much of its flexibility. In a few months >it will start to break up. A couple of years and it will be gone. > >Painting it with a couple of coats of primer will stop this, but will >make it difficult to render later.

Also it's not a closed cell foam so it will soak up moisture like a sponge which could lead to rot problems in the future. I'm very careful where I use it.

[Grunff]

I've heard this said quite a few times, but I'm really not sure. Think about how it's formed - lots of bubbles of propellant expanding away in a PU matrix. I'd say it is largely closed cell, with only a few through paths. Its moisture absorbance is quite low.

[fred]

Yes, logic suggest this, but embarrassing stories win over logic every time:

Chum decides to make boat dock pontoon out of fibreglass and, to guard against flooding in case of damage, fills it (them actually) with expanding foam. Inevitable damage does occur and pontoon sinks faster than you can say impervious steam liner :-)

[Andrew Gabriel]

I used it as replacement insulation on bottom of a freezer after the initial fibre matting became waterlogged (or rather, ice logged). I also assumed it was closed cell and wouldn't need any further surface sealing, but I was wrong, although it did take about 3 years before it became completely water/ice-logged.

[Newshound]

I'd say you can leave a vertical surface exposed to sun and rain for a few months. Eventually you need to fill and seal, having excavated any crumbly stuff.

[[news]]

hahahah. even if it's not true that's hillarious :-)

RT

[fred]

In article , fred writes

On reflection (this was a while ago), I think it was wave action breaking over the pontoons, rather than damage, that ended up with them waterlogging, but they definitely ended up sinking.

But (back on topic) I agree that short term exposure, of a matter of weeks, will do no harm

[chris French]

I had some filling a rather large hole around pipe - it was left exposed for at least year, when I eventually cut the excess back and mortared over the top it seemed pretty much as sound as it ever had been

>

[Andy Dingley]

It's effectively open cell, just slow. It doesn't matter if it's a "mostly closed" cell foam, if you need it really sealed.

If you use the two-part foams, not the squirty can stuff, there are grades of those that are real closed-cell foams.

[Grimly Curmudgeon]

It was somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember chris French saying something like:

Ditto. I've left filled holes unpainted for ages and the foam's been fine underneath the dark surface.