Sir Percy Posted June 23, 2021 Report Share Posted June 23, 2021 Question for anyone who's used expanding foam: I've just bought some cans of Soudal expanding foam (gun grade) for filling in gaps around Celotex slabs fitted for hull insulation. The directions on the can say to spray water on surfaces to help it cure. Not sure that I really want to do that in case excess water gets trapped. Am I worrying about nothing? Link to comment Share on other sites More sharing options...
dmr Posted June 23, 2021 Report Share Posted June 23, 2021 22 minutes ago, Sir Percy said: Question for anyone who's used expanding foam: I've just bought some cans of Soudal expanding foam (gun grade) for filling in gaps around Celotex slabs fitted for hull insulation. The directions on the can say to spray water on surfaces to help it cure. Not sure that I really want to do that in case excess water gets trapped. Am I worrying about nothing? I think a fine mist of water is advised to make the surface damp rather than wet. I also don't like the idea of this. Sprayfoam is mostly used on brick rather than steel. I believe it will still set without water but will take a fair bit longer, it might not stick as well but that's not really a problem. I need to do something related before too long, but I want it to stick directly to steel (under the cants). As you have a gun maybe you could do a few experiments and let us know what you find out? ...........Dave Link to comment Share on other sites More sharing options...
Sir Percy Posted June 23, 2021 Author Report Share Posted June 23, 2021 Just now, dmr said: I need to do something related before too long, but I want it to stick directly to steel (under the cants). As you have a gun maybe you could do a few experiments and let us know what you find out? ...........Dave Ta. What sort of experiments do you have in mind? I bought a kit of 5 cans so may have a little spare. p.s. on the internet, about half the price of similar Soudal kit from Screwstation. Link to comment Share on other sites More sharing options...
dmr Posted June 23, 2021 Report Share Posted June 23, 2021 1 minute ago, Sir Percy said: Ta. What sort of experiments do you have in mind? I bought a kit of 5 cans so may have a little spare. p.s. on the internet, about half the price of similar Soudal kit from Screwstation. Squirt a blob onto a bit of dry steel and see how long it takes to go hard and confirm that it sticks reasonably well. It would be good to have confirmation that water is not essential. It would be best to do this at the end of some other project otherwise there is a risk of wasting an entire can of foam if the nozzle blocks. ............Dave Link to comment Share on other sites More sharing options...
nicknorman Posted June 24, 2021 Report Share Posted June 24, 2021 The foam does need water to cure, but it can get this from the air. So my suggestion would be to do the job when the humidity is fairly high. Shouldn’t be too difficult bearing in mind British weather! Link to comment Share on other sites More sharing options...
Idle Days Posted June 24, 2021 Report Share Posted June 24, 2021 It's years since I used the stuff but I recollect spraying a little water as per instructions because it helps the foam to expand fully. Link to comment Share on other sites More sharing options...
Chewbacka Posted June 24, 2021 Report Share Posted June 24, 2021 It is thickness dependant, so a ‘thin’ foam layer will cure with humidity, but a thick layer will take a long time to cure if moisture has to diffuse a long distance. On steel, I would wipe with a damp cloth to leave a film of water, then immediately apply the foam otherwise the water will have evaporated, when foam is applied, spray (plant mister) a little water on the surface. 1 Link to comment Share on other sites More sharing options...
Machpoint005 Posted June 24, 2021 Report Share Posted June 24, 2021 (edited) 16 hours ago, Sir Percy said: Not sure that I really want to do that in case excess water gets trapped. Am I worrying about nothing? Since the (small amount of) water is needed as part of the chemical curing process, I would think there won't be any excess water -- provided you don't apply it with a fire hose, of course. 1 hour ago, Idle Days said: >>it helps the foam to expand fully<< Exactly. ETA: I've recently used this foam at home (on brick and concrete) and it swells up far more than you might expect! Edited June 24, 2021 by Machpoint005 Link to comment Share on other sites More sharing options...
Tony Brooks Posted June 24, 2021 Report Share Posted June 24, 2021 You can get low expansion foam. Maybe it should be lower expansion. Link to comment Share on other sites More sharing options...
Sir Percy Posted June 25, 2021 Author Report Share Posted June 25, 2021 Okay folks, I'll try a light misting. Cheers Link to comment Share on other sites More sharing options...
Sir Percy Posted October 2, 2021 Author Report Share Posted October 2, 2021 On 23/06/2021 at 20:01, dmr said: I need to do something related before too long, but I want it to stick directly to steel (under the cants). As you have a gun maybe you could do a few experiments and let us know what you find out? ...........Dave Sorry it's taken so long to get back to you; 1) about a good half an hour to go touch dry / stiff 2) yes, it'll stick, but the trick is to get it to stay in place initially while it cures. Careful, slow, progressive application might get you there. Link to comment Share on other sites More sharing options...
blackrose Posted October 2, 2021 Report Share Posted October 2, 2021 (edited) I never saw this thread earlier. The fine water mist on the surface of whatever you're spraying it on is required to get the foam to stick rather than to get it to expand or cure. It's always expanded and cured whether the surface was damp or dry in m my experience, but without a damp vertical surface it can fall off before it expands and cures. I think you were worrying about nothing. Even if some water did become trapped rather than being incorporated into the foam, a small, finite amount of water can only generate a small, finite amount of corrosion. Edited October 2, 2021 by blackrose 2 Link to comment Share on other sites More sharing options...
Ex Brummie Posted October 3, 2021 Report Share Posted October 3, 2021 12 hours ago, blackrose said: I never saw this thread earlier. The fine water mist on the surface of whatever you're spraying it on is required to get the foam to stick rather than to get it to expand or cure. It's always expanded and cured whether the surface was damp or dry in m my experience, but without a damp vertical surface it can fall off before it expands and cures. I think you were worrying about nothing. Even if some water did become trapped rather than being incorporated into the foam, a small, finite amount of water can only generate a small, finite amount of corrosion. And also, if the foam has sealed, then there will be no oxygen to feed corrosion. Link to comment Share on other sites More sharing options...
nb Innisfree Posted October 3, 2021 Report Share Posted October 3, 2021 Possibly not relevant to OPs case but I once saw some steel discs left over from portholes being cut post spray foaming, some had been primed before foaming and some left unprimed, the difference was very noticeable, foam was easily removed from bare steel discs, in fact it came away in one piece while it was very difficult to get it off the primed discs (bare steel was dry and rust free) Lesson for me was to paint with a good quality primer before foam is applied. Link to comment Share on other sites More sharing options...
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