prepping steel for spray foam insulation

[dreadlockpasta]

What's the best way to prep steel for spray foam? bare steel or primed, smooth or rough sanded?

What experiences ,have folks had ,of diy jobs ?

I have about 38m2(the cabin above the gunnel) of steel to spray.Can anyone recommend a kit for that kind of meterage?

cheers

[Arducius]

We are about to have ours done by professionals (couldn't be doing with toxic gases etc) and they said no flakey rust, everything primed if possible, didn't say anything about sanding. I think it's pretty sticky stuff.

 

I suppose you could call and act like you're interested in getting it done and ask what they'd recommend you do before they arrive, then do that before your DIY job.

[Guest]

Mine was sprayed onto bare clean steel ten years ago. I was never 100% happy with it going onto bare steel, so when I cut the hole for the flue collar, I kept the piece of steel with foam attached to it, and left it exposed to the elements for some years. Pleased to say the foam never came away from the steel, and when I eventually scraped it off, the steel was like new underneath.

[Captain Zim]

I've done both professional and DIY.

 

In both cases the prep was pretty basic paint prime over decent ish metal. Nothing fancy.

 

The professional job was excellent and sticks like the proverbial. The DIY whilst a bit cheaper to buy, is a pain and unless you get the temperature and mix of the two parts bang on can be a bit hit and miss. I read a worrying article the other day about poor mix continuing to give off VOC's long after application.

 

Having now done 4 DIY jobs of areas that I couldn't do in the first professional stage, I wish I'd had it all done together in one hit. It would've been cheaper in the long run. Having said that, I would now consider I've got the measure of the DIY kits but it's taken me 4 attempts to get there and about £1200. For half that the pros would've done the same area.

 

If you do decide to DIY, PM me and I'll send you the link to te companies I've used. To be honest though, I think they are all much the same.

[Bee]

I used up all the old gloss in the shed anywhere I thought get damp but the stuff covers all the little crevices. Don`t worry about stickability, it sticks to any surface, hair, dogs, eyebrows, everything, I don`t know of any kit suppliers these days but I did my own a few years ago and would only advise to cover everything you don't want sprayed with sheets or something, windows, floor, carpet, cover everything or you will be scraping it off for weeks.

[blackrose]

I don't think it really matters as long as it's not greasy steel. A fine water mist spray onto the steel will help the foam bond to it. If you can't mask then a thin smear of vasaline is good to protect any small areas you don't want foam to stick to.

[nb Innisfree]

A neighbouring diyer didn't manage to prime all his interior before the sprayfoamer arrived resulting in half being foamed over bare steel. Some months later when he cut holes for fender eyes he noticed that the foam over bare steel could be fairly easlily removed, coming away with a slight twist from the steel discs he had removed, whereas the primed ones couldn't easily be removed, in fact it had to be scraped off.

[blackrose]

A neighbouring diyer didn't manage to prime all his interior before the sprayfoamer arrived resulting in half being foamed over bare steel. Some months later when he cut holes for fender eyes he noticed that the foam over bare steel could be fairly easlily removed, coming away with a slight twist from the steel discs he had removed, whereas the primed ones couldn't easily be removed, in fact it had to be scraped off.

 

Perhaps the unprimed steel hadn't been degreased?

 

The steel on my boat wasn't primed and the sprayfoam is well bonded.

Edited October 3, 2013 by blackrose

[Guest]

I guess it hadn't been degreased, too. Then again the primer probably wouldn't have stuck either? I have inspected the foam on mine over the years, at times when I've had panelling off, roof vents out etc, and have found all visible foam to be firm. Overall I've been very pleased with the sprayfoam.

Edited October 3, 2013 by Guest

[nb Innisfree]

 

Perhaps the unprimed steel hadn't been degreased?

 

The steel on my boat wasn't primed and the sprayfoam is well bonded.

No it hadn't but I wasn't aware of any greasiness on our hull from the same workshop and it took primer well, inside and out. Maybe it had some light surface rust forming which would likely reduce adhesion?

Be interesting to experiment sometime.

[Guest]

No it hadn't but I wasn't aware of any greasiness on our hull from the same workshop and it took primer well, inside and out. Maybe it had some light surface rust forming which would likely reduce adhesion?

Be interesting to experiment sometime.

Millscale coming away perhaps?

[nb Innisfree]

Millscale coming away perhaps?

No, a bit rusty here and there but otherwise sound. Our original Intertuf blacking peeled away from the millscale though.

 

ETA: The metal discs were cut out with a hole saw and were quite hot, maybe that weakened the adhesion?

Edited October 3, 2013 by nb Innisfree

[dreadlockpasta]

Hi thanks for all the replys.My main reason for planning on doing a diy job,is that the roof is ready to do now and the cabin sides wont be ready for another 2 months.The hull won't be spray foamed ,but kingspan to make it easier for future welding.

 

any idea of the cost per m2 for a pro job?I guess that the thickness is also going to affect the price.

[Guest]

No, a bit rusty here and there but otherwise sound. Our original Intertuf blacking peeled away from the millscale though.

 

ETA: The metal discs were cut out with a hole saw and were quite hot, maybe that weakened the adhesion?

Possible effect of the heat I suppose?

Our first blacking came off with millscale; the millscale was coming away with the pressure washer for the 6 inches around the waterline. It is going to be grit blasted and two packed for its tenth birthday.

[nb Innisfree]

Hi thanks for all the replys.My main reason for planning on doing a diy job,is that the roof is ready to do now and the cabin sides wont be ready for another 2 months.The hull won't be spray foamed ,but kingspan to make it easier for future welding.

 

any idea of the cost per m2 for a pro job?I guess that the thickness is also going to affect the price.

Can.t comment on the cost but a fellow diyer fitting out his narrowboat went the Kingspan/Celotex route. He stuck it directly to the steel and filled gaps with aerosol foam, finishing with 6mm ply stuck on top. The results were impressive, consistent thickness throughout and a really solid finish, hitting it hard with the side of the hand felt like you were hitting solid steel, I wish I had done It that way instead of sprayfoam.

Possible effect of the heat I suppose?

Our first blacking came off with millscale; the millscale was coming away with the pressure washer for the 6 inches around the waterline. It is going to be grit blasted and two packed for its tenth birthday.

We grit blasted our hull but made the mistake of doing it too soon, a lot of the millscale was still intact and grit blasting couldn't remove it all, the bloke doing the blasting said shot blasting was needed against millscale.

[Guest]

Can.t comment on the cost but a fellow diyer fitting out his narrowboat went the Kingspan/Celotex route. He stuck it directly to the steel and filled gaps with aerosol foam, finishing with 6mm ply stuck on top. The results were impressive, consistent thickness throughout and a really solid finish, hitting it hard with the side of the hand felt like you were hitting solid steel, I wish I had done It that way instead of sprayfoam.

 

We grit blasted our hull but made the mistake of doing it too soon, a lot of the millscale was still intact and grit blasting couldn't remove it all, the bloke doing the blasting said shot blasting was needed against millscale.

I see, so some rust would need to lift the millscale, then grit blasting could remove it. That'll be why they can get away with grit blasting ours now?

[nb Innisfree]

I see, so some rust would need to lift the millscale, then grit blasting could remove it. That'll be why they can get away with grit blasting ours now?

Yes, if grit blasting leave metal unrotected until all the scale has rusted off, blasting will then easily get back to virgin steel. If bitumen based blacking is being used then as soon as blasting is finished any dust needs brushing off and a priming coat of very thin blacking applied, leave for an hour or two to go off them slap on a coat of thicker stuff.