Diy spray foam

[shan]

If there is an air gap against the outer skin condensation will occur there, and stay there, wetting the back of the panels. As I understand, cured foam is closed only until you crush it or pierce the 'crust', which forms on the surface in curing. Make a piece and try it before committing.

You are confusing single component open celled PU foam with 2 component closed cell PU foam.

 

[fisherman]

You are confusing single component open celled PU foam with 2 component closed cell PU foam.

I would have hoped so, but the latter is what I asked the question about. Happy to be proved wrong, it would help my next project....

 

[Graham_Wright]

Can foam absorbs water as it is open cell. Not suitable for use on boats as any condensation will be absorbed.

…………and the consequence would be?

As long as it stays absorbed, so what?

 

[shan]

I would have hoped so, but the latter is what I asked the question about. Happy to be proved wrong, it would help my next project....

2 component closed cell foams actually tend to have the most broken cells in the skin layer and first 5mm of foam. Assuming the component ratio has been correctly proportioned and the temperature has been adhered to, you will end up with a rather good finish and the majority of cells should be unbroken and impervious to moisture. Too much polyol mix and you will end up with bubblegum; too much isocyanate and you will end up with a very crispy finish with neither having the desired properties. If you are going to DIY make sure follow the instructions to the letter being especially cautious about application temperature & nozzle changes; if you get in a 'professional', make certain you have a 'professional' - check his previous work or look for reviews.

Problems with PU foams tends to be about the formulation going off ratio, which is inevitably user-driven.