How do I sprayfoam a ceiling?

[Murflynn]

I think everyone is getting het up over nothing.   The concept of using an insulation material, whether it is polystyrene, polyurethane (Kingspan) or whatever is not necessarily compromised by air gaps in the structure.  The theory is that you use a layer of air or an inert gas which is held in place by a matrix of foam or rockwool or whatever and as a result you also prevent air movement.  Air (or any other gas) is an excellent insulator as long as you prevent convection currents forming.  Air is a better insulator than the solid material that forms the matrix.  If you used the chemical without introducing air or inert gas (which is what happens during the foaming process) it would provide minimal insulation.   Blackrose's method is just fine.  

[jddevel]

Drytherm is not Rockwool. Two different base products. Whilst Kinspan has the best lambda value then Celotex then other including Drytherm. Drytherm 32 being their best. Drytherm made of glass (I believe Rockwool is literally rock dust) and is recyclable unlike the Kingspan and the Celotexss` of this world which will I believe be extremely difficult to recycle. Certainly wont burn easily. The problem with Drytherm it s thinnest is 75mm. I also suggested a air barrier.

[W+T]

Just seen this post and thought i would share a method i use at times for insulating using tins of expanding foam. 

 

This can be done in one large section if you get to know how much the foam expands to fill the cavity, or do it in sections. 

 

Batten out with a good adhesive like CT1 or Sikalfex , short battens of 4-6 inch around the area to be foam filled to say minimum 25mm deep. 

 

If say an area of 2 Sqf is to  be done then get your ply lining and drill 8mm holes or what ever the tube diameter is with the tin foam so it fits through the hole, in a grid of 150mm. screw the lining ply to the battens and fill the cavity working from back to front. 

 

One thing be careful not to over fill the cavity as the foam can push the lining board out of shape, you will get used to it the more you do.

 

Or instead of doing it in one large section or you are cautious in doing one large area, then do it in 150mm sections so you can see it filling the over section.  So if again on a 2 Sqf area, fill one 100mm x 600mm strip/cavity and when its about to over expand screw up the next section to the battens etc etc

 

And get a mist bottle filled with water and cover all the area to be filled to very lightly dampen it before spraying / filling. 

 

Tip if doing in section then screw  strips over the joint to keep then level.

 

Works a teat for me when doing uneven surfaces on cruisers. 

 

 

Admiral Faffer

Edited December 29, 2019 by W+T