would you recomend the use of SPF to prevent water infiltration inside a basement on exterior walls?

Closed cell SPF has been sprayed to “dry” interior masonry walls blocking the water penetration. This is considered a temporary fix to an existing problem or backup to an external water barrier/drainage system. Below grade masonry needs to be designed and maintained to route the water away from the exterior side. When an unusual occurrence of excessive water (from blocked or broken gutter or such) penetrated the exterior side, the SPF will block the water from passing thru the interior side, which would prevent any water damage. For unusual occurrences, this water would then dry out. If the masonry wall routinely has water penetrating through it, (as with every significant rain fall), the SPF would probably trap the water in masonry block cavities. This would not be a good thing and the problem should be addressed on the exterior side of the wall to repair the cause of the water getting to the wall and rerouting the water with proper drainage.

if High density => lower R value how is it possible that 1.8 to 2.2 lb density => highest R value Isn't this in contraction with itself? Please advise Thank you CF AIA

The closed cell SPF must be dimensionally stable and strong enough to withstand the expansion/contraction forces of the changing temperatures to which it will be subjected. With a typical spray SPF system there is a trade off of density to R value. Most insulation SPF in the 1.8 to 2.2 lb density ranges provide the maximum R value, while maintaining the strength to remain a stable product. If may be possible to spray a 1.5 lb system with higher R value that would not be strong enough to not crack when subjected to cold temperatures, or split the cell walls when subjected to the expansion if the cell gas at higher temperatures. Consider that the SPF insulation must remain stable as a membrane with a temperature differential across the thickness of the SPF. A house in the winter may have 2 ½ “ layer in the wall, with the inside being 70ºF and the exterior side 10ºF. The closed cells must be able to withstand the forces and remain as closed cells holding the insulating gas, or they break open and become an open cell system, further lowering the effective R value for the thickness of the membrane. For a roofing application, exterior tank insulation or other special application, the SPF may need to be a higher density to provide greater strength to withstand foot traffic, repeated loading/unloading from snow & ice or such. So typical roofing SPF systems are formulated with higher densities to be stronger, but they then, typically have a lower R value. A 2.0 lb insulation foam may be R 6.4 per inch where a 3.0 lb roofing foam may be R 5.8 per inch. The insulation may have a compressive strength of 26 psi with the roofing 3.0 lb SPF having a compressive of 54 psi. This is a very simplified answer to a complex question of chemistry and thermodynamics and not intended to completely answer the question, but to provide some context to the situation. All reputable producers of SPF systems work closely with their applicators and designers to ensure the proper system is selected for any given application. All SPF systems should have a Physical Properties sheet or Technical Data Sheet listing the information necessary to make a proper selection for an application.