26 Questions Answered on Expandable Polyurethane Spray foam Sealant, Insulation foam sealant

What is in the PU foam can and how does it work ?

The can is filled with a group of chemicals .When these chemicals are combined during manufacture, a reaction occurs to create a prepolymer in the can that subsequently reacts with moisture in the air when it is dispensed—this is what creates the insulating foam sealant.

What is a Expandable Polyurethane Foam Sealant ?

Expandable Polyurethane Foam Sealant  is dispensed as a frothy liquid which expands and moisture-cures into a solid foam insulation and sealant. One-component foam is used to fill and seal small cracks and voids such as around door and window frames, sill plates, electrical devices where air leakage and energy loss can occur. Formulations are available for general use and specific applications such as sealing windows and doors, fire blocking, and construction adhesive.

Where can I apply PU foam sealant?

Insulating foam sealants are useful for sealing holes, gaps and cracks around your home where air leakage could occur. Some possible areas to consider sealing around include:

  • Window and door gaps
  • Baseboards and vents
  • Sill plates, pipe and duct penetrations
  • Sink plumbing, floor/wall junctions, around electrical boxes (not inside)

Can I use insulating foam sealant outside?

Yes, you can. Exterior uses could include the following:

  • Where the siding meets the foundation
  • Gas and electrical penetrations
  • Garage ceiling and wall joints
  • Around outdoor faucets and exterior vents
  • Landscaping applications such as stone wall repair, pond/waterfall fillers and repair, as well as to secure landscape blocks

Is PU foam a barrier to insects and rodents ?

Polyurethane foams do not contain chemical rodent deterrents or rodenticides.

Use of expanding polyurethane foam has been found to be an easy, means to help prevent insects and rodents from entering structures through voids, cracks and crevices.

Completely fill holes around the structure, such as in the siding close to the foundation, around cables and pipes that penetrate the structure and all openings in areas with evidence of rodents, such as gnawed items and rodent droppings. Do not overlook small holes. Some rodents, such as house mice, can squeeze through holes that are as small as ¼-inch across.

While mice and rats can chew through polyurethane foam, this barrier will generally block mice from entering the area.

Is it necessary to moisten the surface before using foam?
We recommend moistening because the system needs water to cure. Other benefits one will get: i. Better cell structure ii. Better adhesion iii. Faster curing iv. Better foam quality If you do not moisten the surface, there is a risk of post-expansion, what means that the foam will harden out in the first few days. After a while the uncured foam will react with moisture and you'll get post-expansion.

Is foam resistant to water?

 Cured foam provides a barrier to moisture. However, over time, small quantities (depending of skin is on the foam) of water vapor will migrate through the foam. If the skin stays on the foam, the weight will only increase by 5%. If the skin is cut away, the weight can increase upto 150%. In that case foam is not water resistant. The water vapour permeability depends on the density and the cell structure of the foam. If you got more open cell structure or a lower density the permeability will increase.

 Does PU-foam provide good adhesion to all building surfaces?
Generally yes. 1K , Gun PU-foams have a good adhesion on the most common building materials, such as brick, concrete, plaster, wood, glass, metal, PS, rigid PVC and PU. Exception: PE, PP and Teflon 

 Is PU-foam UV resistant?
 All PU-foams are not UV resistant. Normally PU-foam is covered, if not, it is necessary to protect the foam (e.g. by painting). If PU-foam is in contact with UV-rays for a longer period, foam will get discolored from yellow to brown. Later on the foam will get even brittle. 

 What is the expansion of PU foam?
The expansion is different for gun and hand-held foam. i. Hand-held foam will expand by 150-200% which means that you only have to fill the joint by 40-50%. ii. Gun foam will only expand by 50-100%, so you have to fill the joint by at least 50%. The expansion depends on the temperature of the ambience, temperature of the can and the humidity.

How should I store an opened can of gun foam?
The best thing you can do is leave the can on the gun. If you do not leave the can on the gun, clean the valve and the gun with Gun & Foam cleaner. We recommend to empty the can in the next weeks.

Is there a negative effect on the foam if the can is not shaken thoroughly prior to use? Polyurethane foam consists of a prepolymer and a propellant gas, which form two layers during storage. The can must be shaken vigorously before use to create a homogeneous mixture. Insufficient shaking will result in poor foam properties such as a coarse cell structure and reduced foam volumes.

How much must the cans be shaken to ensure a homogeneous mix of the two constituents?
A canister should be shaken 15 to 20 times.

Does the canister need to be shaken again during use?
It is recommended to shake the can occasionally during use, and especially after interruptions, to avoid re-separation of the propellant und prepolymer.

How does the foam get the right amount of moisture?
Fresh foam absorbs moisture from its surroundings. In particularly dry environments it makes sense to wet the surfaces to be joined. But standing water droplets are to be avoided, as in this case the water would actually become a barrier to proper adhesion.

What happens when there is insufficient moisture on the surfaces or in the surrounding environment and no water has been sprayed onto the foam?
 A lack of moisture leads to inefficient curing of the foam and, depending on the amount of foam applied, may lead to foam compression - even months later.

Does the foam develop and exert pressure during expansion and curing?
Yes, the foam exerts a pressure during expansion and through hardening. It is therefore advisable to fill gaps and cavities by no more than one third.

Is there any way to accelerate the curing process?
Yes, wetting; ideally from a spray gun. This will help to speed up the hardening process.

Is cured foam subject to ageing? Cured foam does not age. 
There has never been a case during the thirty years that polyurethane foam has been in use that any failure has occurred through ageing.

What should I do with excess foam such as that round doors and windows?
Cured excess foam can be cut away with a knife, saw or any similar implement.

Can gaps between polystyrene insulation panels be filled with one - component polyurethane?
 Yes, one-component polyurethane foam can be freely used for such applications. It is free from solvents and does not attack polystyrene.

Is it OK to leave half-empty canisters attached to applicator guns?
 Yes; in fact we recommend leaving a partially-full container attached to the gun. To store the gun and canister safely, the security screw should be tightened to secure the trigger.

Is it necessary to remove excess foam from the adapter, or can I simply insert the next canister?
a. Though the adapters are constructed from a non-stick material, it is advisable to remove any excess foam straight away with gun cleaning fluid: well-maintained tools last longer.

How long can a partially used container be left attached to a gun?
a. If the trigger has been completely secured with the security screw, a canister can be stored attached to the gun for a period of one to two weeks.

Are all PU foam sealants basically the same?

No, not necessarily. There are different grades of insulating foam sealants for different uses. Refer to the product label for information on appropriate product uses.

Can I leave the cured sealant exposed?

Generally, it is considered acceptable to leave cured or “hardened” insulating foam sealant beads exposed when it is used to seal small gaps and cracks. Manufacturers may recommend painting the material if it is exposed to UV light.

Bibhas Agarwal