Frame foam – the specialist for interior doors

Doors should absorb day-to-day impacts without wobbling. This is why there is special frame foam that is used to attach door frames allowing them to withstand continuous heavy loads. What does window foam need to be able to do? Frame foam needs to be highly adhesive and strong, and also needs to harden quickly and reliably. Also, it should be dimensionally stable after a very short time and not spread. Find out here how to work with frame foam and what you need to be aware of:

What assembly foam is best suited for door frames?

1-component or 2-component foam for door assembly?

You can install interior doors with both 1-component and 2-component foam. However, most special frame foams are 2-component foams that do not rely on humidity to harden. Instead, the can contains a second hardener component that the user needs to activate before use. This allows it to harden very quickly. Also, this foam is more firm that conventional 1C foams that need to react with ambient moisture to become hard.  

Shear strength: The most important criterion for a good fit and durability

To ensure that the door sits reliably for years, the foam should be particularly firm. How can you recognise a firm foam? A look at the product data sheet of the selected PU foam will help you here. Look for the keywords 'shear strength' or 'tensile shear strength'. For a foam suitable for door installation, the value should be greater than 80 kilo-pascals. The higher the value, the firmer the foam. Sometimes the value is also given in Newtons per square centimetre (N/cm²). In this case, the figure should be greater than 8. 

You can find more information on the subject of shear strength in our chapter on quality criteria. 

PU foam expands even further after application and can exert great pressure. To prevent the door frame from being deformed by this pressure, it must be fixed with spreaders at the points where the foam is applied. 

How long does door foam take to dry?

The advantage of 2C foam is that it hardens quickly and in a controlled manner. Shorter hardening times ensure that you can carry on working after a short time. The entire curing process is divided into the following four stages.

Stage 1: The foam is tack-free

Ideally, a frame foam is tack-free after just five to eight minutes. This means that it has formed a skin and no longer sticks when you touch the foam. 

Stage 2: You can cut the foam (cuttability)

After eight to twelve minutes, you can cut the foam. In other words, remove the excess foam with a sharp knife. However, this does not mean that the door is fully mounted after a quarter of an hour. 

Stage 3: When can you remove the spreaders? (Spreadability) 

Spreadability is also important for the installation of your door. To prevent the PU foam from pressing into the door frame while it hardens and expands, it must be held in place with spreaders.  

The spreadability indicates after how many minutes you can easily remove these spacers. This should be the case after around half an hour to a whole hour. Only then should you remove the door spreaders with which you have fixed the door frame. 

Stage 4: When can you hang the door after foaming? (Load-bearing capacity)

After around four hours, the cured frame foam is fully loadable. Depending on the weight of the door panel, you can now install the door. The foam can then bear the weight. For particularly heavy doors, the frame must be supported with mounting blocks or the foam surface increased. 

How to mount interior doors with frame foam

Here, only 20 to 30 percent of the upright frame surface needs to be adhered, when mounting the door frame. To do this, apply the frame foam at six to eight points of the door frame, preferably at about the same level as the hinges. This is also where the struts need to be attached. No additional attachment is required for interior doors.

The surface of the door frame should be strong, clean, and free of dust and grease to ensure good adhesion of the assembly foam. The foam will adhere to almost all surfaces, for instance wood, concrete, brick, metal or aluminium. There are some restrictions in the case of plaster, glass and ceramics. PU foam will not adhere to polyethylene, polypropylene, silicon and oily surfaces.

How much assembly foam is required for each door frame?

The question remains as to how many cans of frame foam you need per door. If the door frame is attached with PU foam at points near the hinges and at about the height of the door lock, a 400 ml can should be enough for two to three doors. If for soundproofing reasons you opt to foam around the entire frame, you will require one can per door. Alternatively, you could also use a somewhat less expensive pistol foam.