How to use 2-Part PU (Polyurethane) Foam

This product is absolutely ideal for filling cavities and for increasing buoyancy! It's strong, rigid, and incredibly simple to use. In this post, we'll tell you a bit more about PU Expanding Foam and also share a video we made a few weeks ago.

Producing the foam

Use two plastic cups to measure out an equal volume of each part, then pour both components into a clean mixing container. Ensure you stir thoroughly, but work quickly - the mixture will begin to thicken in just 25-35 seconds, reaching its maximum rise in about 150 seconds. 

The uncured mix is highly adhesive and will bond to most materials. While the mixture is foaming, take care not to inhale the fumes. 

Immediately after mixing, the liquid foam is poured into the cavity to be filled, then left to foam and cure. It will reach a sticky condition in about 4 minutes, and will be completely cured in about half an hour. 

If you are filling a deep cavity, it's a good idea to pour in a series of layers (around 25mm each), leaving the foam to cure between pours. This is because the exotherm (internal heat) generated during the curing process increases with greater volumes of foam, and this can cause problems.

Each liquid kilo of polyurethane yields approximately 0.08m2 (1 cu.ft.) of rigid foam.

Calculations

PU foam is supplied in several pack sizes and it is necessary to calculate the volume of the foam required so as the correct pack size can be selected to minimise wastage. 

This can be done by measuring the cavity and simply multiplying length by width by height (in metres) and dividing by 0.0283. 

This calculation will give the total amount of foam required in kg. 

Example:A buoyancy tank measuring, 0.5m (length) x 0.5m (width) x 0.5m (height) = 0.13m3. 

Divide this figure by 0.0283 = 4.59 

Therefore the total liquid foam required is 4.59kg (1 x 5kg pack)