Foam agent properties.

Foam agents for making Foam Concrete:

Not just any substance that creates bubbles.

There are DIY enthusiasts who are using dish wash liquid or shampoo and claim to be totally happy with it, because it works for what they are making.

Xanthan Gum as an additive to make the foam stronger came up in one of the papers I was reading. It claimed the make a better FC when this was added to the agent. This could be an option if you want to use a detergent.

Types of Foaming agent

Protein based

For some time the protein based foams were preferred to synthetic ones because of their qualities. The protein based agents use animal offal, and other animal parts as protein base, some people object to living in a house where this foaming agent is used. Other issues are the smell some of these agents give off, and the shelf life. However there are manufacturers who have been able to improve these agents.

An FC manufacturer claims that protein based agents produce an FC with 10 to 15% higher MPa when making FC for insulation purposes.

Synthetic based agents

Synthetic agents are made from petroleum products. As far as I have been able to discover, some of them use a base material that is the same as used in shampoo. From there on there are other ingredients added that makes it more suitable as foaming agent to make foamed concrete.

Plant based agents

These are made from plant material and do not have the objections from some people to use them as the protein or synthetic based products. I have not found any more information on them than one manufacturer who also has the agent in a powder and liquid form.  Sapindus rarak is a species of soapberry that is used to make soap, that’s all I know, please help me put here if you know more

Foam properties

Bubble size

The bubble size has an influence on the strength of the FC, my finding is that a bubble of 0.5 to 1 mm with 90% of the size close to the 0.5 mm had the best results in MPa after 90 days. I have not found a study comparing foaming agents and foam making methods that investigates what product and method produces the best results. I love to find that, so if you know of any, please let me know.

Bubble strength

Because the foam has to withstand considerable forces when it is mixed into the mortar, and sometimes pumped up into the form-work up to 10 m high and over a distance of 50 m trough pipe it has to have a strong bubble.

As it can take up to 4 hours or more, the bubble has to resist collapsing for all that time.

Bubble stamina

The test to check how long the foam “stands up” and how well is easily done is simple. Pour the foam into a 1 liter measuring vessel, and check how much fluid collects over time on the bottom.  The good ones do not collect any fluid on the bottom and stand up to 12 hours! However, this tests only the agent, not how it behaves when mixed with mortar, but it is a start when you want to use detergent or shampoo. The real test is to make FC and see how much it shrinks and microcracks in before it is set. If you do any such tests, let me know with photos please.


As we put additives in the mortar to make the FC suitable for our purpose, some of them may react with the foaming agents and other additives we use. There are special anti-foaming additives on the market, and some products we want to use as additives may contain anti foaming agents as well. (Without telling us on the packaging). It could be a trial and error process until we find the optimum combination of additives.


All foaming agents need to be diluted with clean water. All manufactures recommend potable (drinking) water. This is because some pollutants may react with the agent ingredients. You may have experienced “hard” and “soft” water, this is refereeing to the amount of calcium there is in water. Soft water has less calcium, and needs less soap to make bubbles. So we can imagine what effect it has on the making of FC. So far I have not seen one study mentioning this aspect.

The dilution rate is different for each product, and usually a recommendation is on the packaging.

I have seen variations from 1:30 to 1 : 80, but 1:40 is the most common. The best dilution rate probably depends on the foam density you want to aim for

I found this conclusion in a study

The foaming agent’s dilution ratio has a great effect on the properties of the foam and the foam concrete. With the increase of the dilution ratio, the fluidity of the foam concrete slurry increases gradually when the dilution ratio of foaming agent is in the range of 20-40 and 60-80, while it increases rapidly when the dilution ratio of the foaming agent varies from 40 to 60. The results reveal that the compression strength and flexural strength of the foam concrete reach the highest value and the drying shrinkage is comparatively lower when the dilution ratio is 1:60. Therefore, the optimum dilution ratio may be 1:60.

Cited from
(reference to tables removed)
Influence of foaming agent on the properties of high density foam concrete
Xingang Yu , Yanna Gao, Lin Lin and Fang Li
College of materials science and engineering, Chongqing University, Chongqing, 400045, P. R. China

Foam density

The most density I have seen used in studies is 80g/m3, but I have seen as low as 30 and as high as 120g/m3.

The foam density is the result of the dilution rate and the ‘hardness” of the water, if this reasoning is valid remains to be seen. Can anyone confirm this?

Cost of foam

This is a tricky one as you have to work out your cost per m³  of FC.

The cost of the agent can be given in cost per liter or Kg. You have to work out the dilution rate, and how much foam you put in your mortar for the density of FC you want to make.

How much foam you need to put in the mortar depends on the effect of the additives on the foam and the amount of bubble collapse occurs during the mixing. The method of mixing and the time you mix it also has an influence on the final result.

Making Foam

There are 2 methods used in making foam, a wet and dry method. The dry method gives the best results for our purpose, this is done by forcing compressed air through a mixing chamber that is filled with diluted agent and mesh or stainless steel wool. There are a wide variety of foaming machines on the market, see the equipment page. It is possible to make a simple foaming machine yourself. Check the web for it.  From what I seen of the results, the ones with a pump are more consistent.

The wet method of creating foam is based on drawing undiluted foaming agent
into a stream water of using the Venturi effect. The wet method does not produce such good quality foam.

It is possible to do it by hand and use a paint mixer on drill.

Last but not least. Clean your equipment with warm water!

I look forward to your comments on this from your practical experience, and a visual recording of this fun activity!

Foam agent suppliers

This is a selection of suppliers I found so far.

If you know of others please let me know.