SELF-BUILDING WITH AUTOCLAVED AERATED CONCRETE BLOCKS: AAC: the easy way to build your own house

By Michael Keating

Large format, print editons of this book, with full colour photos ilustrating the text descriptions, can be purchased at www.mybestseller.co.uk/M.Keating
This is the story of our house build in Germany. This book is intended as a birds-eye view of the work, not a guide to absolutely everything involved with the process. I wrote it is to inform you, the prospective self-builder, on the work involved, in order to help you decide whether this is something you feel you could do yourself. It will not be physically possible to do absolutely everything by yourself, you will still occasionally need a helper or two and the building process may vary slightly in other countries due to availability of specific materials, but the basic procedures in the book remain valid.

When we signed the contract for our building materials we were given a German book on self-building with AAC. I didn't speak German and could not find an appropriate English language book, so I decided to photo-document our entire construction process and write a book on it. Many of these photos are included in this book to aid to full comprehsion of the house build (there are no photos in the e-book).

• Language: English
• Publisher: BuilderMaker
• Release date: Mar 22, 2024
• ISBN: 9789403723839

Michael Keating

MICHAEL KEATING is Professor of Politics at the University of Aberdeen and the University of Edinburgh and is Director of the ESRC Scottish Centre on Constitutional Change. He is a fellow of the British Academy, the Royal Society of Edinburgh and the Academy of Social Science. He has been writing about Scottish politics for forty years and is published extensively on nationalism and territorial politics throughout Europe.

Book preview

The Background to this book

This book outlines the basic steps and methodology on self-building with Autoclaved Aerated Concrete (AAC) blocks. It is based on the construction of our own house in Germany. This is the story of our build.

Upon moving to  Germany, we sold our house in Britain and used the funds to build a new house. When we signed the contract for  the building materials, we were given a book on self-building with AAC. My German was terrible and I was unable to read it. I was also unable to find an English language guide to the AAC building process, so I decided to write one myself as I built my house.  The sequence of the book mirrors the sequence of the build. Hopefully, this book will serve to de-mystify the building process and further encourage self-building with AAC, a brilliantly simple and effective construction material.

This guide outlines the building process, methodology, and pitfalls to avoid. Since it is based on our build in Germany, it may differ from the building process in other countries, not least due to availability of materials. Nevertheless, the basic building process remains the same, although modifications may be necessary. The book is intended as a birds-eye view of the work. It is not a guide to absolutely everything involved with building; rather, it‘s purpose is to inform prospective builders about the work involved, to help decide whether this is something you could do by yourself, or not. If you do decide to self-build, the use of occasional paid labour, or friends, will occasionally be necessary due to such pure practicalities as weight, dimensions and the best practice of concreting a complete section before any gaps start to set. One example of this would be no access to a concrete pump and thus having to use buckets to fill shuttering on top of a wall.

Misconceptions about AAC

In the process of researching this book, I discovered widespread misconceptions in the British and Irish building trade. Many workers believe that AAC cannot be used in rainy countries because it soaks up water too easily. This is not true.

I believe these misconceptions arises from the fact that most British and Irish workers are unfamiliar with AAC, since it not sold in builders markets or DIY stores. It is possible to buy  lightweight, aerated concrete blocks –but these are NOT AAC. These lightweight blocks easily soak up water and, unlike AAC, become much weaker when wet. I suspect people may have confused these blocks with AAC. I also suspect that there are vested interests in the construction industry, who are satisfied with the status-quo and have no desire to change anything. Perhaps green building practices have a lower profit margin?

AAC is a green, lightweight, fire-proof, energy-saving building material that has been in use for over seventy years. It is manufactured from natural materials:  water, sand, lime, cement and a small amount of aluminium powder. When the ingredients are mixed, gas is produced from the reaction between the lime, aluminium and water. The gas produced is hydrogen. This gas expands and creates many tiny bubbles, causing a doubling is size of the material, in the same way that carbon dioxide causes bread dough to rise.

The still soft, expanded mixture is moulded, sliced, and then heated under high pressure steam (autoclaved) for 12 hours. The temperature required for autoclaving is far less than that required to fire traditional bricks. The autoclaving process creates a solid material which is AAC. The hydrogen gas dissipates during the process (hydrogen is the smallest element and escapes easily), leaving precisely formed AAC blocks, or plan elements.

The pores in the AAC are sealed, they do not interconnect. The upper and lower surfaces of the blocks are completely smooth. Water does not soak into the blocks easily and construction can continue in rain. Pores in AAC are well closed, only surfaces will be wet during rain and water will not penetrate deeply. During factory testing, samples had to be submerged for 3 days before they absorbed 70% water (reference, Aircrete.com).

Provided mortar is applied correctly, it is perfectly possible to build with AAC in inclement weather. AAC blocks are supplied to the customer on pallets, sealed in heat shrink plastic, and can be left in the rain indefinitely.

Self-building: a comparison between the U.K. and Germany

We built our house in the former DDR (East Germany), where it is relatively easy to acquire a building plot. The German housing industry runs the gamut from family run, to SME, to large corporations. Conversely, the UK is dominated by mega-companies which purchase large tracts of land and build as many houses as they can, at minimum cost and maximum profit, with seemingly little concern for aesthetics or modern, green construction methods and materials. They commonly land-bank property, preventing anyone from building on it and creating an artificial shortage of land zoned for residential housing.

In theory it should be possible to purchase a building plot when one becomes available. In practice however,  building land is in very short supply in Britain and when previously unavailable land is re-zoned to allow construction of domestic dwellings, it is usually done in relatively large amounts which are quickly snapped up by major developers; small builders do not stand a chance. The large builders, in-effect, shut out people wishing to buy a single plot and build their own house.