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Below we offer self-build advice and answer some of the most often asked questions about building with aircrete blocks.

What mortar mix should be used with aircrete blocks?

Traditional aircrete blockwork above the Damp Proof Course (DPC) level should be used with a cement:lime:sand mortar mix of 1:1:5 to 6 provided structural considerations don’t demand a stronger mix and the masonry is protected during construction from saturating and freezing.

Below DPC level, mortar should usually be 1:1/2:4 cement:lime:sand, particularly where there is a risk of freeze/thaw.

Can aircrete be used in foundations?

Yes, Celcon Blocks can be used to build foundations and there are many benefits to doing this. See ‘where to use aircrete'. In fact, Part L of the building regulations recommends using aircrete foundation blocks where aircrete is being used in the construction of external walls to ensure continuity of insulation levels within the building fabric.

How do you cut aircrete blocks?

H+H Celcon Blocks can be easily cut using a handsaw, no power tools are required. We recommend investing in a good quality masonry saw, preferably one with a tungsten tip which will make cutting easier and should last well beyond your self-build project.

For tips on cutting aircrete check out this video on our YouTube channel.

Are aircrete blocks loadbearing?

Yes, aircrete blocks are loadbearing and are available in different strengths, accommodating different home designs. Celcon Blocks Standard Grade 3.6N/mm² and Celcon Blocks Solar Grade 2.9N/mm² are normally more than adequate to meet the structural requirements of two storey housing.

For multi storey construction walls or piers under high vertical loads higher strength blocks may be required. Celcon Blocks are also available in High Strength Grade (7.3N/mm²) and Super Strength Grade (8.7N/mm²).

Can you render aircrete blocks?

Aircrete blocks can easily be externally rendered. There are a few golden rules to remember when rendering blockwork:

  • Before applying any render on blockwork it is essential to make sure your wall is clean and free of any dust or loose mortar.
  • Traditional sand:cement render mixes should never be stronger than the backgrounds onto which they are applied. Each coat of render should also be weaker than the one before it.
  • One coat will not be enough, generally two coats is fine.
  • The undercoat needs to be combed or scratched to give a key for the following coats. These scratches should be wavy, not straight, to avoid cracking later on.
  • The undercoat of render should be about 12mm thick and the final coats should be about 6mm thick.

You can find further information from our technical expert on how to render a blockwork wall here.

Can you plaster an aircrete wall?

Yes, most types of plaster can be applied to H+H aircrete. As with render, traditional sand:cement (dense) plasters should not be stronger than the backgrounds onto which they are applied. An M4 or equivalent is the strongest mix recommended for direct application on to aircrete walls.

For gypsum (lightweight) plasters the manufacturer’s recommendations should be followed as to the appropriateness of their plasters for application on to aircrete.

How do you fix plasterboard to an aircrete wall?

There are two methods of attaching plasterboard to blockwork, by bonding directly to the blockwork or by using battens.

The most common way to fix plasterboard to blockwork is using the ‘dot and dab’ method. With this technique you apply dabs of plasterboard adhesive to a clean, dry blockwork wall and then press the board into position.

The second method is with a timber or metal furring system, essentially a framework which is screwed into the blockwork and on to which the plasterboard is attached.

Can you screw into aircrete blocks?

Fixing internal wall fixings to H+H aircrete blocks is easy. Plugs with screws or nails as appropriate will provide a very secure and reliable fixing. The best fixings for aircrete blocks depend on the weight of the fixtures. You can find detailed advice in our Designing & Building with Aircrete document.

RAAC - your questions answered

Reinforced autoclaved aerated concrete (RAAC) planks were building materials used between 1950s and 1990s, primarily in public buildings such as schools and hospitals. They were used in fast assembly building projects, typically as roof panels.

RAAC planks derive their structural strength from metal reinforcing bars within the planks. Failure occurs primarily when the reinforcing bars corrode. This typically happens when the planks have been exposed to water over a prolonged period of time. Corrosion weakens the bars and causes the plank to lose its intended loadbearing capacity. None of these failures are associated with the AAC material.

The aircrete blocks manufactured by H+H UK and used to build the foundations and walls of houses and low-rise commercial buildings do not use reinforcing bars.

H+H aircrete blocks are not liable to the failures being seen in RAAC products.

H+H aircrete is manufactured to the standard BS EN 771-4 and BBA certification confirms that “walls constructed from the products will have durability equivalent to walls of traditional masonry.”

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