Really soft breeze blocks, why...???
Chris Wilson
blocks used as the inner leaf of some cavity walls "breeze blocks",
dunno if that is a universal term. Anyway, just moved into a new
bungalow, built 18 years ago. The outer leaf is conventional brick,
the inner leaf is of a grey, cellular type breeze block that are so
soft one can push a screwdriver into them or scrape lines in them with
a fingernail. This makes fastening shelving and stuff a PITA as plugs
tend to tun with the screws in the blocks. WHY did they use this type
of block? They seem to have gone away from this sort of block in more
recent years and gone to a much denser and harder, more concrete like
block. They also seem very prone to stress cracks.
--
Best Regards,
Chris Wilson
(Race car preparation and development)
http://www.formula3.freeserve.co.uk
Andrew Gabriel
Chris Wilson <ch...@formula3.freeserve.co.uk> writes:
>Firstly a terminology thing. I am in the UK, and we call the grey
>blocks used as the inner leaf of some cavity walls "breeze blocks",
>dunno if that is a universal term. Anyway, just moved into a new
>bungalow, built 18 years ago. The outer leaf is conventional brick,
>the inner leaf is of a grey, cellular type breeze block that are so
>soft one can push a screwdriver into them or scrape lines in them with
>a fingernail. This makes fastening shelving and stuff a PITA as plugs
>tend to tun with the screws in the blocks. WHY did they use this type
>of block? They seem to have gone away from this sort of block in more
>recent years and gone to a much denser and harder, more concrete like
>block. They also seem very prone to stress cracks.
They are thermally insulating blocks.
Recently when fitting wall brackets for a heavy microwave, I decided
the only thing to do was to drill right through the wall (internal,
so no cavity to worry about), and use nuts and bolts with large
washers. On the other side, they are recessed so I can plaster over
them when I get a round tuit.
--
Andrew Gabriel And...@cucumber.demon.co.uk
Consultant Software Engineer
Tony Bryer
> Firstly a terminology thing. I am in the UK, and we call the grey
> blocks used as the inner leaf of some cavity walls "breeze blocks",
> dunno if that is a universal term.
Real breeze blocks are a dark grey in colour, fairly rough texture,
sometimes with holes through them to reduce weight. IIRC they are made
from a mixture of cement and ash. Used in the earlier post war period?
> Anyway, just moved into a new
> bungalow, built 18 years ago. The outer leaf is conventional brick,
> the inner leaf is of a grey, cellular type breeze block that are so
> soft one can push a screwdriver into them or scrape lines in them with
> a fingernail. This makes fastening shelving and stuff a PITA as plugs
> tend to tun with the screws in the blocks. WHY did they use this type
> of block? They seem to have gone away from this sort of block in more
> recent years and gone to a much denser and harder, more concrete like
> block. They also seem very prone to stress cracks.
These sound like aerated concrete blocks (Thermalite, Celcon etc). They
are also made from cement and fine ash but with added aluminium powder
(IIRC) that makes the mix foam up: if you cut a block it has the texture
of an Aero choc bar - much better insulation and easier to handle. IME
fixing to them is not a problem: you can drill a small hole and just
screw a screw in with no plug; if you want to use a plug you want a
pattern that expands without a lot of turning force. You also want to
try and make sure that the plug is well within the block so that when it
expands it doesn't just tend to blow the face of the block.
The cracking is mainly due to shrinkage as the blocks cure, caused
either by (i) too strong mortar; (ii) no movement joints; (iii) blocks
used too soon after manufacture; (iv) blocks allowed to get saturated
with rain on site.
--
Tony Bryer SDA UK 'Software to build on' http://www.sda.co.uk
John Schmitt
=====
>Firstly a terminology thing. I am in the UK, and we call the grey
>blocks used as the inner leaf of some cavity walls "breeze blocks",
>dunno if that is a universal term. Anyway, just moved into a new
>bungalow, built 18 years ago. The outer leaf is conventional brick,
>the inner leaf is of a grey, cellular type breeze block that are so
>soft one can push a screwdriver into them or scrape lines in them with
>a fingernail. This makes fastening shelving and stuff a PITA as plugs
>tend to tun with the screws in the blocks. WHY did they use this type
>of block? They seem to have gone away from this sort of block in more
>recent years and gone to a much denser and harder, more concrete like
>block. They also seem very prone to stress cracks.
The underlying reason that these things exist is because they are
Large and Inexpensive. The drive for penny-pinching among the multiple
house-builders has driven this, and it is only after you have bought your
new house that you find that you are trying to fix shelves to the building
industry's answer to Madeira cake.
The blocks are made, as has been pointed out, with a cement/sand and
probably PFA (Pulverised Fuel Ash, a byproduct of the power industry)
mixture foamed with aluminium powder. The aluminium reacts with the free
lime created when the cement reacts with the water to give hydrogen gas.
The resulting mousse which is about as structural as shaving foam, is
then steam autoclaved at high temperature (and therefore pressure) for
approximately half an hour. This means that the cycle time for production
is very short by comparison with, for example, bricks. Sand cement and PFA
are all sold by weight (I do mean weight, not mass. Force measurement is
far more common in building product gauging than mass comparison) Foamed
autoclaved blocks give a far higher volumetric yield than other materials.
To sum up, the labour, material and transport costs are lower, but the
blocks are a pain to fix into. You can screw direct into them, but if you
want to remove and replace something, the holding power will be appreciably
reduced. There are specialist fixings, which I mentioned a short time ago
"plasplugs schmitt" should throw it up at groups.google.com .
John Schmitt
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Chris Wilson
says...
Thanks for the detailed explanation, great post. Also appreciation for
the post on the fixings suitable for these blocks. The bungalow is
otherwise very well built, but as you say, the blocks are a Royal PITA
to fix to, in the workshop I am resorting to wooden boards secured to
the mortar lines, which in turn take any heavy shelving. Are the
blocks as structurally sound as a harder block?
Bob Mannix
"Chris Wilson" <ch...@formula3.freeserve.co.uk> wrote in message
news:MPG.156dde1c5...@news.freeserve.net...
>
> Thanks for the detailed explanation, great post. Also appreciation for
> the post on the fixings suitable for these blocks. The bungalow is
> otherwise very well built, but as you say, the blocks are a Royal PITA
> to fix to, in the workshop I am resorting to wooden boards secured to
> the mortar lines, which in turn take any heavy shelving. Are the
> blocks as structurally sound as a harder block?
They will support an RSJ (eg 3-4m supporting an external upstairs wall), if
a concrete pad is placed between the RSJ and the Thermalite blocks. FWIW my
kitchen wall units have been hung with plastic plugs in the blocks for about
10 years with no problems. Most wall loads give mainly a shear stress on the
screw anyway, so use the correct expanding plugs (in the right size holes!)
and don't overtighten the screws. An abnormal load like a large microwave
might give problems as another poster indicated.
Bob Mannix
Stuart Grant
> You can screw direct into them, but if you
> want to remove and replace something, the holding power will be appreciably
> reduced.
>
and replace fully but do not tighten until the pva has cured. You should then
be able to remove and replace several times with little or no wear.
Stuart Grant (s...@cwcom.net)
Adam
> WHY did they use this type
> of block?
You may find they are high (for the time) U value insulation blocks.
--
Our Homes Are Small & Expensive
Because We Are Not Allowed To
Build On Land That Is Plentiful.
Make Land Available For The
People To Own & Use in the UK
http://www.oneworld.org/tlio/
Andy Woodward
>> want to remove and replace something, the holding power will be appreciably
>> reduced.
>>
>Remove the screw and squirt some pva liquid into the screw hole. Oil the screw
>and replace fully but do not tighten until the pva has cured. You should then
>be able to remove and replace several times with little or no wear.
Same works with epoxy.