Dry stacked block column

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Re: Dry stacked block column

Postby Andyfteeze » Wed Oct 05, 2016 7:08 pm

Yes keeping the sun off is important, but you also have to understand, when its a constant 32/34 degrees, heat will penetrate through to the ambient temperature eventually. Thats where a
Thermal mass can act as a dampener. Something like a slab on the ground in conjunction with aac block walls can give you a quasi constant temperature which is far more comfortable to live in, not to mention minimises air con usage.
From all i have read, a cavity between aac blocks is a waste of time. Better to just butt them up against each other. Its to do with thermal transfer delay rather than pure R rating.
I am as guilty as everyone thinking a cavity was good for aac blocks. But the more i read, the more i am convinced it makes no logical sense. Especially when its open to the environment. Its like buying 6 tyres for your car but only using 4. A high performance car designed with 98 octane running on 91 octane. Sure it runs, but its not performing as designed. You get the drift.
Think of it this way, thais have substituted cement roof tiles for thatched roofs, has that worked out well? Its ok if you like ovens. Its a clear substitue without a thought about the issues about real suitability. Its replaced one problem with another, long life for thermal disaster. So to me, a cavity with aac blocks is on the same level, a misunderstanding of its properties and best usage.
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Re: Dry stacked block column

Postby Sometimewoodworker » Wed Oct 05, 2016 8:16 pm

Andyfteeze wrote:Yes keeping the sun off is important, but you also have to understand, when its a constant 32/34 degrees, heat will penetrate through to the ambient temperature eventually. Thats where a
Thermal mass can act as a dampener. Something like a slab on the ground in conjunction with aac block walls can give you a quasi constant temperature which is far more comfortable to live in, not to mention minimises air con usage.
From all i have read, a cavity between aac blocks is a waste of time. Better to just butt them up against each other. Its to do with thermal transfer delay rather than pure R rating.
I am as guilty as everyone thinking a cavity was good for aac blocks. But the more i read, the more i am convinced it makes no logical sense. Especially when its open to the environment. Its like buying 6 tyres for your car but only using 4. A high performance car designed with 98 octane running on 91 octane. Sure it runs, but its not performing as designed. You get the drift.
Think of it this way, thais have substituted cement roof tiles for thatched roofs, has that worked out well? Its ok if you like ovens. Its a clear substitue without a thought about the issues about real suitability. Its replaced one problem with another, long life for thermal disaster. So to me, a cavity with aac blocks is on the same level, a misunderstanding of its properties and best usage.

There is more than one reason for a cavity with AAC blocks. I have 3, first for the electrics 2nd for the water and 3rd so I don't have protruding columns, there could be more. FWIW mine are not open.
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Re: Dry stacked block column

Postby Andyfteeze » Thu Oct 06, 2016 7:05 am

Hahaha, thats really only one, decorative. Hiding pipes and walls. Nothing to do with their main function which is a solid thermal barrier.
I really mean open cavity walls with weep holes.
An open cavity in effect cripples it's benefits.
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Re: Dry stacked block column

Postby ajarnudon » Thu Oct 06, 2016 4:56 pm

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Re: Dry stacked block column

Postby Sometimewoodworker » Thu Oct 06, 2016 6:47 pm

Andyfteeze wrote:Hahaha, thats really only one, decorative. Hiding pipes and walls. Nothing to do with their main function which is a solid thermal barrier.
I really mean open cavity walls with weep holes.
An open cavity in effect cripples it's benefits.

Decorative or not they are reasons to have a double wall of AAC blocks with a gap. Other reasons include not having to be concerned about where chases are so being able to fix to any part of the wall.

So your statement was "that cavity walls with AAC make no logical sense" I have just given you a few reasons why they can be useful.

While I agree that weep holes/ventilation is redundant lipstick on a pig due to the poor water transmission of water through AAC I doubt that they are as bad as you suggest.
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Re: Dry stacked block column

Postby ajarnudon » Thu Oct 06, 2016 9:37 pm

and certainly not redundant if you have the concrete blocks outside with AAC inside, as Pipoz has done with good effect (and as I will also do). Do you consider that the air temp in a confined cavity will be lower than in a vented one (auto forced ventialation as required)? And if not, which air body will have the lower thermal transmission to the inside wall? Reflective foil is very cheap I might add.
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Re: Dry stacked block column

Postby BKKBILL » Fri Oct 07, 2016 2:25 pm

Sometimewoodworker has it right here are a few more pluses for AAC cavity walls.

Energy saving
4-8 times more energy efficient than solid clay brick. It will reduce the
transference of heat from outside to inside of the building.

Lightweight
2-3 times lighter than solid clay brick and 4-5 times and lighter than normal
concrete without losing any strength.

As air is the real insulator and the layer of air in the cavity being a non-conductor of heat reduces the transmission of heat from the external face to the internal one and as such cavity walls are best suitable for a tropical country. Tests have revealed that cavity walls have 25% greater insulating value than solid walls.

As there is no intimate contact between the two walls except at the wall ties (which are of impervious material), there is no possibility of the moisture travelling from the outer leaf to the inner.

Accurate
Has precise dimensions, helping the builders produce smooth finishes.

Rapid assembly, Noise resistant
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Re: Dry stacked block column

Postby Andyfteeze » Fri Oct 07, 2016 5:52 pm

Let me address what you just wrote bkkbill. Firstly, yes air is a great insulator when it is STILL.
"Tests have shown " is about "brick cavity walls" . Yes two skin brick cavity walls are better than single skin brick walls.
Yes air is a great insulator when contained in small pockets. Ie AAC. Blocks!
You guys need to get your head around the properties of aac blocks and pay attention to the science rather than quoting out of context. I assumed the same level of misinformed opinion until i read carefully.

The properties you quoted are for aac blocks, not cavity wall.

No possibility of moisture from the outside skin leaking onto the second skin is the part that troubles me because it makes assumptions. One, that aac blocks will be wet. Two that they are to be direct substitutes for bricks with no other consideration.
There is no reason for the outside skin of aac blocks being exposed naked to the elements. They are NOT clay bricks or High density cement bricks.
All the literature says that they are to be "rendered". So if they are not wet, why do you need an open cavity?

Also i downloaded this from Hebel australia
"The facts: Think again. Testing conducted by CSR Hebel showed that an uncoated, 100mm thick Hebel wall was only 10% saturated after 48 hours of water – compared to other masonry products (clay brick, concrete block and calcium silicate bricks) that were fully saturated. A Hebel wall with 3mm thick render was also tested and showed no sign of moisture penetration at the end of seven days of simulated wind-driven rain. (Test conducted in 1989 to BS 4315 Part 2 1970 ‘Methods of Test Resistance and Water Penetration’.)"

air is also a fluid, and as such large volumes of air are great at convecting heat. If you have a large air current, it will transfer heat from hot to cold pretty effectively. Once you have an air cavity more than 1/2 an inch wide, the ability for the air to circulate within the cavity starts to rise, and air becomes less effective as an insulator.
Thats why aac blocks are great, they trap air in small, non migrating pockets. So why are you trying to put large migrating air pockets between two aac block walls?
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Re: Dry stacked block column

Postby Andyfteeze » Fri Oct 07, 2016 6:38 pm

Just reading the literature from Hebel, its a much more nuanced read than whats available here in thailand.
By far the best insulating method using their blocks, Has gypsum on battens and insulation sqeezed between with NO CAVITY. Next comes two panels/blocks with a polyester/polystyrene sandwiched in between, again no cavity.
But and there is always a but, thats all and good if you are only chasing R values. Acoustically , a closed air gap is better.
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Re: Dry stacked block column

Postby Sometimewoodworker » Fri Oct 07, 2016 6:53 pm

ajarnudon wrote:and certainly not redundant if you have the concrete blocks outside with AAC inside, as Pipoz has done with good effect (and as I will also do). Do you consider that the air temp in a confined cavity will be lower than in a vented one (auto forced ventialation as required)? And if not, which air body will have the lower thermal transmission to the inside wall? Reflective foil is very cheap I might add.


Your point about the silver radiant barrier being cheap is true. But it is designed as a radiant barrier and used in that way it is effective. It isn't designed to be efficient as either a conducive or convective barrier. So it will assist in reducing the heat from the outside blocks but have little effect on any heat from the air in the cavity.

I am still interested in your reasons for using concrete blocks in your outside wall. As they are more expensive to use than AAC taking into account the cement needed, time to lay and block cost. Even the special AAC render is cheaper than the smooth topcoat render.
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Re: Dry stacked block column

Postby BKKBILL » Fri Oct 07, 2016 9:30 pm

Nothing to get my head around as I was referring to ACC cavity walls. Using brick unless it is for cosmetic purposes doesn’t seem to make sense due to the equal or higher cost of construction. The gap between cavity wall here is normally 5 cm if the wall is properly sealed there would be little air current in a cavity wall via convection that could cause significant temperature differences, of course I’m sure this could be measured scientifically. If as you post no moisture can penetrate ACC blocks then the weep holes are also redundant making for even fewer convection currents.

I believe enough reasons for a cavity walls have been posted and I’m sure Ajarnudon would sooner hear about dry stacked block columns on this thread.
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Re: Dry stacked block column

Postby spg » Wed Oct 12, 2016 7:23 pm

Andyfteeze wrote:Also i downloaded this from Hebel australia
"The facts: Think again. Testing conducted by CSR Hebel showed that an uncoated, 100mm thick Hebel wall was only 10% saturated after 48 hours of water – compared to other masonry products (clay brick, concrete block and calcium silicate bricks) that were fully saturated. A Hebel wall with 3mm thick render was also tested and showed no sign of moisture penetration at the end of seven days of simulated wind-driven rain. (Test conducted in 1989 to BS 4315 Part 2 1970 ‘Methods of Test Resistance and Water Penetration’.)"


I don't think this is necessary relevant. My AAC is around 15-16% water when not exposed to rain, that's because of local 95% humidity. AAC absorbs water vapour, it acts like a dessicant; it will also expel vapour into the air (regardless of render - the render is required to be vapour permeable), but if the humidity is constantly high then it will stay basically damp.

According to Hebel's documentation AAC should not be rendered if it exceeds 18% (it should be allowed to dry first, otherwise it expels too much water); my experience in fact is if not rendered the blocks will reach up to around 25-30% water.

So AAC should basically be protected from rain, and rendered when it is not excessively damp. If it is rendered then the render will provide some water protection.
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Re: Dry stacked block column

Postby MGV12 » Thu Oct 13, 2016 6:21 pm

spg wrote:
I don't think this is necessary relevant. My AAC is around 15-16% water when not exposed to rain, that's because of local 95% humidity. AAC absorbs water vapour, it acts like a dessicant; it will also expel vapour into the air (regardless of render - the render is required to be vapour permeable), but if the humidity is constantly high then it will stay basically damp.

According to Hebel's documentation AAC should not be rendered if it exceeds 18% (it should be allowed to dry first, otherwise it expels too much water); my experience in fact is if not rendered the blocks will reach up to around 25-30% water.

So AAC should basically be protected from rain, and rendered when it is not excessively damp. If it is rendered then the render will provide some water protection.


The use of AAC blocks is increasing [exponentially?] here in Thailand. I have yet to see any opinion from Hebel on best practice in utilising AAC blocks in Thailand house builds .. both directly from them or from those under legitimate licence... in the environment experienced by our members.

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Re: Dry stacked block column

Postby Roger Ramjet » Thu Oct 13, 2016 8:17 pm

spg wrote:I don't think this is necessary relevant. My AAC is around 15-16% water when not exposed to rain, that's because of local 95% humidity. AAC absorbs water vapour, it acts like a dessicant; it will also expel vapour into the air (regardless of render - the render is required to be vapour permeable), but if the humidity is constantly high then it will stay basically damp.

A lot of disinformation there: Firstly on any given day who can tell the relative humidity in all areas of Thailand. I have two clocks that show humidity, I placed one outside and one inside, the one outside was showing 78% and the one inside 43%.
During the great flood my AAC blocks were under water for days, weeks and months, yet within less than a week exposed to the air they were dry enough to render both on the inside and outside. The render is still there with no cracks.
If your AAC blocks are around 15-16% water, how did you know? Did you measure the water content? If so which university performed the experiment?
I have over 4,000 AAC blocks in my house and garage construction and have absolutely no problem with them at all.
Please stop making rash statements that can mislead other people.
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Re: Dry stacked block column

Postby spg » Thu Oct 13, 2016 11:08 pm

Roger Ramjet wrote:
spg wrote:I don't think this is necessary relevant. My AAC is around 15-16% water when not exposed to rain, that's because of local 95% humidity. AAC absorbs water vapour, it acts like a dessicant; it will also expel vapour into the air (regardless of render - the render is required to be vapour permeable), but if the humidity is constantly high then it will stay basically damp.

A lot of disinformation there: Firstly on any given day who can tell the relative humidity in all areas of Thailand. I have two clocks that show humidity, I placed one outside and one inside, the one outside was showing 78% and the one inside 43%.


Who needs to tell the humidity in ALL areas of Thailand? I said LOCAL humidity. That's local to me, which is actually in Sumatra, 3.5 degrees North of the equator.

During the great flood my AAC blocks were under water for days, weeks and months, yet within less than a week exposed to the air they were dry enough to render both on the inside and outside. The render is still there with no cracks.
If your AAC blocks are around 15-16% water, how did you know? Did you measure the water content? If so which university performed the experiment?
I have over 4,000 AAC blocks in my house and garage construction and have absolutely no problem with them at all.
Please stop making rash statements that can mislead other people.


Yes of course I measured the water content; I used a German-made moisture meter (it's possible the water has not penetrated through the block - I haven't smashed any blocks up). I have some blocks inside which are at 24% moisture, they feel cool/damp to the touch. Others nearby, which presumably were not. I have also in the past weighed blocks (no university required!) and it's clear large amounts of moisture are retained.

Hebel say:

"While the moisture content of Hebel AAC decreases during construction, if construction schedules require quick occupancy, dehumidifiers may be desirable during the first year of occupancy. These temporary dehumidifiers would take care of the excess moisture being emitted from the walls and roof systems"

"All buildings must be protected from the influence of external moisture sources"

" By the end of the autoclaving process, the AAC contains approximately 30% (by weight) water, which dissipates naturally over time to stabilize at a moisture content of 4% to 8%.

The initial drying-out process includes two different rates of water dissipation. First, as the internal moisture content of AAC exceeds 18%, it experiences rapid diffusion. Vapor permeable coatings on wall surfaces and interior roof panels do not hinder this diffusion process in most situations. Although, depending on the time of construction, moisture levels can be at or below 18% by the time the building is “dried-in”. With expedited construction schedules, dehumidifiers may aid in the initial phase of drying."

" Vapor barriers should not cover AAC at this stage due to this natural process of water diffusion. After the internal moisture content of the AAC material falls below 18%, the rate of diffusion is reduced. Generally, the rate of drying is low enough that additional moisture and humidity entering the building can be effectively removed by the HVAC system. The moisture from the AAC is minor and unnoticeable to occupants"

"High moisture levels are common in building materials during the first few months after construction. Moisture protection is achieved by proper design, detailing and construction practices. To expedite equilibrium of moisture content in AAC,"

Here you can see unrendered AAC with no protection, just visible around the corner, blocks covered by a canopy. The blocks are not going to dry out unless given some protection

The UK's primary AAC manufacturer is H+H. They offer various grades of AAC:

Solar (2.9N/mm^2 compressive strength, 460kg/m^3 density, 0.11 W/mK thermal conductivity)
Standard (3.9N/mm^2, 600 kg/m^3, 0.15W/mK)
High Strength (7.3N/mm^2, 700kg/m^3, 0.18 W/mK)
Super Strength (8.7N/mm^2, 700kg/m^3, 0.18 W/mK)

Their advice for render is split according to the 'wind-driven rain index', i.e. the amount of wind-driven rain in your particular area, which will hit the wall.

Basically the advice is:

(a) if you have not got movement joints in your wall (@3 metres from corners): use metal lathing reinforced traditional render with three coats of 12mm, 9mm and 6mm successively; or a proprietary manufacturer-approved render, which may permit one coat according to manufacturer recommendations
(b) if you have got movement joints then you can use two layers of unreinforced render IF you are not using the low-strength (solar) blocks, AND you are in sheltered or moderate conditions.

Render must be relatively weak with a maximum of 1 part cement to 1 part lime to six parts sharp sand for the harshest conditions, and for less harsh conditions 1 to 2 to 8.

" All blocks (as with other materials) should be protected. Keeping the blocks dry will ensure minimal drying out movement."
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