Cavity wall - leave to breathe or close?

[JimShortz]

23 hours ago, sometimewoodworker said:

No saving at all as the AAC render is cheaper than the render for cinder blocks.

Just to be clear, I haven't been using the cheap cinder blocks with the holes down the middle. The solid Lightweight Concrete Blocks I have used are in many ways like AAC blocks, but not autoclaved. They are the same dimensions and degree of dimensional accuracy, have similar thermal and sound insulation properties (something like 15% less good, but still excellent). They are also are slightly heavier (more dense), absorb water less readily since the "bubbles" are closed, and they can take regular render (again, due to their more "closed cell" makeup. They are not widely available, but can be found, as I described in another post.

 

[sometimewoodworker]

1 hour ago, JimShortz said:

On 9/24/2019 at 4:12 PM, sometimewoodworker said:

No saving at all as the AAC render is cheaper than the render for cinder blocks.

Just to be clear, I haven't been using the cheap cinder blocks with the holes down the middle. The solid Lightweight Concrete Blocks I have used are in many ways like AAC blocks, but not autoclaved. They are the same dimensions and degree of dimensional accuracy, have similar thermal and sound insulation properties (something like 15% less good, but still excellent). They are also are slightly heavier (more dense), absorb water less readily since the "bubbles" are closed, and they can take regular render (again, due to their more "closed cell" makeup. They are not widely available, but can be found, as I described in another post.

I assume you are using CLC blocks (there is no information on SLP blocks that I can find, so assume a trade name), which can be a lot less or more dense than AAC, virtually all the other properties range from slightly less to slightly more than AAC,

 

Mass 800~1800 kg/m³ , AAC 1,600~1,920 kg/m³

water absorbion 7.5% ~ 12.5% by weight, AAC not more than 10%

sound reduction 37db ~ 42db, AAC 40db ~ 45db

Thermal conductivity 0.32 ~ 0.54 W/m K, AAC  0.21 ~ 0.42 W/m K (lower is better)

             -------                -------

However the AAC bags of render are cheaper than the finishing bags of regular render, there wasn't a big difference, but that was true for our build and when you buy pallet loads or truck loads it adds up.

 

So where exactly does your massive saving come from?

[sometimewoodworker]

14 hours ago, JimShortz said:

regular sand and cement render is much cheaper.

Until you add in the time and labour to get render quality sand.

[JimShortz]

aah... I though I had explained. My apologies if this is still unclear for anyone. I'll try again, as clearly as I can: 

If thicker render is needed to deal with posts, lintels, village building, etc. then the cost of bagged plaster for AAC blocks mounts up rapidly versus a sand and cement based render as used on my Lightweight Concrete Blocks (large (same size as AAC), aerated cement blocks, not cinder).

Labour costs for me were low, using "village builders", but thicker render was needed. The overall finish obtained this way has been excellent and I love the stronger walls and ease of adding fixings (I just shelved out a full height 3 sided pantry with regular plugs - strong and simple). AAC is a perfectly viable alternative, and can work great - I'm just sharing my experience of how I got what I am happy with, at a price that worked out great for me. YMMV.

I don't know about special "render quality" sand, but the sand that was used was bought for that purpose at a reasonable price. Once dried out, all walls were then lightly sanded with a 40 grit sandpaper to remove any sharp surface grains of sand (by me and my family - no cost, if you ignore listening to moaning teenagers!  ???? ), before filling of any minor imperfections, application of the raw concrete primer and then two top coats of quality acrylic paint. The overall finish is excellent - just the stipples of a rollered finish, no indication of sharp sand or imperfections.

My intention was to help others see alternatives to AAC, since this isn't much talked about elsewhere. Have a nice day. I hope you are all equally happy with your choices  ????

[sometimewoodworker]

5 hours ago, JimShortz said:

If thicker render is needed to deal with posts, lintels, village building, etc. then the cost of bagged plaster for AAC blocks mounts up rapidly versus a sand and cement based render as used on my Lightweight Concrete Blocks (large (same size as AAC), aerated cement blocks, not cinder).

Your points are interesting but totally off regarding needing thicker render for AAC, having looked at your walls they are certainly less smooth than any AAC walls I've seen, they would certainly need a a greater depth of render that mine or another's I've seen.

 

this is a reasonabley typical AAC wall

 

5 hours ago, JimShortz said:

I don't know about special "render quality" sand, but the sand that was used was bought for that purpose at a reasonable price. Once dried out, all walls were then lightly sanded with a 40 grit sandpaper to remove any sharp surface grains of sand (by me and my family - no cost, if you ignore listening to moaning teenagers!  ???? ), before filling of any minor imperfections

That clearly demonstrates that your plasterers did not do a good job, didn't know their job, or that the material was substandard.

 

A good plasterer will spend a reasonable time polishing the surface, maybe as much as ¼ of the time, after that no, or virtually no sanding or filling is needed.

 

On part of one of our walls the finish was like that and those plasterers lost their job. 

 

It is good that you got a job that worked for you, unfortunately you are mistaken in some of the concepts you have regarding AAC 

[JimShortz]

15 hours ago, sometimewoodworker said:

Your points are interesting but totally off regarding needing thicker render for AAC, having looked at your walls they are certainly less smooth than any AAC walls I've seen, they would certainly need a a greater depth of render that mine or another's I've seen.

That clearly demonstrates that your plasterers did not do a good job, didn't know their job, or that the material was substandard.

Jeez... no wonder so few people want to come near Thaivisa anymore! It has become the butt of jokes about grumpy old men on many Facebook groups...  After this post I give up trying to share my experiences and opinions, because apparently I am wrong all of the time!  This is my last effort to try and help you understand what I am sharing. If I wanted constant correction I would go and see a strict mistress, not post on Thaivisa!  ????  My apologies if that is rude, just feeling very frustrated right now!

Just to clarify for you, once more, as simply as I am able... I don't think that AAC per se, needs thicker render (I know they don't - it is common knowledge!), BUT, if you are using village builders (as I clearly am from what I wrote), with associated minor inacuracies in posts, lintels and/or blocks then a thicker render would be desireable for a high quality finish, hence NOT using AAC (my walls are NOT AAC, hence being "less smooth than any AAC walls I've seen" - no shock there!). This is what I did, and why I did it. Is that okay with you?

The plastering deal is much the same. Note the part about village builders... this is the key to understanding. The final finish they produced was excellent barring some surface roughness. Yes, they could have polished it, had I asked (and they did on selected areas that I won't paint, BUT, this is how I chose to do it). It is not wrong, just not the same as you chose. My overall finish is excellent, as I am sure yours is, and my builders are good local men, known to my family for a long time, who have become "friends" - and they won't be having me shot!

Two ways to a different end! Just maybe, some other people don't have "master builders" and "superior materials". They may like to see an alternative way - working with competent village builders, using materials they understand and are good with (albeit with a slightly different block, but one that can be used with traditional mortar and render), to reach a very acceptable end product.

AAC and master builders are not the only way...  In fact, my stronger walls and ease of fixings is a major boon for me. As I stated in an earlier post I do have an AAC building (4m "cube" workshop). For both the strength and the fixings I wish I had built that with LCBs too - JUST MY OPINION THOUGH. Others can make their own judgement; if we are allowed to share information/opinions in peace!

Bye, bye, Thaivisa... so long, and enjoy the grump!  ????