Two simple questions about breeze blocks

[mlse]

Hi all,

I am planning to build a two-block high raised bed out of these blocks: http://www.ebuildingsupplies.co.uk/product/100mm-73n-440x215mm-solid-dense-concrete-block-/1001554/ Are these the right ones to use? I've chosen them because they're dense and solid and seem the right choice for an outdoor wall that will have soil behind it.

My other question is, what does the "N" bit mean? I see it against all blocks on the 'net, either "3.6N" or "7N" or "7.3N" or "10N", although it's not explained anywhere. Can somebody tell me what it means?

Thanks!

 

[RedHerring2]

N stands for Newtons and refers to the strength. You don't need to worry about that for a 2 block high garden wall.
Hollow or dense concrete block will be fine.
Think about a dpm draped down the back of the wall to prevent damp leeching through and staining the outside.

Also, consider how you want the outside finish to appear, because you can get "paint-finish" blocks which are smoother and will take a stone paint straight on without any rendered finish.

 

[mlse]

Many thanks!

I have some liquid DPM left over from when I did some damp-proofing in my conservatory, so I'll use that up the back of the wall.

When you say "paint finish", I guess you mean either open-face of closed-face? I've seen both in reference to blocks. I will be painting them with white masonry paint.

 

[RedHerring2]

I don't think paint finish is interchangable with open/closed face blocks.
Open/closed face blocks refer to the end of the block and how it is installed to its neighbour.

Paint finish blocks are what you want. They have a smoother finish to the faces and take less paint easier and give a more pleasant appearance when painted.
Just ask your supplier for them.

 

[freddiemercurystwin]

They have a smoother finish to the faces and take less paint easier and give a more pleasant appearance when painted.
Just ask your supplier for them.

Still look pretty crap though.

 

[mlse]

Many thanks for the replies that are informative and constructive!

 

[freddiemercurystwin]

Well they do look just as crappy as normal blocks when they're painted!

 

[Emeraude119]

Hi mise

Blocks at 7.3 N/mm2, or stronger are deemed suitable for use in the freeze thaw conditions which are likely to occur at or below ground level (typically down to around 600 - 700mmm below ground. where ground temperature stabilizes at around + 4 degrees Celsius in the UK)
Blocks which will be used below ground level must also be resistant to soluble sulfates which can occur in building grounds, so you would need to check that the specific block type being used, is cleared for use in sulfate soils that might exist on your site.
Generally any block down to 2.9 N/mm2 strength`could' be used below ground, provided it has been tested and cleared for use in this position.
but not all blocks below 7.3 N/mm have sufficient sulfate resistance.

For external / garden walls dense aggregate blocks are best as their laid weight (mass) helps prevent them from being blown over in high winds.
but these normally must not exceed the single person repetitive handling limit of 20 kg per block.

Paint Quality blocks are just that, Paint Quality blocks, and should not be confused with fair race / architectural masonry blocks which are about 3 to 4 times the price of a PQ block, and must be delivered and handled differently to provide the required final appearance.
Where a uniform background is required a paint finish `must' be used, and for external work, this should be a good quality external grade masonry paint applied in accordance with the manufacturers recommendations..

 

[tony1851]

Hi Emeraud,
I think he's probably built it and painted it by now!

 

[Emeraude119]

Hi Tony 1851 - you are right, it does seem as though postings here are
fairly few and far between, but I thought I would just put my few pence worth in in case not, or if someone else might be thinking about building the same type of wall.
Cheers!

 

[ban-all-sheds]

Few and far between?

Dunno what you consider to be not FAFB, but until you replied to it this topic would have been on page 158, over 7850 topics ago, and a huge number of posts ago.

Anyway - to anyone contemplating such a wall, FMT was quite right. Rather than paint, screw lengths of hardwood or pressure treated softwood to the outside. Or there are techniques to encourage moss and lichens to grow, if you fancy that.

 

[Emeraude119]

Hi Ban all sheds. I guess I just meant on this particular topic, there are
many on other subjects as you point out!
Best Regards.