Advice on building outside wall, please?

[Mike Barnard]

Hi.

I want to build a wall across the back of my garden, dividing us off from a service road. I have the layout I want in my mind, but my question is about the correct matereils to use. I'm on the south coast of the UK, a mile from the sea. The wall be be on the north facing aspect.

It will not be loadbearing, apart from resting one end of a carport style roof on it. It will be in two sections, with a wide wooden gate in the middle.

I don't want the waste of using bricks. It's out of sight from the house and will have a shed and plants covering our side. Blocks it is, but which ones for exterior use and what mortar mix for longevity?

I guess areated blocks would be a little fragile for an external wall? Build Centre lists the following Dense Aggregate Concrete Blocks:

H12912 * 100MM DENSE HOLLOW CELLULAR BLOCK 6.22 per Square Metre H12907 * 100MM DENSE SOLID CONCRETE BLOCK 7N 9.29 per Square Metre H12911 * 140MM DENSE CONCRETE BLOCK SOLID 13.42 per Square Metre H12914 * 140MM DENSE HOLLOW CELLULAR BLOCK 12.73 per Square Metre H12925 * 215MM DENSE CONCRETE BLOCK 20.11 per Square Metre H12920 * 215MM DENSE HOLLOW BLOCK 17.58 per Square Metre H12902 * 75MM DENSE CONCRETE BLOCK 8.12 per Square Metre

(I hope the formatting is not too bad for you.)

75mm and 100mm are too thin. 140mm seems OK and I'm wondering if 215mm may be too thick; I'm not building a castle! Hollow blocks are cheaper and probably lighter but I'm unsure about precise fitting and cutting for wall ends and angles.

I *have* googled, but not come up with an understandable, concrete (sic) answer. So, anyone willing to give me a hint or two, please?

Many thanks.

[Mike Barnard]

Sigh, I must proofread before posting. Hangs head in shame!

[Owain]

How high and long is wall?

Is wall straight or curved?

Can/will you have buttresses?

Is there a graffiti/vandalism problem at the location?

Will cars be able to knock/scrape the wall or will there be kerbing on the service road side?

Owain

[dg]

Why is 100mm too thin? And aerated blocks are frost rated

I would go for a 3.5N 100mm solid block for this type of wall.

Hollow blocks can crack under the slightest movement, and a 7N block would be a pain to lay. Also 140mm is overkill and way too heavy for this application.

Don't forget to build a peir at each end of the wall for stability.

I also like the way you have thought about the aesthetics - covered from your side and a nice grey mass from the other side. Don't forget to leave all the mortar snots hanging on that side too, just for completeness

dg

[Jeff]

"dg" wrote

well I laughed

Regards Jeff

[Chris Bacon]

How high will it be? How long?

[Christian McArdle]

I'd build it out of wood, myself, with tongue and grooved boards facing the road. Unfaced concrete looks just too rank.

Christian.

[meow2222]

so it is loadbearing. Do you know what a layer of snow weighs?

the mortar mix for max strength is 3:1. Saving =A31 by using something weaker doesnt seem to make much sense to me. Make it right and it'll last a lifetime.

If your roof is full height and rests on the wall, maybe the wall is also full height. If it is, you'll need 9" thickness minimum.

There are 2 ways to design these walls, thinner with buttresses, or same thickness all the way along, but thicker. The latter looks much better.

Bear in mind you dont need blocks at all, if you want you can pour the whole wall in concrete.

I gather aerated blocks would need rendering (I've not used them outdoors) so they'd make for more work.

With hollow blocks and outside walls you're liable to end up with things growing in the wall, and in time breaking the wall apart. I presume theres no expansion problem if you pour filled a hollow wall, someone else will know for sure.

Finally you can make your own blocks if you want, need a simple wood frame on a flat sheet, line it with polythene, and pour in load after load. A 4x8 mould is 2 m^2 or so of blocks, so with 9" blocks you can work out what you'd save.

I'm going to start a separate thread on the wide range of possibilities that making your own blocks opens up, and you do need to read it :)

NT