# Forum Home Renovation Brickwork  Retaining Wall and Slab advice

## AlexJ66

Greetings all, we had an old brick retaining wall holding back the dirt in our front yard, which started to give way, so I have removed it to put in a new Besser Block one. For a number of reasons I am not doing a pine sleeper one, and am tossing up whether the Besser Block wall needs to be core filled or not. It is 2 metres long by 1 metre high, and there is already a good solid concrete footing there. Should I put the rebar through it and core fill it? We can build a retaining wall of 1 metre or less without council and engineers input, so I don't need to go through them. I have looked at all other types of retaining walls, and I am definately going the Besser Block way, I would just like to know, what would YOU do in relation to core filling and using rebar?  
There is also a 10 metre x 3 metre concrete slab in the front yard, and one section of it had broken off, perhaps because of sinking dirt, maybe caused by the deteriorating retaining wall. I have made a nice clean straight cut, and removed the broken section of slab, roughly 3 metres x 3 metres. After the retaining wall is completed, I am going to pack down new dirt, and build a new section of slab before we pave over the whole lot. My question is, should I attach this new section of slab to the remaining section of slab before paving over it? If so, how should I do this? I was considering drilling into the side of the existing slab and inserting sections of rebar that would join them. But maybe this isn't the best idea. 
Thanks for your help  :Smilie:

----------


## Metung

I'm going to build a similar wall but will have to pour the footing. I'm going to put starter bars in the footing and reinforce and core fill the wall too. It would seem to me that in your case it wouldn't make sense to just reinforce and core fill the wall because you will have a plane of weakness, at least compared with the rest of the wall, between the bottom of the first course and the footing. I think I would be drilling some holes in the footing and putting in some reo.
I've never done any block laying before (or bricklaying for that matter) so I was rather keen on an idea suggested by Bloss in another thread - to simply glue/liquid nails the blocks together. There's not much meat on those blocks to sit the mortar on so I think I am going to have some problems if I use mortar.

----------


## AlexJ66

Thanks Metung, sorry, I was actually thinking of adding a further footing with the starter bars inserted as I agree, it would not be very strong. The original footing is well below the ground level, so there isn't any problem with adding more to it  :Smilie:  As for glueing the blocks, most brickies only use mortar, and I have used mortar before with besser blocks, so I will go that way again. I think the core fill helps hold it all together, so really we have just answered my first question  :Biggrin:  
The only part now is getting the mix right, as I don't want to order in a truck for a small amount of core fill  :Smilie:  I might just core fill it as I build it if I am careful,enough  :Smilie:  
So, now I just need someone to tell me whether I should join my cement slabs  :Smilie:

----------


## autogenous

You will need starter bars and concrete core fill and a footing 500mm - 600mm wide for a 1 metre high wall.
You really should get an engineers detail. If you get it wrong you aren't saving money. :Smilie:

----------


## Master Splinter

For tying the slabs together... 
R16 galvanised dowels 400mm long at 450 centers is the 'you can drive a car over this' solution...but you could probably be just as happy with some R12 bar at 600 centers (just try to get some that is galvanised to keep the rust faeries away!) for pedestrian traffic.  Your local reo place should have some to suit. 
Remember that you'll still have to put an expansion joint in anything hard (like tiles) that goes across the join - it's only for height control and doesn't provide lateral restraint.

----------


## pawnhead

I couldn't imagine doing any height of block retaining wall without reo and core fill.
A builder I worked for a while ago built a small (three course 600mm high) block wall, rendered and completely finished except for the core fill, which was due to go in the next day. Without much thought, he had the labourers backfill the wall before the concrete went in, and sure enough it rained that night. The next day the wall had bulged all over the place and the render was all cracked up. 
It was an expensive lesson for him.

----------


## sundancewfs

I did a 3 course high block wall, rebar (into the footing) every second cavity and concrete fill for the entire wall, on a 600mm deep by 300mm wide footing with 2 layers of trench mesh separated by Z-bars. Its been up for a year and forms part of our driveway. No movement or cracks.

----------


## AlexJ66

Thanks very much Master Splinter, exactly what I was after  :2thumbsup:  
As for not core filling the retaining wall, I have heard of Besser Block walls being built without core fill, but they were of a a lesser height. I was 95% sure I was going to core fill it but just wanted to obtain some others thoughts, I also believe it would be foolish to not core fill a 1 metre high wall and will definately be doing so. I will also be including the lateral rebar. I will get away with a standard size footing as there will not be a great deal of sideways pressure on it. 
Thanks all for the assistance  :Smilie:

----------


## PlasterPro

> I'm going to build a similar wall but will have to pour the footing. I'm going to put starter bars in the footing and reinforce and core fill the wall too. It would seem to me that in your case it wouldn't make sense to just reinforce and core fill the wall because you will have a plane of weakness, at least compared with the rest of the wall, between the bottom of the first course and the footing. I think I would be drilling some holes in the footing and putting in some reo.
> I've never done any block laying before (or bricklaying for that matter) so I was rather keen on an idea suggested by Bloss in another thread - to simply glue/liquid nails the blocks together. There's not much meat on those blocks to sit the mortar on so I think I am going to have some problems if I use mortar.

  http://www.boral.com.au/product_inde...den&site=boral 
check out the morterless connex system, they just dry stack together then core fill

----------


## AlexJ66

Master Splinter, another couple of questions about joining the slabs if I may? What sort of glueing compound (epoxy) should I use to secure the dowels? Was thinking of liquid nails, but didn't know if that would be a stupid idea  :Frown:  Also, in another topic on these forums someone advised to have the dowels in on angles like this  / \  / \. Does it need this or can the be straight in?
I have done a LOT of concreting over the years, but this type of job is new to me  :Smilie:  I already have some R12 reinforcement bar floating around, which I could cut into dowels, and the only galvanised ones I can find are 16mm, which would you go with? The paved area will only be for light foot traffic. 
Thanks again  :Smilie:

----------


## pawnhead

> http://www.boral.com.au/product_inde...den&site=boral 
> check out the morterless connex system, they just dry stack together then core fill

  Looks like an easy system, but at $4.50 per block, it's $2.00 dearer than a normal cinder block. You can buy a lot of mortar with two bucks, and it would add up quickly in a decent sized wall. Mind you, with the connex you'd save a bit of labour after you've laid the first course dead level. 
Interesting.

----------


## Master Splinter

As it's a large area of concrete you are adding, don't use anything to secure the dowels - drill a hole to fit in the old concrete and slip them in. (they should be able to move, so not a 'hammer the buggery out of it' fit!) 
Avoid the   / \  / \ layout - it can lead to stress cracking in the concrete unless you've got an engineer working out the strengths and stresses and all that sort of headache inducing stuff. 
An ideal solution would be to make a 30-40mm deep (not deep enough to hit the reo mesh, but deep enough to help the concrete crack below that point) sawcut about 400mm back from the edge of the old concrete surface.  
Then break the 400mm of old concrete away with a [beloved $80 Ozito non-rotary hammer or alternative], exposing the mesh.  Attach new mesh to old as per standard mesh overlap, and pour new concrete.  Whoo-hoo - rock solid!  
If you can't do that, I'd go for the galvanised dowels simply because of the rust aspect - but if you've only got a 75mm thick slab, then the R12 may be a better way to go to avoid thinning the concrete out too much...but then you have rust to worry about.    
Maybe some long galvanised bolts could be used (I've seen 'em in Bunnies at pretty close to 400mm long) - slip the threaded end into the existing concrete (maybe cover in a heaping swadge of grease for luck) and the other end has a nice deformed head to anchor it in the new concrete!!

----------


## AlexJ66

Thanks very much once again Splinter, I really appreciate the excellent advice  :Smilie:  I will go buy the 16mm galvanised dowels, as the concrete is 100mm and more in some areas. I assume they are not secured to allow for the contraction and expansion? 
Cheers  :2thumbsup:

----------


## Metung

Splinter, your avatar reminded me of a quote from Rodney Dangerfield that I read recently "I remember the time I was kidnapped and they sent a piece of my finger to my father. He wanted more proof". 
Thanks for the info on the Connex blocks Plasterpro - unfortunately I already have the normal blocks so will be using them. 
It also occurred to me that I reckon I have seen heaps, excuse the pun, of brick retaining walls around the 600-800mm high and I can't imagine them being any stronger than a core filled block wall.

----------


## pawnhead

> It also occurred to me that I reckon I have seen heaps, excuse the pun, of brick retaining walls around the 600-800mm high and I can't imagine them being any stronger than a core filled block wall.

  A mass, or Gravity retaining wall  (without being tied in to its footing) relies on its own weight to hold back fill, as does a gabion type wall. With a brick retaining wall, it must get wider at the base, as it gets higher. This wall is shown retaining at least 800mm of backfill, but I'm certain that it should be wider than just 350mm at its base. I have a diagram in a brickwork textbook that I used at tech many years ago, and it shows (from memory) a 9" brick retaining wall growing by one course (120mm) every four vertical courses (344mm). This would make a 1 metre high brick wall five courses (590mm) thick at the base.

----------

