To Movement Joint or to Not!

[Jimbo37]

Hi all, a steer, please...

I am building a 2 story house 13m x 7.5m, cavity - both leaves are 100x215x440 block and external is sand and cement render.

Structural Engineer has recommended a movement joint along the 13m stretches. The problem is I don't want to as I have no downpipes etc to hide it behind, and the whole design is minimal - would I be crazy to ignore the SE advice? Has anyone built 13m+ without movement joint?

[markc]

Most houses have walls long enough for ExpJ to be recommended.

if you were adding onto an existing the yes it would be advisable but as a stand alone the two ends can both move so I can’t see any problem

Edited June 9, 2023 by markc

[Mike]

For that length it's normally advised. The downside if you don't is the risk of a random crack which, in a minimalist wall, would probably look worse than a neat vertical joint.

[nod]

He’s right You do need a movement joint on a 13 meter stretch 

If I was rendering it I would put at least one movement joint in the render 

 

 

[Jimbo37]

47 minutes ago, markc said:

a stand alone the two ends can both move

Just so I follow your logic @markc - you think because the entire wall is sitting on the same (really big fundations, because we are on a brown-field that had a lot of fill), there is less chance of cracking, right?

I really want you to be right, but Im mindful of  @nod and @Mike comments too

What is the expericnce of those who have built 13m without movement joint, if they are reading?

Edited June 9, 2023 by Jimbo37

[nod]

5 minutes ago, Jimbo37 said:

Just so I follow your logic @markc - you think because the entire wall is sitting on the same (really big fundations, because we are on a brown-field that had a lot of fill), there is less chance of cracking, right?

I really want you to be right, but Im mindful of  @nod and @Mike comments too

What is the expericnce of those who have built 13m without movement joint, if they are reading?

I don’t think it really matters what any of us think 

You will have a hard time getting this past BC 

If you are using sand and cement Painted I presume You can put two stock beads back to back 

I would void any guarantee on a long stretch of render without joints Especially Sand and cement which is more prone to cracking 

[Mike]

1 hour ago, Jimbo37 said:

because the entire wall is sitting on the same (really big fundations, because we are on a brown-field that had a lot of fill), there is less chance of cracking, right?

The wall & render are liable to cracking due to expansion and contraction of the materials used. The foundations don't influence that, at all.

 

If you have cracking due to foundation movement you have a whole different problem.

[nod]

8 minutes ago, Mike said:

The wall & render are liable to cracking due to expansion and contraction of the materials used. The foundations don't influence that, at all.

 

If you have cracking due to foundation movement you have a whole different problem.

No

who told you that 

Foundations are designed to suit the ground 

[Mike]

17 minutes ago, nod said:

Foundations are designed to suit the ground 

Correct. I should have said correctly designed foundations don't influence that, at all.

[nod]

20 minutes ago, Mike said:

Correct. I should have said correctly designed foundations don't influence that, at all.

I phone call to BC would be your best option 

 

[Eric]

I think our builders installed them on anything greater than 6m so definitely fit them.

They are probably on your drawings?

[ADLIan]

This is down to brick and/or block type. Manufacturers will advise, 10m(?) for brick, perhaps only 6m for block (and render?).

[saveasteading]

Any walls of my own design are without movement joints.

Where specified by others, they are built, usually with a steel behind to compensate for the weakness created. None have been a problem.

 

 

 Bricks expand after manufacture, as they cool down. Blocks shrink, as all concrete does. Get aged, cold bricks, and aged blocks and nothing moves.

But that is me with my own insurances. Best do what you are told.

[Gus Potter]

3 hours ago, Jimbo37 said:

Hi all, a steer, please...

Here is some food for thought.

 

Concrete blocks tend to shrink mostly. The stronger the block the more shrinkage you get. ie a 7.0 N block will shrink less than a 10.0N block as the 10N block tends to have a higher cement content. Concrete blocks can swell, mainly to do with thermal expansion on a very hot day, the outside face expands more than the inside. During prolonged heat the whole wall will expand. But the thermal expansion is relatively small in comparison to the concrete shrinkage.

 

Clay bricks are a bit more tempremental. Generally they also expand as the minerals in the clay and chemicals resulting form the firing process react with the air for a good number of years. They also shrink / swell as the moisture content changes. Think of a clay brick more as living material. It can swell and shrink where as a concrete block tends to mostly shrink.

 

In summary when designing I would for standard builds look at putting a movement joint every 6.0 m maximum in a block wall and 9.0 -12.0m in a brick wall depending on the brick selected and then review. But it gets a bit more complicated than that. You also need to know what other walls are framing into the wall; corners (internal and external), window / door lintel positions. All these features introduce stiff and weak points. This variation encourages the movement to take place in an uneven way and that encourages cracking.

 

To do a good job you do want to have a look at the founds, even if to say, yeh I had a look and know I have checked the following. You may have a set of cross wall strip founds but heavily loaded external founds.. both will move a little differently. Also you may have a big set of bifolds with large point loads, the found will tend to settle a bit more or less here depending on how it is designed.

 

The other thing we need to consider is the strength of the mortar as generally this has a cement content. Too strong and it locks the blocks together and shrinks and swells in its own right.

 

@Mike and @nod can see where you are coming from here. Often separating the found from the superstructure is a plastic DPC which should allow the wall above to slip about on the underbuilding thus relieving the stress. But how much stress relief that develops is a bit of a guess. Ideally if the bedding was perfectly flat this may work.. but in real life on site this is hard to achieve in the heat of battle.

 

In summary for blockwork under the usual conditions that apply on a building site I would not hang my hat on a block wall longer than 6.0m without some kind of joint. There are two main reasons for this. I need to be sure that the wall won't crack for safety reasons.. and also if it does crack and becomes unsightly I'm going to get in the neck anyway.

 

Now.. the fun part. many years ago, some 25 plus (did not know then what I know now) when I did a self build as a young lad I wanted no joints in I think a 9.0m block wall. I was just starting out and had employed an old school SE. He suggested that I use concrete block but in a lime mortar. I did not know enough about lime mortar back then so bottled out and just put in a joint.

 

But I wonder.. would I design something like this now? In theory I would have a look at it. Maybe start with an NHL 3.5.. and if the exposure is benign maybe just have a look at NHL 2.0.. oooh! Now the lime mortar moves and lets (in theory) each block shrink as an individual unit... and that will let you build a longer wall beteen joints.

 

My concern here would be the render and the practical side of this. What kind are we going to use? We are talking doing big panels in one hit.  to make a good job.. a change in the weather, someone twisting their ankle on site, getting a dose of the runs and you could end up with an expensive and frustating out come.

 

If you could get it work structurally, in the round I would want to balance the risk of cracking, a rough uneven finish with using standard joints. My gut feeling is to go for the tried and tested method of joints at 6.0m or less in blockwork if you don't fancy taking too much of a risk.

 

Would be interested to know if anyone has used concrete blocks with lime, if so how did you get on?

 

 

 

 

 

 

 

 

 

 

 

 

[nod]

As I stated earlier BC will follow the rules and insist on at least one 

Personally As a render contractor I’d put two in regardless of block work arrangements Simply to protect the render Two stop beads back to back will be barely visible 

[Jimbo37]

16 hours ago, nod said:

I phone call to BC would be your best option 

 

Will do, thanks all - Ive come around to the idea after the initial groan

[George]

- buy the blocks 6 months early and leave them under cover

- put in bed joint reinforcement around the openings

- leave the rendering for as long as possible so if any cracks do occur, they can be made good

 

 

The render system will have its own MJ requirements. 

[Jimbo37]

15 hours ago, Gus Potter said:

If you could get it work structurally, in the round I would want to balance the risk of cracking, a rough uneven finish with using standard joints. My gut feeling is to go for the tried and tested method of joints at 6.0m or less in blockwork if you don't fancy taking too much of a risk.

Thanks @Gus Potter for all that - the stuff we dont even think of - advice above noted.

[saveasteading]

Overspecification of these wind posts  is my grouch

Making a weakness in a wall and then reinforcing it doesn't make much sense.

I had my own made once at 1/3 the cost.

 

[Oz07]

A movement joint would look neater than a crack. I know what i'd do

[saveasteading]

1 hour ago, Oz07 said:

movement joint would look neater than a crack. 

Agreed. I just never had a crack in umpteen walls with no gaps. I suppose I'm saying that the rules may be slightly conservative, probably inspired by the windpost and filler manufacturers who commissioned the tests. 

Perhaps also they assume hot from the oven bricks and still dripping blocks...Both of which I have encountered

[Oz07]

Why does a movement joint need wind posts? Isn't there a standard detail with cavity ties either side or over a certain height do you need wind posts?

[saveasteading]

6 minutes ago, Oz07 said:

cavity ties either side

There are several solutions: sliding ties across the gap or into a post.

[Oz07]

Yeh the ties with the condoms that's what i've used with cavitiy ties every joint on the blockwork

[Jimbo37]

Sorted - and went with the majority advice and put in the MJs. Thanks all