Tuning cavity width for Flemish Bond

[MortarThePoint]

The outer leaf for most of the house's cavity walls are going to be flemish bond. We'll cut bricks in half to make 'header' part of the bond as you'd expect. What I was wondering is whether we should widen the cavity slightly to make the laying easier. Half a standard brick is 215 / 2 = 107.5mm whereas the standard brick width is 102.5mm. The blade of the grinder will take a bit off, but it's enough work to cut bricks in half let alone cut a slither off. The cavity is to be 100mm mineral wall.

 

Should we tweak the cavity width to say 105mm to make life easier or could that create it's own issues? I discussed it with a pair of brickies, one said no as he likes a 'tight cavity' whereas the other said yes and the compromise was to go with 102.5mm, but I wanted to see what others thought.

Edited April 27, 2020 by MortarThePoint

[Oz07]

Your brickies will not be that accurate you're overthinking it. Just stretch the cavity width to max whatever your cavity lintels allow.

[MortarThePoint]

15 minutes ago, Oz07 said:

Your brickies will not be that accurate you're overthinking it. Just stretch the cavity width to max whatever your cavity lintels allow.

 

My day job is as an engineer and I'm used to dealing in um so it's sometimes hard to adjust to the tolerances.

 

I was hoping to do lots of the brick laying myself, but Covid-19 may make that non-viable unfortunately.

[Oz07]

I'm a chippy and I get told off by these rough arse wet trades for being to precise so you're in for a world of pain!

[Declan52]

Just make life easy for yourself and widen the cavity.

[PeterW]

TBH I would go for a 125mm cavity and use retaining clips on the insulation. 

[Oz07]

Just be aware if widening the cavity you need better ties and different lintels 

In reality I've seen 5" cavities with 4" ties and lintels but I wouldn't have it on one of mine

[epsilonGreedy]

My brickie opened the cavity 5mm for my English bond walls. The trowel/whack cut headers are irregular but the cavity batts fit around these.

 

I fear the OP won't be happy with the internal look of the part built outer leaf, English or Flemish bond looks very rough viewed from inside.

 

Is it Flemish all around? In my part of the world the posh bond is presented to the road and something lesser like English Garden wall bond is ok sides and back. I wonder if the planners would approve a variation? 

[Brickie]

Opening it up by by 2 or 3mm isn’t going to hurt. 
Btw I’d insist on plumb peeps for Flemish bond-any drift off plumb shows up straight away,especially with metric bricks,where the ratio of header to stretcher is slightly different to imperials. 
A lot of care needs to be taken in the setting out. I’d sacrifice a day to dry bond the whole build,setting out the openings & dropping broken bond under the windows where needed to give you nicely bonded piers with header/queen closer and stretcher on top. 

[MortarThePoint]

11 hours ago, epsilonGreedy said:

My brickie opened the cavity 5mm for my English bond walls. The trowel/whack cut headers are irregular but the cavity batts fit around these.

 

I fear the OP won't be happy with the internal look of the part built outer leaf, English or Flemish bond looks very rough viewed from inside.

 

Is it Flemish all around? In my part of the world the posh bond is presented to the road and something lesser like English Garden wall bond is ok sides and back. I wonder if the planners would approve a variation? 

 

I'll be fine with the rough internal look of the outer leaf, it's not the finished face and I can't imagine it any other way. 

 

This straw pole seems to support opening the cavity slightly, I'm not keen to go as far as 125mm, but adding a few mm does feel sensible.

 

Once I started noticing brick bonds I started really appreciating them. I wondered about Monk bond (stretcher-stretcher-header). It's going to be Flemish all round as it is in keeping with the broader style of the house.

[MortarThePoint]

6 minutes ago, Brickie said:

Btw I’d insist on plumb peeps for Flemish bond-any drift off plumb shows up straight away,especially with metric bricks,where the ratio of header to stretcher is slightly different to imperials. 

 

Is that a typo (weeps or perps) as I'm not familiar with peeps?

 

 

6 minutes ago, Brickie said:

A lot of care needs to be taken in the setting out. I’d sacrifice a day to dry bond the whole build,setting out the openings & dropping broken bond under the windows where needed to give you nicely bonded piers with header/queen closer and stretcher on top. 

 

Completely agree! Not something to be rushed as it is a demanding bond, important not to undermine the visual appeal by not making good layout choices.

Edited April 28, 2020 by MortarThePoint

[Brickie]

56 minutes ago, MortarThePoint said:

Is that a typo (weeps or perps) as I'm not familiar with peeps?

56 minutes ago, MortarThePoint said:

Perps! 
Blondy iPhunk predumptank texi!

[Russell griffiths]

Perps, the vertical joint between the bricks. 

As @Brickie said this is crucial to it looking good

a good bricky will use his level to put a small vertical pencil mark to show where the next header will drop in place

 

if you look at most of the modern brickwork look up at a tall wall and it will make you feel drunk as they wander all over the show. 

 

 

[Brickie]

1 hour ago, Russell griffiths said:

a good bricky will use his level to put a small vertical pencil mark to show where the next header will drop in place

I tried a method I heard about,where you mark the line with a pen,instead of marking the wall & constantly putting your trowel down to walk back & forth with your level. The results were pretty good,I have to say. 

[Russell griffiths]

24 minutes ago, Brickie said:

I tried a method I heard about,where you mark the line with a pen,instead of marking the wall & constantly putting your trowel down to walk back & forth with your level. The results were pretty good,I have to say. 

As long as you are using corner blocks and don’t keep moving the line back and forth. 

[epsilonGreedy]

One extra aesthetic tip which applies to English Bond but not sure about Flemish. At the corners of English ( + Garden Wall ) the pseudo headers should step up or down a course as would happen in a genuine double brick wall.

[Mr Punter]

I have used a masonry saw to cut a load of halves.  You can do 4 at a time.  A pallet of bricks is fairly easy to do and you get two good halves.

 

With fibre insulation +-10mm will not be any problem, although 100mm does not sound like it will give a very good u value.

 

@tonyshouse used 300mm on his place!

[MortarThePoint]

6 minutes ago, epsilonGreedy said:

One extra aesthetic tip which applies to English Bond but not sure about Flemish. At the corners of English ( + Garden Wall ) the pseudo headers should step up or down a course as would happen in a genuine double brick wall.

I don't understand this, are you able to share a picture?

[joe90]

I had a 200mm cavity built full fill with rockwall batts.

[Russell griffiths]

40 minutes ago, epsilonGreedy said:

One extra aesthetic tip which applies to English Bond but not sure about Flemish. At the corners of English ( + Garden Wall ) the pseudo headers should step up or down a course as would happen in a genuine double brick wall.

That would happen whether it be double brick or single 

they change course as they go around the corner. 

 

 

[MortarThePoint]

3 minutes ago, Mr Punter said:

although 100mm does not sound like it will give a very good u value.

 

@tonyshouse used 300mm on his place!

 

Using Knauf Dritherm Ultimate 32 Slab insulation and considered various cavity widths:

• 100mm : U-value 0.27, DER 9.80 kg/m2
• 125mm : U-value 0.22, DER 9.76 kg/m2
• 150mm : U-value 0.19, DER 9.41 kg/m2

Overall the benefits of going thicker did not stack up for us, but it's a personal thing really as everyone has their own set of priorities on a build. We live at about 17-18 C during the winter and there are two stoves in the house that we can use. If it was to be oil heated, I'd fit a larger tank given prices, but it's going to be ASHP.

[MortarThePoint]

8 minutes ago, Russell griffiths said:

That would happen whether it be double brick or single 

they change course as they go around the corner. 

 

 

 

I follow you, like this:

With Flemish you put a stretcher next to the queen closer.

 

                      Face 1         Corner         Face 2

[Stretcher-][Head][Stretcher-][Q][Head] | [Stretcher-][Head][Stretcher-][Head]

   [Head][Stretcher-][Head][Stretcher-] | [Head][Q][Stretcher-][Head][Stretcher-]

[Stretcher-][Head][Stretcher-][Q][Head] | [Stretcher-][Head][Stretcher-][Head]

 

Where's my daughter's Lego when I need it?

[Brickie]

1 hour ago, epsilonGreedy said:

One extra aesthetic tip which applies to English Bond but not sure about Flemish. At the corners of English ( + Garden Wall ) the pseudo headers should step up or down a course as would happen in a genuine double brick wall.

Known as ‘change direction,change bond.’

Applies to the garden wall variety as well-the header courses should be equidistant to each other on adjacent planes. 

[epsilonGreedy]

1 hour ago, Russell griffiths said:

That would happen whether it be double brick or single 

they change course as they go around the corner. 

 

 

Not necessarily, my brickie team overlooked this at their first two corners as they were so heads down. I noticed the error after a couple of hours but did not have the heart to order them to take down the first 300 bricks laid. The error only affects a single story utility wing and the other 4 main 2-story corners are correct, so the error will just be a talking point in the future and I will challenge technically minded visitors to spot the error.

 

When my self build neighbour saw the change of course at a corner on his own house (i.e. his brickie team got it right from the outset) he thought they had made a mistake and was annoyed for a coupled of minutes until I put him right. 

[bassanclan]

I imagine your bricks will use a brick as the cavity spacer when setting out, so will naturally go up to 103-105mm.

Rather than dritherm etc have a look at pumping in EPS beads. It works out around the same price and offers a better u value and full fill.