How thick is a 100mm block? Not a trick question.

[epsilonGreedy]

I am about to order a block and beam floor with measurements supplied for my actual block footings. Prior to ordering I spent two hours measuring footing sections with a steel tape measure including the block then I decided to quote all dimensions as clear spans and so subtracted 200mm.

 

This evening while doubled checking the footing plan with a laser, all my spans were out by 10mm too small. A bit of cross checking revealed that my footing blocks are 95mm thick and not the 100mm I had assumed when converting to clear span dimensions.

 

Delving into this further I measured the thickness of 3 different block types onsite. The original footing heavy concretes, the Hemlites and Fibolites were all 95mm thick. Is this normal?

 

 

[Jeremy Harris]

20 minutes ago, epsilonGreedy said:

Delving into this further I measured the thickness of 3 different block types onsite. The original footing heavy concretes, the Hemlites and Fibolites were all 95mm thick. Is this normal?

 

Yes, it's normal.  Many of the dimensions used in building are not exact, some because we've metricated imperial measurements, some because traditionally dimensions were for pre-finished materials, and some because dimensions are just rounded up or down to make them easier to refer to.

[epsilonGreedy]

15 minutes ago, JSHarris said:

Yes, it's normal.  Many of the dimensions used in building are not exact, some because we've metricated imperial measurements

 

 

Ah ha, hence facing bricks being quoted as 102.5mm i.e. 4" plus 1mm.

 

15 minutes ago, JSHarris said:

some because traditionally dimensions were for pre-finished materials, and some because dimensions are just rounded up or down to make them easier to refer to.

 

 

This must explain the block 5mm discrepancy.

 

Good thing I requested a delay to dinner this evening, had I not double checked my floor beams would have been seated by just 90mm on my 95mm footing blocks. Not a disaster given the agricultural technology involved but I was mindful of @RA's undersized floor joist ordering hic-cup.

[Russell griffiths]

i Would rather they where too long than short, it is not uncommon to see beams poking into the cavity. 

If you have a dwarf wall in the centre you generally have them overlapping on the middle span, this gives you your cock up factor. 

[Temp]

Timber seems to be measured before they plane it smooth. So 50*50mm planed timber has a finished size of 44*44mm.

 

 

[Temp]

My builders rule was never order off plan if you can measure it on site. He remeasured all the window openings before ordering windows.

[ADLIan]

Manufacturing tolerance on thickness normally +3mm to -5mm so expect to see bottom of tolerance range for most production runs. 95mm it is!

[Declan52]

It's when you get blocks like yours that are 95mm but the concrete bricks they supply are 104mm that the fun starts.

[Brickie]

Hell of a lot come in at 210mm high now,too. No fun if you’re having to bump up at all to keep level with the existing house. 

[Mr Punter]

The 5% reduction in material costs must be a consideration for the manufacturer

[epsilonGreedy]

2 hours ago, Brickie said:

Hell of a lot come in at 210mm high now,too. No fun if you’re having to bump up at all to keep level with the existing house. 

 

 

When the rain stops I will go and check height of my various block types.

 

And since you mention it my block perp mortar joints have been looking fat as I keep to a spacing plan dictated by my brickie's tape measure, I wonder if my block widths are short as well.

[epsilonGreedy]

2 hours ago, epsilonGreedy said:

When the rain stops I will go and check height of my various block types.

 

And since you mention it my block perp mortar joints have been looking fat as I keep to a spacing plan dictated by my brickie's tape measure, I wonder if my block widths are short as well.

 

 

Yup the Hemlites are 435 wide which explains the fat perps as I kept to gauge following  the brickie's tape measure. Ho hmm I can correct this going higher as I am just two courses above the garage floor and the wall is 11 blocks long. Those 95mm cut end blocks will have to be 120mm so keep the bond overlap well above the 1/3 minimum.

 

At least the Hemlites are a regulation 215 high.

[Carrerahill]

Mine appear to be about bang on 100mm.

 

I had a lintel on Sunday that was 100mm at one end and 110mm at the other!

 

 

[Brickie]

1 hour ago, epsilonGreedy said:

Those 95mm cut end blocks will have to be 120mm

If you cut them at 109mm you’ll get 4 out of 1.