Tolerances to expect

[Mr Punter]

50mm overall is just OK  +-50mm (difference of 100mm) is not.  I note that lots of subbies like to say +- whatever, as it sounds better.

[MortarThePoint]

 

1 hour ago, Brickie said:

I’d really rather not,though. 
Seriously,armed with extremely basic kit (a dumpy & two pieces of 4x2srewedto make an inverse ‘T’) is there any reason footings shouldn’t come in within 20mm for level?

 

Don't trades worry what the next one in line is going to think of their work? I couldn't work in a way that has contempt for the next guy when it's relatively easy to take some pride.

[MortarThePoint]

49 minutes ago, Mr Punter said:

50mm overall is just OK  +-50mm (difference of 100mm) is not.  I note that lots of subbies like to say +- whatever, as it sounds better.

 

I'm a fan tolerances like +something/-0 (e.g. +50/-0 mm) as it conveys which way pain lies.

[Oz07]

39 minutes ago, MortarThePoint said:

 

 

Don't trades worry what the next one in line is going to think of their work? I couldn't work in a way that has contempt for the next guy when it's relatively easy to take some pride.

No they don't give a s**t generally, especially if site lads working on a price

[Brickie]

On 10/05/2020 at 17:04, MortarThePoint said:

 

 

Don't trades worry what the next one in line is going to think of their work? I couldn't work in a way that has contempt for the next guy when it's relatively easy to take some pride.

You should see some of the scaffolds Im asked to work on. Need a wand,not a trowel. 

[Hobbiniho]

In the times that i have laid foundations anything more than 10mm out i would have got a slap, there was 1 job i was working on where i managed to lay the blinding 15mm too high and the site manager had a right go at me, the solution was to remake the shuttering smaller. 

 

There really is no excuse for having any measurements out by more than 10mm when doing foundation work, not sure what is acceptable with brick/block as iv never worked with it but with timber frame if you are out by more than 5mm you either need new glasses or a new tape measure

[Miek]

23 minutes ago, Hobbiniho said:

 

 

There really is no excuse for having any measurements out by more than 10mm when doing foundation work

 Really? "Any" measurement? I'd love to see someone try and dig all found trenches to 10mm accuracy, not going to happen and very dependent on soil type.  You can get the concrete pour to 10mm within level though especially if it's pumped in IMO. 

[Hobbiniho]

On 12/05/2020 at 07:06, Miek said:

 Really? "Any" measurement? I'd love to see someone try and dig all found trenches to 10mm accuracy, not going to happen and very dependent on soil type.  You can get the concrete pour to 10mm within level though especially if it's pumped in IMO. 

 

no you are quite right, i wouldnt expect the actual width of the trench to be within 10mm but the centre should be within 10mm, it really isnt hard to use string lines to set out a foundation any "tradesman" that cannot set it out to within those tolerences is either not competent or simple doesnt give a toss, i will say that i have only ever worked with timber frame so if you get the block underbuilding out by 10mm your timber frame wont fit the hardest site that i have had to shutter and pour strip foundations onto was at about a 40 degree angle which made it difficult but not impossible, a concrete pour that is more than 10mm out on level isnt really acceptable in my opinion however this may be fine if working with brick/block or have a lot of underbuilding to take make up the difference, dont forget that if you make a good job of the foudations it makes everything else easier as you arent chasing mistakes and trying to fix them on subsequent build stages

[MortarThePoint]

Well I have sent the text below to the guys doing the below ground blockwork. It's tighter than the figures discussed above but then I can accept mild exceedance. Saying I specified +/-5mm, knowing I actually needed +/-10mm, and got +/-15mm makes the discussion clearer. I think all of the things are reasonable. I'll let you know how I get on ?

 

"Dimensions:

• Lateral construction drawing dimensions +/-5mm (i.e. brick or block lateral placement +/-5mm)
• Brickwork or blockwork flat +/-3mm over 10m (after 450mm of blockwork from foundation concrete)
• Brickwork or blockwork level +/-5mm (after 450mm of blockwork from foundation concrete)
• Cavity gap +/-3mm
• Plumbness +/-1mm over 1m

Mortar:

• Check the Structural Engineer's Construction Drawings but I think it specifies class (ii) / M6 below FFL.
• "Site mixed mortar should be batched consistently and accurately using batching boxes or buckets. The use of shovels for proportioning should not be used."

Full joints (no tipping and tailing or deep furrowing).

 

Other:

• The concrete fill in a cavity wall should stop at least 225mm below the base dpc

Any drawings, building regulations and accepted best practice (including NHBC guidance) that sets tighter tolerances or additional requirements apply."

[PeterW]

3 hours ago, MortarThePoint said:

"Dimensions:

• Lateral construction drawing dimensions +/-5mm (i.e. brick or block lateral placement +/-5mm)
• Brickwork or blockwork flat +/-3mm over 10m (after 450mm of blockwork from foundation concrete)
• Brickwork or blockwork level +/-5mm (after 450mm of blockwork from foundation concrete)
• Cavity gap +/-3mm
• Plumbness +/-1mm over 1m

 

I think you are going to struggle here - especially with the cavity gap as concrete blocks are +/-6mm on every dimension to standard and I would want the outer faces run straight.

 

 

[MortarThePoint]

9 minutes ago, PeterW said:

 

I think you are going to struggle here - especially with the cavity gap as concrete blocks are +/-6mm on every dimension to standard and I would want the outer faces run straight.

 

 

 

You're right, I had some sour faces over that. They were OK with reaching the other tolerances, but not the plumb / cavity ones due to exactly what you said.

 

When it's above ground it will be the face that needs to be accurately plumb.

 

Unfortunately, they were generally put out by it all. I'm used to having my work specified and am uncomfortable doing work for people without a clear specification. Trades seem to take it as a lack of faith thing which is unfortunate as it isn't personal. We are using precast floor slabs that set a tolerance on the wall.

[Vijay]

One thing you may need to think about is how desperate builders are for your work. They may look at what you're asking for as too much trouble (slightly out and they may not get paid), so they will pass your job for their bread and butter work. Will you struggled for a builder to do your job???

[Ferdinand]

In terms of your neighbours, not very ....

 

[MortarThePoint]

19 hours ago, Vijay said:

One thing you may need to think about is how desperate builders are for your work. They may look at what you're asking for as too much trouble (slightly out and they may not get paid), so they will pass your job for their bread and butter work. Will you struggled for a builder to do your job???

 

It's a fair point Vijay. I'm not trying to be difficult It's just that I don't have years worth of experience to rely on to be able to spot a good job when I see it and there are various things that need to line up. They were out by 150mm with a section of foundation and my very nearly preordered (I bottled placing the order when I saw the foundation misplacement) floor slabs have a tolerance of 10mm + 0.1%. I hadn't given them a spec for the foundation presuming that the drawings and accepted best practice gave sufficient guidance.

 

I think I should have asked them what specification I should expect from their blockwork and that's what I'll do with the brickie. I can then evaluate what they come back with.

Edited May 16, 2020 by MortarThePoint

[PeterW]

On 15/05/2020 at 10:56, MortarThePoint said:

We are using precast floor slabs that set a tolerance on the wall.

I doubt this is an issue. Are they dry set or wet set slabs ..?? They will be +\-25mm on length and 5mm on thickness anyway so you’re not going to get a perfectly engineered floor anyway. 
 

Material tolerances in the building trade seem to  be up to 5% -  not including anything that shrinks or expands - so you need to probably sit back a little and relax as otherwise you will be forever winding yourself and your trades up asking for the impossible. 
 

It is also why you need to measure - plan - measure - order for anything like kitchens or bathrooms. This isn’t precision engineering and even a couple of 5mm variations can mean your perfectly planned kitchen won’t fit ... 

[Dave Jones]

not reallty any excuse not to get footing conc bang on. Can either knock pegs into the trend every meter or so and level the them with a laser then conc to top, or just laser the conc in as you go. 1 man on the staff another on the rake, overhead conc pump job done.

[tonyshouse]

Within 5 or badly done 10mm