How to make a High PC Concrete Lintel

[frank999]

I am starting a loft conversion.

I require 8 High PC Concrete Lintels as padstones to bear the steels onto, they are all 150mm high, 100 wide - and varying lengths (330-900mm, average 700mm). Trying to work out the value of concrete, for costing - say if the big one is 0.150x0.100x0.900=0.0135 cu mt ... is that correct ?? its a tiny volume)

Could I make these myself, they come to £300 pre-made.
Looking at a cross section of premade's, they have 2 strips of rebar running through, and I assume a particular mix designation.

How long should they be left to cure.

Would the building control inspector be fussed ? ie require receipts of purchase to confirm where they'd come from.

 

[PrenticeBoyofDerry]

I would suspect that relevant crushing tests would be required to prove that the required newtons of strength has been obtained by your mix design.

Normally a wet cast mix would consist of 6-10mm limestone gravel, and fines and cement with the addition of water.
I would be looking at 2-1-1 in volume. Should get a tasty crushing strength.
Would also consider for lengths exceeding 400mm some reinforcement.
If you have 8 units averaging 700mm x 150mm x 100mm, your cubic volume would be 0.084 cubic metres.
To reach maximum strength could take weeks/months but 28 days is recommended before use.

 

[RonnyRaygun]

Or you could build engineering brick padstones. The size will be the same as it's the crushing strength of the masonry below that governs.

Use Class B engineering bricks in a 1:3 mortar to the same length as the specified concrete padstones.
Ensure the height is half the length to ensure sufficient spread of load.

 

[RonnyRaygun]

Duplicate post...

 

[tony1851]

they come to £300 pre-made.

Good grief!

Buy a coule of lengths of 150 x 100 pre-cast concrete beams, hire a disc cutter, and cut them to the various lengths you need.

 

[themiddleagedun]

they come to £300 pre-made.

Good grief!

Buy a coule of lengths of 150 x 100 pre-cast concrete beams, hire a disc cutter, and cut them to the various lengths you need.

Spot on, but just to clarify to the OP, I'm sure you meant to type concrete lintels.

 

[frank999]

I found some at my local Selco, but they are 100x140 (not 100x150) - would the Building Control officer pull me up on 10mm, they may also be 10mm short when cut out of larger peices ??

Cost from Selco (£60) was much better than a company specializing in making lintels (£276)

0.084 sq mts checks out with me, just seems a tiny volume. On that basis I calculated it to be roughly £30 + £10 shuttering if I was to make them here.

 

[RonnyRaygun]

100x140 is the correct size. It allows a 10mm mortar joint to course to 150mm.

 

[tony1851]

Spot on, but just to clarify to the OP, I'm sure you meant to type concrete lintels.

beam/lintel, lintel/beam? I'llhave to go back to college!!!

 

[tony1851]

I am starting a loft conversion.

I require 8 High PC Concrete Lintels as padstones to bear the steels onto, they are all 150mm high, 100 wide - and varying lengths (330-900mm, average 700mm). [/quot
Looking back, these lengths seem excessive for padstones in a domestic situation. The loads are not normally that high.Has your SE got these right?

 

[RonnyRaygun]

Looking back, these lengths seem excessive for padstones in a domestic situation. The loads are not normally that high.Has your SE got these right?

True, even allowing for 5N brick in M2 mortar you could drop 56kN onto a 900mm long padstone...

Presumably it's the same "architect" that did the volume calc for the hip to gable...

 

[tony1851]

Frank; before you start heaving up 900 long pads, ask your designer for an explanation. Get him to give you a copy of the calcs so we can see them here. As R.R. confirmed, these things are massive.
You just do not get loads like that in loft conversions. Maybe the engineer/architect has put the decimal point in the wrong place; remember, from previous experience, his maths is not that good!