Padstone when fitting CH50/100 lintel

[garyo]

Hi everyone!

I'm installing a 1500mm cavity lintel. The existing wall has a concrete lintel on the inner skin, and the outer skin only has a door frame keeping it together. I'm widening the structural opening from 1000mm to 1200mm.

Catnic have recommended a CH50/100 and specified that one side will only have a reduced 100mm bearing due to the way that the wall it's sat on is perpendicular to the lintel direction. You can see what I mean in the picture below.

My question is, what kind of padstones do I need? Both skins are traditional brick. Is the padstone there to distribute the load over a wider area, or to avoid too much mortar directly under the lintel which might crumble over time - i.e. packing out the joint with slate?

Thanks

Gary

(please note, in the diagram below I was considering two box lintels of differing length. Catnic have recommended a single cavity instead, with 100mm bearing on the left, 150mm on the right)

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• garyo
• 7 Apr 2010
• 2

 

[DSA]

A padstone is used to spread the concentrated force at the end of the lintel across a large enough area so as not to overstress the masonry below. The size of the padstone is therefore dependent on the load applied to the lintel. See BS5628-1 cl. 34 for a design method.

 

[hotrod]

Catnic have recommended a CH50/100 and specified that one side will only have a reduced 100mm bearing due to the way that the wall it's sat on is perpendicular to the lintel direction. You can see what I mean in the picture below.
My question is, what kind of padstones do I need? Both skins are traditional brick.

I don't see a problem with you using 100mm bearings either side for a span of that width, it's only a tiddler . Additionally, Assuming your bricks aren't spalling and flaking all over the place I don't see the need for using padstones. Maybe, use a couple of Class B's / Concrete commons / Staffy Blues if you want to be ultra cautious.

Catnic have recommended a single cavity instead, with 100mm bearing on the left, 150mm on the right

I'm not 100% sure about that - I'm sure that's not a recommended practice to install it 'off centre' as it were. But if that's what Catnic have told you, who am I to argue

 

[Static]

100mm bearing on left and 150mm on right should be fine.. but as hotrod says check the blockwork where the lintel bears and if any is cracked or damaged then replace with some solid brickwork..

 

[theoldun]

Gary, Both Hotrod and Static are right in what they say. If bearing is a bit iffy, stick a staff blue in. 100mm bearing over that span is acceptable.
Can not understand why Catnic have specified a CH which is heavy duty, I would only have put a CG standard in over that span. With a CH heavy duty you will have to take another two course out on the back above lintel to get it in, due to the top back lip on lintel Have a look at the Catnic brochure, you will see what I mean.
Assume you are plastering in porch therefore I would have used 65x100 pre stressed concrete on face work and 65 x 150 ditto inside.
Regards. oldun

 

[garyo]

There are a couple of floor joists around four courses above the lintel, so perhaps they've increased the spec to CH to cover themselves for this unknown. Also it wouldn't surprise me if they added a 40% 'just in case' factor to their choice to cover themselves too.

The 1500mm long CH is only 150mm high, and then I think they get taller when they go 1800mm, or longer, so I'm hoping that I'll be able to get it in by only removing two courses.

Cheers

Gary

 

[Static]

Try Keystone lintels.. they may be able to provide one that doesnt need the two courses removed on inner

 

[theoldun]

Gary, Couple of ways of fitting open back lintels.
CH 150mm high. Cut opening. Cut out for bearing 150mm deep below lintel height Clean out any insulation from cavity and cut out any tie irons in cavity where lintel is to go. Place lintel on bearing and spread 12mm muck bed down each bottom flange. Push lintel up into cavity, put acrow underneath and jack up tight. Make good to the two course on bearings.
GH and GX 150mm high. Cut opening. Cut bearing at lintel height. Take out two course of brick or one course of block, depending what inner skin consists of. Muck bed to front flange. Slide lintel in and make good all round.
As previously said can not slide a GH or GX up cavity due to top back lip.
Our work is new houses and extensions, we only use a standard CH on ground floor unless we have pot and beam, or concrete slabs to first floor, then we use GH. We also use GH to three storey town houses. GX if we are on spans of around 4.000.
oldun

 

[garyo]

Thanks oldun.

I now have the lintel sat in the porch, so I'll have a go at fitting it this weekend.

I follow everything you say above, although I think you might be using keystone terminology whereas I'm using catnic names. Still, I see what you mean about the rear/top lip preventing the lintel being raised up with two mortar beds in place.

Is there a reason I can't leave the outer skin in place, lay out one mortar bed on the front of the lintel, and then slide it into place from the back, and then build-in the rear skin. I can see that some of the mortar bed might get squashed out of the way, but it seems like it'd save some of the pointing work at the front.

I have the CH from this diagram by the way, so 150mm high:

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• garyo
• 27 Jul 2010
• 1

 

[theoldun]

Gary, Made a typing error right at beginning of post. CH should read CG.
Read down post to GH and GX. What I have said here is same as what you suggest. No need to touch front skin, work from back. We never use keystone, only catnic
oldun