No Acrow Props / Strong Boys for door opening??

16 Jun 2015
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United Kingdom

So a builder has begun fitting a T Lintel to an existing window opening at the end wall of Victorian terrace extension in order to instal some double doors. There are a number of things I'm concerned with though as follows (see images attached):

1. No supports have been used anywhere. I would have thought 2 to 3 acrow props supporting the joists inside and 2 to 3 acrow props with strong boys to support the brickwork from the outside. The builder said he was happy with the support the beam inside offered (that the joists sit on). But that means that one beam is supporting the entire solid wall and floor.
2. The packing between the lintel / padstone and lintel / beam is a mixture of slate and wet (certainly not dry) mortar. I thought a dry mix should be used and it should be packed in without the use of slate as all this will do is impede getting the mortar in nice and tight. Some of the slate packing is also loose with little or no mortar in and around it.
3. The lintel has been set too high (about 100mm). The builder has said once the door is in place bricks can be used to fill the gap. Surely you should just sit the lintel at the correct height and how would the door frame be able to support two courses of bricks unless some kind of plate spanning both courses was used?
4. The lintel is a a CN51C (T style) however in the plans a CN81C (box style with lip for outer course of brickwork to sit on) has been specified. This seems like a big oversight!

Adding all of these points up I'm a little concerned as to the quality of work especially given the builder will then be doing the side return extension which involves a lot more structural work.

Any views would be very much appreciated!



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Hope you haven't paid them. I'm slightly confused by your description and relationship with the photos.
What is the beam in place on the photo? It doesn't look like a CN51.
What reason do they give for changing the specification of the beam?
Which beam did they quote for?
Why did they not fit the beam at the correct level?
Sorry for the questions but were there reasons for the changes?

Either way infilling the gap between beam and doors with brick is nonsense. It just won't work. I also doubt very much that a CN51 is sufficient for the loads. Off the top of my head I'd say it was capable of no more than about 10kN and you've definitely got more than that there. Tell them to do the job as specified or pack up.
Thanks Jed.

You're right it's actually a CN50C so 90mm in height not 170mm (so even less substantial). The reason they used it is that when they went to their lintel supplier yesterday they say they hadn't heard of that one, so the next best (appropriate) thing was the T lintel. I assume they quoted for the correct one. This opening is part of a much bigger quote for all structural work though. Regarding the level of the lintel I suppose as I hadn't instructed them they fitted it tight against the wooden beam. So I suppose I should have been more specific, although they could have asked.

Shouldn't there be some acrow props to support the wall and joists plus is using a wet mortar with slate okay? Regarding the use of props he assured me that for a day or two it would be fine as it is.
Openings can be cut with little or no propping depending on the quality of the mortar. As long as there is no excessive shifting above during the process, once it's packed and secure it should be fine. You are right about wet packing. Semi dry packing is normal because wet packing is much more likely to shrink. Of course that doesn't mean it will shrink - just that the risk is greater. Slate packing is fine.

My main concern would be the lintel though. What about building control. Has it been inspected?
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Thanks again Jeds! No the lintel hasn't been inspected. I suppose the best thing is to speak to the structural engineer again and find out whether the T lintel will suffice.

Had a look at the link too. Looks fine in that instance however that looks like new (solid) mortar, it's only single skin, plus the opening is half the width. The mortar in my wall all needs repointing and is crumbly victorian stuff on the inside. The only good thing is that it's been replastered inside (upstairs) so there's a whole load of bonding keeping the bricks together.

In case it's of any interest, this is what the opening looks like now.


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Another update. Three bricks have just fallen down of their own accord plus if I put pressure on the bricks above I can see them move very slightly. Don't think that's good!
As you say, speak with your SE. Do so before it's enclosed though.

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