Lintel keeps breaking away after concreting in

[men8ifr]

I have a 9-10 foot lintel over my 7 foot garage door.

The reason I got the lintel was to provide some support to the top of the walls at either side particularly as 1 wall carries a lot of weight/twisting due to a very heavy door. I don't think there's much movement in the wall though because I can't see any movement when the door is opened and no cracks are visible to indicate the blocks are becoming detached.

I've concreted the ends 3 times now and each time after a week or so the lintel has detached you can see the crack where the concrete joins the lintel and lift the lintel by hand!

The last time all surfaced were cleaned, the lintel scored with a angle grinder to give the concrete more bite and the mixture carefully checked so it's 1/2 way between a standard and strong mixture. All surfaced were wetted as well so the concrete does not dry too quickly.

I'm thinking I may just have to drill through the lintel and bricks and put some bolts in since concreting doesn't seem to work...

The only question mark I have is the concrete is a year old - would this cause the problems? But there again teh wall was done with the same concrete and that's very strong.

 

[PrenticeBoyofDerry]

Do you soak the joint or just dampen it slightly, did you apply packings under the lintel?
If you soaked it, this could cause a problem, if it was slightly damp this only needs to be done in hot weather, packings will help keep the joint even and stop the mortar pushing out, whilst the joint cures.

 

[theoldun]

Reading your post, it would appear that you have bedded a precast concrete lintel over your garage door to provide some form of lateral restraint for the two flank walls of the garage. It would appear that no loading is on top of this lintel, as you say that you can lift it up after the bed joint has cracked.
This is never going to work my friend, as with no load above the lintel, every time you open your door the wall supporting the door will move just a fraction and break the bed joint, and you are back to square 1.
You say that you are considering bolting the lintel to the brickwork. The same thing will happen to the brickwork as to the lintel. Over a period of time it will crack the top course of brickwork.
Twp choices.
Cast a 225x225mm in situ reinforced concrete lintel over opening but even that may not give enough meat over the top.
Local steel stockist. 75x50x10mm angle iron, cut bent and welded. Top to be 2mm smaller than inside dimension of garage, and two 90 degree legs approx 900mm long, with 4 holes in each leg. Bolt to walls just behind opening at ceiling level with legs bolted to walls and tension spread down the 900mm length. Reason for 2mm smaller than width, so that strap will go in, then pack behind strap with plate washers etc.
This should give you sufficient lateral restraint.
oldun

 

[Agile]

As said a precast linton is not really the solution to your needs.

However, it seems that even what you are doing is likely to even less likely to work because you talk about cracks within a week.

That implies to me that you are not giving enough time for your new concrete to even set before disturbing it. Even in this warm weather I would say you need to not disturb it at all for at least a week.

But even so its not going to give you the solution you want if this beam is immediately under the roof with no weight of wall over it and extended into the wall on either side.

Tony