old lintel, masonry: what's it made of?

[George]

We think our house was built in the 1920's. The walls are solid (not cored) cement block. Replacing a cellar window, I got looking at the lintel over the opening. The surface is cementitious, but smooth, like a casting. (The wall blocks have a pronounced raised texture.) When I drilled into the bottom for a (Tapcon) screw, it seemed to be at least partly hollow.

I'd appreciate any information (or even informed speculation) on what a lintel from that period might be made of.

Thanks, George

[hrhofmann]

A photo (or two) would certainly lead to a better reply.

[dadiOH]

Cast concrete? Common now, don't know about then. They used to use steel - and still do - but that would be obvious. Go back far enough and they used cut stone.

[dpb]

Yes, was also a possibility. The church here uses quite a lot of roughly that age. Also could be real stone and the OP is mistaken about what he thinks might be hollow -- some of the limestones/sandstones aren't all _that_ hard. Or, of course, it's possible (albeit not particularily likely in a residence) the real support is steel and this is simply a decorative facade.

Knowing where this might be as well as the suggestion of pictures would likely elicit a lot more informative guesses than otherwise.

--

[George]

(OP) no mistake. The foundation wall is limestone. I've drilled it, so I know the difference The surfaces of the lintel are flat, but not troweled smooth.

(I'll see if I can post a picture somewhere. Where would be a good place?)

[nestork]

The lintel will be made of steel.

Back then, that was the only material strong enough (short of a Stonehenge size slab straddling across the two walls) to support the weight of the masonry above the window.

Check with a small magnet.

There were also "cast lintels" in use by the 1960's. This was a form in which steel rebars would set and the concrete poured around them. Nowadays, that's called "reinforced concrete". The idea behind reinforced concrete is as simple as the concept of drywall. In order for drywall to bend, the paper on one slide or the other has to stretch to accomodate the new shape. But, since paper is quite strong in tension (given't it's weight), dryall is actually very rigid (considering what It's made of).

Exactly the same principle applies to reinforced concrete.

By embedding layers of rebar in a concrete slab just a few inches from the top and the bottom of that slab, then in order for that concrete slab to bend, then the rebar on either side of the concrete slab has to stretch, and since steel is very strong in tension, the steel rebar in a properly designed slab won't allow the slab to bend far enough to cause the concrete to crack from excessive stretching on the side of the slab that's experiencing tension.

So, I expect your lintel is steel, and you can check it with a magnet, but it may be made of reinforced concrete. I just don't know when reinforced concrete lentils first started being used. I know my building was built in 1960, and it has steel reinforced concrete lintels over the apartment door ways, but only steel lintels over the apartment windows. That's only because the door way lintels are visible as long concrete blocks over the door ways, and that matches the the concrete blocks making up the hallway walls.

Dunno if this helps.

[George]

I didn't feel anything with the magnet. And, I drilled into its face, and met no serious resistance. It acts a lot like it's just a long cement block.

George