Thread: What is this building material?

I inspected a unique custom-designed home by a well-known architect built in 1950. The floor structure was 8" deep wide-flange steel beams at 24"oc supported on steel girders. The floor finish material is hardwood strip flooring, ceramic tile, with carpet in bedroom areas. Floors are very stable with no perceptible deflection.

Question: What is the black material on the underside of the subfloor? I am assuming a wood subfloor. See picture.

I should have taken the time to examine this more carefully but I had a very short window of time to inspect the house and was constantly interrupted by the buyers. There is no chance for a follow-up inspection to get a second look. Any help is appreciated.

Thanks.

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Looks like a wire mesh with tar paper. I've never seen it.
You may have some asbestos pipe wrap there too, but you probably already know that.

Yes...it does look like tar paper with mesh. But like you, I've never seen it before. And what would the purpose be? I know about the "suspect" asbestos.

When they poured the concrete that is what held it up til it could dry.

Originally Posted by Stanley Chow

I am assuming a wood subfloor. .

I wouldn't.

Originally Posted by Vern Heiler

When they poured the concrete that is what held it up til it could dry.

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That's the one.
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OK....but it is hard for me to imagine that the flimsy wire-reinforced tar paper - alone - is used to hold up the concrete pour, unless you are saying that it is an underlayment for the concrete form or underside of the concrete pan. If it's just an underlayment, why does it need to be reinforced...and wouldn't visqueen be sufficient?

This is a good discussion....

Keep it coming.

Originally Posted by Stanley Chow

OK....but it is hard for me to imagine that the flimsy wire-reinforced tar paper - alone - is used to hold up the concrete pour, unless you are saying that it is an underlayment for the concrete form or underside of the concrete pan. If it's just an underlayment, why does it need to be reinforced...and wouldn't visqueen be sufficient?.

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Stanley,

Hambro Concrete Composite Floor w. Metal Studs.avi - YouTube
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Construction Materials and Building Practices change over time ( house built in 1950 from your op). Link will show one way to pour a floor abet without a vapor barrier.

Your picture shows a combination of reinforcement and vapor barrier.
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I watched the Hambro video, it's really kool!

Stanley, did you touch the undersider in that area? Is it hard like concrete?

That is not just regular old felt paper, the paper is reinforced with string (keeping it simple in this description), and that reinforced paper is then further reinforced with wire mesh. The end result being that the paper and its reinforcement is strong enough to hold the concrete until it cures.

In Billy's link to the Hambro system, visualize this reinforced paper in place of the plywood, except that the reinforced paper is not removed as the plywood is in the link Billy posted.

The concrete floor has steel reinforcement in it which allows the concrete to become a structural slab, and the enforced paper is just the bottom form. It is not unusual to find torn areas in the paper where the concrete has started to break through, the contractor either leaves that concrete hanging down or simply breaks the concrete off at the paper level (or wherever the concrete happens to break when they hit it with the sledge hammer to break it off).

You guys are great and this forum is fantastic. I've been reading all the various posts quietly for several months and have learned alot.

It's difficult for me to visualize how felt paper - even reinforced with strings and mesh - can be used as a concrete form. I can see how the plywood is used because you can walk on it and it's still done that way by many contractors today. I've been doing commercial construction for a long while and have seen how light-gage metal decks can blow-out when concrete is loaded onto a floor under construction. How do you spread out, float and finish the concrete without falling through the felt paper yourself? The steel joists are 24" apart. But if you guys say so...I'll have to believe it.

Steven...I did not get a good chance to touch the underside. I had a short time to do the inspection and was followed around by a gang of 6 that keep interrupting my normal sequence of inspections. Otherwise I would have known right away that its concrete and not wood.

Thanks for all the great input.

Originally Posted by Stanley Chow

You guys are great and this forum is fantastic. I've been reading all the various posts quietly for several months and have learned alot.

It's difficult for me to visualize how felt paper - even reinforced with strings and mesh - can be used as a concrete form. I can see how the plywood is used because you can walk on it and it's still done that way by many contractors today. I've been doing commercial construction for a long while and have seen how light-gage metal decks can blow-out when concrete is loaded onto a floor under construction. How do you spread out, float and finish the concrete without falling through the felt paper yourself? The steel joists are 24" apart. But if you guys say so...I'll have to believe it.

Steven...I did not get a good chance to touch the underside. I had a short time to do the inspection and was followed around by a gang of 6 that keep interrupting my normal sequence of inspections. Otherwise I would have known right away that its concrete and not wood.

Thanks for all the great input.

Stanley, when they shadow you and it becomes a distraction, stand and look at a wall or roof til there eyes glaze over. They will find something more interesting to do while you finish the inspection.

Thanks for the tip Vern. I try to be as helpful and customer-centric as possible but sometimes it bites me in the butt and I end up losing my train of thought and momentum. If it weren't for the fact that this was a very expensive home, I would have done what you suggested. It did cross my mind!!

Another method I use is to take a lot of pictures. Hey its part of the job! Nobody wants to be in pictures. Again, they disburse at there own will, and I go on with the inspection.

I just did a library a few years ago that had that system. they put that down then pour concrete about 2 - 2.5 inch thick. the concrete is normally a lightweight version.

Mike

Originally Posted by Stanley Chow

I inspected a unique custom-designed home by a well-known architect built in 1950. The floor structure was 8" deep wide-flange steel beams at 24"oc supported on steel girders. The floor finish material is hardwood strip flooring, ceramic tile, with carpet in bedroom areas. Floors are very stable with no perceptible deflection.

Question: What is the black material on the underside of the subfloor? I am assuming a wood subfloor. See picture.

I should have taken the time to examine this more carefully but I had a very short window of time to inspect the house and was constantly interrupted by the buyers. There is no chance for a follow-up inspection to get a second look. Any help is appreciated.

Thanks.

Thanks to everyone for all the great info. I appreciate the assistance.