How to tell tempered glass from polycarbonate

[Kent Adams]

I bought a couple of these doors: http://www.homedepot.com/p/Masonite-36-in-x-80-in-9-Lite-Unfinished-Fir-Front-Door-Slab-87315/100075801 which I'm finishing with Waterlox Marine. The borg's website says they have tempered glass, but I can't tell by the "tap" test that it is in fact glass.

Because I'm using Waterlox Marine, which has mineral spirits in it, I'm concerned about the "glass" with the overflow of Waterlox on it. If its actually polycarbonate, I've read that MS can cloud it up. Is there a way I can test to make sure it's actually glass, other than trying to scratch it?

[John Aperahama]

Tempered glass is expected to have a stamping (etching) on it during manufacture. I personally have always thought that these doors from HD are not tempered.
Probably not poly tho.

[Kent Adams]

Tempered glass is expected to have a stamping (etching) on it during manufacture. I personally have always thought that these doors from HD are not tempered.
Probably not poly tho.

It does have a stamping on it, but I can't read it for the life of me.

[Wade Lippman]

If it does cloud up with MS you can take them back.

[Jason Beam]

Take one out and look at the edge ... AFAIK tempered glass is green on the edge.

[Jamie Buxton]

There are glues intended for polycarbonate. They're mostly solvent, and dissolve the plastic at the joint to make the bond. I'm pretty sure they don't dissolve glass -- darn near nothing attacks glass.

[Kent Adams]

Take one out and look at the edge ... AFAIK tempered glass is green on the edge.

Unfortunately, that's not possible unless I want to destroy the stile and rails.

[Ole Anderson]

Scratch test with a steel point in a corner of the pane?

[Jamie Buxton]

Scratch test with a steel point in a corner of the pane?

Trying to scratch tempered glass is not a great approach. Tempered glass is strong because the surfaces are in high tension. If the surface gets a stress riser -- aka scratch -- the panel is likely to collapse into a pile of chiclets.

[Peter Quinn]

They are almost definitely using glass. Poly carbonate turns an off color after long exposure to UV, sort of clouds and yellows, not a good feature in a door. I'd be pretty surprised if masonite were using anything but glass in a door.

[Justin Ludwig]

Throw a rock at it. If it shatters into a thousand little pieces then it's temper glass. Buy new glass.

[Jason Beam]

Unfortunately, that's not possible unless I want to destroy the stile and rails.


So you have no way to replace one if it breaks?

[Gary Muto]

I had a door like that many (~20) years ago. It was single pane tempered glass. I think by law it has to be tempered but I'm not sure if the glass is that far from the floor. Anyway the glas can be replaced. You remove the 1/4 round trim on the in-side to replace the glass. The outside trim around the window (what's it called?) is part of the respective rails and stiles.

[John Aperahama]

Replacing said glass would probably cost more than the door.

[Lee Schierer]

If you tap on tempered glass with a ring or other metal object you will get a click. Do the same on polycarbonate and you will get more of a clunk.

[Allan Speers]

Lee beat me to it.

The sound is VERY different.

I think also they react differently to heat. Glass is a great insulator, so maybe: Heat it up with a hair dryer in just one spot, then put your fingers a few inches away from the area you heated. I'm not positive, but I think with polycarb the heat will radiate out, while with glass it won't.

- but don't quote me on that!

[John TenEyck]

You got that backwards. Glass is a pretty good conductor of heat compared to plastic. But I wouldn't use a heat gun on either product. Tapping it with a coin or similar should identify if it's glass or plastic. And, as said earlier, do NOT try to scratch it. Tempered glass will literally explode if you scratch through the tempered layer.

John

[Justin Ludwig]

Replacing said glass would probably cost more than the door.


You need to find a new glass shop.

Anywho... I hope he knew I was kidding. Don't throw stones in glass houses, or at glass doors.

[Myk Rian]

Trying to scratch tempered glass is not a great approach. Tempered glass is strong because the surfaces are in high tension. If the surface gets a stress riser -- aka scratch -- the panel is likely to collapse into a pile of chiclets.
He doesn't have to purposely scratch the glass. If a piece does scratch, it's polycarbonate.
Just stick a pin to the pieces. That will tell you what you have.

[Allan Speers]

You got that backwards. Glass is a pretty good conductor of heat compared to plastic. But I wouldn't use a heat gun on either product. Tapping it with a coin or similar should identify if it's glass or plastic. And, as said earlier, do NOT try to scratch it. Tempered glass will literally explode if you scratch through the tempered layer.

John


Hmmm. Maybe "conduction" is different from "insulation." According to several sources, glass is a much better INSULATOR than acryllic / plexiglass. (it has a significantly lower lambda value.) That may or may not apply to the scenario I was describing, though.

Interesting.

[David L Morse]

Hmmm. Maybe "conduction" is different from "insulation." According to several sources, glass is a much better INSULATOR than acryllic / plexiglass. (it has a significantly lower lambda value.) That may or may not apply to the scenario I was describing, though.

Interesting.


Can you provide links to those sources? What is lambda? According to this source (http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html) the thermal conductivity of glass is around 1W/(m-°K) while polycarbonate is around .2W/(m-°K). So the poly has 5 times the thermal resistance of glass. In other words it insulates five times better than glass.

[Kerry Wright]

Glass is an excellent "conductor" of heat (think baking dishes), but it is also an excellent "insulator" of electricity (think power lines and poles).

[Vince Shriver]

Just my experience, but FYI, tempered glass can get kinda spendy.

[Joe Adams]

I would call Masonite's technical support and ask them what kind of glass they put in it.

[John Stankus]

I would call Masonite's technical support and ask them what kind of glass they put in it.

I was going to +1 this, but then I looked at the product overview which says " tempered, single pane glass" in the OP's link. On that basis I think I will say it is tempered glass. :)


John

[Pat Barry]

Come on people, Polycarbonate will easily scratch with a pin or razor blade and Glass will not. Its not rocket science to figure this out. The glass isn't going to explode!

[Hoang N Nguyen]

You guys are making this more difficult then it should be. Put on a pair of polarize sun glasses, if it's tempered glass then you will see circles/dots in different shades of color. If you've ever looked through your car window at an angel with polarize sun glasses, you'll understand exactly what I'm talking about.

Outside of woodworking, I also keep salt water aquariums as a hobby and we drill our own tanks for plumping more often then not and the sun glass test is how we can tell if drilling is an option or not. A lot of the tanks we buy has a temper glass sticker on the bottom of it, but not all the glass panels are tempered and most of the time only the bottom glass panel is tempered.