Plywood vs OSB

[Gazerro]

I was wondering why osb is used on the bottom part of a mortar rack and not plywood?

[displayfireworks1]

That is great question and a chance for all of us to learn something about this. My initial thought is a cost factor. Just so everyone knows what OSB is here is a picture.
.
Oriented strand board (OSB), also known as sterling board, sterling OSB, aspenite, and smartply in British English, is an engineered wood particle board formed by adding adhesives and then compressing layers of wood strands (flakes) in specific orientations.
.
https://upload.wikimedia.org/wikipedia/commons/b/b6/OSB-Platte.jpg
.
Here is something from the internet
.
.
OSB’s Pluses

OSB has more going for it than just cost. Resource-efficient builders appreciate that it can be made from small, fast growing trees, many of which come from tree farms rather than forests. It can also be bought in 9 foot sheets, which means you can sheathe a wall from the top plate to the bottom of the floor joists with single, vertical sheets, leaving no horizontal seams. OSB panels can be manufactured in lengths up to 16 feet (or sometimes even higher), while plywood is generally limited to 8 to 10 feet.

OSB boasts a more consistent density. While a sheet of plywood might be 5 to 7 plies thick, a sheet of OSB is made from as many as 50 strand layers packed and compressed into the same thickness. There’s no equivalent of the weak spots that can be left in plywood when knotholes in adjacent plies overlap.

On the downside, the material is a bit heavier than plywood—two pounds or more per sheet depending on its thickness and intended use—but this difference has no effect on the panels’ performance. It just takes a bit more muscle to handle on the jobsite.

Plywood’s Superior Wet Performance

The biggest difference between the two panels is how they react when exposed to large amounts of moisture over extended time periods. With the exception of projects in very arid regions like the Southwest, sheathing and flooring panels are routinely covered with rain, snow, and ice during construction delays. It’s here that plywood has the edge.

When plywood gets wet, it tends to swell consistently across the sheet, and then returns to its to normal dimensions as it dries out. It dries out relatively quickly, and the swelling is usually not enough to affect floor or roof finishes.

OSB takes longer to get wet than plywood but also takes longer to dry out. When used as a roof sheathing, this tendency to hold moisture means it can degrade faster than plywood when exposed to chronic leaks.

When OSB does get wet it also tends to swell along the edges, and those edges stay swollen even after the material has dried out. Swollen edges have been known to telegraph visible ridges called “ghost lines” through asphalt roof shingles.

Manufacturers insist that OSB’s moisture problems have been corrected, thanks to the development of water-resistant edge seals. But of course that edge seal is lost when panels get cut on site, as they often do.
.
Here is one of videos from 2010. It is about scrap wood at Home Depot.
.

https://www.youtube.com/watch?v=W7NY1Sz62AQ

[PapaBearPyro]

AAAAAAH yes-The Home Depot discount pile. At my local HD its located near the custom cut saw in lumber. I see the discount Du jour color was blue LOL. I got 1x4 pine
14 footers for $1.24 each and the Gentleman cut them in half and bundled them no charge. I got 8 of those pups 112 foot for a tad over $10 (that day purple paint). On
another day while cruising through the caulk aisle Liquid nail was on clearance (yellow tagged). It was near its expiration date and the had it at like .40 a tube. While there
for misc. projects I always check these areas for deals. Good stuff :)
PBP

[PyroJoeNEPA]

Hmmm--is the glass half full---or half empty?
On the OP question--the "popular consensus" [I don't know WHO that is, so please don't ask] is that the osb on the bottom is "safer" in the event of a tube blowout in the fact it will blow apart in chunks instead of splinter like the plywood would.
That being said, I use plywood on the top & bottom side rails....
I took apart on old coal bin in a commercial building I own [circa 1923] and salvaged all the tongue & groove wood from it. That has also become some nice side rails! Some people use 1X3. Whatever works!

[Westpapyro]

I use osb on bottom sides, and 1X or plywood on top sides. I believe in a Cato you want the bottom side to expand with the pressure, allowing just some small pieces of wood to break off. With 1X it tends to splinter the entire piece, or blow off completely. With most of the pressure being absorbed into the osb lower sides, the hard 1X up top tends to stay upright. Keeping the rack together and pointed up in the air,as best as possible. Have had it happen to my own racks! With a harder bottom side wood, I believe the racks blow apart more destructively, therefore not helping to keep racks pointed up or together as well? I'm sure there are millions of opinions on this, but I think the main reason is osb absorbs energy and pressure better?

[displayfireworks1]

I don't have an opinion either way, but what I do have is a video of a salute blowing up in a rack.
Video is from 2009.
.

https://www.youtube.com/watch?v=Ha32Zk_NWpM

[Northern Sky]

Glue and Screw.

[Gazerro]

Does it make a difference to use osb board on the bottom of a rack, and does it make it safer? Because what I have found is that plywood and osb are pretty much identical, except one handles moisture better. Im trying to be as safe as possible while building my racks, but don't want to spend extra money on OSB if it doesn't have any safety features with it in case of a blowout over plywood. So, will it really make a difference if I used my bottom board with plywood as opposed to osb? And is there better wood I could or should be using the will make my rack safer in case of a blowout? Sorry for all the questions, I have a 4 year old son, who loves to watch fireworks, So Im just trying to build as safe as I possibly can, all suggestions will be appreciated.

Thank you

[Westpapyro]

Does it make a difference to use osb board on the bottom of a rack, and does it make it safer? Because what I have found is that plywood and osb are pretty much identical, except one handles moisture better. Im trying to be as safe as possible while building my racks, but don't want to spend extra money on OSB if it doesn't have any safety features with it in case of a blowout over plywood. So, will it really make a difference if I used my bottom board with plywood as opposed to osb? And is there better wood I could or should be using the will make my rack safer in case of a blowout? Sorry for all the questions, I have a 4 year old son, who loves to watch fireworks, So Im just trying to build as safe as I possibly can, all suggestions will be appreciated.

Thank you

Distance is your friend as far as safety is concerned!
When you say bottom you do mean bottom sides correct?

[Northern Sky]

It was stated above that the front-bottom could/should be OSB because there will be less structural damage to the rack. In addition to that, having the OSB at or just above the mortar plug limits rack damage.

In response to your 4 year old, I'd have him stick to safe and sane. Let's keep our members off the evening news for child endangerment.

That lady, gun advocate, with the 4 year old shooting her from the vehicle back seat sure is getting some airtime.

[PapaBearPyro]

Sent you a pm
PBP

[kmosmen]

Has anyone used metal strapping when making racks?

http://m.homedepot.com/p/Basset-Products-3-4-in-x-50-ft-Perforated-Duct-Strap-DS50-1-22B/205871087

Surround the top with this in case of a bad lift charge!

[JmFnG]

Has anyone used metal strapping when making racks?

http://m.homedepot.com/p/Basset-Products-3-4-in-x-50-ft-Perforated-Duct-Strap-DS50-1-22B/205871087

Surround the top with this in case of a bad lift charge!


Unlikely as it may be, I would be concerned about the shrapnel factor.

[Rick_In_Tampa]

Wow... Good thing the remaining tubes didn't fall over and shoot towards the crowd. That could have been a real bad day for everyone.