MDF "warping" question

[Louis Brandt]

I just bought a 24 x 48 inch piece of 3/4 inch MDF at Home Depot. Our local Home Depots carry quarter size sheets of MDF. When I examined the piece in the store, it looked fine and didn’t seem to be warped in any way. I had a guy in the lumber department cut it for me on their panel saw, so that I wound up with a “working” piece about 48 inches by 18 inches, with the remainder as waste.
When I got the big piece home, I found that it was warped, badly enough so that I couldn’t use for its intended purpose. I’ve brought home many pieces of 3/4 inch MDF in the past, and I still have most of them in my garage, and they don’t seem to be warped.
My question is this: Could the fact that the piece was cut cause it to warp? In other words, could the fact that as soon as it was cut, a new edge of the material was exposed to the heat, causing it to warp? I need to add that I live in Louisiana, and our current summer temps have been running about 99 or 100.
Thanks,
Louis

[John Lucas]

Louis,
I think the only answer could be one of moisture...and a lot of it. ANd I suspect not just from the ride home or differences of storage areas. I would wonder if at HD it got a thoruogh soaking and it appeared dry but wasnt.
Remember, MDF can be shaped by a steam box much faster than our favorite hardwoods. What you experiemced may well be just a taste of that. The good side is that if you place it under weights for a night, it may well be flat tomorrow.

[pat warner]

Was said panel in the back of a pickup truck on the way home, uncovered?

[Louis Brandt]

No, it was laying flat on the back seat of my car.
Louis

[pat warner]

Did the sun hit it?
What I'm getting to here: It doesn't take long to permenently pretzel MDF.
5 or 10 minutes in direct sun can do it, especially if that sheet was not the top sheet in the supply stack.

[Louis Brandt]

No, the sun didn't hit it, but it wasn't in a "stack" at Home Depot. It was stored with other sheets vertically in a small bin (the bins that they use to hold the "quarter sheets").
Louis

[mike roe]

I have used those for a lot of projects. they are super handy if you need somehting smaller than a 4x8. I never had that happen though. even keeping sheets in a very humid garage never did that to me.

I noticed recently that the price of those sheets went way up. I know everything has gone up... but I used to pay something like 7 dollars and last weekend they were 10.37.

[Mike Cutler]

Louis.

Lay it flat like John described and you should be fine. I've left MDF out overnite on humid nites to bend to a form, and have bent them back.

This works with drywall also if you ever have to drywall a curve, or arch.

I hate working with MDF( dust!:eek:), but it's a pretty versatile material.