Warping plywood

[poolhound]

I bought some birch ply at the weekend to use for a project. I took time selecting a good piece at least in its 4x8 form. When I cut it into its various dimensionally correct parts I found some of the pieces began to warp. Mostly convex/cave along their length. Not by much but enough to be a worry. I know I could have gone and found some of the really expensive ply but did not think it necessary. The two questions are:

1. is this going to happen with all plywood no matter or is some guaranteed to stay flat.
2. Is there a way to straigten/flatten it?

I have currently clamped it into its final form without glue and have left it while I am travelling this week. I hope it will be OK when I get back at the weekend.

Jon

[gmack5]

This almost sounds like your material has gotten "damp", not wet, just damp. This sort of thing happens frequently when you lay wood (of any kind) on a concrete floor. By allowing one side to get damp, you've created a moisture imbalance, which is causing the warpage.

Concrete, while not wet, IS damp most of the time. Seems the moisture wicks up from underneath and into what ever is laying on it. wood, carpet, etc.

That's why you should always "sticker" any wood that you plan to use for a project. Or stand it up on end with a plastic or wooden plate on the flooor under it to keep your "Good Stuff" OFF the floor.

[poolhound]

While my shop is in my garage and therefore has a concrete floor I never lay material flat on it. I usually stand it on end, will this have the same problem?

If I create a simple storage system thats off the floor should this prevent future occurances?

Jon

[Tequila]

Standing it on end will still allow moisture to wick in. In my basement shop, I left a scrap of MDF standing on the floor and leaning against a cabinet. After a couple of months, the bottom few inches were visibly discolored from moisture.

All of my lumber, including cutoffs, is off the floor either on a rack or in a bin. I rarely see any problems with warping since I've moved the material off the floor.

[Warren]

I've found that smaller pieces of quarter inch will warp no matter where it is. Perhaps it's just the humidity. I haven't experienced the problem in thicker pieces.

[poolhound]

I can understand moisture seeping in if left on end for some months. This happend to me overnight.

My other problem shich is pretty unsolveable is I live in Phoenix and the temps are very high. we have just crossed the triple digit barrier and with temps above 100 I would guess this might be a contributing factor.

Anybody know the effects of heat and if there is any solution other than fitting and running AC in my garage 24x7.

I do have other wood in there that has been around for a year+ and it is still straight and clean so it may be a material specific issue.


Any other Phoenicians have any experience and/or solutions?

Jon

[poolhound]

I've found that smaller pieces of quarter inch will warp no matter where it is. Perhaps it's just the humidity. I haven't experienced the problem in thicker pieces.

I would agree with 1/4" stuff but this was 3/4"

Jon

[LarryG]

Plywood <> flat.

Contrary to popular belief, plywood is not highly resistant to warping, especially the common veneer-core kind. It doesn't have to lay on a damp floor to warp; even unbalancing the airflow from one side to another can do it. That's why you often see plywood cabinet doors that aren't straight: there's free air circulation on the outside of the cabinet, but not on the inside.

Higher quality cores -- lumbercore, MDF, industrial-grade particleboard -- will help it stay flatter, as will increasing the number of plies. Otherwise, the best defense is to use it in assemblies in which the various components help to hold it flat.

[gjbivin]

I had a piece of 5/8" ply (the cheap BORG kind, I admit ) bow on me a couple of weeks ago. Fortunately, it was just destined for a cutoff bin I was putting together in a feeble attempt to bring some order to the chaos in my shop. I was able to force it straight enough with dadoes and lots of screws.

Living in Gilbert, AZ (20 miles E. of Phoenix) I have the same problems as Jon -- uncooled garage and 105 F today. My cooling system is a rollaround swamp cooler which works just fine here in the desert: and yes, I know, the humidity swings are probably not the best thing for my projects. But I run it with the garage and side doors open for cross-ventilation, so hopefully the humidity doesn't build up too much. It doesn't help as much during monsoon season, though (July and August), when the ambient humidity goes up and the rate of evaporation in the cooler goes down.

[jabe]

Larry G. got it right, use cabinet grade plywds, 9 ply, 13 ply or lumber core. Use the 5 or 7 ply for spreaders, nailers or toe kicks, for things thats not critical if a little warp. Store your cabinet grade sheet material on a flat surface with at least 4 stickers per sht.

[poolhound]

Larry G. got it right, use cabinet grade plywds, 9 ply, 13 ply or lumber core. Use the 5 or 7 ply for spreaders, nailers or toe kicks, for things thats not critical if a little warp. Store your cabinet grade sheet material on a flat surface with at least 4 stickers per sht.

Any good alternatives for those of us that dont have the room to store 4x8s flat?

[jabe]

I park my new truck outside the carport so I can set 2 saw horses with 3-2x4x8' and stack my plywd on it. I don't store my plywd very long as I go through 15 to 20 shts a month. If you have high celings, you probably can make a rack attched to a wall & rafters but, I wouldn't stack too many plywd shts. on it. If you don't store the plywd long, standing it on long edge is OK. I understand the space issue most of us have with storing materials so the best way is to use the materials up fast and get it out of the shop/garage/basement/carport. Better choice is to get a bigger shop if finances allow. Another thing I do is to throw/give away the drop offs/scraps if you think you might not use in 2 months. I know it hurts to throw it away but, you don't want a fire hazzard.

[L. D. Jeffries]

Bent Plywood

This is a sorta rant! Was building some medical records storage units for a local Dr.'s office last month. Using 3/4 a-c ply for the carcus, and 3/4 ply for the shelves. Well came up one sheet short, or rather needed part of one sheet. Sent LOML down to nearest lumber store;(name withheld casuse I'am still so po'ed) she came back with a piece of ply that was so bowed that had to actually screw it to the work station in order to cut what I needed from it. I used what I needed and then called them up and said a few very naughty words and told them that since it was a woman they were sell to they must have figured "she won't know any difference"! Unfortunately my dear LOML is what you might called "wood challenged" and DIDN'T know they were cheating her on purpose! Which goes to show, "not all crooks are in jail"