Spar Urethane for Pressure treated wood

About a month ago we built a small 8 foot handicap ramp out of pressure treated plywood. Didn't treat it with anything. We had a lot of rain. Noticing a long of cracking going on along the vertical plane.
Also made side barriers using plywood. The porous sides face horizontally. I'm getting a bit of warping already. Need to seal off the top. I have some door weather strips I'm going to seal off the openings.
Found a can of Minwax Indoor/Outdoor Helmsman Spar Urethane in the cellar. I was thinking of spraying it over all the surfaces. Probably give it a few coats. Would this be the way to go or should I apply something else and/or use a brush?
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New pressure treated is wet, maybe 40%-50% moisture, wood need below 15% to varnish. It can take months to dry, the only way to know is buy a moisture meter. Varnish is not for pressure treated, stain is. Cracking is normal for pressure treated, but your plywood was a mistake as its interior grade im sure. Wait till its dry and stain it, forget the varnish.
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I built a new floor for an old truck bed out of pressure treated 3/4 plywood and covered it with many coats of spar varnish. Within months it had all yellowed, cracked, and peeled. There has to be something more suited to the application.
-rev
Charlie S. wrote:

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Charlie S. wrote:

A varnish is no good for a deck. Its a lot of maintenance. Also, pressure treated lumber is very wet and will crack, split and warp as it dries. Normally for a deck, once it dries out. We recommend a penetrating oil like Penofin or Sikkens. Plywood is terrible outside (Not as bad as particle board) but will de-laminate when it gets wet. Even "exterior" plywood will do this eventually.
I'm not sure the best think to do for your ply. Replace it with a suitable material would be best. Aside from that. A good exterior primer and paint may extend its life the best. For the pressure treated the sikkens is available as a sold color stain that could be tinted to match or compliment your color choice for the deck stain.
Good luck.
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Hello I was wondering if anyone would be willing to answer a few questions in regards to wood choices in home renovations/projects.I am conducting a market survey in the wood treatment and wood preservation industry in Europe. I am currently speaking to DIYers/home renovators and people involved in chosing treated wood for home. My goal is to understand the customer(end-user) and address the unmet needs of the consumer. The only requirement is that you must have bought or used treated wood over the last 3 years. Please email snipped-for-privacy@martec.de Thank you!
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