Weatherproofing plywood

Hi! A complete DIY newbie here, so please be gentle:

I am building a makeshift weightlifting platform for outside use, and the centrepiece of that is two 18mm thick 2440x1220 sheets of plywood screwed together for stability. I've purchased "Hardwood Throughout External (WBP) Plywood EN636-3S", but I now realise that it needs to be treated somehow to safeguard it from the elements.

Given I do not care about the looks, but purely want to avoid it absorbing moisture, rotting or deforming in any other way, what would be the easiest solution to treat it, please?

Ideally, I would want something I can pick up from my local B&Q, as there is one pretty much next door. I would also very much prefer something that does not require 24h drying, as I want it all done tomorrow (the urgency is strong with this one).

Thanks very much in advance and sorry to trouble you with something so trivial

 

'Tis a valid point!

Thanks, I'll look into these.

What about something like Ronseal line of wood stains, either for decking or external doors? No bueno?

And what would one use for the said action of sealing?

I am indeed. Most weightlifting platforms use lacquered ply or some hardwood, so it's not usually an issue.

Like so:

 

Astro turf wouldn't work too well, as it has too much give, which you don't want under heavy load. Most people use horse stall mats for that reason, but I went with some gym flooring (also non-compressible like stall mats), as I managed to get some on during Christmas sale.

 

I've got the ply already (got delivered today), so I need to make work with what I've got. Should have probably gone for something that was treated to begin with, but as I said, I am a newbie with these things...

 

Thanks. Would this work: Ronseal Natural Decking Oil? Says it's "rainproof" in two hours and can be given another recoat in six.

 

Sorry, I was thinking more broadly, i.e. using this Ronseal Oil on the surface, as well as to seal the sides (as you suggested).

I am not bothered by not being able to overpaint, so assume a tub of the cheapest multi-purpose silcione sealant will do the trick to seal the sides, correct?

 

Perfect, thanks for your help. I'll coat them both on one side first, then turn around in two hours or so, cover the other side and then after two hours screw them together, and then seal with silicone on the sides. Should do the trick (he says crossing his fingers).