What is the most appropriate plywood for outdoor applications that won't fall apart?

[jp2000]

I need a single sheet pf plywood for our pool filter enclosure. It will be outdoors so I had assumed marine ply would be best. Something like this:

https://www.bunnings.com.au/1220-x-610mm-12mm-plywood-hardwood-marine-aa-grade-12mm_p0320031

However, there are a lot of one-star reviews on that product where people find that the plywood easily comes apart. Is there a better product available?

[JacobZ]

Hi @jp2000,

Plywood can be used outdoors if it is sealed well; however, it is not the best material for use outdoors, as water will cause delamination of the plies if it is not sealed up perfectly.

I would instead recommend using a fibre cement sheet product. Fibre cement sheet products are entirely water resistant and will not delaminate in the same way plywood will if water gets in. They can still be painted to alter their aesthetic; however, they would also be fine without the paint.

If you don't want to use fibre cement sheets, marine plywood can be used, but it will need to be sealed on all sides using 3 coats of Marine Clear Timber Varnish or exterior paint.

Alternatively, you could use formply, but you would need to sand the face to remove the shine from the coating and then paint it on all sides with exterior paint.

Ultimately, if you use plywood, there is a risk of delamination, but by carefully sealing it, this risk is greatly reduced. If you don't want any risk, use fibre cement.

Let me know if you have further questions.

Jacob

[jp2000]

Thanks for the advice. If I go with a sheet of fibre cement, is that easy enough to cut down to size? I only need around 1200x900 but it's not a square rectangle, and one corner will need a bit of a notch taken out.

Then can I just use regular exterior paint on it?

[JacobZ]

Hi @jp2000,

Fibre cement sheets are easy enough to cut. You can score and snap the sheet using a Trojan 200mm Laminate/Fibro Cutter. This is good for long straight cuts. 

For notches, you can use a Craftright Rubber Grip Handle Fibro Cement Sheet Cutter.

Yes, you can use regular exterior paint on fibre cement sheets.

Let me know if you have any further questions.

Jacob

[AlanM52]

Hello @jp2000,

Use a sheet of corrugated polycarbonate roofing.

https://www.bunnings.com.au/search/products?page=1&q=poly+roofing&sort=BoostOrder

If you prefer a flat profile use this.

Twinwall Polycarbonate Sheet

https://www.bunnings.com.au/sunlite-8-1-2-x-0-61m-clear-twinwall-polycarbonate-sheet-1200mm_p1010852

Cheers