View Full Version : Ply wood water proofing

12th March 2021, 04:44 PM
Hi All, me again.

I have been "given permission" to work on my man cave. This man cave is a tin roof and (very solid) brick wall, concrete floor. I want to convert it into a small activity/games room. With the below ground pool, I am wanting to also install a small shower in one corner of the cave- yes I have a sewer line to attach to. During summer it gets up to 50deg in there and in winter (literally) -50deg.

I want to place some form of ceiling on the roof as well as insulation. The beams holding the foof are at 900mm apart, so installing gyprock or fibro sheeting is not good as it will sag in the middle.
My other option is to use plywood sheeting. (looking at the 9mm thick as its easy to handle and cheap. not sure about the 6mm - but would take advice on that.)

My plan is to install some batt insulation then the sheets attached to the jarrah beams.

I have sourced some reasonably cheap plywood which would do the job.

NOTE: I want to do this with a very restricted budget as at the end of the day its only a garage/shed.

Any feedback, advice etc muchly appreciated.

Can I paint all the panels (all the surfaces) with a water proof paint to protect from moisture?. Remember that in winter moisture is still around in the air. Also, will this help with potential termites.
What suggestion of waterproofing paint do you suggest.

This would also help where the shower is with steam whilst having a shower.
The jarrah is immuned to the termites but I would think a softer wood like ply it would love if it was around.

Once all up and attached I would then paint it an appealing colour.


12th March 2021, 05:06 PM
Why not put battens across the beams(opposing) at the appropriate width to take plaster/gyprock use wet area gyprock, insulation check sealed check, paint it whatever colour floats your boat, treat the solid brick wall the same.
I think 9mm ply would sag at 900mm centre but there are many more knowledgeable on this forum than I so there is my 2 cents, although I suppose it should be 5 cents as it is the lowest denomination available.

12th March 2021, 05:24 PM
I'd forgo the ply/gyrock altogether and get yourself some foil backed foam insulation panels. Easy to install and do a reasonable job at insulating the space. I don't think you can paint it, but personally i don't mind the look

Foil Insulation - Rigid Foil Insulation Panel - Foilboard (https://www.foilboard.com.au/foil-insulation/)

12th March 2021, 10:37 PM
You are in for a great enlightening if you think Jarrah is immune to Termites as said above battens and Gyprock, you will also need a moisture barrier in the sower section, plus one or exhaust fans and address the moisture form the pool

13th March 2021, 05:34 PM
Regarding the Jarrah comment with termites. The original home was built in the 1950's and the shed in the early 1960's. No evidence so far with any termites. Basing it on that.

But take your word. If it lasts another 30 years who cares, right - we would be long gone from this home and the next owner would most likely demolish anyway.

13th March 2021, 07:49 PM
9mm ply wonít span 900mm unsupported successfully. The other issue you have is you are still going to need to do a lot of framing to support the sheets as they will be 2400x 1200 unless you cut them down to 1800 which will mean a lot of wastage and the joins will still need support framing regardless
The easiest and cheapest option is to battern out the ceiling and sheet with FC sheeting with either an expressed joint or cover strip
Pricewise it is similar to plasterboard but you donít need to set the joints and it is much more resistant to moisture if that is an issue
You could also use the plywood and paint it if that takes your fancy but you will need to do some support framing regardless of product you choose

14th March 2021, 04:50 PM
so with the FC, I would need to remove the roof sheeting, place that down then reattach the roof?

Looking at the instructions sheet that is what it appears how that works. Almost like roof sarking. :?

14th March 2021, 04:56 PM
When I say FC ( fibre cement) I am referring to fibro.
I wasnt suggesting to remove the roof sheeting just battern out the underside and line with your preferred sheeting

16th March 2021, 10:18 AM
Apologies, I thought it was in relation to the foil insulation suggested above.
In order to the do the fibro, I would need to add additional battens. As the main beams are 900 apart. This would make it sag. Hence why I was thinking the more stiffer (than fibro/gyprock).

I want to try to keep the work to a min