Plywood or alternative.

Nasher · 14-09-2021, 10:56 AM

Another thread that starts – I know there are experts in lots of things on here.
I'm hoping that perhaps Mr Gazza will be here at some point.

About 20yrs ago I built a cupboard into the corner of our Ensuite, had a large piece of Mirror glass cut for the door(@1500mm x 500mm), brought a sheet of 12mm ply from somewhere like B&Q or Wickes, cut it to size and glued the mirror to it with the special mirror adhesive.

I painted the back, hung it on the new frame I’d built and it’s been fine ever since, except some very small areas around the edge where the damp environment has got under the mirroring.

After several redecorations I’ve recently put a new suite in and retiled the whole room. Lady Nasher wanted the large Mirror door back in place, but with a new mirror because of the damp ingress, which is fair enough.

So I ordered a new sheet of Mirror Glass and when it arrived brought a sheet of 8mm ply to reduce the weight.
I cut it to size, glued the mirror on the front with the special adhesive, painted the back and hung it on the hinges.

The following morning the £80 mirror was in 3 pieces because the ply had warped. The top corner of the non-hinge side was about an inch away from the frame where it had been touching the afternoon before.
I was obviously annoyed, especially as we don’t have the heating on yet, and hadn’t yet used the ensuite because I was still working on it.

So I ordered a new piece of glass and brought a sheet of 12mm ply from Wickes which I cut to size and laid flat on the floor in the spare room.
I planned to hang the door and mount the mirror with it in place so the adhesive would take up any small discrepancy due to warping.

Within a couple of days the 12mm ply laying flat on the floor was propeller shaped by @1/2 inch on two opposite corners.

It’s not damp at all in our spare room, and we don’t have the heating on yet, so I’m putting it down to cheap Wickes plywood.

So, what spec ply should I be looking for to ensure it doesn’t warp after cutting to @ 1500 x 500mm?
I'm sure the old favourite of generic 'Marine Ply' doesn't exist any more.

Thanks

Nasher

Davy · 14-09-2021, 11:01 AM

The ply nowadays is rubbish because of the water based glue they use. Maybe you could use a sheet of laminated multi layered ply for shelving. It won’t warp and will probably come in that size.

slob · 14-09-2021, 11:54 AM

https://plydirect.co.uk/ list BS1088 marine ply in 6 and 9mm thicknesses

then a couple of coats of yacht varnish to seal it?

Kato · 14-09-2021, 12:19 PM

What Slob said, but leave in the house a week to acclimatise before you use it, this sort of stuff is stored in cold damp conditions and will shrink when taken indoors

Nasher · 14-09-2021, 12:28 PM

Thanks Guys.

I think that's the issue, it's shrinking when taken indoors, but is warping too much as it shrinks to be of any use.

And yes Davy, it's no doubt because the ply I brought 20yrs ago was laminated up with Solvent based adhesive that is now banned.

Thanks for the link Slob.

Darkness · 14-09-2021, 12:40 PM

I think the roofing ply I bought recently came from Brazil as deck cargo: on a submarine!

Mr Gazza · 14-09-2021, 01:10 PM

8mm ply was too flimsy for that weight of glass. It's very humid at the moment, so you will notice a bit more movement in untreated timber.
As a general rule you should always treat both sides of a panel the same, so when you put adhesive on one side which presumably shrunk a little upon curing? Then the other side of the ply was exposed to the moist atmosphere. There would be a lot of tension in the ply.. evidently as the mirror broke.
I have never glued a mirror to anything it sounds horrendous especially on that area.
I would lay it in a rebate with a little silicone round the edges to stop it rattling and help keep the moisture out of the silver, then screw a board over the back to retain it, preferably in a stepped rebate.

WBP ply would be minimum requirement sealed both sides. 1088 sounds a bit extreme, in fact I would go for MR MDF (Green, moisture resistant), again sealed both sides.

So it broke into 3 pieces? Not safety glass then? Regs state that any door glass must be safety glass, either toughened or laminated so as to fail without causing injury. Any glass within 600mm of a door must also be safety glass. Any glass less than 800mm above a floor must be safety glass.
Can you get toughened mirrors? I don't know. Do you want 1500 x 500 of float glass on hinges in your bathroom where you will be naked and slippery?.. Not on my watch!..

Nasher · 14-09-2021, 01:22 PM

Hey Mr G

The back of the first piece I did paint at the same time as using the adhesive on the front, so both were sealed, but as you say it was too thin really.
The second 12mm piece was laid flat on the floor on carpet untreated either side.

slob · 14-09-2021, 03:01 PM

I’d try and weigh it down evenly, if you can find enough heavy things round the house, to encourage it to stay flat during its aclimatisation period.

PPuxley · 14-09-2021, 03:44 PM

I'd be using moisture reistant MDF for that. It uses a resin binder that makes it much more stable.

Tim88 · 14-09-2021, 04:18 PM

I made a large ( 7ft x 40 in) bathroom mirror using an old sliding wardrobe mirror door which I mounted in a giant picture frame made out of mdf and rebated. Reinforced the mitre corners with little splines. I covered the back of this mirror with a very thick sort of sticky back plastic from the glazing shop before screwing the whole thing to the wall through the frame, the mirror thus floats slightly from the wall and is not stressed in any way . It may crack in an accident but can not fall out, so should be safe. The other mirror for over the sink (5ft x 3ft about, maybe a little bigger) I used the same sort of mirror with the sticky back plastic/ aluminium tape stuff on the back but this time glued to a sheet of hardboard with silicone. This mirror is attached simply with little mirror mounting clips screwed into the wall. No problems for the last 20 years. These giant sheets of heavy plywood or mdf seem like overkill and are easily capable of cracking the glass if they distort.

Jez900ie · 14-09-2021, 08:15 PM

I think you need to use Marine Ply which is made from tropical hardwoods. Google will find you a nearby supplier hopefully.

Nickj · 14-09-2021, 08:23 PM

Mr G this would be an ideal set of conditions to use Tricoya to stick the mirror to??

Good marine ply is actually quite hard to get hold of at the mo, I've been after some and am being picky as it's for constant water exposure

Nasher · 14-09-2021, 09:07 PM

Thanks guys

The mirror is also a door to a cupboard, so needs to be stuck to something that will not only enable it to accept completely hidden hinges, but also support it over it's whole area whilst it's being moved.
It's not in a frame at all, which is why it's so expensive as it has fully polished edges.

For 20yrs it's worked fine with the old ply, but of course it would be almost impossible to remove the old mirror from the old ply to reuse the ply.

Being stuck over it's whole area means there is little chance of any broken pieces coming loose if it breaks.

I've had a chat with somebody at the company Slob linked to and they've suggested their FSC Birch S+/BB grade which should resist warping.

I'm going to have the same conversation with somebody at a local timber specialist in the morning and see if they agree.

Tim88 · 14-09-2021, 09:43 PM

Could you just buy a nice flat door and glue your mirror onto that? I don't think I have ever come across an office quality door that has warped and even a cheaper domestic one is very rigid owing to its construction. You could adjust the dimensions of a standard door to suit your applicartion. The final product may be a bit thicker than your ply solution but would be lighter and more stable I would guess.

14-09-2021, 10:56 AM	#1
Nasher Registered User Join Date: Jul 2014 Location: Portsmouth Bike: M900 Posts: 1,510	Plywood or alternative. Another thread that starts – I know there are experts in lots of things on here. I'm hoping that perhaps Mr Gazza will be here at some point. About 20yrs ago I built a cupboard into the corner of our Ensuite, had a large piece of Mirror glass cut for the door(@1500mm x 500mm), brought a sheet of 12mm ply from somewhere like B&Q or Wickes, cut it to size and glued the mirror to it with the special mirror adhesive. I painted the back, hung it on the new frame I’d built and it’s been fine ever since, except some very small areas around the edge where the damp environment has got under the mirroring. After several redecorations I’ve recently put a new suite in and retiled the whole room. Lady Nasher wanted the large Mirror door back in place, but with a new mirror because of the damp ingress, which is fair enough. So I ordered a new sheet of Mirror Glass and when it arrived brought a sheet of 8mm ply to reduce the weight. I cut it to size, glued the mirror on the front with the special adhesive, painted the back and hung it on the hinges. The following morning the £80 mirror was in 3 pieces because the ply had warped. The top corner of the non-hinge side was about an inch away from the frame where it had been touching the afternoon before. I was obviously annoyed, especially as we don’t have the heating on yet, and hadn’t yet used the ensuite because I was still working on it. So I ordered a new piece of glass and brought a sheet of 12mm ply from Wickes which I cut to size and laid flat on the floor in the spare room. I planned to hang the door and mount the mirror with it in place so the adhesive would take up any small discrepancy due to warping. Within a couple of days the 12mm ply laying flat on the floor was propeller shaped by @1/2 inch on two opposite corners. It’s not damp at all in our spare room, and we don’t have the heating on yet, so I’m putting it down to cheap Wickes plywood. So, what spec ply should I be looking for to ensure it doesn’t warp after cutting to @ 1500 x 500mm? I'm sure the old favourite of generic 'Marine Ply' doesn't exist any more. Thanks Nasher __________________ Heaven doesn't want me, and Hell is afraid I'll take over.

14-09-2021, 11:01 AM	#2
Davy Registered User Join Date: Aug 2007 Location: Derry Bike: M900 Posts: 358	The ply nowadays is rubbish because of the water based glue they use. Maybe you could use a sheet of laminated multi layered ply for shelving. It won’t warp and will probably come in that size. __________________ 1994 M900 Black

14-09-2021, 12:19 PM	#4
Kato Dismantled Join Date: Feb 2006 Location: East Molesey Bike: Multiple Monsters Posts: 2,228	What Slob said, but leave in the house a week to acclimatise before you use it, this sort of stuff is stored in cold damp conditions and will shrink when taken indoors __________________ "Political correctness is just intellectual colonialism and psychological fascism for the creation of thought crime" Last edited by Kato; 14-09-2021 at 12:25 PM..

14-09-2021, 12:28 PM	#5
Nasher Registered User Join Date: Jul 2014 Location: Portsmouth Bike: M900 Posts: 1,510	Thanks Guys. I think that's the issue, it's shrinking when taken indoors, but is warping too much as it shrinks to be of any use. And yes Davy, it's no doubt because the ply I brought 20yrs ago was laminated up with Solvent based adhesive that is now banned. Thanks for the link Slob. __________________ Heaven doesn't want me, and Hell is afraid I'll take over.

14-09-2021, 12:40 PM	#6
Darkness . Join Date: May 2007 Location: Stockbridge Bike: M900 Posts: 1,984	I think the roofing ply I bought recently came from Brazil as deck cargo: on a submarine! __________________ Original and Best since 1993

14-09-2021, 11:54 AM	#3
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,713	https://plydirect.co.uk/ list BS1088 marine ply in 6 and 9mm thicknesses then a couple of coats of yacht varnish to seal it?

14-09-2021, 01:10 PM	#7
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,834	8mm ply was too flimsy for that weight of glass. It's very humid at the moment, so you will notice a bit more movement in untreated timber. As a general rule you should always treat both sides of a panel the same, so when you put adhesive on one side which presumably shrunk a little upon curing? Then the other side of the ply was exposed to the moist atmosphere. There would be a lot of tension in the ply.. evidently as the mirror broke. I have never glued a mirror to anything it sounds horrendous especially on that area. I would lay it in a rebate with a little silicone round the edges to stop it rattling and help keep the moisture out of the silver, then screw a board over the back to retain it, preferably in a stepped rebate. WBP ply would be minimum requirement sealed both sides. 1088 sounds a bit extreme, in fact I would go for MR MDF (Green, moisture resistant), again sealed both sides. So it broke into 3 pieces? Not safety glass then? Regs state that any door glass must be safety glass, either toughened or laminated so as to fail without causing injury. Any glass within 600mm of a door must also be safety glass. Any glass less than 800mm above a floor must be safety glass. Can you get toughened mirrors? I don't know. Do you want 1500 x 500 of float glass on hinges in your bathroom where you will be naked and slippery?.. Not on my watch!.. __________________

14-09-2021, 01:22 PM	#8
Nasher Registered User Join Date: Jul 2014 Location: Portsmouth Bike: M900 Posts: 1,510	Hey Mr G The back of the first piece I did paint at the same time as using the adhesive on the front, so both were sealed, but as you say it was too thin really. The second 12mm piece was laid flat on the floor on carpet untreated either side. __________________ Heaven doesn't want me, and Hell is afraid I'll take over.

14-09-2021, 03:01 PM	#9
slob . Join Date: Jul 2003 Location: East London Bike: Multiple Monsters Posts: 9,713	I’d try and weigh it down evenly, if you can find enough heavy things round the house, to encourage it to stay flat during its aclimatisation period.

14-09-2021, 03:44 PM	#10
PPuxley Registered User Join Date: Apr 2021 Location: Reading Bike: M900 Posts: 600	I'd be using moisture reistant MDF for that. It uses a resin binder that makes it much more stable. __________________ Golf-My favourite game. While my wife plays I'm in the workshop.

14-09-2021, 04:18 PM	#11
Tim88 Registered User Join Date: Mar 2016 Location: London Bike: M1100evo Posts: 98	I made a large ( 7ft x 40 in) bathroom mirror using an old sliding wardrobe mirror door which I mounted in a giant picture frame made out of mdf and rebated. Reinforced the mitre corners with little splines. I covered the back of this mirror with a very thick sort of sticky back plastic from the glazing shop before screwing the whole thing to the wall through the frame, the mirror thus floats slightly from the wall and is not stressed in any way . It may crack in an accident but can not fall out, so should be safe. The other mirror for over the sink (5ft x 3ft about, maybe a little bigger) I used the same sort of mirror with the sticky back plastic/ aluminium tape stuff on the back but this time glued to a sheet of hardboard with silicone. This mirror is attached simply with little mirror mounting clips screwed into the wall. No problems for the last 20 years. These giant sheets of heavy plywood or mdf seem like overkill and are easily capable of cracking the glass if they distort.

14-09-2021, 08:15 PM	#12
Jez900ie Pleasantly surprised! Join Date: Nov 2016 Location: Stoke on Trent Bike: M900ie Posts: 780	I think you need to use Marine Ply which is made from tropical hardwoods. Google will find you a nearby supplier hopefully. __________________ Monsters don't hide under the bed, they sleep inside the shed

14-09-2021, 08:23 PM	#13
Nickj Too much time on my hands member Join Date: Jun 2007 Location: Forest Of Dean Bike: S2r Posts: 3,195	Mr G this would be an ideal set of conditions to use Tricoya to stick the mirror to?? Good marine ply is actually quite hard to get hold of at the mo, I've been after some and am being picky as it's for constant water exposure __________________ "The final measure of any rider's skill is the inverse ratio of his preferred Traveling Speed to the number of bad scars on his body." Song of the sausage creature

14-09-2021, 09:07 PM	#14
Nasher Registered User Join Date: Jul 2014 Location: Portsmouth Bike: M900 Posts: 1,510	Thanks guys The mirror is also a door to a cupboard, so needs to be stuck to something that will not only enable it to accept completely hidden hinges, but also support it over it's whole area whilst it's being moved. It's not in a frame at all, which is why it's so expensive as it has fully polished edges. For 20yrs it's worked fine with the old ply, but of course it would be almost impossible to remove the old mirror from the old ply to reuse the ply. Being stuck over it's whole area means there is little chance of any broken pieces coming loose if it breaks. I've had a chat with somebody at the company Slob linked to and they've suggested their FSC Birch S+/BB grade which should resist warping. I'm going to have the same conversation with somebody at a local timber specialist in the morning and see if they agree. __________________ Heaven doesn't want me, and Hell is afraid I'll take over.

14-09-2021, 09:43 PM	#15
Tim88 Registered User Join Date: Mar 2016 Location: London Bike: M1100evo Posts: 98	Could you just buy a nice flat door and glue your mirror onto that? I don't think I have ever come across an office quality door that has warped and even a cheaper domestic one is very rigid owing to its construction. You could adjust the dimensions of a standard door to suit your applicartion. The final product may be a bit thicker than your ply solution but would be lighter and more stable I would guess.