Polycarbonate vs acrylic

[Neeves]

All our windows are acrylic. We have a lot - and they are quite big. We replaced 7 or 8 of them, about half the number we have, like for like - without any problems. We replaced the windows because the developed a single crack - no crazing. I don't know why the crack developed, it was not impact might have been heat (the windows are tinted - it is Australia.

I was wondering what is there advantage of acrylic or polycarbonate over the other?

Jonathan

 

[Graham376]

I was wondering what is there advantage of acrylic or polycarbonate over the other?

Polycarbonate is stronger but softer surface more easily scratched.

 

[VicS]

Polycarbonate is stronger but softer surface more easily scratched.

Maybe also a difference in cost.

 

[PetiteFleur]

I fitted.new acrylic (perspex) windows in my previous boat, again with acrylic. The original windows were badly crazed. Out of interest I tried to break them in my workshop - it was very difficult, only after clamping in a large metalwork vice and hitting with a large lump hammer did they break. I was impressed.

 

[rogerthebodger]

Polycarbonate is stronger but softer surface more easily scratched.

And do suffer from going milky from UV.

Polycarbonate is also more flexible than perspex so if big could be kicked out if not bolted in.

My big wheelhouse windows are made from 2 sheets of toughened glass laminated together. clear do not scratch or vissial degrade.

My deck hatches and washboard are perspex.

 

[ltcom]

Agree with all above. Go acrylic.

 

[C08]

And do suffer from going milky from UV.

Polycarbonate is also more flexible than perspex so if big could be kicked out if not bolted in.

My big wheelhouse windows are made from 2 sheets of toughened glass laminated together. clear do not scratch or vissial degrade.

My deck hatches and washboard are perspex.

Yes my wheelhouse front window in polycarbonate despite being UV resistant claimed went quite milky after 2 seasons and my side windows in acrylic are pristine. Also poly about 50% more expensive than cast acrylic.

 

[europe172]

Go for cast acrylic it is far better at uv resistance

 

[Iliade]

Agreed, laminated or toughened glass is the way.to go! ;0)

Especially if you want windscreen wipers...

 

[Neeves]

Our windows are largely flat, but big. The ones that cracked - one crack slowly migrating across the pane - were relatively easy to replace. We did one per day as it took so long to get the old ones out, cleaned up, abraded a huge overlap, painted the edges and then re-fixed. We still have plenty to replace - -if when they crack. However we have 2 curved panes, they are about 1m square (except they are diamond shaped). I' wondering what the options are if they crack. Polycarbonate was the obvious as it bends, or can be bent (thick acrylic has the bending ability of glass) but its lack of resistance to UV is a real deterrent (of which I was not aware). In the past there have been people who have bent acrylic over a former but I suspect its more difficult than described (and expensive if you get it wrong).

I know toughened glass is the way to go - but not for curved glass.

So - I'm not sure what the answer might be.

We have acrylic 'fabricators' who claim to bend acrylic - and I suspect their service might not be cheap.

I'm sitting here hoping they do not crack!

But - many thanks for the answers. For flat panes - acrylic seems the way to go. As was posted - when its thick its inordinately strong.

Jonathan

 

[Rappey]

Drill a tiny hole at the end of a crack to stop it.
Differences Between Acrylic and Polycarbonate | The Plastic People

 

[Graham376]

We have acrylic 'fabricators' who claim to bend acrylic - and I suspect their service might not be cheap. I'm sitting here hoping they do not crack!

Acrylic bends quite easily when heated, the trick is to heat it evenly which is done commercially in an oven with a flat surface and electric heating elements above. I would be surprised if there aren't Youtube videos showing DIY methods.

 

[Neeves]

Graham,

There have been threads here on YBW setting up a heat source over acrylic sheets and letting the softened acrylic 'flop' onto the former underneath. heat on top, over the acrylic with former underneath. It sounds feasible but getting the heat source even might be important, and more difficult. I'm keeping it at the back of my mind - but a sheet of acrylic roughly 1m square and heating it evenly might be easier said than done.

If I decide to go that route - I'll be taking a lot of photos!

And Rappey - I do recall reading, here on YBW, that drilling a small hole stopped the crack, but I had completely forgotten. Thanks. I now have another question - why (not why drill the hole - but) why does it stop the crack propagating?

Jonathan

 

[rogerthebodger]

For you wish to put a curve in acrylic you will need a form to hold the acrylic in shape while it cools.

This is the costly part.

Glass can he bent in the same way except the temperature for glass bending is much higher.

Glass

bending and lamination.

 

[Graham376]

There have been threads here on YBW setting up a heat source over acrylic sheets and letting the softened acrylic 'flop' onto the former underneath. heat on top, over the acrylic with former underneath. It sounds feasible but getting the heat source even might be important, and more difficult. I'm keeping it at the back of my mind - but a sheet of acrylic roughly 1m square and heating it evenly might be easier said than done.

Many years ago, I did a large storage racking job in a factory making shower bases, baths, special products, etc., from acrylic and spent much time watching how they did it. The ovens were Heath Robinson affairs, made from Dexion with spiral wound fire bars (as in old domestic fires) as heating elements. When heated, the acrylic was taken out, clamped in a frame and vacuumed into a former or blow moulded sometimes for aircraft canopies. Other formers were male and the acrylic was just allowed to droop over by gravity until it cooled. If supported underneath, your existing window may make a suitable former if you only need a slight curve.

 

[Neeves]

Hi Roger and Graham

Thanks.

Actually making a former is the easy part, I could do it tomorrow. It simply needs two profiles of the top and bottom curve, and they could be made from heavy duty MDF and then MDF bent over the 2 curves. If MDF would be adequate? If something more robust was needed then add a thin sheet of aluminium over the bent MDF. The heat would need to be applied from the top, so the acrylic could sag over the former

To copy the curve use a 'thing' like they use to develop profiles to cut tiles - sort of like a comb with movable teeth (which must have a name but it alludes me). I made one previously - a long batten with holes and used chopsticks as the teeth, cheaper than buying round rod. It would be impossible (or very difficult) to remove the old window without breaking it, though we might remove a large enough piece to 'drape' MDF over it. We have removed 'flat' windows and replaced them and when we removed the old windows - the crack tends to propagate.

I'm note sure how to bodge up a heater large enough for a 1m diamond shape, the window effectively bends through 90 degrees - especially as its a one off. If laying the acrylic on the former and playing a heat gun over it....... I can see a domestic 'bar' heater working - but not of the size I'd need. I'm struggling to think how to apply the heat needed over a large area - evenly.

A machine like the one in the video looks much better

Jonathan

 

[r_h]

And Rappey - I do recall reading, here on YBW, that drilling a small hole stopped the crack, but I had completely forgotten. Thanks. I now have another question - why (not why drill the hole - but) why does it stop the crack propagating?
Jonathan

It turns the sharp point of a crack into a smooth rounded shape from which it's harder for a crack to propagate.

its lack of resistance to UV is a real deterrent (of which I was not aware).

I was not aware of that either - yet I have 6 year old polycarbonate windows on my boat in Greece, which still look like new. I chose the material because the forward ones have a pronounced compound curve. It may be worth researching whether there are uv-stabilised grades of polycarbonate available.

 

[Quandary]

Taking account of the bend being 90 degrees, the size of the panes and the cost of acrylic if you get it wrong; it migh be better to consider getting it done by a fabricator, you should not have to go that far to find one.

I replaced my acylic windows and hatches last winter, the supplier (Hadlow Marine) sold me a polish which they assert if used twice a year prevents/ reduces UV penetration and prevents crazing. He claimed a considerably longer life based on personal experience and I am inclined to trust him.

 

[Plum]

Our windows are largely flat, but big. The ones that cracked - one crack slowly migrating across the pane - were relatively easy to replace. We did one per day as it took so long to get the old ones out, cleaned up, abraded a huge overlap, painted the edges and then re-fixed. We still have plenty to replace - -if when they crack. However we have 2 curved panes, they are about 1m square (except they are diamond shaped). I' wondering what the options are if they crack. Polycarbonate was the obvious as it bends, or can be bent (thick acrylic has the bending ability of glass) but its lack of resistance to UV is a real deterrent (of which I was not aware). In the past there have been people who have bent acrylic over a former but I suspect its more difficult than described (and expensive if you get it wrong).

I know toughened glass is the way to go - but not for curved glass.

So - I'm not sure what the answer might be.

We have acrylic 'fabricators' who claim to bend acrylic - and I suspect their service might not be cheap.

I'm sitting here hoping they do not crack!

But - many thanks for the answers. For flat panes - acrylic seems the way to go. As was posted - when its thick its inordinately strong.

Jonathan

You can't compare uv discoloration resistance between polycarbonate and acrylic. Each material can have uv blocking additives so each could be better or worse. That is why you will always find someone who will give you opposing experiences. Depends on the specific formulation of the material. Car headlamps are polycarbonate and although some vehicle manufacturers have not always specified correctly, most still have clear headlamps for 15 years. Genuine "perspex " brand acrylic scores well.

www.solocoastalsailing.co.uk

 

[lw395]

You can get polycarbonate with an anti-UV coating on one or both sides and also anti-scratch coatings.Aside from the UV weakening the plastic window, it will also trash the interior of the boat over time.