Best sealant for acrylic windows?

[SAWDOC]

I am currently renewing my boat windows fitting new plexiglas windows in aluminium frames. The plexiglas/acrylic is fixed to the aluminium frames with a sikaflex sealant(recommended by supplier) and then new window rubbers are inserted. Has the forum a view on the effectivness and longetivity of Sikaflex (sikasil-P) in this application or is there a better sealant?

thanks

 

[VicS]

I am currently renewing my boat windows fitting new plexiglas windows in aluminium frames. The plexiglas/acrylic is fixed to the aluminium frames with a sikaflex sealant(recommended by supplier) and then new window rubbers are inserted. Has the forum a view on the effectivness and longetivity of Sikaflex (sikasil-P) in this application or is there a better sealant?

thanks

Its important that the sealant does not contain any solvent detrimental to the acrylic

If the sikasil-P is suitable for use with acrylic and UV resistant then fair enough.
It is a solvent free marine grade silicone with good UV resistance and said to be suitable for mineral and "organic" glazing!

The "marine" product from Sika for sealing and bonding acrylic and polycarbonate glazing is Sikaflex 295 UV but note that it is an adhesive sealant

Sikaflex Users guide



.

 

[vyv_cox]

Quite a few years ago I made the mistake of using Sikaflex 291 to bed polycarbonate windows. The following weekend every window was cracked. I replaced them all and bedded on Sikaflex 295 instead, which was still fine when I sold the boat. I heard later that many motorbike crash helmets, also polycarbonate, had cracked after people put adhesive stickers on them, due to stress corrosion caused by the solvent in the adhesive.

 

[michael_w]

To ensure a really satisfactory job Look at the Sika application guide sand use the horribly expensive cleaners and primers it recommends. It's a job you only want to do once!

 

[Frayed Knot]

Whatever you use I advise having a pot of industrial cleaning wipes to hand - "Big Wipes" from B&Q are fantastic for cleaning up (and surface-finishing) silicon products.

 

[GrahamM376]

I use Arbosil 1096 for acrylic into aluminium. Widely used throughout the glazing trade and cheaper than Sika. More likely available through glazing or builders merchants than chandlers.

 

[Gordonmc]

Any thoughts about using butyl tape?
I need to replace windows which have been sealed using sika or something similar. Most of the perspex has cracked and/or crazed.
I will replace using polycarbonate, hopefully re-using the old plastic outer frames, if they will comce away without disintegrating.
I was thinking about butyl because of its long term flexibility.

 

[JimDL]

+1 for arbosil 1096

 

[Mistroma]

+1 for arbosil 1096

Ditto. I called their tech. support guy many, man years ago and described what I was doing. He told me exactly what to do and even sent me a sample to check it would work. Great guy, he had approx. hatch measurements and sent a big enough "sample" to do the work (and some windows as well). I seem to remember that he also sent a sort of mastic tape to bed the hatch in place whilst the goo set.

It was an awful long time ago but I remember that I was able to replace the forehatch with polycarbonate and it remained in place and waterproof for at least 10 years (still going strong when I sold the boat).

 

[graeme.toms]

I am currently renewing my boat windows fitting new plexiglas windows in aluminium frames. The plexiglas/acrylic is fixed to the aluminium frames with a sikaflex sealant(recommended by supplier) and then new window rubbers are inserted. Has the forum a view on the effectivness and longetivity of Sikaflex (sikasil-P) in this application or is there a better sealant?

thanks

Hi I have used sikaflex on my ferro boat over the past 4 years, and in some cases I find it works well, I have also used CT1 and found better results, and as the weather is quite damp, it can be used in damp condition.
good luck Graeme

 

[SAWDOC]

I use Arbosil 1096 for acrylic into aluminium. Widely used throughout the glazing trade and cheaper than Sika. More likely available through glazing or builders merchants than chandlers.

I looked up Arbosil 1096. Hadlow marine windows describe it as being suitable for glass windows in aluminium frames while Arbosil 1081 is referenced as suitable sealant for acrylic windows.

http://hadlo-43547-001.dsvr.co.uk/

 

[GrahamM376]

I looked up Arbosil 1096. Hadlow marine windows describe it as being suitable for glass windows in aluminium frames while Arbosil 1081 is referenced as suitable sealant for acrylic windows.

http://hadlo-43547-001.dsvr.co.uk/

I used 1096 on recommendation of the makers - didn't send me a free sample though

Sealant in ally framed windows and a Lewmar hatch, all with perspex, still OK after 5 years in Algarve sun.

 

[Mistroma]

I used 1096 on recommendation of the makers - didn't send me a free sample though

Sealant in ally framed windows and a Lewmar hatch, all with perspex, still OK after 5 years in Algarve sun.

Ditto, for polycarbonate as already mentioned. The shelf life was great as well and I still had some left a couple of years ago so it must still have been OK about 8 years after opening (unbelievable).

I was so impressed tha I took a piccy in 2010 so that I'd remember which type to order in future.

 

[Runnerboy]

Don't use Sika, use butyl tape

Quite a few years ago I made the mistake of using Sikaflex 291 to bed polycarbonate windows. The following weekend every window was cracked. I replaced them all and bedded on Sikaflex 295 instead, which was still fine when I sold the boat. I heard later that many motorbike crash helmets, also polycarbonate, had cracked after people put adhesive stickers on them, due to stress corrosion caused by the solvent in the adhesive.

While exchanging the polycarbonat/acrylic windows a couple of years ago, I was advised NOT to use any Sika,/silicon or any produkt that dries out .
So i ordered 12 m BUTYL tape. It never dries out but leaves black tracks when touched, But can easily be sealed with. ...Sika.

 

[KAM]

I would not use Arbosil. Silicone sealants are very weak in thin layers and prone to failure under movement or differential expansion. I used Arbomast BR on aluminium to acrylic windows. It's a non setting Butyl rubber. It's very easy to use and has been totally effective.

 

[GrahamM376]

I would not use Arbosil. Silicone sealants are very weak in thin layers and prone to failure under movement or differential expansion. I used Arbomast BR on aluminium to acrylic windows. It's a non setting Butyl rubber. It's very easy to use and has been totally effective.

According to the manufacturers, 1096 is the correct sealant. BR, as you can read on the datsheet, is not for use in situations exposed to UV. http://www.arbo.co.uk/download/arbo_sealants/mastic_sealants/Arbomast-BR-tech1.pdf

 

[KREW2]

To ensure a really satisfactory job Look at the Sika application guide sand use the horribly expensive cleaners and primers it recommends. It's a job you only want to do once!

Exactly, that is what I did with my fore hatch. The materials cost over 60 quid, but it's a proper job.

 

[KAM]

In my application the acrylic is under the frame and not exposed to any UV. I think this will be the case with most aluminium/acrylic window systems. There is a big difference between the thermal expansion coefficient of aluminium and Acrylic sheet. 4 to 1. There will also be movement of the structure itself. If the silicone is compressed to a thin layer it will fail. If the silicone is thick it won't be a problem. Most people will be familiar with failed silicone when bedding deck fittings. I know this from bitter experience in industry where my company suffered enormous warranty costs despite using a very expensive product under tight quality controls. Arbrosil 1096 has a recommended minimum thickness of 6 mm probably for this reason.

 

[SAWDOC]

From the Arbomast tech sheet:

It is not recommended for use against bituminous materials,
expansion and other joints subject to high degrees of movement.



Does this not suggest it is unsuitable for applications such as boat windows subject to movement stresses?

 

[KAM]

I had a look at the data sheet. I think by expansion joint they mean the large 20mm type gaps often seen in buildings. These would be subjected to tensile loads during contraction/expansion which the non setting sealant would clearly not withstand. I think the problem with manufacturers specs is that they will seek to imply the widest possible range of uses whilst at the bottom in small print will be several get out clauses and warranty disclaimers. From practical experience I removed and resealed one of my windows using silicone sealant which I already had. It failed again after a few months. I then removed and resealed all my windows using the butyl material. It appeared to be the same as the sealant which had been used when the boat was built 30 years ago. It has been watertight for 3 years now. I hope this helps. It's not a job you want to repeat too many times. In the end you will need to use your own judgement.