Fiberglass encapsulated PVC

I am in Thailand and not a professional boat builder. We of course have plywood here and some of it is even sold as "water proof". I seriously doubt there is a plywood here that would be considered "marine grade". I am starting to see some repairs being made in the boat yards using pvc flat sheet to replace rotted plywood.

Polyester resin is the norm here as is csm. Other materials can be found if you make the effort. I did a search in this particular forum and found one unrelated use of the term PVC. I believe, but I'm not sure, that pvc becomes brittle with prolonged exposure to UV. My question is about the durability of this sandwiched pvc technique, is this a good solution?

 

That will depend upon many things.

Some PVC's are better protected to UV than others, in the first place. If you use it on the inside, or coat it properly, the UV risk goes down.

But, by nature, PVC becomes brittle over time.

 

PVC as a building material is weak, heavy for it's strength and stiffness and very difficult to bond to, so maybe some of the "repairs" you're seeing, will come back as repairs again in the near future, which usually isn't the best way to approach these things.

 

I cannot recommend PVC at all for hulls or decking. It is good for plumbing, drains, and some drainage piping. Also because it may have plasticisers in it which prevent proper bonding with resins such as polyester you cannot be sure of it's strength or its bond integrity. Note it does have a special adhesive for plumbing purposes, and that is specific to PVC to PVC bonds.

Other uses are exterior 'roof' sheeting in corrugated form and greenhouse 'glass'.
I use it for transom flaps on my racing dinghy.

In the hot sun with high UV I have seen sheets go from clear to brown in weeks in the UK. Inevitably as pointed out it becomes brittle, and prone to cracking up as well as providing no strength to a structure.

You would be better off getting better quality plywood made, or make you own. Quite a few resins will work resourcinols, urea formaldyhydes, epoxies etc and will remain waterproof. This will give a better long term solution.

 

PVC is heavy. Not a good choice for core material.

As for plastic boats , I see many small work boats, harbour craft, fish farm craft constructed of polyethene . They seem to hold up well to industrial use

http://www.rhinomarineboats.com/

 

Where I saw it used was the underside of the overhang. It has no load on it and is not exposed to direct sunlight. Moisture exposure would be from what ever upper deck seepage did in the original plywood. They roughed it good and coated it in polyester resin and csm and then paint. I see that boat regularly and 2 years later it looks like the day they put it in. I do believe you about bonding problems but there do not appear to be any in this instance. Does that show up over the long run?

I was thinking of using it for cold molding of parts like a flybridge control console and maybe a hardtop. Has anyone else seen it encapsulated in fiberglass? I do know that plywood can last for many years if properly sealed with epoxy resin and glass. If you did the same with pvc it seems the known downside is that it's heavier. Also other than weight, why could not be used for decking? I've seen it at .75" for sure and there might even be a thicker sheet.

 

Flame treating is the common way to adhere epoxy to PVC and various plastics. I quess it works with polyester resin

Flame treating a plastic surface for bonding

To flame treat a plastic surface, hold a propane torch flame about 4" to 6" from the plastic (with the tip of the flame just above the surface) and move it across the surface at a rate of 2 or 3 inches per second overlapping the previous pass slightly. Keep the torch moving and only allow the exhaust gases to hit the surface. If done correctly, the surface will not discolor or burn in any obvious way. This technique oxidizes the surface and improves adhesion. For best adhesion, bond to the surface within 30 minutes of treatment.

To test the oxidation success of your flame treatment technique , pour water over the treated plastic. If the water sheets off , the treatment was succesful. If the water beads you have not correctly oxidized the surface and must re flame treat.

 

I suspect there is some kind of a misunderstanding here, are we talking here about solid PVC or foam PVC ? It has to be the latter, why would you fibreglass it otherwise ? And 3/4 inch thick......that would be as dear as poison. Vinyl ain't cheap !

 

No, this is solid pvc sheeting sold as thin as 3 mm and on up. The price per sheet is comparable to the local "waterproof" plywood and I cannot currently quote a price but back when this was being done it did not strike me as outrageous. Nothing like coosa or what's it called.

My understanding was that it was fiberglassed to keep it from uv deterioration and add strength not to mention being able to fair the glass/epoxy.

Am I the only one that's ever seen this done? It's that far off the mark?

 

OK, I'm pretty certain this is not solid PVC, which has a SG of 1.4, but something like this called "Azek" which has a micro-cell internal structure, and a SG of 0.55.

PROPERTY UNITS VALUE ASTM METHOD
PHYSICAL
Density g/cm3 0.55 D 792
Water Absorption % 0.15 D 570
MECHANICAL
Tensile Strength psi 2256 D 638
Tensile Modulus psi 144,000 D 638
Flexural Strength psi 3329 D 790
Flexural Modulus psi 144,219 D 790
Nail Hold Lbf/in of penetration 35 D 1761
Screw Hold Lbf/in of penetration 680 D 1761
Staple Hold Lbf/in of penetration 180 D 1761
Gardner Impact in-lbs 103 D 5420
Charpy Impact (@23°C) ft-lbs 4.5 D 256
THERMAL
Coefficient of Linear Expansion in/in/°F 3.2 x 10-5 D 696
Burning Rate in/min No burn when D 635
flame removed
Flame Spread Index -- 25 E 84
Heat Deflection Temp 264 psi °F 150 D 648
Oil Canning (@140°F) °F Passed D 648

 

It may very well be expanded PVC sheet goods (Azek is one brand), which are fairly common. They're are non-structural, quite flimsy, even in thicker sheets or dimensional "board" stock (plastic siding boards, for example). It is UV stabilized to the degree it can be (it still de-polymerizes) and the physical attributes clearly show it's a decorative, non-structural product, with a significant expansion rate.

Used as described above, it wouldn't take much to pop it out of whatever it was bonded to. A good shot or two with a hard object, will break the bonds and the PVC will literally pop out. In fact, I use this exact product for making textured deck treatments and for flat surfaces. I apply the textured PVC over wet goo and peel it off when cured or use it as a solid, smooth base and cast something over it, again peeling it free after the cure. Peeling it off is very easy.

 

At one time I did great deal of glassing onto PVC and the bond can be surprisingly good.

There are polyester resins formulated for bonding to either acrylic, ABS or PVC, these resins will be difficult to purchase in small amounts and even harder in smaller markets, so this may not be an option.

The other option is to use THF (tetrahydrofuran) as a cleaner prior to glassing, this will soften the surface and improve the bond.

 

Ondavar, were you able to evaluate long term results? Any problems with durability, delam, water problems? Care to comment on my control console and hardtop idea?

 

We made water filtration systems, so it was in constant immersion, we never had any problems with delam, some of those systems have been in place for almost 30 years now.

We didn't have any formal testing done at the time, just in-house stuff to let us know it would work for our application.


Here is a link to one resin.

https://host2.ccponline.com/pdfs/040-4502.pdf

 

How dynamic where the loads in these "water systems"?