Welding fiberglass.

[s/v Beth]

I have got a weird one. I have just recently became aware of welding for plastics. Various plastics, including HDPE, can be welded by a heat source and rod material. Well, our boats are really just plastic, and a lot of it. So- Can our boats be welded back together instead of glued with epoxy? I have done internet searches on this and found nothing about welding fiberglass. Has anyone tried this?

[Andrew Troup]

AFAIK the only plastics which can be welded are thermoplastics, not thermo-set plastics and definitely not catalysed resin-set, reinforced plastics.

However it's not my field, so hopefully someone else will clarify.

[Jim Cate]

Newt, I fear that Andrew is correct -- a little experiment with some scrap FRP and a heat source will likely convince you of this unfortunate fact!

Jim

[s/v Beth]

Most Polyesters (which fiberglass is commonly made of) are thermoplastic. I don't know if our Polyester yachts are (which is why I am asking the question)
Polyester - Wikipedia, the free encyclopedia
I did the basic homework on this one- I just need to know what type of polyester resin is in fiberglass.

[thinwater]

No. Andrew said it all. Neither polyester not epoxy resin melt; they burn.

[boatpoker]

Google search on "ultrasonic welding polyester"

Just for fun ......

Google "self healing polyester resin"

[skipmac]

As said, doesn't work for FG. Wrong kind of chemistry. Fiberglass resins set by a chemical reaction and once cured the process cannot be reversed. Plastics like PE, PP and others are polymers that can be melted and worked without changing their molecular structure so can be remelted and welded together.

[glenn.225]

Never heard of it either. Since FG gets most of it's strength from the glass fibers and the resin helps to bond it together, I'm not sure how it would be able to be welded. But brighter people than me have figured out a lot of things.

[minaret]

Yes, welding for fiberglass exists. It's called Plexus.

[s/v Beth]

Fair enough. I have learned something about plastics tonight. I have sailed a HDPE cat before. Just a Hobie but lots of fun. I wonder why it hasn't been used for larger boats. Works for milk bottles.
OK- my impressions of the material- very tough, but probably a magnet for marine growth.
It was great for a beach cat, and it didn't seem to be slower than the FG Hobie's running around.
Anybody make a boat of HDPE? (this comes from the guy that wanted to make a Nickel hull a while back )

[Canibul]

I just used a version of this for my own benefit. I stupidly broke off two plastic "ears" from the rear hatch interior door panel of a KIA Sportage. I was fixing the rear washer hose, blah blah. Anyhow, I tried regluing it with plastic cement, no go. Tried epoxy. Nope. Tried contact cement. No luck. Then suddenly I realized nothing was sticking to this just like the ABS I use in my 3-D printer.

So I clipped off about a foot of the 3mm back filament the printer uses, put the flat tip on the soldering gun, and just welded the pieces back on to the big panel. Dang if it didn't work beautifully.

[roverhi]

A big problem with welding FRP layup, if it was possible, is the break in continuity of the fibers. The strength in FRP is the fiberglass cloth/matt. If you butt the boundaries between the glass, the butt will be a weak point as the glass strands won't overlap the butt joint. Repairs to FRP layups involve multiple layers of cloth/matt that bond to a large surface area of intact layup on either side of section needing repair. You wouldn't get that with a butt weld.

[s/v Beth]

I would agree with all the above, just sometimes welding is useful. The guys that weld Polyethylene sometimes inbed a stainless mat for the same effect. It would be nice if I could weld my tanks to the hull, even if they were easy to remove the same way. I am going to look at making a HDPE dingy. It would be light and very tough. I think that is what the Portland Pug is made out of. I don't know if I have ever seen a HDPE boat with a hole in it.

[nimblemotors]

Originally Posted by s/v Beth

I would agree with all the above, just sometimes welding is useful. The guys that weld Polyethylene sometimes inbed a stainless mat for the same effect. It would be nice if I could weld my tanks to the hull, even if they were easy to remove the same way. I am going to look at making a HDPE dingy. It would be light and very tough. I think that is what the Portland Pug is made out of. I don't know if I have ever seen a HDPE boat with a hole in it.

HDPE is relatively heavy compared to other materials.
This dude has made a river jetboat from HDPE:

see the details in the boat design thread.

I've been working on my cat dinghy, and have starting looking making an LDPE inflatable, and maybe even an inflatable LDPE 40ft cataraman.
LDPE is softer and easier to weld.

[minaret]

Originally Posted by s/v Beth

I would agree with all the above, just sometimes welding is useful. The guys that weld Polyethylene sometimes inbed a stainless mat for the same effect. It would be nice if I could weld my tanks to the hull, even if they were easy to remove the same way. I am going to look at making a HDPE dingy. It would be light and very tough. I think that is what the Portland Pug is made out of. I don't know if I have ever seen a HDPE boat with a hole in it.

Walker Bay, about the most common dinghy around, are made of plastic. High Impact Polyethylene, IIRC....