joining fibreglass angle

[smashweld]

what would be the besy way to butt 2 pieces of 3" radius fibreglass angle together so you can't see the join and they become one piece

the horizontal piece needs to stay whole and the vertical one shaped to butt up against like in the middle of the pic, anything can be done on the 'inside' (rough side where you can see the strands) to reinforce but want it looking like the one on the right from the outside

from the little I've read I think the idea is to taper/feather down away from the join on both pieces? but would it be better building it up from the inside then shaping/sanding?

it'll eventually be painted so losing the gelcoat finish at the join not important

zero experience with fibreglass... any thoughts appreciated

cheers

 

[Bobtail4x4]

easy fix
grind the surface, use surface tissue,
inside grind again and add chopped mat,
fill the outside and paint

 

[smashweld]

when you say fill...what with?

want to avoid any body filler etc as it'll be on a truck body so some flex/vibration

was thinking making it all fibreglass would avoid the risk but maybe there's something better?

 

[CompoSimmonite]

You can buy ready make angles like the picture as they are used for edging fibreglass flat roofing.

 

[Bobtail4x4]

it will need a thin smear of filler, unless you over glassfibre it and grind back,
thinking about it, for a small part its easier to make a complete new item than join two bits together,
a one off mould from papier mache and lay a new part up.

 

[smashweld]

unless you over glassfibre it

put more fibreglass chopped mat? on the outside of the corner then grind/sand it to shape? I'm not too sure what surface tissue is used for btw...if you were going to grind/sand it back in to shape then it makes no difference?

 

[Bobtail4x4]

surface tissue as its name suggests is a finer glassmat, so gives a nice finish,
not good enough to paint but.........

 

[smashweld]

Just to clarify....

Fibreglass....chopped mat or surface tissue cant be painted....and that's what the filler is for?

Or is it just how smooth the surface is...even after sanding?

 

[ajlelectronics]

To joint two pieces is straightforward..

Taper the edges of the two pieces with a stone grinding disc or coarse abrasive. Screw them down to a piece of wood to keep them in alignment, then clean with Acetone. Mix some resin and apply liberally to the feathered areas to be joined and press in a piece of fibreglass mat. Stipple resin into it and then lay up another in the same way until you have rebuilt a slightly raised profile.

If you don't need it to be pretty, that will do, otherwise when dry, turn it over and grind back the other side in the same way without breaking through. Lay up again in the same way. When hard, flat off both sides to whatever standard you need.

 

[smashweld]

finally had a chance to mock up a test piece with 2 bits of fibreglass angle today....just to see how it went before doing the actual job, now I've had a go have got a few questions...


how much of the gelcoat should you remove and how far back to feather/taper away from the joint?

how exactly to cut/ lay the mat? would it be better to cut a say, 10mm strip and lay it along the length of the joint...then a 15mm, then 20 etc....start bigger? Or better to rip little bits off and push them in to the 'root'?

if the fit up is bad like in the pic what's the best way to tackle that?

 

[RichardM]

Filler will give a better surface for paint than CSM / Tissue. P38 or UPol will allow limited flex, as much as the existing gel coat will allow.
What thickness are the pieces to be joined?
I would taper at 50mm minimum for each side.
P40 will hold the joint together and allow you to sand it down (rotary grinder even better - wear dust mask etc) to get the proper shape prior to laying the glass in.
You will not get the glass to lie in a sharp angle unless you use something to keep it in place while going off.

 

[smashweld]

they're both 3mm thick in the pic but the pieces for the job will be about 3mm and 5mm thick...the 3mm piece having the shape cut out and the 5mm piece staying whole

 

[smashweld]

You will not get the glass to lie in a sharp angle unless you use something to keep it in place while going off.

Not too bothered about a sharp angle but have read it’s better to tear pieces off rather than cut but trying to tear small bits it just ended up as strands...should you start with strands then 2 or 3 layers of mat?

 

[smashweld]

Results of the test piece not too good. Took a fair bit of pulling but I managed to separate the 2 parts by putting it in the vice and pulling. The fibreglass bonded to the feathered edge much better than the face of the other part....needed to hit it with a big hammer to break it but still broke at the join.

 

[RichardM]

Cutting will give you a sharp line, ripping/feathering the edge will give a better taper.
Rough the piece up well that you are bonding too, have a look at how much surface area you have created for the bonded area, looks like the curved section you are bonding to is too small a surface area.

 

[smashweld]

I just used an alu slitting disc that was already in the grinder to take off the gelcoat and taper. I was thinking that would rough it up but maybe it made it more glazed than rough with the heat/speed?
Will have another go and use some coarse grit paper this time and grind further back too