Split in GRP

[Forbsie]

I have a split in my hull below the waterline where some idiot dropped it on the sharp end of a sleeper. A friend suggested last night that I should drill the end of the cracks (the split is like a capital I). Unfortunately, this was after I had patched the inside of the crack.

West Systems say to cut out the whole damaged area but others advised to leave the crack intact. I think that the hole would be too large for me, as a novice, to repair if I'd cut it out.

So what should I do now?

- Drill the holes and redo inside and out
- Complete the repair on the outside
- Cut out the damaged area and start again

All advice most welcome.

 

[ccscott49]

It would be best to grind down the outside, around the crack, rebuild with mat and resin, then fill the rest and repaint. you dont need to cut out the crack, but you do need to feather it down, by reducing the thickness, to allow a decent repair. A kit from a car type ple will give you all you would require. Otherwise its a specialist job to build it up and re-gelcoat it.

 

[Forbsie]

Thanks Colin. That's what I have done so far on the inside of the crack and have ground down the outside to do today. Will it make any difference repairing inside and out separately? I realised that I didn't have anything to clamp the mat with in a sort of upside down position.


BTW Is an Oilfield Bender a directional driller?

 

[ccscott49]

Yes, it will be no problem doing it in two halves, it will still all bond together. Yes I'm a directional driller.

 

[Guest]

Gordon, I've sent you a PM

 

[oldsaltoz]

G’day Forbsie.
Sounds ok to me, but you should wash the outside before grinding or you will spread any wax from the internal repair; a simple scotchbrite and plain water is all that is required, when the water no longer beads it,s clean; you will also have to take the shine off the new glass if any is showing from the internal repair.
Also consider using epoxy resins as the bond will be up to 40% stronger. And when feathering the outside make sure you go past the end of the original crack by at least 2 inches (50 mm) to strengthen the weak and possibly damaged glass.

Avagoodweekend Old Salt Oz.

 

[Guest]

drilling cracks is meant to stop the crack propagating, and works in crystalline materials (steel, ally etc.) by reducing the srtess concentration at the tip of the crack. In GRP, as the mat runs in all sorts of directions, at any point in front of the crack there will be fibres at right angles to the direction of cracking. Thus, cracks in GRP do not propagate anyway...

What is the issue with 'burst' GRP like this is delamination: the fibres tear away from the resin, and lose their integrity, at the same time making the thing vulnerable to osmosis. If you intend to repair yourself, grind out the 'loose' mat (or just rip it out). You end up with a big, ugly hole, but no loose glass fibre. Then you can start to repair, making sure the mat is thoroughly soaked with resin.

Actually, you should try to make a mould first, so you can press this in place from the outside, coat it in release wax and slop on gelcoat, before you lay in the glass mat. It's not complicated, but it is tricky to make it pretty, but if it's below the waterline, does pretty matter?

 

[Forbsie]

Thanks for your advice, Graham. I completed the outside yesterday but am concerned that you and OldSaltOZ both mention release wax. (

I was sure that I had heard of it somewhere but definitely didn't use any in my repair. Is this a problem?

 

[ccscott49]

You only need release wax when you use a mould, don't worry about it, you don't need it. It's to allow the thing you're moulding to come out of the mould after its set, you put it on the mould first, then lay up the component.

 

[Forbsie]

Whew, thanks Colin. I just sent my mate to look at it on his way home in case I had made a mess of it.