Fibreglass - repair or not repair? That is the question.

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orbitals

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Dear friends, please would you help me with this one. I'm in the process of renovating a 19ft Stuart Stevens cabin cruiser. I've uncovered an ominous looking crack on the inside of the hull. Exterior looks fine no chipped gelcoat, all good. I think the crack has come from a trailer roller pushing too hard.

I've not repaired fibreglass before, and really had no intention of doing so. But is it worth cleaning up and putting some sheets of repair kit over the top?

Your thoughts and comments are appreciated.
 
The trouble with this sort of choice is that the visible crack may be substantially smaller than an area of damaged laminate beneath the surface. It is a choice, but ideally you would grind out the laminate from the inside until you are finding no sign of damage within the structure. The edges must be chamfered so that the join between the new layup and the original extends over a wide area, spreading the load,so as to speak. Once ground back the area can be made good with new layers of chopped strand mat and resin. A good laminator can make the repair almost invisible, except the colour may differ slightly.

If you choose to go the simpler route, you will never know whether the patch is sufficient to the task - unless it isn't. To patch over, clean and abrade the surface ad use an epoxy resin for better adhesion than you would get with polyester resin. Ask suppliers about suitable cloths to lay up with epoxy as the readily available chopped mat is bound together with a compound designed to dissolve into polyester resin and doesn't dissolve in epoxy, so it is almost impossible to wet it out completely.

Most people doing DIY repairs apply resin with a paintbrush , lay on the cloth and then stipple more resin on to saturate the cloth. It improves it if you use a consolidating roller to work the components together to ensure voids and dry spots are eliminated. Rolling chopped mat tends to pick up fibres and start to destroy the mat, so usually allowed to cure and then dressed off with a grinder/sander.

Visiting West Systems website opens up a wealth of guidance and advice!

Rob.
 
Thanks Rob. Very thorough, much appreciated. Now I'm slightly more concerned about the crack. It's clearly not a case of slapping some of "David's fastglas" over the top.

But one thing, are you suggesting I grind away until you can't see any crack? I guess potentially grinding right through the hull.

I'll look up some repair companies, just as a back-up plan.

Thanks, Andy

Here's the issue:

IMG_1189.JPG
 
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It does look a bit like that may be right through, I'll bet the outside has been filled, but DON'T PANIC. Grind back until the crack disappears. If right through, grind back out and in side, feather away from the middle to nothing. Sometimes it is easier to wet out mat and polyester resin on a board away from the work, max three layers of 600gm at a time, then apply after painting on a layer of resin. Old GRP will only allow a mechanical rather than chemical bond, so initial abrasion is important. If it's any comfort a 32 ft FV went ashore in a storm and had an entire new side put in, 30 years on it's still fine.
 
I'd be inclined to do it. You meay never have the hull stripped to this extent again, so now's the time to bite the bullet! Even if it isn't a problem, the boat might go back on a trailer one day and it could open up, so you may as well reinforce it now. It's up to you whether you go for polyester resin or epoxy. The latter is better but a bit harder to use and you can't put polyester over it. That said, I repaired a hole below the waterline on Avocet more than 20 years ago with polyester and it's fine. Only think I'd add to the excellent advice above is to buy (if you're going for polyester) a tin of "Flowcoat" and paint that over the top of the whole repair on the inside of the hull to cover the "hairy bits" of fibreglass mat when you've finished. It looks liek that's what was done on your original hull. You can get it pre-pigmented in white.

Grinding the old stuff will make HUGE amounts of dust, so an old vacuum cleaner with the hose taped near the grinding implement will pay dividends!
 
Use epoxy with woven mat.
To fully wet the mat lay a piece of polythene on a flat surface .
lay the glass mat onto the polythene so that the mat fully covers the size you need you can use a paper pattern to get this right
pour a fairly liberal quantity of resin all over the mat
Place another piece of polythene over the mat so the mat is sandwiched between the 2 layers of polythene.
mark with a felt tip pen the shape of the piece you want on the polythene. Cut a paper pattern & mark round that is you are not sure.
using a small roller such as a wall paper seam roller to roll the resin into the mat so it goes colourless as you push the rein about. once the matt is fully wetted start to push the resin away from the mat so you squeeze it out of the mat. If the polythene is oversized the resin just runs between the 2 layers of polythene & does not make a mess on the bench.this leaves a minimum amount of resin in the mat so it is strongest when dried. You should not have too much resin . just enough to wet the mat
Prime the area to be covered with resin making sure surface is clean & dry

Using a pair of scissors cut around the pattern line you put on the polythene & discard the waste polythene along with the excess resin you pushed out
Flip the trimmed sandwich over & remove the bottom layer of polythene. from the " sandwich" & place the mat onto the desired position on the hull. The top piece of polythene helps retain the matt shape & allows you to position it fairly accurately.
Roll the mat in place through the polythene . When hardened remove the polythene leaving a smooth finish

trying to wet the mat with resin in situ as suggested earlier is not always a good idea as the mat moves about & you may not get the right amount of resin or it may run. plus surface will not be smooth

best try with a 6 inch piece as a practice first
 
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I repaired a crack on the hull of my old boat - admittedly above the waterline - where a chain plate had cracked the moulding and you could see right through it. You'd be amazed how strong fiberglass repairs can be and although the chain plate was secured to a bulkhead below we never had any problems. All good advice above but if you are like me cosmetics are secondary to effectiveness. If in doubt use a bit more! I have a plaque in the garage as a present from my wife that says 'If you can't fix it with duct tape you haven't used enough'. Same principle applies. By all means try to make a neat repair but if it's strong and not as neat as you'd like as least its going to do the job.
 
The cruciform black crack line showing is probably what you're concerned about, but I'd suggest you also take a close look at the line running fore and aft along the strake. Incidentally, should you go right through when grinding back the damaged area, you can jam a ply pad against the outside of the hull to lay up agaianst, although it will need a polythene layer in between to prevent the ply getting incorporated into the layup!

It's a bit of a gutsy job, particularly the grinding, and you should wear a dust mask as there will be clouds of dust at this stage. Gloves and full length clothing too, skin can get really irritated and sensitized both by the dust and any splashes of resin. Gutsy, but not technically difficult or too time consuming. Most people are relatively insensitive to epoxy, but polyester resin contains styrene which is said to make laminators depressives even if they aren't dermatalogically sensitized! Work in a well ventilated area, better still outdoors.

Rob.
 
Needs fixing as others have said.

To avoid grinding through the gel coat when working from the inside shine a bright light directly onto the outside where the crack is. You will then see if you are getting close.

I would definitely use epoxy and cloth rather than polyester and mat. If you want to have a neat finish on the inside get some peel ply.

How to use peel ply http://www.clcboats.com/shoptips/epoxy_and_fiberglass/peel-ply-release-fabric.html
 
Ok, thanks for all your help. Much appreciated, and i'm feeling much more confident in my fibreglass knowledge. I've used the grinder on the hull today and it appears some of you were right, it does go through to the gelcoat. Damn! Thanks TQA for the bright light tip.

Anyway, its very positive that I did grind through as I don't think it would've been the best maiden voyage.

Here's the latest picture:

IMG_1259.JPG


Would you recommend chipping the gelcoat away completely or glassing over the crack using the gelcoat as a guide, then filling from the underside? I stopped at this point, just to assess the situation.

Thanks again!
 
orbitals said:
Ok, thanks for all your help. Much appreciated, and i'm feeling much more confident in my fibreglass knowledge. I've used the grinder on the hull today and it appears some of you were right, it does go through to the gelcoat. Damn! Thanks TQA for the bright light tip.

Anyway, its very positive that I did grind through as I don't think it would've been the best maiden voyage.

Here's the latest picture:

IMG_1259.JPG


Would you recommend chipping the gelcoat away completely or glassing over the crack using the gelcoat as a guide, then filling from the underside? I stopped at this point, just to assess the situation.

Thanks again!
Click to expand...

Looks like really neat grinding!

Grind totally away everything that shows some damage and put a nice 12:1 chamfer on the surrounding area. You can use plastic film over thick cardboard or better still thin ply taped and propped onto the bottom to give you the shape back. Alternatively you can drill a few holes and temporarily "stitch" the ply and film to the repair with string to hold it in place. Small holes are easily filled with a little thickened epoxy. The resin won't stick to the plastic film. Best bet IMHO after that is put a layer of pigmented, thickened epoxy down first onto the plastic film, let that go off a little, then put layers of *epoxy compatible* CSM and resin down until you've built it back up to full thickness.

If you aren't bothered about the cosmetics internally then you could support from the outside as discussed, put some thickened epoxy or other epoxy filler down to replace the gelcoat, grind around the area to create a key, then put a few layers of matt and resin down over the whole area with a good wide border around it. It will be proud internally but strong.

But wait for a couple more opinions and take the average.

That covers the small area - what about that much longer crack in the original picture? That looked even more important to me.
 
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A bit late now but I would not have done so much grinding. The area is covered by floor boards so a build up on the inside will be OK. I would have just grind to get a clean surface for epoxy to adhere to. Yes use epoxy. Better adhesion and less shrinkage.
I would not bother with the wetting out between 2 layers of polythene. Yes this will give the best resin to glass ratio so best strength to weight ratio. However the old GRP will still have to be well wetted out so negating the squeeze out effort and that squeeze out will be messy.
Rather I would lay glass cloth (not too thick) over the cleaned area and saturate with epoxy preferably in a warm environment. use a brush to stipple out all all bubles and get the glass saturated. Then add another layer in the same way. Use perhaps 8 or 10 layers of thin cloth. End up with a repair thickness at its thickest similar to the hull thickness. You start with a large area piece overlaping the whole area of damage. Then after 2 or 3 layers of a large area you reduce the size of the patch progressively so that you don't get a sharp transition from heavily reinforced bottom to no reinforcement. This will alow the whole to flex not just at the weak transition.
Considering how far you have ground out the crack I would suggest that you try to get the remaining edges to meet ie looking smooth on the outside. If the GRP is so thin at the crack edge you will have to support the outside while you do the patch on the inside. Polythene or cling wrap on the old GRP held in place by sand bag jack or bracing to support the outside. Once the inside has gone hard you can grind out the outside a little to expose the new GRP repair material then lay up some cloth on the outside cut to match the ground area. The samller the repair area on the outside the better for appearance. The real work comes in trying to get the outside smooth and cosmetically neat. You might need to paint the outside to finally cover the repair.
Speed boats can take a huge pounding in choppy water at speed. The flexing may have caused the damage or as said may have been a trailer roller with excess weight on it. Rough roads and long distances can cause damage too. If it is a roller try to fix it. Rollers under the centre keel tend to take most weight hopefully each with a share of the laod. Side rollers take a small weight if any and are only to stabilize the hull from sideways rocking.
good luck olewill
 
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I think you can patch this on the inside, make it as big and thick as you like so you feel totally happy about it, then just grind back a little on the outside to make a base for the cosmetic work.
 
Thanks all. Work got in the way of progress on this. I think i'm going to gently grind back and layer-up from the inside, then worry about the outside. It's anti-fouled anyway, so it shouldn't be a tough job.

The longer crack (along the strake) is yet to be ground back, but i'll try and do this with a Dremel tool and again layer-up from the inside.

Just hope my grinding skills are up to it! Stay tuned for more pictures.
 
Hi there - sorry for the huge delay. I've finally made my repair, just need to do the outside of the hull next (open to suggestions on the best approach). I spoke to someone, who suggested wetting out from glass with Gel Coat filler. That seems like a brittle finish to me?

Here's the result so far... I used around 6/7 layers.

IMG_1286.JPG
 
I was sure I already replied - obviously not!

I haven't glassed up the outside yet - I was actually waiting to see what peoples thoughts might be on this. It was suggested to wet out some glass with gel coat filler - but i'm not so sure on that.

I used polyester resin in the end after talking with a local boat builder - he made me up a kit with some slow hardener.
 
You may have noticed that you have a sticky surface finish. Not too bothersome inside but a pain on the outside.

Polyester resin is a general-purpose resin suitable for a wide variety of applications. Methyl Ethyl Ketone Peroxide (MEKP) must be used as the catalyst to begin the curing process. Catalyzation rates can be varied with polyester resins in order to adjust for various environmental conditions. In thin laminations or when gel coat is sprayed as a topcoat, the surface may remain tacky and not cure properly if left exposed to the air. To get a complete cure, thin laminations or top coats must contain either styrene wax solution of have a coat of polyvinyl alcohol (PVA) solution sprayed over them to seal out the air. With the former, the wax "floats" to the surface as the resin cures, acting as a barrier to the air. Styrene wax must be sanded off after curing, but PVA can be rinsed off with warm water.
Click to expand...

A simpler solution is to use parcel tape.
 
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