GRP impact damage

single

single

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The picture below is not mine but the best example i could find. The plan is to grind the area out into a concave then lay circles of matting getting bigger each time with West system.Is this the best way to repair damage similar to this? Any other tips or advice?

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Can you get to the underside of that area? If so, grinding the underside (just abrading it really, rather than going deep into the laminate) and then laying up underneath (ending up (say) 6" bigger than the damaged area all round, would be better. You'd then do as you suggest, grinding out at the top (once the mat underneath was cured so that you're not weakening the laminate too badly) and filling. West epoxy will stick very well, but it's hard to pigment it to match the surrounding gelcoat (probably impossible in the long term as epoxy isn't good at resisting ultraviolet light). You'd be fine with epoxy if you planned to paint the repair afterwards though. If you do that, it might be best to epoxy to just below the surface with a mixture of epoxy and microfibres for strength, then use epoxy and microballoons for the last bit (it's easier to sand).
 
Remove all the damaged material.

If you want to re-gelcoat the area you will have to use polyester resin. If you paint I would use the West System and 200g or less cloth. Chopped strand is usually referred to as Mat ..... and therefore only usable with polyester ..... and it is only bulk anyway .... not much strength.

As for ways of laying up the cloth :
Tape off the area
Wet the area out with epoxy
Lay the first piece of cloth over the damage and wet out to the extent of the damage ..... there's no need to trim the cloth to size provided it allows the cloth in the repair to stay put.
Choose another piece of cloth to place on top of that, and so on until you've built up the thickness
After 24 hrs grind it back so it is slightly below the required surface and over fill with 407
Another 24 hrs .... sand with a sanding block, finish with 200 + grit and paint.

I'm sure there will be other suggestions, including some that will suggest you mixing polyester with epoxy .... but that's what the forums about ...
 
As said you need to grind out all the damaged GRP. This would include an inspection of the other (in) side of the GRP. If you end up grinding right through then you can use polyester resin with layers from both sides bonding in the middle. (before they go really hard). This gives a lock of the new GRP ino the hole.
However if you just repair from the outside then possibly polyester is OK. It can be pigmented to be the final finish and is OK in UV. Epoxy will stick better but must be painted to protect from UV. The paint then being hard to match to the original gel coat.
One of the difficulties is that you may want to sand off layers put down before applying more layers with filler or final coat. You need to apply the next coat before the lower coats have gone fully hard. But this less than hard GRP will just clog up sand paper etc. So try to get a flat surface when soft to avoid sanding. good luck olewill
 
The damage in the pic doesn't look too bad to me. Largely confined to the gel coat by the looks of it? Chisel or grind out enough to reach good layup, & if not too deep, you'll likely get away with plastic padding gel coat filler in this case.

a simliar repair myself recently.

Having had occassion to hang the entire boat by the pulpit a while back (a story for another day), the pulpits' aft leg crushed into the fordeck about 5-6 times the depth of the gelcoat. I dug out the damage, cleaned with acetone, filled with plastic padding epoxy filler and then applied a film of pp gel coat filler before the epoxy set. Made good with 60, 240, 600 & 1200 wet and dry.

A bit of an experiment, I wanted a completed repair within a couple of hours & I was curious to know just how "poorly" gelcoat sticks to epoxy.

Anyhow, I've since refitted the pulpit and torqued down that particular leg pretty hard. Jobs good enough for a fussy fella. :encouragement:
 
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Fiberglass repairs are easy in principal but difficult in practice. Make sure you have everything to hand before you start, wear disposable gloves and get plenty of acetone to clean brushes and tools and surrounding areas and clothes. Don't use SWMBO's best scissors for cutting mat get some cheap but sharp ones of your own.
 
Can you take a picture of your damage.
The one shown is really just a gel repair.
Just a check inside to see if there's any delamination and if there is a quick sand with 40 grit and a layer or two of mat inside.
As has been said above remove the old gel,
I use and old but sharp chisel and then a dremel to put a shamfer on the outside edge of the damage.
You can get a good finish with Gelcoat repair paste as long as you do thin layers to make sure you don't get tiny air bubbles.
I would use topcoat gelcoat, cheap as chips from most grp suppliers.
CFS glassfibre in Cornwall are quick and efficient.
 
Although id agree with the above - what is the consensus on using a pre mixed P40 on something like this once gound out and keyed for fresh material?

Im only curious as its compound is generally designed to fill such things and can be a little easier to sand dependant on how good you are at applying mat.
 
ghostlymoron said:
Fiberglass repairs are easy in principal but difficult in practice.
Click to expand...

That is very true !

single said:
The picture below is not mine but the best example i could find. The plan is to grind the area out into a concave then lay circles of matting getting bigger each time with West system.Is this the best way to repair damage similar to this? Any other tips or advice?
Click to expand...

There is loads of practical advice on repairs using epoxy, with info on the materials, glass, resins, fillers etc on the WEST SYSTEM website http://www.wessex-resins.com/westsystem/index.html.

Also a book published some years ago by Tylers on GRP repairs on Bluemoment at http://bluemoment.com/downloads/grp_repair_manual.pdf

You can spend an awful lot of money on epoxy and associated materials do do a small repair if you are not careful. ( dont ask how I know)
For something non structural I would stay with the ordinary polyester materials
 
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VicS said:
That is very true !



There is loads of practical advice on repairs using epoxy, with info on the materials, glass, resins, fillers etc on the WEST SYSTEM website http://www.wessex-resins.com/westsystem/index.html.

Also a book published some years ago by Tylers on GRP repairs on Bluemoment at http://bluemoment.com/downloads/grp_repair_manual.pdf

You can spend an awful lot of money on epoxy and associated materials do do a small repair if you are not careful. ( dont ask how I know)
For something non structural I would stay with the ordinary polyester materials
Click to expand...

Agree with VicS - polyester has many benefits for such a repair.
It's usual, if the damage is from the gel coat side in, to build up with polyester & mat on the inside, with a generous overlap, then make good and replace the gelcoat on the outside.
 
P40 I'd only use for filling voids or filling in non structural areas like web between keel and hull, fairing in skin fittings etc.

On a polyester layup use polyester.
You can use epoxy though your prep needs to be good.
I've seen a lot of epoxy repairs fall off polyester or take very little persuasion to come off.
It is not the cure all that many people believe.

btw, if you can't get hold of polyester gelcoat topcoat but do have normal gelcoat,
fill the repair with gel and simply cover with a good quality masking tape.
This will cut the air and allow the gel to cure hard.
I use thin plastic I know won't melt with the styrene (the cut out sides of a mixing pot) and tape it on.
When its cures I have a shiny finish requiring little finishing.
 
The only reason an epoxy glass repair won't work is if the prep is bad or the mix is wrong ..... and that would be more so for polyester.

Polyester shrinks more during cure so the bond line is under greater stress, also it's adhesion strength is much less than a good epoxy resin.
 
I did it today after lots of reading.It looks ok but will need sanding tomorrow. I'm planning on sanding then another couple of coats of epoxy resin, sand again, prime, paint? Just to be safe i'm doing the inside too. I'm sure it would be fine as the hull is about 25mm thick.
 
single said:
I did it today after lots of reading.It looks ok but will need sanding tomorrow. I'm planning on sanding then another couple of coats of epoxy resin, sand again, prime, paint? Just to be safe i'm doing the inside too. I'm sure it would be fine as the hull is about 25mm thick.
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Epoxy and mat level with surrounding area. Then let it cure and grind down a couple of mm and use flowcoat just a bit proud of the required finished surface. (you can use gelcoat but it needs a plastic covering over it as it doesn't cure when exposed to air (apparently)). Sand with fine abrasive to finished level then polish.
 
Avocet said:
That's certainly the impression I always had. In which case, I think once the decision to start the repair with epoxy has been made, finishing off with flowcoat / gelcoat would be impossible.
Click to expand...

I'm not sure other than painting.If its not in sunlight i guess adding pigment to the final epoxy coats would be ok then rubbed down and polished.
 
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