Boat Maintenance & Repair Forum

Hull GRP repair

by Malc » 30 Nov 2017, 20:38

New to boat repair. Die grinding below waterline holes and filling with plastic padding epoxy filler. One specific chip is about 3mm deep and appears to have fibres so thought it might be the GRP. But when ground back the fibres seems to be flakey epoxy, now think it’s the gel coat (white) and the GRP is still good. What I think is the GRP is a brown colour and hard like plastic.

Do you think I’m right? Is there some way of telling if the GRP is compromised?

Photo attached

Malc
Attachments
5E73F093-88A9-44AB-8925-9D55AC970AA2.jpeg
5E73F093-88A9-44AB-8925-9D55AC970AA2.jpeg (155.47 KiB) Viewed 1291 times
Malc
Able Rate
Able Rate
 
Posts: 6
Joined: 30 Nov 2017, 20:19

by Ianfs » 01 Dec 2017, 16:21

Hi Malc

Welcome to the forum and good on you mate for tackling something for the first time.

I'm no expert at this sort of thing but I'm sure someone with a little more knowledge than I will be along soon. However with my limited know how, fibre glass boats are normally built from the Gel coat upwards, so you get a smooth gel coat then the lay up's of the glass fibre impregnated and rolled or vacuum packed with the resin.

In the photo it looks like there is some fibre just under the surface layer then a resin coat then more fibres. I am wondering if this may be an old repair.
Ianfs
Captain
Captain
 
Posts: 1671
Joined: 24 Nov 2014, 18:40
Location: Hampshire, by the Sea

by Malc » 01 Dec 2017, 21:41

That makes sense. The more I read up, tending to agree. I'm surprised the gel oat is so thin. Just expected it to be thicker. Still, cleverer people than me designed the thing lol
Malc
Able Rate
Able Rate
 
Posts: 6
Joined: 30 Nov 2017, 20:19

by Ianfs » 02 Dec 2017, 11:04

I'm surprised the gel oat is so thin. Just expected it to be thicker.


The older I get and the more I learn, I realise how little I actually know about boat construction.

Here's some of my limited experience and forgive me if this is Granny teaching you to suck eggs. Nearly all plastic boats are made out of shredded/mat GRP of differing weights and types impregnated with polyester resin in a process called laying up, although nowadays a lot of boats use Vinylester resins. Polyester has great chemical strength and is laid whilst still wet, but is not as good as Epoxy when it comes to mechanical strength i.e. as a glue . Epoxy resin is water proof and has greater strength to weight ratio and has great mechanical and chemical strength, but is much much more expensive, whereas I believe polyester resins are not waterproof and not as strong but are so much cheaper and therefore the cost to benefit ratio makes them the better choice for boat builders.
A Gel coat is therefore added for embellishment, making the boat smooth and shiny and doesn't contribute to much strength, although it does add weight and helps with water resistance, although I learned a while ago that it is not entirely waterproof. Consequently 1 square metre of gel coat , I think weighs about 1/2 a kg and there are a lot of m2 of it on a 20ft boat. So you see, if it was made thicker, you have just added a lot of weight for not much benefit.
Ianfs
Captain
Captain
 
Posts: 1671
Joined: 24 Nov 2014, 18:40
Location: Hampshire, by the Sea

by Malc » 03 Dec 2017, 22:03

Very helpful and thank you! Your explanation must be the reasoning behind painting as a finish rather than gel coating. Much appreciated
Malc
Able Rate
Able Rate
 
Posts: 6
Joined: 30 Nov 2017, 20:19


Return to Boat Maintenance & Repair Forum

cron