What is Gelcoat

[ontheplane]

Silly question?? Read on pls.

I am familiar with cars. I know a car is (generally) made of metal, with a coat of primer on the top, then a coat of paint, then a coat or 5 of lacquer....

I know the primer protects, the colour colours, and the lacquer then protects the paint and gives the gloss...


Now, If I scratch a car I know how to fix it, and if it's dull, I know what I can and can't do to get the shine back...

But gelcoat? That's a mystery to me. Is the gelcoat coloured, or is there the equivalent of a lacquer over the top of the colour? Assuming boat companies don't "paint" the boat, is there such a thing as a "paint code" to match gelcoat if it needs repair?

If it is dull, I know it can be compounded and then waxed - but can it also be sanded with wet and dry like paintwork can (2000 grit or finer of course!).....

So the question is, can someone explain to me (or point me at a website) that explains how a boat is laid up, what the layers are and what they do, and how would one go about getting small marks / stress cracks repaired like you would on a car.

Thanks....

 

[omega2]

make a "blank" i.e the shape of the hull/topsides you want, then on the inside of said blank apply releasing agent, followed by a GEL COAT a mixture of resins and colour, then apply chopped or woven matt with lots of resin and hardener, keep doing this until you think it will be strong and waterproof, when happy upturn blank and remove, leaving a nice shiny hull/topsides. Nothing to it LOL YES YOU CAN BUY GEL REPAIR KITS, colour is a bit of problem though due to the original gel discolouring with age/use.

here is a more difficult way of going about it!!

http://practicalaction.org/practicalanswers/product_info.php?products_id=270

 

[ontheplane]

Thanks,

So how thick is the gelcoat layer - a couple of thou like paint on a car, or a few mm or even cm??

So as I thought - the major problem is going to be matching the colour then?

 

[gjgm]

Thanks,

So how thick is the gelcoat layer - a couple of thou like paint on a car, or a few mm or even cm??

So as I thought - the major problem is going to be matching the colour then?

About 1-3mm I would say, depending on the thickness being sprayed into curves/corners and the like-it varies over the hull.
It is brittle, meaning that if the GRP flexes the gel will crack-might be flexing,impact, or stress. Gel is not totally waterproof(but very good) so it stops water interfacing with the grp-hence the potential problems from above mentioned damage.
If the boat is newish, manufacturer supplied gel will probably colour match, but older boats may well need a pro to colour match. Possible problem then is that the new gel fades at a different rate to the surrounding old gel, but I cant say I have seen obvious cases except on very old boats.
Most boats apart from some more recent top marque boats are white,off white or blue. OK, that can still be a headache for colour matching, but not the 000s of car colours, but it would be matched by hand as it were.

 

[ontheplane]

So in reality, unless it were a very small area, it's a case of a pro needed?

I ask because the boat we're "discussing" at the moment has a couple of stress cracks, and so on near cleats.

I suspect they are from it being moored badly rather than any defect in design as it's a quality make, and the cracks are tiny. Having said that, they are there, and this boat is going to cost a bit more than we wanted to pay, so I need to get a feel for whether this was a DIY or pro repair - and I get the feel it's pro only...

 

[gjgm]

So in reality, unless it were a very small area, it's a case of a pro needed?

I ask because the boat we're "discussing" at the moment has a couple of stress cracks, and so on near cleats.

I suspect they are from it being moored badly rather than any defect in design as it's a quality make, and the cracks are tiny. Having said that, they are there, and this boat is going to cost a bit more than we wanted to pay, so I need to get a feel for whether this was a DIY or pro repair - and I get the feel it's pro only...

If it is around cleats and very obvious, then there is a fair chance the GRP underneath has been fractured. If they are fairly fine, then it might just be the gel itself cracking as the cleat moves a tiny bit.
DIY, you can use a dremmel and grind out, and fill with £8 tube of gelcoat repair. For full pro repair the cleats come off, the grp repaired, and full colour match.. I'd guess £3-500, but half of that is travel costs.
But that should stop you buying a boat?

 

[ontheplane]

No not stop us at all - it's more a question of the offer we make (to allow for the work) and also trying to establish if it needs doing at all!

It could be as the cracks are very fine that it doesn't need doing and we can leave it - but useful to know that £300 or so may be able to fix it.

Thanks for the help.

 

[rafiki_]

About 1-3mm I would say, depending on the thickness being sprayed into curves/corners and the like-it varies over the hull.
It is brittle, meaning that if the GRP flexes the gel will crack-might be flexing,impact, or stress. Gel is not totally waterproof(but very good) so it stops water interfacing with the grp-hence the potential problems from above mentioned damage.
If the boat is newish, manufacturer supplied gel will probably colour match, but older boats may well need a pro to colour match. Possible problem then is that the new gel fades at a different rate to the surrounding old gel, but I cant say I have seen obvious cases except on very old boats.
Most boats apart from some more recent top marque boats are white,off white or blue. OK, that can still be a headache for colour matching, but not the 000s of car colours, but it would be matched by hand as it were.

I would be very surprised if the gelcoat is as thick as 1 mm, my guess is nearer to 0.5 mm. This means it can be sanded with a fine wet and dry if you get scuffs, but if you go at it too hard, you will go through the gelcoat. Thjrere are specialist rubbing compounds for tidying up gelcoat, then a decent polish to get a good shine. Repairing crazing, the cracks you describe in the gelcoat around the cleats, is not an easy job. It is a diy job if you have the time to get the right dremel tool along the crack to get a reasonable Vee to fill with gelcoat filler. Don't forget to drill a small hole at the end of each crack to resist propogation. Most boats are white, and the colour matching is only really a problem with coloured gelcoats or boats where the coat has changed colour due to ozone decay or neglect. I have done some minor repairs on Rafiki. She is 8 years old now and been quite well looked afeter, and the repairs are not visible.

 

[PaulGooch]

No not stop us at all - it's more a question of the offer we make (to allow for the work) and also trying to establish if it needs doing at all!

It could be as the cracks are very fine that it doesn't need doing and we can leave it - but useful to know that £300 or so may be able to fix it.

Thanks for the help.

Given your obvious lack of boating knowledge (no offence intended), i would suggest you get a professional survey done on the boat and engine/s. A boat can easily contain a few grands worth of hidden costs, even on a "cheap" boat.

 

[ontheplane]

Oh I intend to!!

Thing is, I do have some boating knowledge that's why I'm asking all these questions - I know they can be money pit's if you think something's cheap to fix, then find out it's not!

I am hoping to get the price down to pretty much as low as it will go, so I know once the survey is done I'm unlikely to get it down any more even if minor things are found - major things of course would be another matter.

 

[gjgm]

I would be very surprised if the gelcoat is as thick as 1 mm, my guess is nearer to 0.5 mm. This means it can be sanded with a fine wet and dry if you get scuffs, but if you go at it too hard, you will go through the gelcoat. Thjrere are specialist rubbing compounds for tidying up gelcoat, then a decent polish to get a good shine. Repairing crazing, the cracks you describe in the gelcoat around the cleats, is not an easy job. It is a diy job if you have the time to get the right dremel tool along the crack to get a reasonable Vee to fill with gelcoat filler. Don't forget to drill a small hole at the end of each crack to resist propogation. Most boats are white, and the colour matching is only really a problem with coloured gelcoats or boats where the coat has changed colour due to ozone decay or neglect. I have done some minor repairs on Rafiki. She is 8 years old now and been quite well looked afeter, and the repairs are not visible.

I mm is pretty small measure, and as I said, it will vary around the boat.
Small cracks around a cleat will probably crack again anyway, but unless some major stress on the cleat (in a storm or towing) are unlikely to be too serious. If you can butter a piece of toast I think you can use a tube of gelpaste
BTW, I have seen recommended for enlarging a crack, one of those old fashioned tin openers- the one that has a sharp V and pierces the tin. Sharpen the V a bit and cut down the crack.