Gelcoat Application

[thewavehumper]

Any chance of a picture of the HUll before you start?

i agree with Jeff about not using the electric sander

[Aging Youth]

Morning All,

You would be ok using a small handheld orbital sander with circular disks. then when polishing use a sheepskin head to buff to glass finish.

The more wax built up the better the finish BUT it is a labour of love.

It would be great to see pictures of each stage to add to this thread for reference.

Good Luck.

[slangley]

I am probably going to start this weekend or during next week. I am just waiting for a colleague of mine to help me dismantle everything and turn the boat over.

I will take pictures this weekend of how it looks now and then at each stage. I will kep them posted on this thread.

Thanks everyone for your help.

[slangley]

Before I start, I just have 1 final question. After applying the final layer of Gelcoat ( the one with wax ), I must go through the grades of wet or dry paper.

How do I know when I have done enough with that grade. I will be doing it by hand in a circular motion but what indication do I have when I need to go on to the next grit.

As an example, if I had a metre square of Gelcoat, how long would I sand with 240grit before moving down. I know that is a very difficult question to answer and the answer is probably 'it depends', but a rough idea would be nice so at least I know I am on the right tracks.

If I do too much then I will take too much of the Gelcoat off and if I do too little then I wont have smoothed enough with that grade.

Also, how long roughly should I leave the final layer of Gelcoat before starting to sand. The books say about 24-48 hours but I seem to remember someone saying dont leave it that long.

[jwalker]

I'm going to presume you end up with a light texture from the roller. 240grit is a bit fine. It will work but it's slow. Try 120. As you have realised, there needs to be enough gel to allow a good deal of it to be removed and still have enough left. You mentioned applying 3 coats. That sounds about right but it depends on the thickness of each coat (obviously). It'll be down to your judgement I'm afraid.
You probably realise this but I'll say it for completeness. Polishing is a process of scratching the surface with finer grades of abrasive until you get to the point that your eyes can no longer discern the scratches. At this point we call in shiney. Under a microscope it would still look like mountains and valleys.

So, you must remove all of the texture with the 120, then remove all of the 120 surface with 320, the 320 surface with 600 and the 600 with 1200. I would actually dodge the 1200 stage and move on to a rubbing compound and then the final polishing compound.
It's probable that you'll loose just over one of your layers provided they are nice and even and of fine texture when you start.
If it's any consolation, after this one, you 'll know exactly how to do the next one.

[Andy Stevens]

Dont use circular motions when rubbing down with finishing paper, they will show up. Also use a block as your fingers will apply an un-even pressure giving an un-even surface. Keep it nice and wet and use a small amount of washing up liquid on the paper to keep it lubed. I think using 120 is too harsh at this stage, 240 briefly moving to 400-600 would be better. Basically you are cutting the tops of the waves off. You will know its ready when the surface is matt, then buff like mad.

Also when I was talking rollers, i mean the FOAM ones not the hairy sheepskin ones. They are cheap as chips from B&Q. You will have to go easy with the hardeners, too much and it will go off before your very eyes too little and it never will, dont mix too much at a time and choose the area you want to paint.

Mechanically a DA sander (orbital) will not dmage the surface but DONT sent it to rotary as it will dig in. The old Gel will come off with 80 grade. Too harsh and you cut the paint badly.

Its patience basically.

[jwalker]

You probably know this too. But, just incase...15 - 20ml of catalyst to 1kg resin. Approx 1.5/2.0%

[TIM]

Use a scales to messure the resin, And then add the catalyst after at the above mentioned ratio's, note, fiberglass will 'go off' even if you mix it well at 0.5% ratio, it just might take 3 weeks!!!

very important, mix it really really well, spend at least 3 mins on it, or until you arm is about to drop off, this seriously improves the strenght and shortens curing time.........

[Matt]

Against the advice of a number of people I resprayed my whole hull with gelcoat. Make no mistake, it's a really huge job, but the results can be as good as original if done well. I did the following steps:

1) Grind down the whole area. Leave it really rough to ensure you get a really good mechanical adhesion (I used 40-80 grit, depending on the area). Some areas where there were cracks, I sanded through the gel completely. If necessary to smooth the surface out again I used filler to bring the whole surface flush.

2) Really thoroughly remove dust, especially if you've sanded paint or coloured gelcoat off and you're gonna spray a different colour.

3) I used normal gelcoat, not flowcoat (so no wax in it), and make sure it's REALLY fresh. Like less than 3 months old. I thinned it with acetone, some people recommend styrene. Can't remember the ratio off the top of my head, but it was quite a lot.

4) Spray onto the hull. Important to use a reasonable spray gun and have a decent facemask against the fumes. Generally you want a nice even covering, but if needed you can really pile it on in some areas, as the spraying flashes all the acetone off so it doesn't run. The advantage of using normal gel without wax is that you can go back and re-do any areas as many times as needed at your leisure more or less.

5) Make sure the ambient temperature is high enough. I did it in february, so I hired 6kw of infra-red heaters for my garage to get the ambient temperature up nice and high. (20C+)

6) As the gel JUST starts to go off, spray it with PVA. I used blue PVA so I could where it was. I was recommended to thin it, but didn't bother after the first attemp. Really cover everything in it so it's dripping off. This is important to seal the gel in to get it to go off properly.

7) Leave until fully cured.

8) Peel the PVA off. Mostly comes off in large sheets. Where tricky, can be scrubbed off with hot soapy water and a stiff brush.

8a) Go back and do any missed bits!

9) Now the job really starts - Sanding! Be very careful of edges, only use 1200+ on edges or you will go through. For surfaces, depending on the finish you got spraying, maybe start with 120 or 240. I've heard of some people being able to start with 400 or 800, but my spraying isn;t that good. Work up progressively all the way to 2000, with rubbing compound and finally some really good polish. This takes AGES, but is worth it.



Pro's:
Great for getting uniform coverage
V. cheap materials
Easy to cover large areas.
Very durable factory finish
Quite forgiving on spraying and preparation.

Con's
Takes AGES to produce a good finish.
Everyone takes the piss saying it can't be done.


Summary:
If I do more any medium sized repair work on the hull, I will definately do this method again, but I probably wouldn't respray the whole hull again, I'd try 2-pack paint next time to hopefully get a result that needs less finishing, as gelcote is very hard, takes a long time to sand down.

Hope some of you guys find this useful.
Cheers
Matt

Edited to say: I used a random orbit sander to do loads of the sanding (re comment above)

[Charles]

I'm exhausted just reading it all - - Well done, any pictures of your handywork?