Latest News: Forums Technical GRP hull painting

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  • #3634
    Laurie
    Member

    Hi,
    Can anyone please help with some advice on how to prepare a Mk 1 GRP hull that was originally white, but has been overpainted blue ?. I would like to take it back to its original colour, but need advice on should I flatten the blue or strip it?, and grades of paper etc.

    Help on which is the right paint would also be a bonus.

    Thanks in advance.

    Laurie
    W2786

    #6346
    Swiebertje
    Participant

    Changing the color in general is a bad idea because any scratch will immediately show the old color. For this reason alone I always tell people to stick to the existing color or a color very similar to the old one. In your case that would mean sanding the blue until its gone. Not an easy job but Winter has just started. 😉

    I would use a belt sander. It is fast but it has a risk of sanding too hard, especially if you hold it on one spot. It should be moved continuously, movement should stop only after the sander has been lifted from the surface. When nearly done switch to an orbital (or oscillating) sander. All difficult spots are done by hand as is the final sanding. After the blue has been removed you may want to apply some filler on spots where the belt sander got its way or to repair damages. Sand with gradually finer sand paper until grain 240 or even finer. Only when the surface is perfectly smooth (feels like a baby’s bum) the boat is ready for a new coat of paint.

    I would use a two pot paint and against all that is written on the pot I would add some thinner. Two pot paints need a xylene based thinner but watch out; most thinners sold at DIY shops are toluene based and totally unsuitable. Add as much thinner (usually 5% to 10%) until the paints feels good and brush stripes disappear a few inches behind the brush. Then apply the paint using a brush to spread it with cross-wise strokes and a roller to finish it. If the paint is not perfectly glossy some seconds after rolling add some thinner or check the temperature. Two pot paint does not like to be applied below 18C.

    You could use two pot Marine paint, for example Hempel’s but I fail to see what is so special about marine two pot paint. Modern cars have lots of plastic parts as well and use two pot paint too. If you think about what the paint has to endure on the road it must be at least as good or better then marine paint. The fun part is that car paint is significantly less expensive then its marine sibling. If you ask me, its the same stuff, but you pay extra for the word “marine”. A fellow Wayfarer sailor has repainted his boat using cart paint all the way and it still looks like new after five years.

    For filler I always use standard polyester filler from my local DIY shop. They carry two types one with and one without glass fibers. Which one to choose depends on how hard and strong you want the repair to be. For small scratches I would recommend to use the type without glass. These fillers are grayish-white and can be colored with some pigment if you like. The DIY solution is to mix a few drops of the paint you are going to use in the filler. Only use the color part, not the kathalist part of the paint in this case.

    Finally, visit the Wayfarer Institute of Technology. There is a good chance there are some essays on the subject to be found there. http://www.wayfarer-international.org/WIT/WITindex1.html

    #6348
    Dave Barker
    Keymaster

    The fun part is that car paint is significantly less expensive then its marine sibling. If you ask me, its the same stuff, but you pay extra for the word “marine”. A fellow Wayfarer sailor has repainted his boat using cart paint all the way and it still looks like new after five years.

    A well-known boat painting and finishing firm has professionally spray-painted quite a few boats from our sailing club (and many elsewhere) in recent years (admittedly most/all? of them woodies). I’m not saying they use car paint, but if you ask what colours are available you’re likely to be referred to Halfords to pick a colour from their charts 😆 . They use a vehicle spray-painting chamber/oven, complete with filtered air etc. We had our Enterprise done a couple of years ago – immaculate finish then and now.

    #6352
    Fantasia
    Member

    An alternative to the brush is to use the mini foam rollers from DIY stores and use a new roller for each application, which saves cleaning with all those horrible solvents and the risk of contamination for the next coat.

    I agree with thinning the two part polyurethane paint and I use the same technique for two pack varnish too. It gives a very even spray-like finish.

    #6356
    Laurie
    Member

    Thanks everyone for the help. I am just about to get dirty with the sander. A quick query, should I remove the wood rubbing strip or leave in place masking off when it comes to paint?.

    Laurie

    #6359
    W10143
    Member

    Laurie

    When I painted my old GRP MkII I removed then later replaced the rubbing strake – the less masking the better!

    David

    #6371
    Swiebertje
    Participant

    One more tip to avoid the dreaded “orange skin” effect:

    Make sure the hull is perfectly dry before you start painting. A good and fast way to dry the hull is having it upside down, optionally on saw horses. Then place a small, 25 watt lightbulb under it and leave it on for a few weeks. The heat produced by the lightbulb is just enough to dry the hull. And don’t worry about isolating, hot air rises up.

    Don’t think this is a woody issue only, while a woody may be successfully painted with some moisture left in the wood, a GPR boat in particular must be absolutely dry! The more you sand the easier it gets to dry the boat. So, sand as soon as possible but postpone painting until just before the sailing season starts to allow maximum drying time (or power dry using a light bulb).

    A light bulb also helps if you are painting in an unheated environment and the temperature is slightly below the optimum for the paint (usually 18C). A friend of mine successfully painted his boat just above 14C using the light bulb method.

    #6372
    Laurie
    Member

    Thanks for all the tips. I have turned the hull upside down onto some tyres covered in thick plastic sheeting. you mentioned supporting the hull on saw horses, I take it that four normal sized ones would support it ok or would six be better?, as the tyres are a bit low to work on.

    Thanks.

    Laurie

    #6373

    HI

    being a bit short on enough saw horses, we bought 3 big bales of ?peat (not real peat) put them into large black bin bags to make sure they were dry against the boat, and turned the boat over onto them (2 at the stern and one under the bow.

    There was even room to get underneath

    #6374
    Laurie
    Member

    Margaret

    Thanks for the advice. I wouldn’t call you the idiot at the front, without you in front the person at the back might not be able to go sailing at all !!.

    Laurie

    #6375

    Hi

    oh blimey – we are not in the front of the fleet, I am the idiot (crew) in the front of the boat !!!!!- son (and helm) is the monkey on the stick so he takes the blame 😆

    #6376
    Swiebertje
    Participant

    @Laurie wrote:

    Thanks for all the tips. I have turned the hull upside down onto some tyres covered in thick plastic sheeting. you mentioned supporting the hull on saw horses, I take it that four normal sized ones would support it ok or would six be better?, as the tyres are a bit low to work on.

    What is a “normal saw horse”?

    I made mine from some left over timber and beams and they are up to the job. Obviously you don’t want an unstable construction but something you can work on safely. I also connected the saw horses with some nails and timber to stabilize them and fix them in to position, similar to what a mason does with his scaffolding. With little effort and some ingenuity (read: nails & timber) you should be able to create a stable platform that fixes the boat safely in position. Good prep makes the job easy.

    Don’t hesitate to put a saw to the legs of the horses or lift them with wedges to level the boat. If the boat is level several jobs are much easier. For example painting a waterline or, what I particularly like, a contrasting color below the waterline.

    #6380
    Laurie
    Member

    Thanks everyone for the help. I have begun to sand the blue off, and it must be single pot as it is coming off nicely. A few days of this and she will be ready for a new coat (when the temperature is enough to put the paint on).

    Laurie

    #6381

    If the boat is already inside but in a cold space, it is worth making a “tent” from heavy duty plastic sheeting. Especially if you make this in two layers to make some rudimentary double glazing you then have a space that is easy to heat, and easier to keep dust free. You must be able to ventilate to get rid of any water vapour.

    This is also useful when do major gluing or resin work.

    I used to race against a crew that stored their boat (a First Class 8) in a greenhouse. The boat was always bone dry and light.

    Gordon

    #6382
    Colin Parkstone
    Participant

    I used to race against a guy who put his Wayfarer in the roof of a big hanger next to the heater.

    Was fun at the start of the season when we used to see him bailing alot as the boat had not plimed up yet and lots of the seams had been opened by to much heat.

    Ones they stopped bailing we did not see them for “Fag Smoke”

    Parkstone joke!!!

    Happy Sanding ,also if it is sanding down that well it could be two pot as that is very hard when cured.

    CP 🙂

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