How difficult actually is it.......

jonathankent

jonathankent

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........ to do GRP work yourself?

The GRP covering across 2 of my cross members in the hull has cracked, and so needs renewing. Now I have never worked with GRP, but, it looks as if the old GRP needs removing and sanding back before applying the new on top. Is it that easy, or do you need to have some knowhow. The boat yard has quoted over £300 to do this work, which at first thoughts I think is rather a lot, and so if it isn't too much work/difficult I could attempt it myself.

Your experiences and advice would be much appreciated.
 
Working with GRP is easy! do let anyone kid you otherwise. Wear a mask, gloves and goggles, not too cold a day, grind it back, soften lightly with styrene, and laminate away. When finished shower in tepid, not hot water, and admire finished job
 
Why shower in tepid water? Judging by some of the crustaceans in our local yards real boatbuilders don't wash!!

In reply to the original post, go for it. It's just a confidence thing. Don't bother trying to hand sand, a disc in an angle grinder (aka power adze) makes it so much easier, but be careful. Materials are cheap enough & if you're not happy, grind it out and do it again.

My first efforts were stitch & taping a dinghy. Second job was new engine bearers and the iron tops'l hasn't fallen out yet! In the words immortalised by a certain sportsware company, Just do it!
 
G'day Jonathan,

Well it's not rocket science, just make sure you clean the area before you start grinding, this will help reduce spreading any contaminants with the grinder, then clean again with some Acetone just prior to applying.

I use a grinding disc designed to grind concrete, it takes less time and makes less dust as the particles removed are larger. Make sure you have a generous radius on all outer corners, this will make glassing easier.

Pre cut all the glass, each strip should be about an inch wider than the one before it. You will need 5 or 6 layers, this will speed the lay up and avoid the risk of resin curing before you can apply it. Mix resin in large containers so it's very shallow, this help prevent heating and premature curing in the pot.

You will need a good quality respirator, a grinder, Acetone, a small steel slotted roller to roll the resin out, a box of latex examination gloves, masking tape and a stack of drop sheets to cover everything inside the boat because your going to make a lot of dust.

I would use an epoxy resin and a cloth designed for epoxy around 250 grams and top this with a 50 to 100 gram roving to give a neat finish and ensure no ends are exposed.

After curing wash with fresh water and a plastic kitchen scourer till water no longer forms beads, then apply 3 or 4 coats of resin wet on tacky. when this cured, lightly sand to remove the gloss prior to painting.

Avagoodweekwnd......
 
If you shower in hot water the pores open and the glass dust gets in. You will then itch for days.
This is allmost the first thing the youth is told on starting . The first of course is making the tea. /forums/images/graemlins/smile.gif
 
A very hot shower in the morning and pad dry( not wipe), then dust wrists, neck, belt line, ankles and any other area that may be exposed with plenty of talk. This gets into the pores of your skin now open because of the heat, they close as you cool off trapping the talc.

The talc helps stop fibres getting in, another very hot shower at the end of the day will flush the talc and any fibres.

When doing some heavy duty grinding I add tape around wrists, neck and ankles and use throw away paper overalls.

Avagoodweekend......
 
Yes, another way round the problem.I concurr with paper overalls and taped holes. Allways use a good mask, the best you can afford.
I've found grinding and laminating carbon even worse as the dust is even finer. It not only gets in to your skin it also gets into the power tool and shorts thrm out!!
 
All this information may be too much for the original poster and put him off, he's only doing a little repair which by the sound of it will not warrant carbonfibre, endless showers, respirators et al.
 
Have you worked out why its cracked? is the bit overstressed,before just slapping on more stuff see if you can improve the design.....apart from that get lot of acetone and several cheap buckets,personally if a lot of grinding is needed i woul pay the 3oo quid!
 
A good resin proof barrier cream is essential.
Be careful with mixing resin and catalyst, and do not listen to anyone who tells you to bung in more catalyst. It should be between 1 and 2 percent by volume, depending on ambient temperature. (I once made a mistake and added 0.2%, and it still went off in the end. Did not use it) It is often easier to wet out the mat, up to three layers 600gm, on a sheet of gash ply or plastic, and carry it to the job rather than trying to wet out a difficult shape. Thicker goes off quicker, and you will find resin in the bucket goes off before resin on the work, so that's a warning to get finished. No more than 3x600, it may get too hot.
 
respirators/good face mask are essential for working with GRP, as the dust once breathed in will not go away and will not break down.
 
Cracked hull members

I had the same problem with my Fulmar, a previous owner had tried to glass over the cracks, which then opened up again and let the hull push inwards aft of the keel.

Probably worth looking into why the cracks have appeared, and check that the hull has not also deformed inwards (I had corresponding cracks on the outside of the hull too, and a big flat section of GRP where the curve of the hull was pushed in by the weight of the vessel on the keel).

If you have the same trouble I had she'll need the cross members cutting out entirely, with repairs inside and outside of the hull, and she needs to be suspended in slings with the weight off the keel when the work is done (or the hull ends up repaired in a permanently deformed shape).

Good luck,

Andy.
 
Re: Cracked hull members

Nah, you dont need to make loads of dust with a grinder. A lot can be done with ordinary woodworking tools. A big sharp chisel and a heavy mallet works really well!

Chainsaw is good for bigger jobs.
 
All the yard was going to do was remove the existing and replace with new, only making it wider to give extra support. They didn't say there was any substantial damage, and there isn't any damage to the actual hull.

It doesn't sound as if it is quite as straight forward as I thought, and hadn't realised the H&S implications. I would like to give it a go, and learn something, but maybe on something a little smaller first. I might try to get a better quote.

Thanks to all for your help/advice.
 
A good mask not only for dust but also gases is not too expensive but nevertheless a must! Polyester as well as epoxy spreads styrene gas when curing and this is carcinogenous (gives you cancer). The protection of hands etc. is not so much for the health hazards of grp, but if you need to wash afterwards you'll use acetone which opens the pores, dries them out and open to dust, glassfibres and germs. And to add to it, the gas from Acetone is also hazardous to your health.

This is not intended to scare anyone, just to remind to use precautionary measures. In the industry, most plants nowadays use active air renewal and filtering whenever people get exposure to resins. The ones that don't, expose themselves to lawsuits as the dangers are well known and proven. In the marine business this is often the case and people do get sick from it.

But doing this work in summer does get awfully hot inside all this protective clothing! The best companies therefore install air purification as well as airco in the workspace.
Victor
 
I think some of the contributors are going a bit OTT here. It's not a big deal but you would certainly be right to try a simple off-the-boat job first. Maybe find a couple of bits of scrap GRP to practice on.

For advice on how to use glass/polyester, contact Glaspiles of Southport and ask them to send their catalogue and info sheets.

Here are a few tips from an old hand (5 40-foot hulls built to date)

- Use a 4.5" angle grinder with a 24-grit sanding disc. It cuts well and follows the surface much better than a rigid grinding disc.

- Chopped strand mat is adequate as reinforcement as long as you squeeze out excess resin with a finned roller but if you can get it, use bi-directional fabric, laid so that the fibres cross any angles at 45°. Bigger GRP suppliers should be able to sell you small quantities (it comes on 50Kg rolls!).

- In easy-to-reach areas you can paint a bit of resin on the surface, lay some glass into it then apply more resin but the following method is great for awkward spots like underneath decks etc. - Get a piece of polythene sheet a bit bigger than the area to be covered. Build up your laminate with glass and resin onto the polythene on a flat surface. Apply the laminate to the area to be patched and squeegee any bubbles & excess resin out of the edges. The polythene will peel off easily once the resin is fully set.
 
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