grp repair

[tyce]

hi im doing my first grp repair so i am a bit of a novice to say the least,
my boat has two cracks both about 10 inch long running vertically and below the waterline.
i have cut out a bulkhead so i can get to cracks on the inside and i intend to put a patch over them on the inside and just gel goat on the outside where i have ground the cracks out, one of the cracks i have had to grind right thro the hull to remove the crack.
would this type of repair be as strong as original or at least be strong enouth for the job or i am i going about it completely wrong.
my other question is one of the cracks when i ground it, i found the fibreglass strands underneath to be dry and flaky is this bad lay up when the boat was made or is it a result of water seeping in the crack because the boat was in the water and in a state of disrepair when i bought it and had been for some time.
hope someone can help as my budget wont stretch to paying some one profesional to do it

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[Elessar]

Buy "hull and deck repair" by don casey from adlard coles nautical.
Excellent book I picked up at LBS that talks through all GRP repairs from minor to very major. Only snag is the american bias but there is a translation page at the back. Am halfway through repalcing my rotten transom and its been very helpful.
Basically I think you need to make the crack wider to feather in the patch then reinforce from behind, but don't trust me get the book.

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[the_wanderer]

Run a grinder over the inside surface about eight inches either side of the cracks and clean with acetone. Care! have plenty of ventilation - a fan or something. Vee the outside back an inch or so. lay about four layers of chopped strand mat inside over the prepared area, well stippled or rollered with the special roller for grp (not expensive). Ensure the outside veed area is filled with layers of chopped strand mat and NOT gel coat. cover the the last layer with a thin coating of gel coat and finish with fine wet and dry paper and soap.
As to the condition of the grp I cannot say without inspection but grind it back to firm material otherwise all your work and expense will be wasted.

Good luck!

Alan.

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[graham]

You mention removing a bulkhead to gain access.

This suggests that the bulkhead probably caused the cracks in the first place.

If the bulkhead is fitted tight against the hull it forms a hard spot which causes the grp to crack parrallel to the edge of the bulkhead as the hull flexes .When you refit it make the bulkhead a good 6 to 8 mm smaller all round and put foam strips or similar in the gap to hold it in place when you gl;ass it back in.

Its not a difficult job to do ,make sure it is all dry and clean before you start.Latex gloves as used by mechanics etc are good for keeping it off your hands.(I thought they would melt on contact but worked surprisingly well).

If the boat is antifouled I would use epoxy filler outside it will be stronger and more waterproof than gelcoat.

Best wishes for a good repair.

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[oldsaltoz]

G'day Tyce,

Sounds like the hull is flexing over the bulkhead, you will need to give it a bit more strength and spread the load to prevent it happening again.

I have repaired bulk head cracks as follows, some of them are now more than 12 years old and still as good as the day they were completed.

But safety first: you will need a good dust mask, not the silly little paper things, some eye protection and a good fan mounted in the companionway with the front hatch wide open: some thin rubber latex gloves will save your skin from chemical reactions and save a lot of cleaning.

Tools: lots of clean ice cream containers, resin generates heat when mixed, so a large shallow container will provide more surface area and keep the temperature down.
A small roller, about 3/8ths of an inch in diameter and perhaps 2 inches long, most are made of threaded aluminium with a wire handle.
Measuring cups or scales to measure your resin and hardener, the ratio is 4 or 5 to one depending on brand. you will only be mixing small quantities so medicine measures will do.
A grinder fitted with a 60 grit flap sanding wheel will not clog, I use a concrete grinding wheel as it lasts a lot longer.

Materials: Resin, only use Epoxy resin as this provides a chemical and mechanical bond, mush stronger than a wax (standard) resin. Also only use mat designed for epoxy resin, not chopped strand as it will hold too much resin and weaken the job, with epoxy resins you are looking for a ratio of one part resin to one part mat, standard wax resins use more like 3 parts resin to one of mat, this makes it more flexible.
Acetone: a couple of litres, used to clean the area and your tools. keep the area well ventilated and replace the lid, this stuff will evaporate very quickly.
Have plenty of clean rags handy.

Method: Start by grinding out any and all signs or cracked damaged or discoloured glass, also any dry spots, if you see a white or brown line or patch follow it with the grinder and remove it completely.

Feather your grinding so that you have an angle around 15 degrees from the bottom of the damages area to the outside, this may result in a patch a foot wide, don't worry, we will re-fill it and make it stronger.

When you have finished grinding clean the area with plenty of acetone and lots of clean rags.

Take you fibreglass mat and cut it to size, start by cutting a patch that will cover the whole area, then use it as a template to cut another patch, the same shape but smaller so that when installed the edge if the second patch will be at the same level as the edge of the first patch, I find that one to one and a half inches smaller all round is a good starting point.
Cut all your glass patches, till you set to the patch about the size of a golf ball.


You should now be ready to start glassing, but, first apply your glass to outside of the hull and aim to all but fill the crack, leaving a very small gap for filling and fairing, use a straight edge to see how close it is, and roll it to the required depth.

Note: the fibreglass will be a bit stiff to start with, but after a few rolls the resin will soak in and will be soft, so don't be in a hurry, it should look all one colour and bit transparent.

Important Note: If you lay up more than 4 layers, keep a finger on the temperature, you don't want the resin to boil as this will mean removing the lot and starting again.

After the underside has cured, progressively fill in the inside area, keeping an eye on the level, you don't want it getting thinner as it closer to the bulkhead, it should be a little thicker, about a 1/4 of an inch higher than the outside edge when finished.

Note: if for any reason you have to stop and the resin cures, you will have to wash it with fresh water and a plastic scourer till the water no longer forms beads, then give it a light sand with new 80 grit paper and carry on.

When all the glassing is finished and cured, wash it as above, when dry apply 3 coats of resin, wet on tacky application will save you more washing and sanding.

Refit the bulkhead and glass it back to the hull if was glassed in the first place, put a bead of filler around the area to be glassed so that the mat will lay on a curve rather than tight into a corner, this is stronger and easier to clean and work with.

When this has cured, give it a wash and sand and it's ready for painting, Flo-coat the inside, on the outside you will need some closed cell Micro-Balloons, fill, sand and coat with resin, 3 coats is good. if you plan to apply Gel-Coat, use a sheet of heavy plastic wedged under the bout to exclude the are and save some sanding.

Well I hope this helps, it's not a major job, just take your time, make sure you roll out most of the resin, measure the resin to hardener very carefully and you should have few if any problems; don't forget to tell us how you got on.

Avagoodweekend...



<hr width=100% size=1> Old Salt Oz /forums/images/icons/cool.gif Growing old is unavoidable. However, growing up is still optional.

 

[stephenh]

oldsaltoz - brilliant - thank you very much...

Tyce - you might find the following useful : -
Tony Staton-Bevan "Osmosis and Glassfibre yacht construction" - Adlard Coles £12.99
Wessex Resins "Fibreglass Boat Repair and maintenance" 01794 521 111 - about a fiver.
Wessex resins also do 1 day hands on repair courses for £100 or so.

good luck and watch the surrounding air temperature - don't do it next week when its freezing !

Stephen


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[tyce]

hi thanks all for taking the time to pass on all your excellent advice, i am now confident to carry on with the job, the damage was caused by the previous owner whom had fitted underated beach legs which buckled and she fell on her side, so it looks like the hull flexed in but the bulkhead stopped the flex and caused a crack and the other crack is just above a stiffening web so looks like the same problem, i am going to tackle the job after the forecast cold spell and im putting a heater in the cabin the day before so hopefully all should go to plan,
thanks again for all the advice.

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[Boathook]

I would add that you should use some professional solvent resistant gloves when using the acetone; it's nasty stuff. Latex gloves are good but can also cause skin problems with some people. If possible use vinyl ones but they seem difficult to get.
Finally, consider covering the outside of the hull where repairing in bubble wrap if it is cool to try and retain the heat

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