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Fiberglass Patching


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Buy some

Polyester resin

Fibreglass matting


Talc powder



Paint brushes


Clean the surface where the hole is and remove any loose bits

Roughen up the area with the sandpaper so that the fibre glass will stick

Bog up the hole so the hole is almost flush

Tear the fibreglass into desired sizes

Mix the resin with a bit of talc powder so that it give the resin a bit of strength

Then add the catalyst to resin (IMPORTANT: The mixing ratio of catalyst to Polyester resin is between 1 and 4% of. resin volume. For example, 100mls of Polyester resin will require 1-4mls)

Mix the resin thoroughly or it won’t set properly

On an old piece of cardboard paint the resin onto the fibreglass matt (both sides) till it has soaked through.

Then apply it to the desired spot

Add multiple layers depending on the size of the hole

Roll with the roller to get any air bubbles out and wait for it to dry

Be sure to not do to many layers on the boat as it will fall off because of the weight when drying

When it is dry sand the edges so that it is flush and won’t create unnecessary resistance when in the water

Give it a coat of paint if you want

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Thanks mate, just with all the things I need. I saw the fiberglass repair kit from Bias, I wonder if anyone has personally bought that kit and used it and is it any good?

Good idea to do everything in a ventilated area and wear a mask and gloves dont get the fibreglass on your or you will itch for days and days.



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Hi groperman,

Just like justin-fish said.

the repair kits are good for small jobs, they don't come with bog,

you need to plug hole , some use card board to hold cloth , then do other side, but you need it solid,I always

use gel coat to finish, makes it watertight.

make sure you are not in confined space, resin can give you one hell of a headache.

you can buy small quanities of resin and cloth, they are not that dear.

If your still not sure, look up fibreglass or gel coat on the web and they will run through it with you.

cheers Rick.

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I use dynal cloth rather than chopped mat, and as per the article, I use microballoons mixed with the resin for a filler. Have been using these materials for years and find that the dynal cloth retains it's integrity and strength above the chopped strand. Equally, the resin / microballoon mix tends to have more "flexibility" over the Epifillers or Auto Putty and thus is more likely to retain its integrity where other fillers are too rigid and can crack or "lift" out. If you have seen body filler (bog) on motor vehicles when it cracks or "lifts" off the surface you will understand my point.

Following is a detailed article on how to repair.

Fiberglass boats are built by laminating layers of woven glass cloth or matt with a liquid resin of polyester or epoxy. The resin then hardens as it cures with a chemical catalyst and the resin saturated cloth becomes a solid structure. Repairing a damaged fiberglass surface or structure involves some of the same processes used in building the boat when it was new. The advantage the builder of the new boat has is that he or she is working with a mold that predetermines the shape of the fiberglass structure that results when the resin that is saturating the fiberglass cloth laminate layers becomes hard. When you are repairing a damaged boat hull, you won’t have the aid of this mold and will have to improvise a way to maintain the proper shape.

Let’s look at what’s involved by taking the worst-case scenario: a hole the size of a baseball right in the bottom of your boat. This repair will require some creative thought as to how to begin. If it is a large boat, on a trailer or dry-docked in a boat yard and too heavy to easily flip over to work on it upside down; you will begin such a repair by glassing from the inside of the hull first. Fiberglass resin, whether epoxy or polyester, does not adhere to smooth plastic, such as visquine, which is sold by the roll in your local hardware store. You can use this material to your advantage by taping a piece of it over the outside of the hole in the hull with masking tape, thus sealing the damaged area so that the liquid resin you apply from the inside will not pour out of the hole.

For new fiberglass and resin to bond to the existing structure of your hull, you must first grind or sand away the finish on the old fiberglass to get rid of the Gelcoat, paint or any wax that might be on the surface. Working inside the boat, grind the area around the hull using a powerful orbital sander or angle grinder, then vacuum up the dust and wipe down the surface with denatured alcohol. Now, if the outside of the hole is sealed with plastic as described above, your are ready to laminate new layers of glass from the inside. Cut a piece of the fiberglass cloth slightly larger than the hole, and completely saturated it with resin mixed according to the instructions on the container. Lay this piece of cloth in position over the hole, and then cut a larger piece that will overlap the edges of this first piece and likewise, wet it out with resin and lay it in position. You may need 3 or more such pieces, each larger than the previous, covering the hole and the underlying layers. Wait several hours for the resin to harden, then remove the plastic from the outside of the hole and repeat these same steps working from the outside of the hole.

Before laminating on layers of cloth from the outside, you may have to mix up some resin thickened with fiberglass microballoons fill the cavity and allow you to fair the damaged edges of the hole by sanding the resin when it cures. The fiberglass cloth you put on from the outside will bond to the layers you put on from the inside, and by applying enough layers, you will build up the fiberglass to thickness equal to that of the rest of the hull.

The final steps are to sand the new layers of fiberglass until the repair blends in with the rest of the hull, both inside and outside of the boat. It may be necessary to apply more resin thickened with microballoons, or even more layers of fiberglass cloth to achieve the final, perfect finish.

This type of repair, of a hole all the way through the hull is the most difficult. Many times, the damage you need to repair will be less severe and can be fixed from one side only. A working knowledge of fiberglass laminating techniques can save boat owners a lot of money when a boat is damaged. Fiberglass work is very forgiving and mistakes can be rectified by simply grinding away and starting over, so learning how to do it is highly recommended for all boat owners.

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If it is your pride and joy and you like it to look pretty beware trying such a large hole as your first go so it might be worth getting someone professional to do it especially if you don't already have the stuff lying around. Can be a mongrel to match and blend in some colours and I look at a few of my average attempts a few years on and just close my eyes - yeah they are strong but not pretty an take away from the value of the boat. A photo might help as unless it is a clean punched through hole you may have other damage around it and be doing a larger area than you first might think as glass flexes a lot before you get a hole and you may have to reinforce a larger area..

If you are insured are you sure this isn't covered?

After years of dealing with yachts one thing I know is that gelcoat isn't waterproof ( fibreglass and resin is ) unless the new ones are better. It is pretty good but it's main purpose was to add a colour layer, smooth polishable surface and protect resin and glass fibe from UV rays that used to break them down.

Edited by pelican
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All the above.

Pelicans right, if its your first time get some one who has done it before to do it for you.

Those kits are basic and dont have the right quantities you require.

Are you local to the innerwest? if so I could have a look at it for you.

Dont use car bog..........its crap.

Build glass sheets up, mix of mesh and loosethread. Mesh on the outside, let dry then build with loodse thread with the resin mixed with a proper glass resin expander then mesh on the out side.

Make sure before doing anyglass you sand the edges of the hole on both sides so the edges come to a point. This will make sure the new glass grabs hold of the old glass and when you sand to smooth it up new overlaps old, on both sides. GOOD HOLD.

Then prime, gelcoat,paint. This will seal from water.

Good idea to do this on both sides(does not have to be pretty onthe inside). Hardware have all the things you need, so does whitworths or bias.

Good luck and pm me if you need more help or to come and have alook at it for you. :thumbup:

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Yup I had a mate to come out and help me out cause he has done it before, the end result was good except i got the wrong colour so the colour was abit lighter. I'll show you guys some photos with the before and after shot.

Good on ya mate, well done.

Its not hard once you have seen it done once. :beersmile:

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