What glass to use for keel repairs?

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m1nder

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Further to my Norman 17 restoration, I had to take out the old side keels as the grp had delaminated and the timbers were rotten. I will soon be refitting them and will need to glass them in.

I am using EPOXY resin and so far for repairs etc, I have been using woven coving which is compatible. But when it comes to tight cornering and wrapping around timber etc, I am wondering what glass cloth to use? I can't use chopped strand matt as it's coated for polyester, the woven coving seems a bit heavy to go around tight corners so I am wondering what to use?
 
Woven roving is very old hat these days as the weave means the density of glass is less than optimal. You should use a stitched bi-axial fabric where the warp and weft are not interwoven but laid flat and held together by very light stitching. When laminating over a sharp angle the glass should be laid so it crosses the join at 45° so the strands don't have to turn through a right angle. The best material I have come across for post-cure bonding is a biaxial with a thin layer of CSM on one side.

I dispute the necessity of using epoxy in these circumstances and have built my boat using prefabricated panels joined by strips of fabric using polyester but if you insist on spending the considerable extra for epoxy your best plan is to lay up the patch on a piece of heavy gauge polythene, slap it on then squeegee out bubbles and excess resin and peel off the polythene when the resin has cured.

Biaxial fabrics
Combination mats
 
snowleopard said:
Woven roving is very old hat these days as the weave means the density of glass is less than optimal. You should use a stitched bi-axial fabric where the warp and weft are not interwoven but laid flat and held together by very light stitching. When laminating over a sharp angle the glass should be laid so it crosses the join at 45° so the strands don't have to turn through a right angle. The best material I have come across for post-cure bonding is a biaxial with a thin layer of CSM on one side.

I dispute the necessity of using epoxy in these circumstances and have built my boat using prefabricated panels joined by strips of fabric using polyester but if you insist on spending the considerable extra for epoxy your best plan is to lay up the patch on a piece of heavy gauge polythene, slap it on then squeegee out bubbles and excess resin and peel off the polythene when the resin has cured.

Biaxial fabrics
Combination mats
Click to expand...

So Bi-axial is the way to go then? The Epoxy is already bought and paid for so that's that!

WRT your last paragraph, I dont understand what you mean by laying up on polythene?

I have timber side keels protruding from the underside of the boat. They are approx 50x100x1020mm. I will glue these in with sikaflex. Then I need to glass over them.
 
You can save a lot of effort and material for fairing if you do use a top layer of CSM but if your resin is epoxy it should be powder bound as the resin bound mat is unsuitable. Most suppliers inc. CFS sell powder bound CSM for this purpose. The main advantage of epoxy is in adhesion, I repaired a friends small motorboat recently that had previously been repaired with layers of polyester where it had been worn when beaching, admittedly it had been done before without proper preparation, and the whole lot peeled away once I got a scraper under one corner.
 
m1nder said:
So Bi-axial is the way to go then? The Epoxy is already bought and paid for so that's that!

WRT your last paragraph, I dont understand what you mean by laying up on polythene?

I have timber side keels protruding from the underside of the boat. They are approx 50x100x1020mm. I will glue these in with sikaflex. Then I need to glass over them.
Click to expand...

G'day Minder,

"WRT last paragraph," this refers to laying out precut sections of cloth and wetting them out, then picking up the whole lot and applying it as required. You can use a sheet of glass or any other material that epoxy does not react with.

By laying biaxial (crows foot) along a corner rather than across the corner the stitching and fabric will form better.

Points to remember:
Epoxy will stick to timber and form a strong bond, poly resins will not last long term.

Epoxy will stick to old poly resin and form a strong bond, poly resin will not bond as well as epoxy to old poly resin.

Any timber having epoxy applied over it MUST be very dry and rot free, or you will seal in problems that will come back and bight you.

The ratio of resin to cloth by weight for epoxy is close to one to one. Poly resin and CSM needs a ration of 3 resin to one mat.

Mix resins in small batches, use wide shallow containers, the more surface area the better to avoid resin heating.

Adding extra epoxy resin will weaken the finished product.

You can thin epoxy resin if you want it to penetrate timber by adding up to 30% by volume of Methylated Spirits.

Always clean up with Acetone and put any is contaminated into a sealed container like a glass jar, leave it overnight, the contamination will settle and you can recover the clean portion.

Always use surgical / latex cloves, put 2 pairs on, you can slip one off when things get sticky.

Good luck. :)
 
Thanks all for the replies

The only place I can find biaxial is CFS in UK. The smallest applicable amount they sell was costing £37 quid, then I got to the checkout where they wanted £28 for delivery. After you convert it all into Euros, it's just too much for the job in hand.

I'll use the patch method described above with a few layers (3 or 4) of my 280gsm woven roving. I might cut it at 45 degrees so I get the biaxial angular benefits. I'm thinking I'll cut the pieces the same size to measure. Then get a bit of polythene, wax it up, lay the cloth on it and wet each piece through. In the meantime, I will have applied epoxy to keel/hull and let it get real tacky. Then take the patch with polythene cover on outside and apply it to keels. Roll it and use a few pinch clamps and a little light pressure etc to press it into place.
 
Fibreglass

For going into tight corners one type of cloth not mentioned is twill weave. This is a thin woven cloth where warp or weft misses 3 or 5 threads and then is woven into the next. It is a bit hard to describe but has a peculiar look. It is designed to bend easily into corners. Of course thinner cloth with more layers works best. As said cut and lay the cloth so threads are at 45 degrees to the bend. ie for the keels 45 degrees from centre line and of course 45 degrees from the square edges of the cloth. Put filler into the corners so that bend radius is reduced.

Yes epoxy is essential for use on wood. Unless you use so much fibreglass and resin that the f/g can stand alone as if the wood were just a mold which can be removed. In which case delamination from wood doesn't matter. But I am sure you are not doing it that thick. good luck olewill
 
Steviecracknell said:
Snowleopard,
Did you glass repair your keel using polyester? how did the resin adhere to the fibreglass, I was told that epoxy was the safest bet, especially when laying up onto old fibreglass.
Click to expand...

No, I built the whole boat by making sandwich panels and bonding them together using combination mat. In every case the bonds were putting fresh polyester/glass onto existing cured GRP. Provided the base is abraded thoroughly (24 grit disc in angle grinder) and the glass is rolled well to remove air bubbles and voids it achieves 85% of the strength of the original in fact I find that when destruction testing a join the failure is often in the original laminate not the join.

The usual mantra is 'epoxy is a glue, polyester isn't' but it works for me and for many hundreds of boats from the same designer.
 
m1nder said:
...get a bit of polythene, wax it up, lay the cloth on it and wet each piece through. In the meantime, I will have applied epoxy to keel/hull and let it get real tacky. Then take the patch with polythene cover on outside and apply it to keels. Roll it and use a few pinch clamps and a little light pressure etc to press it into place.
Click to expand...

Good plan but a couple of pointers-

Don't wax the polythene. It will peel off just fine. If it won't come off clean you are being too impatient. Once the resin is cured it will come off easily.

DON'T 'wait for it to get tacky'. You must assemble the laminate BEFORE it starts to cure. It's not like e.g. Evostik

Use a squeegee e.g. a square of stiff plastic to force the resin into the glass on the polythene then apply it straight away to the repair. Use another squeegee over the top of the polythene to force out bubbles & excess resin. The objective is to get the maximum glass to resin ratio in the laminate. Over-saturated glass is heavy and weak.
 
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