Glass cloth advice

[melidman]

Hi all i have bought some 600 gsm Triaxial Glass cloth for the outside of my hull, not having used this type of cloth before decided to cover my centerboard which has turned out with a good finish but used a lot of resin as i work in the building industry i tend to beef things up rather, that's why my model aircraft always had to have a larger engine than stated on plan. And made more of a mess when i crashed (which i was fairly good at)
Have i done it again would a lighter cloth have done ok ?
does a biaxial cloth use less resin ?
also i have made my rudder blade out of teak what's the best way of removing oil of teak before applying epoxy ?
i was thinking a wipe with thinners

[Jeremy]

600g cloth is very heavy, most small boats would use 300g woven, either plain weave, or, if the hull has complex curves, twill weave.  Most people get away with using 300g plain weave, as it's easy to wet out, gives a nice smooth finish and is generally flexible enough to accommodate most 3D curves OK.  The general rule is that the weight of epoxy should equal the weight of the cloth, so for 300g cloth each square metre should have around 300g of resin.  In practice more resin is needed to fill the weave, although adding resin like this actually reduces the strength.

My personal preference is to squeegee the resin to around a 40% ratio (40% weight of resin to weight of cloth), using polyester cloth overlaid on the glass as a peel ply layer.  It needs a fair bit of work to get the resin out of the cloth to get the best ratio, but is worth it, as the result is a light, strong and smooth surface, almost ready for paint.  

Assuming that you are going to paint, rather than varnish, then it's best to use a lightweight filler next, rather then more epoxy.  Once the lay up has fully cured, remove the peel ply and very lightly sand.  The next stage is to use some 410 microlight filler, added to epoxy and mixed so that it is stiff enough to stand up on it's own without slumping (adding a small amount of colloidal silica will stiffen it up, but make it slightly harder to finish sand).  Apply an extremely thin layer of filler, using a wide squeegee (the yellow plastic ones that West sell are excellent).  The aim is to get just enough microlight on the hull to fill the weave, no more.

Once this has cured you'll find that it is very easy to sand the microlight to a very smooth finish.  It's my favourite filler by far, as it is extremely easy to fair with very little effort.

If you want a clear finish, then you can use unadulterated epoxy to fill the weave, at the expense of slightly reduced stength.  This is best applied with a foam roller, rather than a brush, as it's easier to get an even coat this way.  Some epoxies are easier than others to use for this, I've found that SP epoxy is a little bit too thin, but West seems to work well.

Jeremy

[melidman]

Wow that's comprehensive advice and I thank you for it, so I have got 10 Meters of 600 gram cloth surplus . I must say that the centerboard is very rigid and will use the 600 gram cloth on my rudder blade

Sent from my Windows Phone

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From: Jeremy [via UK HBBR Forum]
Sent: 19 May 2011 07:11 PM
To: melidman
Subject: Re: Glass cloth advice

600g cloth is very heavy, most small boats would use 300g woven, either plain weave, or, if the hull has complex curves, twill weave.  Most people get away with using 300g plain weave, as it's easy to wet out, gives a nice smooth finish and is generally flexible enough to accommodate most 3D curves OK.  The general rule is that the weight of epoxy should equal the weight of the cloth, so for 300g cloth each square metre should have around 300g of resin.  In practice more resin is needed to fill the weave, although adding resin like this actually reduces the strength.

My personal preference is to squeegee the resin to around a 40% ratio (40% weight of resin to weight of cloth), using polyester cloth overlaid on the glass as a peel ply layer.  It needs a fair bit of work to get the resin out of the cloth to get the best ratio, but is worth it, as the result is a light, strong and smooth surface, almost ready for paint.  

Assuming that you are going to paint, rather than varnish, then it's best to use a lightweight filler next, rather then more epoxy.  Once the lay up has fully cured, remove the peel ply and very lightly sand.  The next stage is to use some 410 microlight filler, added to epoxy and mixed so that it is stiff enough to stand up on it's own without slumping (adding a small amount of colloidal silica will stiffen it up, but make it slightly harder to finish sand).  Apply an extremely thin layer of filler, using a wide squeegee (the yellow plastic ones that West sell are excellent).  The aim is to get just enough microlight on the hull to fill the weave, no more.

Once this has cured you'll find that it is very easy to sand the microlight to a very smooth finish.  It's my favourite filler by far, as it is extremely easy to fair with very little effort.

If you want a clear finish, then you can use unadulterated epoxy to fill the weave, at the expense of slightly reduced stength.  This is best applied with a foam roller, rather than a brush, as it's easier to get an even coat this way.  Some epoxies are easier than others to use for this, I've found that SP epoxy is a little bit too thin, but West seems to work well.

Jeremy

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[Port-Na-Storm]

Hi,
Of course I agree with everything Jeremy has said.

I have used biaxial cloth on centre-boards and rudder blades, its fairly bomb proof but I think its over kill for hulls. Unless you're building an icebreaker. I just wet it out and then fill the weave with a thin layer of fairing compound, followed up with a buffing from the orbital sander.

Having said all that if I was making a rudder blade out of Teak I wouldn't want to cover it in glass of any type.

I'd just oil it and admire the grain.

cheers
Graham  

[melidman]

Yeh the teak was given to me and it was in thin strips of differing colours so does not look that good I could always clearcoat of varnish to look more natural

Sent from my Windows Phone

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From: Port-Na-Storm [via UK HBBR Forum]
Sent: 19 May 2011 09:21 PM
To: melidman
Subject: Re: Glass cloth advice

Hi,
Of course I agree with everything Jeremy has said.

I have used biaxial cloth on centre-boards and rudder blades, its fairly bomb proof but I think its over kill for hulls. Unless you're building an icebreaker. I just wet it out and then fill the weave with a thin layer of fairing compound, followed up with a buffing from the orbital sander.

Having said all that if I was making a rudder blade out of Teak I wouldn't want to cover it in glass of any type.

I'd just oil it and admire the grain.

cheers
Graham  

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[Michael Rogers]

Hi Jeremy

Apologies for not quite following one part of your May 19 post, particularly as others obviously do! When you've got a moment, could you amplify a bit the technique you describe in the second para. How exactly do you go about achieving this 40% business, and could you explain your use of polyester fabric as peel ply - is this the stuff sold as peel ply by West Systems and the like?

I should perhaps explain that I shall shortly be doing a lot of this sort of epoxying as I start work on my Swallowboats Trouper 12. However I had to go into hospital to have some entrails removed, which has put back my sailing and boatbuilding plans for the summer. I'm actually making excellent progress with recovery, but at present I'm feeling constrained and a bit frustrated, so I'm prowling round various forums (?fora?), such as this one, to enjoy a bit of 'vicarious' boatbuilding and hopefully benefit from the expertise of experts such as yourself.

[Jeremy]

Hi Michael,

First off, peel ply is just thin polyester fabric.  You can buy the stuff from composite suppliers but I use off cuts of aircraft covering fabric that I've collected over the years.  You can probably just buy the stuff on ebay, what you're after is lightweight plain weave polyester cloth, the sort of stuff used to make cheap (and nasty) shirts many years ago.  I've heard of people using old nylon sheets, although I've never tried it.  The important thing is that the fabric has to be 100% synthetic, so that it's both strong and doesn't bond well to epoxy resin.

The way you use it is to wet out the glass cloth with resin, as normal then lay the peel ply carefully over the top.  Next, starting from somewhere near the middle you use a squeegee (West sell nice big yellow ones) you work the excess resin out towards the edges.  The peel ply tend to stop air getting back into the glass cloth and helps to stop it floating up; as you push the excess resin out the peel ply wets out and sticks down to the surface.  At the edges you will need to wipe away the excess resin.  For awkward curves, the application of very gentle heat from a hair drier sometimes helps to both make the resin less viscous and easier to work and softens the peel ply a little so that it conforms more easily to the shape, but you may need to cut darts in the peel ply or add extra bits to cover any awkward areas.  I've found that you can happily overlap peel ply and still get a good result.

When the resin has cured, you grab the peel ply and give it a good strong pull.  It will tear away from the surface, leaving a faint imprint of the weave of the peel ply, which is finer than the glass cloth weave and much easier to fill and fair.  It also leaves the resin surface free from contaminants, like amines from curing, as these will all be left on the surface of the peel ply.

As an alternative to peel ply for seam taping, I've seen thin strips of vinyl plastic sheet used.  The technique is to put masking tape either side of the area where the glass tape is going to go, lay the glass tape and resin as normal between the masking tape lines, then lay and tape the plastic strip over the top, leaving the ends untaped.  The excess resin is then carefully squeegeed out towards the ends, using a soft rubber squeegee that conforms to the desired curve, leaving nice smoothly taped internal joints that need only minimal sanding afterwards.

I hope the bit of "entrail removal" goes OK and that you're back building again soon.

Jeremy