Figuring the weight of glass

[cs]

Okay say you use a 10 oz cloth and roughly 3 times the weight of the glass in epoxy (can't remember where I heard that). That way you end up with 40 oz, right? Is that per square foot?

Chad

[Norman Bernstein]

Nope... I'm pretty sure it's 10 oz. per square yard.

[Columbia 112]

That's right, woven reinforcing is expressed in oz. per square yard and chopped reinforcing (mat) is per square foot. If you are ever trying to calculate the thickness of your laminate it's usually 0.001" per ounce of woven fabric but for mat it's all up to how much resin you add. At work we struggle with mat laminates that can double in thickness if an operator adds too much resin.

Ross

[cs]

Just trying to calculate weight. Is the ratio I posted above good?

Chad

[mmd]

In an ideal world, the resin-to-glass ratio for structural laminations should be around 1:2, but in practical use it is more likely to be 1:1. Being resin-rich is not a bad thing in sheathing because extra resin will create a more impermeable surface and protect the glass fibres from abrasion damage and keep moisture from wicking along the fibres. Therefore, if your cloth is 12 oz. per square yard, then to get mass per square foot, divide by nine.

12oz / 9 sq. ft. = 1.33 oz per sq. foot.

Resin will be the same weight per square foot as the cloth, so resin = 1.33 oz. per sq. foot

Total sheathing weight = 2.66 oz per sq. foot, or 0.17 lbs/sq. ft.

[ssor]

I always weigh the resin and the glass and try for 1:2 resin /glass but mix for 1:1. I hate to come-up short in the middle of a lamination. I found that to get 1:2 ratio I had to really pay attention to rolling out the air and compacting the glass especially with a mix of csm and woven layers.

[George Roberts]

I always thought that the resin:fiber ratio depended on both the fabric and weave.

For Plain weave glass the ratio is 50:50 (1:1).

For Satin weave glass the ratio is 40:60 (1:1.5).

edited to correct the numbers

[ 12-01-2005, 01:40 AM: Message edited by: George Roberts ]

[Cuyahoga Chuck]

Chad,
It depends on what you are doing.
The rule of thumb for a max strength lamination on wood is oz./sq.yd of 'glass =oz.of epoxy/sq.yd. That leaves you with an exposed weave pattern.
On an exterior lamination the weave is usually buried so a minimum of 3 coats of epoxy is required. I've never seen an estimate of weight for the fill coats. I would assume the fill coats would be somewhat less than the initial coat because the fibers of the cloth have been fully sturated.
Charlie

[ssor]

I think that if you were able to vacuum bag then you could depend on those ratios. I think that for hand layups you can never achieve the ideal. In hand layup CSM really complicates the ratios. I have found that a single layer of CSM can look starved but when I lay 24 once woven roving on top and roll it down there is enough resin to wet the roving. I can't claim comprehensive knowledge but I have used 250 yards of CSM and 120 Yards of roving, so I have some experience.

[P.I. Stazzer-Newt]

Oops, sorry - I think I was the one who came up with the "3" figure.
The assumption was twice the weight of resin that you had glass - faired and finished.
This is at best a rough guess - mmd points out that resin rich is the way to go - better than resin starved for a variety of reasons and Chuck notes that 1:1 gives the best theoretical strenghth but more resin is required for a fair finish.
If you really need a more accurate answer then you will need to know how well you can consolidate the glass and resin - so make a test panel and measure it.