Resin:glass fibre ratio

[Romany 135]

 I've been advised by the product supplier (not a Burnsco/NZ Fibreglass type retailer) that the ratio is roughly 1:1 ;I.e. resin weight/m2 = matting weight - so, using 290gsm woven cloth u would expect to use approx same in mixed resin per m2. 

Maybe a liddle bit more to account for soakage, but user based f*ck ups like leaving it in the sun. Doh.

Last week i did some glass on my cockpit floor, which has had the old cork/resin non skid over the top of glass sanded right back to almost fly sh*t thickness, and allowing for the solar issue, I reckon i used 1.5 times that weight of resin.

Theories being good and all that, does anybody have an opinion to offer which is based on practical experience?

[Psyche 454]

When I do wet epoxy layups I weigh the cloth and mix up the same weight of resin, and it works out as a pretty good rule of thumb to avoid wastage and get good coverage etc. Generally you want less resin more (fully wetted)glass. Using more resin is expensive and doesnt add strength, but on a cockpit floor it doesnt matter 

[alibaba 59]

I can supply some information here, as my son did an experiment as part of a class Science project. He used West System, which is nominally 5:1 ratio of resin to hardener. He then glued standard butt joints together with varying mixes, ranging from 1:1 to 10:1 ratios, and then measured the breaking point of the joints.

To my surprise, there was little difference until the ratios were well away from the norm. All joints from 3:1 to 8:1 were of equivalent strength. I think that there is a fair amount of leeway built in for us.

Of course, I have no idea how the ratios would pan out over time or indeed with exposure to the elements, particularly u/v.

I don't think you should be too concerned if you are slightly out.

[Gappy 9]

1 hour ago, alibaba said:

I can supply some information here, as my son did an experiment as part of a class Science project. He used West System, which is nominally 5:1 ratio of resin to hardener. He then glued standard butt joints together with varying mixes, ranging from 1:1 to 10:1 ratios, and then measured the breaking point of the joints.

To my surprise, there was little difference until the ratios were well away from the norm. All joints from 3:1 to 8:1 were of equivalent strength. I think that there is a fair amount of leeway built in for us.

Of course, I have no idea how the ratios would pan out over time or indeed with exposure to the elements, particularly u/v.

I don't think you should be too concerned if you are slightly out.

Sorry It's not what he's talking about he's talking about once the resin is mixed is the weight ratio of resin to glass so if you have one square meter of 200gram glass you should use around 200grams of resin. 

But if you are using chopstrand that ratio doubles the 1 to 1 ratio tends to only apply to woven and double bias clothes.

[Guest 26]

1:1 is diy standard hand laid , quite achievable as long as you are methodical. 
If substrate is porous, prime it with a fast mix and let tack off.

Divide resin up to layers. Disc rolling the each layer. First layer slightly more than 1:1 so by the the time it fully wets out you have enough to wet the underside of the next. Don’t frantically squeegee/roll, let the resin do the wetting out- even distributed resin is key. Size mix on what you can distribute for panel size without pot exotherm. Use appropriate hardener for ambient temp to give yourself time.
Peelply last layer to get any excess resin on top to be removed with Pp. who likes sanding? Wet on wet or tacky is always better, if you can. Kevlar and carbon are a little more difficult to judge saturation owing to colour/permeability. So more care required or best bagged.

On west mix ratios. I go up to 6.25:1 for a more flexible application. Peel, tensile and compression characteristics suffer tho. Can’t quantify as did Alibaba. Never use less than 5:1 owing to free amine. No reason to be careless with ratios if you are organised  especially if you expect component to perform optimally. Nice to know that you did it right when shf.

And glass over raw ply, hot coat on temp cooling cycle not reverse. Outgassing!

Sorry bit OTT. Memory lane and no brakes.

. Btw,CHopped strand is for swimming pools and compost bins….

 

[Romany 135]

Thanks for replies. Yesterday i did more and 1:1 is about right so I'm going with beginners luck or lack thereof, as the reason i used too much.

Another question for those of u who know... i watched a boat builder who is working elsewhere in the yard, and was intrigued/impressed to see him do a fibreglass layer on now ply, and then 2 or 3 hours later apply fairing to that same area.. no sanding! That made sense to me cos it seems that freshly laid fibreglass prior to final cure is the ultimate surface to receive fairing. Is that common practice or just a cunning old fox at work?

[Romany 135]

..new ply...

[Ex Machina 283]

9 hours ago, Guest said:

Btw,CHopped strand is for swimming pools and compost bins….

 

And Aussies 

[Psyche 454]

You want to see the weave on the glass, a beginners mistake is to try and fill it with resin or make it look smooth. As mentioned try and use peel ply as much as possible.  When I havent used peel ply, as soon as its gone off enough not to move around, Ive faired it because it saves time and no blush issues.

[Romany 135]

Oh well i better bust out my 16 grit discs

[waikiore 300]

Guest has nailed it and unless in very moist/cold conditions you can fair as Psyche says.

[SloopJohnB 314]

Something buried deep in my computer.

[aardvarkash10 820]

11 hours ago, SloopJohnB said:

Something buried deep in my computer.

pounds feet and inches!

Was the original on papyrus?

[waikiore 300]

It is still that way across the pacific.....

[SloopJohnB 314]

That's why I said I had to dig deep into the computer, sorry the human memory banks can't remember where I found this information.......... but yes I can still remember ft &  ins and pds even pennies, shillings and pounds.