What resin to use?

[Jonathan Strain]

Can you get around the binder issue with epoxy by wetting both sides of the strand mat with epoxy?

 

[John Milmont]

No. You need the polyester to dissolve that binder or the mat will never lay right.
Why would you want to use epoxy on a chopped strand mat anyway? If you want a tougher, stronger resin, you could use a vinylester; but for bodywork, any high quality polyester should be more than fine!

 

[EGLITOM]

it is true that most fiberglass mats are not for epoxy but you can buy mat that is made with a binder that is compatible with epoxy resin. I have used it on many of my molds for aircraft parts. great for thickness build up on the molds. I never use it for actual parts it is not very strong and it makes very heavy parts.

what you talking about ?
To my knowledge every high strength fiber part ( carbon or glass) is made with epoxy resin. If you are looking for lightweight high strenght parts, the only way to go is using wooven mats, lay it up in the correct direction ( according your main load needs), using the correct epoxy resin ( according your temperature and shere strength needs). If one wants to have the infinite strenght to weigth ratio use prepregs, vacuum and pressure ( autoklav).

If you talk about bonding strenght. polyester is the weakest, than follows vinylester and then epoxy. All the high shere strenght glues are epoxy based.

OF course it takes more time to cure, but it will give the better parts if used correct.
We made a fairing for a BIMOTA SB9 recently. It is a rather complex mould (13 parts) but i allowed us to use epoxy, wooven mats , corefoam and vacuum it. The finaly part weighted only 1050 grams and it is of exceptional strength and stability. THe only drawback is that the bloody painter added almost the same weight in paint.

Pretty clear for home use polyester and vinylester ( you need to accelerate it, otherwise it will be sticky for a long time) is the most easiest and practical to work with. Especiallywith using vinlyester don´t forget the correct work protection.

TOM

 

[Lynn Erickson]

what you talking about ?
To my knowledge every high strength fiber part ( carbon or glass) is made with epoxy resin. If you are looking for lightweight high strenght parts, the only way to go is using wooven mats, lay it up in the correct direction ( according your main load needs), using the correct epoxy resin ( according your temperature and shere strength needs). If one wants to have the infinite strenght to weigth ratio use prepregs, vacuum and pressure ( autoklav).

If you talk about bonding strenght. polyester is the weakest, than follows vinylester and then epoxy. All the high shere strenght glues are epoxy based.

OF course it takes more time to cure, but it will give the better parts if used correct.
We made a fairing for a BIMOTA SB9 recently. It is a rather complex mould (13 parts) but i allowed us to use epoxy, wooven mats , corefoam and vacuum it. The finaly part weighted only 1050 grams and it is of exceptional strength and stability. THe only drawback is that the bloody painter added almost the same weight in paint.

Pretty clear for home use polyester and vinylester ( you need to accelerate it, otherwise it will be sticky for a long time) is the most easiest and practical to work with. Especiallywith using vinlyester don´t forget the correct work protection.

TOM

what I am talking about is chopped strand glass mat . what you are referring to we call woven fiber glass cloth. standard epoxy resin is a medium strength resin if you want high strength resin you need to use ceramic or brominated resins. there are types of polyester and vinyl ester resin that are stronger then some epoxys. vinyl ester resin is an epoxy resin and used on many aircraft structural parts. you would want to use medium promoted vinyl ester resin with MEKP as a curing agent when doing hand layed parts for cars or aircraft.

 

[EGLITOM]

there are types of polyester and vinyl ester resin that are stronger then some epoxys. vinyl ester resin is an epoxy resin and used on many aircraft structural parts.

Lynn,

I think we are both correct. Generaly there are so many types of resins that the general rule always find an exception.

My experience is, that i can do much stronger and lighter parts with a woven mat EP combination versus a stranded mat PE combination.
May be one of the reasons is that EP allows me as an homebuilder with limited equipment resources to "laminate it out" . Means the resin percentage in the final product is much less than i can achieve with PE due to the longer open time of EP and more time to properly laid it out and impragnate without using to much resin. One drawback of EP is that one usually need to temper the final part to achieve the final strenght. I build myself a oven out of stryrofoam plates and heat it with a electrical heater to 60°C ( this is the curing temp of the resin i usually use).

Back to Big B´s question, here my reco would be vinylester resin and woven mat. ( i use exactly what your recommanded , preaccelerated VE with MEKP hardener). IN one of the previous post i saw the reco of using aluminium to reinforce. I would rather use finished glassfiber-plates, they are available in different thicknesses and give a much better adhesion within the material combination.

TOM