Fiberglass resin working time

[raddksn]

The resin I'm using calls for 12 drops hardener per oz of resin. My question is can I get a longer working time by using less hardener? I'm replacing the deck on my bosses boat and I think he bought $100.00 or so of the wrong resin.

Thanks in advance for any advice/input!

 

[theoldwizard1]

Check over at iboats.com, but I think the answer is yes. Ambient temperature has a lot to do with cure time.

 

[Guster]

Not advised to use less catalyst as you run the risk of the resin not fully curing.
Rather:
* Mix smaller batches at a time.
* Do not work when it is hot(ie. warmest time of the day)
* Work out of a wide/shallow container to reduce the risk of the resin 'exotherming', that is the heat that it gives off while curing compounding and decreasing the working time.

Sounds like you are dealing with normal polyester resin/MEKP catalyst. You can sometimes get away with doing a slightly undersaturated mix followed by a final hot-coat of resin with a few more drops than normal to help it cure. To be honest dealing with un-cured/partially cured resin on a nice boat will cost you more than $100 to clean up or fix if it is botched.

 

[Stinger]

Yes, but there is a point where it will basically never harden so don't expect miracles.

 

[racer1]

Get a big bucket of ice water. put your smaller bucket of resin in it. keeping the resin cold will give you lots of working time. Put the right amount of hardener it it.

 

[theoldwizard1]

Get a big bucket of ice water. put your smaller bucket of resin in it. keeping the resin cold will give you lots of working time. Put the right amount of hardener it it.

Brilliant !

 

[Guster]

Get a big bucket of ice water. put your smaller bucket of resin in it. keeping the resin cold will give you lots of working time. Put the right amount of hardener it it.

As long as it does not become to thick to work with, ie. like cold syrup, making it hard to wet out fibreglass.

Depending on what you are doing the right tool also helps reduce the work time. A good roller can speed up wet out and is not expensive. Also doing all preparation before mixing the resin is important. I've been to shops where they mix resin first then start looking for scissors, gloves, start cutting reinforcements before complaining that the resin worktime is too short.

 

[racer8432955]

Yes, but there is a point where it will basically never harden so don't expect miracles.

+1 Here. I'm no expert, and did this once. it never cured, or at least in the week + I let it sit. what a mess.........

 

[ddawg16]

Follow the above advice.....there is NOTHING worse than an un-cured fiberglass part.

It's about par to painting your car and the paint never drying.

 

[tauruck]

All of the above advice is spot on.
You can get away with using less catalyst but the drops/ounce is worrisome.
Resin manufacturers work on percentages of hardener to resin by weight most times.
If you have a small electronic scale you'd be better off.
My experience is that you can alter the pot life by using less hardener with Polyester resin and it will cure in good weather because they all have accelerators in them already. You could go 6 drops in summer IMO.

 

[BBChevro]

Not advised to use less catalyst as you run the risk of the resin not fully curing.
Rather:
* Mix smaller batches at a time.
* Do not work when it is hot(ie. warmest time of the day)
* Work out of a wide/shallow container to reduce the risk of the resin 'exotherming', that is the heat that it gives off while curing compounding and decreasing the working time.

Sounds like you are dealing with normal polyester resin/MEKP catalyst. You can sometimes get away with doing a slightly undersaturated mix followed by a final hot-coat of resin with a few more drops than normal to help it cure. To be honest dealing with un-cured/partially cured resin on a nice boat will cost you more than $100 to clean up or fix if it is botched.

...Sound advice

Get a big bucket of ice water. put your smaller bucket of resin in it. keeping the resin cold will give you lots of working time. Put the right amount of hardener it it.

I hadn't heard of that before, but it sounds feasible.



I wouldn't advise messing about with the resin/MEKP ratio too much.
When I first started making/modifying panels for my car a few years back, I initially just used guesswork - I soon learnt (the hard way) that it was not a good idea.
Fortunately, the bad batch (it did firm up to a certain degree, but remained sticky) was covered by subsequent laminations.
After that I started measuring (by weight) & had no more problems.

One more bit of advise, heed the safety warnings for MEKP - nasty stuff.

 

[ddawg16]

As an FYI......

Fiberglass and Composites have a lot in common....except the strength and Catalyst.

Because of the above issues of 'working time', they do not put a catalyst in the resin of carbon fiber cloth......along with other reason.

Instead, Carbon fiber cures require external heat to cure the part.

BTW...most of those rice rockets with carbon fiber hoods....they are not real carbon fiber...just black fiberglass. Easy to tell....lift the hood...'real' carbon fiber will look like 'Denim'. If it looks like random fibers...it's fiberglass.

 

[Guster]

As an FYI......

Fiberglass and Composites have a lot in common....except the strength and Catalyst.

Because of the above issues of 'working time', they do not put a catalyst in the resin of carbon fiber cloth......along with other reason.

Instead, Carbon fiber cures require external heat to cure the part.

BTW...most of those rice rockets with carbon fiber hoods....they are not real carbon fiber...just black fiberglass. Easy to tell....lift the hood...'real' carbon fiber will look like 'Denim'. If it looks like random fibers...it's fiberglass.

Actually there is no catalyst in any of the reinforcements. The only thing some have is a dissolveable binder mostly in chopstrand mat for use with polyester resins only.

Some reinforcement are pre-impregnated with a resin hence referred to as pre-preg and the resins are heat cured requiring it to be put in an oven or autoclave. Difference being that an autoclave is is plumbed for vacuum to the mold and can be put under pressure to assist in maintaining form to the mold while the heat cures the resin. Some resins are also UV or gas cured where the resin catalyses when exposed to a specific gas like CO2 or ethylene for example.

There are also many different types of weaves. Carbon comes in roving, twill, bi-axial, tr-iaxial weaves as well as unidirectional which is the straight running fibres you refer to. Some even with a hybrid mix of kevlar, glass, dyneema and other fibres. Same with glass which also comes in chopstrand. Glass can also be co-coated with shiny alumium which comes with colour options. Then there is the new popular basalt fibre and hemp.

Some ricers do have cheap glass hoods and bits covered with vinyl or hydro-transfer 'carbon' graphics though.

 

[Guster]

One more bit of advise, heed the safety warnings for MEKP - nasty stuff.

Absofreakinlutely. The MSDS on that stuff is a massive list of will make you sick, will harm you for life, will possibly kill you if not definitely kill you!

 

[gte718p]

As an FYI......

Fiberglass and Composites have a lot in common....except the strength and Catalyst.

Because of the above issues of 'working time', they do not put a catalyst in the resin of carbon fiber cloth......along with other reason.

Instead, Carbon fiber cures require external heat to cure the part.

BTW...most of those rice rockets with carbon fiber hoods....they are not real carbon fiber...just black fiberglass. Easy to tell....lift the hood...'real' carbon fiber will look like 'Denim'. If it looks like random fibers...it's fiberglass.

I beg to differ. I've done several hundred wet layups of very real carbon fiber and cataylized epoxy. The resin matrixs are different. Carbon uses a two part epoxy vice a polyester resin. Carbon with fiber glass resin does not work out well. Fiberglass with an epoxy resin does work well. No heat required.

The best way to work with carbon fiber is prepreg. It is a hell of a lot easier to work with, but it requires the fabric to be frozen until you want to use it and it does require heat to setup properly.

To the OP I don't mess with the mixture. Especially with a MEKP catalyzed resin there is a quick drop off were it will not harden. Keeping it cold will slow it. They also make different resins with different cure times. Get the right product of your needs and you climate.

 

[K13]

You can safely adjust your mix ratio by about 10% anything more than that and you can start to run into problems. The other thing you should check is the age of the MEKP it degrades quickly especially if it has be exposed to UV at all. If it is more than a year old it is going to be weaker than intended and will not properly cure.

 

[ddawg16]

I beg to differ. I've done several hundred wet layups of very real carbon fiber and cataylized epoxy. The resin matrixs are different. Carbon uses a two part epoxy vice a polyester resin. Carbon with fiber glass resin does not work out well. Fiberglass with an epoxy resin does work well. No heat required.

The best way to work with carbon fiber is prepreg. It is a hell of a lot easier to work with, but it requires the fabric to be frozen until you want to use it and it does require heat to setup properly.

To the OP I don't mess with the mixture. Especially with a MEKP catalyzed resin there is a quick drop off were it will not harden. Keeping it cold will slow it. They also make different resins with different cure times. Get the right product of your needs and you climate.

I was trying to keep it simple. If you start talking about wet layups, RTM, OOA, Thermoset, TOW, etc, we loose them fast.

BTW...The below is what I do for my day job....

 

[Professur]

Just a FYI .. old margarine containers may seem ideal for mixing a batch, but be warned that they're not thermally stable. I had to use one while doing a quick fix on a canoe ... and left fingerprints in the soft plastic .. and no little skin with it.