Fibreglass gel coat - use of cobalt solution at 1%

[David HK]

I have made wooden mould and brushed in a gel coat soloution which comprises:-

80 grams gel coat resin

8 grams green pigment

1.6 millilitres cobalt solution at 1%

1.6 millilitres of MEKP

I have searched the Internet to try and determine what the Cobalt solution exactly does in the process, but cannot find an answer to my satisfaction. I know its an accelerant, but what part of the mixture does it accelerate? And how?

Please cure my headache.

The ambient temperature here in Hong Kong is around 33 degrees Celsius.

Having regard to the above information what would you estimate to be the curing time? I have read 3 hours on one website and 4 to 6 hours on another.

I am much confused.

The end product is a bowl for salad ingredients on a table.

David in Hong Kong

[TrackerJack]

you might be referring to a cobalt blue that is use to detect imperfections in the gelcoat.
you spray it over the gelcoat and as you sand smooth it leaves the blue into cracks and
imperfections that otherwise would not be seen.

[David HK]

Tracker Jack ,

Thanks for the post, but I think it's not quite the connection I am looking for.

The following text may be helpful:-

In order to obtain optimum performance it is advisable to operate as follows:

· Promote with 0.5-1.0% of 1% Cobalt solution

· Temperature between 18 and 25°C

· Cure with recommended MEKP 50% catalyst solution; adjust amount between 1-2%

· Thickness of the film 400-600F


David in HK

[DanG]

In vinyl ester resins MEKP (methyl ethyl ketone peroxide) is used at a ratio of about 1 to 2 percent to catalyze the resin...

The raw resin is usually supplied pre-treated with cobalt naphthenate "promoter" lending a purplish hue to the bulk resin.

Combining the two acts as co-catalysts to get consistent glass-hard VE, something about cross-linking...

http://en.wikipedia.org/wiki/Cobalt_naphthenate

[David HK]

Dan,

Thank you for your reference note.

The Gel coat solution is different to that of the resin you mention. I am au-fait with vinyl-ester resin and its slightly purplish colour tone.

The Gel coat soloution I am using is thicker (thixiotropic) to prevent it running and sliding down vertical mould faces.

Mixing ratios of MEKP bearing in mind ambient temperatyre I am aware of.

The search for an explanation continues.

Thanks to all so far.

David in Hong Kong

[David HK]

I'm slowly finding answers. The following URL contains useful advice:-

http://www.make-stuff.com/formulas/multipl.html

This extract is a useful guideline -

Mix the Laminac 4134 and 4110 in the proportions specified in the above formula. Add the cobalt naphthenate accelerator and mix thoroughly before adding the methyl ethyl ketone peroxide catalyst. The catalyst will react violently with the pure accelerator so make certain these materials are incorporated separately. Add talc to the mixture to thicken it so that application to a vertical surface will not produce sags.

David in HK

[David HK]

Dan,

Your note has proved to be a good pointer.

Whilst searching with Google I came across a fair number of manufacturer PDF's for fibreglass resin and in the technical details most mention that the resin contains an already mixed in cobalt solution. Hence the purplish colour hue.

The gel coat I am using is best described as a creamy colour and logic suggests that the cobalt solution used as an accelerator has to be added separately.

This all makes sense now.

What i did do wrong in my first mix was to throw in the cobalt solution and MEKP together which may not have been a wise move. The note in my post above suggests that the cobalt solution is thoroughly mixed in first, and is them followed by the MEKP.

I think this seems to explain my question satisfactorily.

I hope readers have found the article interesting knowledge.

David in Hong Kong

[David HK]

A bit more knowledge -

Catalysts and accelerators
To cure (harden), resin requires a catalyst and an accelerator.

Resin can be ordered with or without the accelerator pre-mixed. Pre-accelerated resin is recommended because the supplier is able to make a more thorough mix; and it is one less step for the user.

If accelerator is purchased separately, a purple liquid (Cobalt Naphthanate) is usually used with Methyl Ethyl Ketone Peroxide (MEKP) catalyst.

When using un-accelerated resin, the accelerator should be thoroughly mixed in first. Accelerator and catalyst must never be mixed directly together as this could cause an explosion.

David in HK