Flowcoat VS Resin with pigment (theory and practise!)

[DHV90]

Hi guys,

Yet another question for those in the know about resins and flowcoats/gelcoats.

I have a practical question, and a theoretical one.

Firstly, if Flow/gelcoat is essentially (from what I have read) resin with pigment added then why does it require exclusion of air to cure (eg with wax of styrene, or pva etc) whereas resin cures in the air?


Secondly, in practise is there any reason to choose premixed gel/flowcoat rather than mixing my own resin and pigment? the latter would work out cheaper for me and also make overcoating substantially simpler if I dont have to de-wax thoroughly and can get away with a light abrasion.

thanks in advance!

 

[lw395]

Layup resin is one thing.
Gelcoat resin is different.

The difference is not pigment.
The base resins are different, one is 'resin A the other B. I forget which.
You can have clear gelcoat.

Flow coat is gelcoat with wax. It does not stay sticky. Again you can get clear flow coat, to which you can add pigment or not.

I have bought separate pigment and clear 'gel coat with added wax' for my dinghy. The pigment will keep for years, I can just buy/scrounge a bit of fresh clear gelcoat resin at any time.

HTH.

 

[DHV90]

that does help, I didnt realise there were different base resins.
Do you know why the two different resins are used and what their property differences are? A lot of people I know use left over resin for adding pigment to create a gelcoat effect and Im curious as to why thats less good than actual gelcoat ( if it is, indeed, less good or less suitable? )

Clear gelcoat is similar in price to coloured gelcoat, and would still need sanding and de-waxing for any further coats or touchups, so the advantages would be lost for me.

 

[Rum Run]

that does help, I didnt realise there were different base resins.
Do you know why the two different resins are used and what their property differences are? A lot of people I know use left over resin for adding pigment to create a gelcoat effect and Im curious as to why thats less good than actual gelcoat ( if it is, indeed, less good or less suitable? ) n price to coloured gelcoat, and would still need sanding and de-waxing for any further coats or touchups, so the advantages would be lost for me.

Gel coat resin is thixotropic so doesn't sag so much as laminating resin when unsupported by glass fibres. It is supplied clear so that you can make it whatever colour you like by adding pigment - not everything is white, even on boats!
Flowcoat can be made by mixing gelcoat, resin and wax-in-styrene in the appropriate proportions if you just need a feW square metres doing, or bought by the tanker load if you are a mass manufacturer.
De waxing if you need to re-coat isn't too onerous, but if you are planning to re-coat immediately you shouldn't be using flow coat. It is the last process before the moulding is finished or as a refinishing process years after the moulding was made.

 

[Amulet]

I believe (maybe wrong) that gel coat is applied to the mould and then covered with resin before complete cure. It has to cure without exposure to air and therefore is a different formulation. This is just a vague memory.