Advice on mixing resins.

[DanTribe]

Can some one give me some simple tips on mixing small quantities of polyester resins please?
I'm doing some basic patch repairs on some Sailing Club training Oppies, so top quality cosmetic appearance is not paramount, but economy is.
The instructions from the resin supplier talks about Mls of catalyst to Kgs of resin.
I want to mix some wax into gelcoat to make Flowcoat and they say 1.5% but not more than 2%.
How do you measure small quantities to that accuracy?
Simple terms please, e.g. ratios in the same units,[not ml per kg] or drips per volume.

 

[prv]

Most fibreglass places sell syringes. Should be able to measure individual millilitres pretty accurately with a 5 or 10ml syringe.

Mix ratio isn't as critical for polyester as for epoxy, because the hardener is just a catalyst to speed up the reaction, rather than part of the finished chemical structure. Not that that means you can just splash it about willy-nilly.

Pete

 

[Clyde_Wanderer]

If the catylist came in a small bottle with a black screw cap use aprox 3/4 of the cap of catylist to a big mug full of resin.
Or a 1/2 tespoon of catylist to a big mug full of resin.
If you are confident you can use the mug full of mixed resin withen a 1/2 hour at aprox 20degree C then you could go a full teaspoon of catylist (Hot mix) to save hanging around.
Dont use either for human consumption purposes after.
Only use Wax in the last coat of Gel that you will be applying, if you use it in earlier coats it will prevent the following coats from adhering.
If applying chopped strand matt (CSM) to a repair, a quick way to do it is to get an old peice of ply or cardboard and wet out the matt on this with a small lambswool roller then lift the wetted matt to the repair, no need to use a consolidating (aluminium paddle) roller until you have all layers of matt in place.
If you find you are struggling to get the repair done before the resin starts curing use less catylist or wet out all your peices of matt at one time on a bigger peice of ply or cardboard, spreading the resin quickley slows down the exothermic heat from building up and speeding curing as would happen with the resin mis in a smaller container, also dont hold container in hand as this can also speed up the curing process.
C_W

 

[2Tizwoz]

Digital kitchen scales

The simple method is to weigh the resin on a digital kitchen scale in a polythene bag.

You can see the reading and operate the scale through the bag but the scales can be returned to the kitchen intact.

The syringe method makes the catalyst and wax addition easy.

The reaction is temperature dependent so experience of your operating conditions will dictate how much catalyst you use.
A bit of sunshine will speed things up, which you may not want.

Plastic milk bottles don't dissolve and can be cut to make a container with a handle.

Nitrile gloves last longer than cheaper latex ones.

 

[nigelmercier]

Most fibreglass places sell syringes...

Or better still, get some of these.

 

[prv]

Or better still, get some of these.

Ta - wish I'd thought of that last year when I was doing lots of polyester work. As well as being more readily disposable than syringes, they'll fit into the neck of MEK and wax/styrene bottles - I was always having to try to tilt the bottle to get the liquid within reach of the syringe, or decant into a small container then tip the rest back.

Just bought two packs for next time.

Pete

 

[DanTribe]

Thanks for all the advice, some good ideas there.
Gloves, syringes, pipettes and scales now ordered.
[too scared to borrow the kitchen scales!]
I do get confused when the instructions mix the units, e.g, so many millilitres to a Kg.
Also I seem to lose the ability to do simple calculations as soon as I put on overalls, so can get the decimal point in the wrong place!

 

[lw395]

Thanks for the link Nigel.
I also use syringes for measuring small quantities of two pack paint, they are usually much cheaper on ebay than at a chandler's.

I think it is always worth measuring the catalyst properly with polyester resin, particularly gel coat.
This time of year, gently warming things with a hot air gun helps. Don't go mad though!

 

[Poignard]

The simple method is to weigh the resin on a digital kitchen scale in a polythene bag.

That's what I do but I like NigelMercier's suggestion of using pipettes and will try that.

 

[electrosys]

For mixing small amounts of epoxy, I use plastic syringes - the one-piece piston sort, not those with a rubber cap on the piston, as they don't last very long (black rubber cap ends-up coming-off - always).

Tip - to prevent the graduated marks dissolving-away or being rubbed-off in useage - a few strokes with a needle file on top of the marks when new will ensure that the syringe lasts the season. I replace mine only once a year. Am I mean ? You bettya.

 

[ianfr]

I have just repaired my rudder after splitting it to check the tangs. One broken tang, all three mild steel

The best buy I made was a cheapo set of kitchen scales from Comet £7.99 if I recollect. Put the container on scales empty and switch on, container weight is zeroed, then add mixture by weight . Takes all the guesswork out.

As a bonus I can probably clean them up a bit and use in the kitchen.

Regards

Ian

 

[DownWest]

I use 1gm accurate kitchen scales for epoxy. But spent quite a bit to get a unit that was close to what it said.
For polyester. 20cc/kg.(2%) So 1cc in a syringe for 50gms. Since polyester is way cheaper than epoxy, and (as above) not so mix dependant. Close enough.

And don't forget that MEKP is not nice stuff.

 

[Clyde_Wanderer]

I use 1gm accurate kitchen scales for epoxy. But spent quite a bit to get a unit that was close to what it said.
For polyester. 20cc/kg.(2%) So 1cc in a syringe for 50gms. Since polyester is way cheaper than epoxy, and (as above) not so mix dependant. Close enough.

And don't forget that MEKP is not nice stuff.

If I were to take time faffing about with scales and syrenges etc I would be doubling the cost of production.
I just bang in what I feel to be withen an accurate guesstimate then stir like a witch for a minute and lay it up.
If its curing too slow for my liking I use the heat gun, if its curing too fast for my liking I sweat like a r****t until the layup is finnished.
Sometimes layup 2.2 x 1.6mtr moulds with 2 x 600grm csm layers on one mix while working directly in the blow of a big oil fired heater, and only get 20 minutes to do it otherwise the 6" paddle roller becomes part of the finnished product!
C_W

 

[DownWest]

CW
If you do it every day, your guesstimates are going to be better than most. When I did it frequently, I had one of those measures in the top of the MEKP bottle, squeeze upto the required c.c. then toss into the polyester bucket. Used marks on the bucket to meaure volume previously set by wt.
DW

I faff around with accurate scales only with epoxy. Where they are needed.

 

[lw395]

If I were to take time faffing about with scales and syrenges etc I would be doubling the cost of production.
I just bang in what I feel to be withen an accurate guesstimate then stir like a witch for a minute and lay it up.
If its curing too slow for my liking I use the heat gun, if its curing too fast for my liking I sweat like a r****t until the layup is finnished.
Sometimes layup 2.2 x 1.6mtr moulds with 2 x 600grm csm layers on one mix while working directly in the blow of a big oil fired heater, and only get 20 minutes to do it otherwise the 6" paddle roller becomes part of the finnished product!
C_W

mmmm, Quality!