Measuring resin/catalyst

[ghostlymoron]

I need to mix small quantities of resin which apparently has to be done accurately. What do others do?

 

[GHA]

Digital kitchen scales and check if mix by weight ratio is different to mix by volume.

 

[Motor_Sailor]

Digital kitchen scales. Works for all quantities from about 20g and up.

Below that is trickier, but graduated cups / syringes / eyeballing all work for various people.

If it's epoxy, most manufacturers sell 'pumps' which dispense in the right ratio. They work well when new / clean.

 

[bluerm166]

For small 'Structural' work with fresh resin : buy two syringes from the chandlers , don't mix them up and they will last for a number of jobs.
For lesser jobs : the lids of two plastic milk containers.

 

[VicS]

I need to mix small quantities of resin which apparently has to be done accurately. What do others do?

Accurately for epoxy resins because they cure by chemical reaction between the two components. I have pumps on the containers but I am limited to whatever the amount ( I forget what it is ) they deliver as the minimum I can mix.

By weight, provided you know the mixing ratio by weight, or can find the densities buried in the technical bumph, is the most accurate method although you will need digital scales with better precision than most/ many kitchen scales.

I would be less happy with the precision achievable with graduated mixing cups .

You refer to "catalyst" so pesumblly you are talking about polyester resin
Mixing ratio is not so important with polyester resins because the "hardener" is only a catalyst. In fact you can vary the proportions a little if you need to extend the cure time............ measuring cups are quite adequate

 

[prv]

Different for epoxy and polyester, because of the amounts needed. Epoxy is somewhere around 3:1 to 5:1 depending on the product, whereas polyester is a few millilitres for a typical small layup or repair job.

For epoxy I use a small digital scale with disposable plastic pots (very similar to the flimsy plastic pint glasses found at some festivals!). Put the pot on the scale, zero it, add the hardener, note the exact weight, multiply it appropriately, then zero the scale again and add the resin.

For polyester I use plastic pipettes similar to what you probably used in school chemistry lessons. The plastic pots have a graduated scale on the side, so I pour in the resin up to the required amount, and then squirt in the corresponding amount of catalyst from a pipette. The ratios are less critical than for epoxy.

I started off using the epoxy pumps, but they had so many problems of gumming up, leaking, dispensing partial squirts that messed up the measuring, and generally being a pain to deal with. A reasonable expedient back when accurate scales were expensive, but nowadays the scales cost less than half what the pumps do...

Pete

 

[ghostlymoron]

I've got polyester resin (Lloyd's approved) which has different percentages 1% - 4% to achieve various setting times at different temperatures. I'm planning to use washing liquid graduated dosing pot for the resin and medical syringe less the needle for the catalyst.
Does the percentage catalyst affect the strength as well as setting time?

 

[Graham_Wright]

Syringes every time. Buy a pair from a pharmacy with capacities in proportion to the desired mixing ratio. Transfer the resin and hardener to small medicine bottles. From my pharmacy, the syringes came with plastic sleeves with graduated diameters so the syringe could be inverted to fill AND it could be left in for next use.

 

[Motor_Sailor]

Does the percentage catalyst affect the strength as well as setting time?

No, with polyester you are merely adding a catalyst to make the chemicals which are already in the 'resin' react together. The more catalyst you add, the more rapid the reaction but the end product is identical.

The catalyst usually comes in a dispensing bottle where you can gauge the amount used. Weigh the amount of resin you think you will be able to use in each work session and add the catalyst accordingly. You need to be in the right ball park in order to get the working time / cure time you need, but you don't need the exact ratios that you do with epoxy.

 

[prv]

Syringes every time. Buy a pair from a pharmacy with capacities in proportion to the desired mixing ratio.

Do pharmacies really stock half-litre syringes for polyester?

Pete

 

[Graham_Wright]

Do pharmacies really stock half-litre syringes for polyester?

Pete

. Probably vets do! But for little jobs, they are great and no wastage (but then I'm a tight wad).

 

[lw395]

I don't believe catalyst in the 1-3% range should affect strength.
My normal mixing containers are cut from the polythene bottles milk is normally sold in.

I use syringes for most things. Pipettes are good for polyester catalyst. all in various sizes from ebay.

I've recently been using rubber boat adhesive, with this I calibrate a container with a syringe and water, then spoon the glue in.
The hardener is 1/25th, so a small syringe was used.

For very small quantities of epoxy, I sometimes just use good old two-tube araldite. If you warm it up you can still add filler and get it to set in less than 24hrs....

 

[PaulRainbow]

Does the percentage catalyst affect the strength as well as setting time?

Between 1% and 4%, no, just curing times (which also vary with temp). But if you add a high % it will affect strength. High ratios also cause excess heat, a high enough ratio can cause damage or in extreme cases start a fire.

 

[savageseadog]

I use a parallel sided container and a stirring stick with lines drawn on with the aid if a ruler for the required ratio. The sticks are available from McDonalds. For the container a clean food tin or whatever I can find. Otherwise I use digital scales, a drug dealers one for small amounts or kitchen scales for larger amounts.

 

[VicS]

I've got polyester resin (Lloyd's approved) which has different percentages 1% - 4% to achieve various setting times at different temperatures. I'm planning to use washing liquid graduated dosing pot for the resin and medical syringe less the needle for the catalyst.
Does the percentage catalyst affect the strength as well as setting time?

Thats the way to do it .........but Id prefer the graduated mixing cups for the resin and graduated plastic teat pipettes for catalyst ...... I find syringes a bit of a fiddle

 

[Lon nan Gruagach]

I use a parallel sided container and a stirring stick with lines drawn on with the aid if a ruler for the required ratio. The sticks are available from McDonalds. For the container a clean food tin or whatever I can find. Otherwise I use digital scales, a drug dealers one for small amounts or kitchen scales for larger amounts.

These http://www.ebay.co.uk/itm/0-1g-500g-Digital-Pocket-Weighing-Mini-Scales-For-Jewlery-Gold-Kitchen-/361579373883?hash=item542fcf653b:g:QtsAAOSwQupXUBBF are mighty fine for small quantities.

 

[PCUK]

Graduated paint mixing cups from car spraying suppliers cost pennies and are ideal.

 

[ghostlymoron]

Thats the way to do it .........but Id prefer the graduated mixing cups for the resin and graduated plastic teat pipettes for catalyst ...... I find syringes a bit of a fiddle

Thanks Vic, you've jogged my memory - I've got some of those little pipette things supplied by my doctor for decanting urine sample. I don't think they are marked but I can soon do that myself.

 

[macd]

Graduated paint mixing cups from car spraying suppliers cost pennies and are ideal.

For epoxy, maybe (although I prefer scales). But for poly- or vinylester, where you might need just one or two cc of catalyst, a pipette or syringe is far more accurate. (That said, I've been known just to chuck a capful in )

 

[prv]

I've got some of those little pipette things supplied by my doctor for decanting urine sample. I don't think they are marked but I can soon do that myself.

Is it really worth it when marked ones cost three pence each?

Pete