West Epoxy measure balance.

[rossd 16]

I am sick of my measuring pumps burping especially when only used now and then so was going to make a weight balance but then read this:  When epoxy mixing ratios are given, they are for volume, not weight. Part A and Part B do not weigh the same therefore the ratio changes if you want to mix by weight. And to further complicate the issue, the weight ratio changes by epoxy manufacturer. Mine worked out to be 1.68:1 for the 2:1 epoxy I used. You could use a kitchen scale and weigh equal amounts of your Part A and Part B to determine the weight ratio or email the manufacturer and ask for the data. To build the balance, I took a piece of scrap ply 18" x 4" and drilled a cup size hole in each end. I put 100 pennies in one cup and 168 pennies in the other. Then I found the balance point and routed a 'v' groove across the board for the fulcrum. I had less than 3 oz resin left over after mixing 3 gallons of epoxy in batches as small as 2 oz. I then got fancy and added a microswitch and light that indicates when to stop adding hardener.

 

This involves to much thinking for my liking. Has anyone done this and what is the distance to each end from the fulcrum?  

[rigger 47]

if mixing small quantities try a few avo syringes.

[wheels 543]

Mixing by weight is the more accurate way, but as you found, it is the slightly more complex way. Mixing by volume is not as accurate, but there is a tiny fudge factor allowed for by the manufacturer. Essentially, the less ratio (like 1:1) the greater the error can be, with no consequence to the hardened product. But as a rule of thumb, low ratio mixes tend to yield lower harden strengths. While on that, lower ratio mixes tend to be slightly less nasty for ones health.
High mix ratios (5:1) tend to be stronger once hardened. The hardener also tends to be more hazardous. The mix ratio is far more important to get right. As I said, there is still a fudge factor and that allows the using a cup to work out ratio and still maintain a cured product of maximum strength.
The reason why measuring by weight is more accurate is due to the different expansion ratios of Parts A & B with temperature. No matter how much one expands, it always stays the same weight.
I just use volume. It's easier.
But, if wanting the accuracy for some reason, like when I use Hot Polyurathane mixes, which can be very high ratios and require very precise measures, I use a "gram scale". I simply measure in the required quantity of the A and then add the required ratio of B on top and mix well.

[Guest 000]

Mixing small quantities of West System is problematic, and I don't know why, other than that the smaller the quantity the more important the correct mix becomes. West say 5:1 for epoxy and for small quantities I use graduated medical syringes and I know they're accurate because it wouldn't pay to deliver the wrong dose when I'm shooting up one of the customers in the back of the ambulance.

I use separate syringes for resin and hardener, squirt the contents into a plastic cup, mix thoroughly and don't use below 15°c. Sometimes it cures normally and sometimes it stays slightly rubbery. Got me beat!

[Clipper 343]

What's the 207 stuff?

[wheels 543]

 

You using the right hardener? I have noticed if you use a slow hardener (West 206) in the cold the resin can go thru quite a rubbery phase but after a while will harden OK. You can also post cook which will harden it nicely. NOTE: Not sure if that is a technicality wise move so I wouldn't recommend it before checking with the nice people at Adhesive Technologies or some other guru first.

Yes you can post cook and it produces an excellent result. 50degC is the best post cure temp.(for these normal epoxy laminating resins that is). But the joint will soften before it goes harder, so if the joint must stay perfectly aligned, you want to keep any mechanical means of holding the joint in position, if that was needed in the first place, till joint is cured.

If you think about it, Epoxy is undergoing a chemical change as it hardens. The molecules of the two components are linking up together and as they link together, the mixture thickens and thickens till it becomes solid. As the mix transitions into a solid, the cross linking becomes more difficult and slower. Heating allows the thick almost solid mix to soften slightly and the cross linking can take place easier again till all the linking has taken place.

 

While some reasons become very slow to harden in temps below recommended minimum temp, the bigger issue to watch out for is moisture. Epoxy is not "sticky" even though it is sticky. Let me explain. You may think epoxy is thick viscous stuff and yes it is, but it has a really unique property. It is called "wetting ability". If you used a high power microscope, you would see that any surface is not smooth. Wetting means the molecules are small enough to sink into every little nook and cranny the surface has to offer. For wood, the fibers themselves are an open matrix of material. When the epoxy hardens, the nooks and crannies act as Keys and the epoxy simply can not let go. If the temp is too low, moisture can fill many of these nooks and crannies and stop the epoxy from getting in. Also If the temp is too low, the viscosity of the mix can be such that the epoxy will not fill the little nooks. For the molecules to fill a nook or a cranny, it must displace the little bit of air that was in that space. Too thick and the air will not displace and the epoxy molecule will not drop into it's place. In fact many may have noticed this exchange of air when they lay up laminating resin onto Ply. You can pour the mix over the play and a few minutes later, you have all these little airbubbles on the surface. Simply, the epoxy has filled the nook and the air has lifted to the surface. In some instances, rolling or brushing a layer of epoxy resin over a ply surface first, then allowing it to tack off, before laying the glass cloth, can be helpful. It stops the air bubbles forming and being trapped under the glass and it stops the resin from soaking into the ply and starving the glass/ply surface of Resin.

There can also be issues with the surface of the cured mix as well, with things like Epoxy "Blooming".

[wheels 543]

 

The hardener to use (in West 205 resin, maybe others as well) if you want to do a clear finish. It doesn't have that yellow tinge.

I'm not sure if it is as structural or whatever in comparison to the 205/206 so check that bit if required.

I got it to try and make a few of the boats non structural internals look a bit bling and purdy.

Errr, you mean 105 resin?

The 207 is a special application and should be 2 to maybe even 3 times the price, depending on where you buy it from. It is clear, although if you look at in the container, it has a sliught yellow tinge to it. That yellow tinge is the UV inhibitor. There are three ways of protecting materials form UV.

The material itself is UV proof, or often called "Stabilised".

An additive that reflects UV. Used mostly in materials you can't see through and simply reflects UV off the surface just like visible light reflects.

An additive that absorbs UV. This is often used in clear products and works by turning UV photons into heat, thus absorbing. Not as good as the top two.

       207 is not totally UV protected though. If it i going to be out i sunlight, It still needs a top protective coating of something else and normally a Polyurathane clear coating with good UV resistance is used over top. The Polyurathane also has better wear/scratch resistance, where as the Epoxy will scratch. So even internally, if the object is going to get high wear, like steps, you want to coat it with Polyurathane. And adding to that, urathane tends to be slightly better at being grippy, where as epoxy is that darn hard, you can slip on the stuff easier. So depends on where you are using it, but even if you are going for a deep gloss table, the urathane stops stuff sliding on it better and stops the scratches better.

 

[white tornado 1]

Once you have the weight proportions, from the resin supplier, for small jobs you can measure very accurately by using small electronic scales, sold on trade me very cheaply. I think they are mostly bought by drug dealers? Next time you have a call from the friendly lads in blue, you may need to explain why you possess some fine white  powder, and accurate small scales.  The scales are much more accurate than most  volume measurements. I just bought 3 at once, as they do break down, but they are accurate when working, and cheap as chips.

[rossd 16]

Sometimes reading instructions is helpful. On the hardener it says 5 to 1 either volume or weight.  

[marinheiro 352]

for small quantities I have got by quite happily using various size spoons, if you do not have any to spare in the cutlery drawer, hop down to the local Hospice/Sallies op shop.

[wheels 543]

 

Errr, you mean 105 resin?

Opps, yes I do.

hehe, I have heard many a story over the years, of people using two pot products and forgetting to add the Part B or forgetting what part the started with and adding it again thinking it was the other and so on. Only to find out after an expert job of laying up or spraying on a beautiful finish to come back the next day and find it all still liquid. Then having to remove it all and starting again.

So far I haven't made such a mistake. My mistakes are usually having a product go off too fast and being left with a container of it too solid to be of any use.

[Black Panther 1,591]

Back in my student days I had a job making ice cream topping by the hundreds of gallons for Tip Top. Managed to stuff up an entire vat and kill half a day's production coz I couldn't remember if I had already added some vital ingredient.

[ScottiE 174]

the cream or the ice!?!?

[Black Panther 1,591]

Long time ago but I think about 100 gallons of liquid sugar. this was the stuff in the plastic bottle that you squeeze over the ice cream - passion fruit was my favourite.

[Black Panther 1,591]

Get me drunk enough and I'll tell you how I got sacked.

[Freedom GBE 27]

Is there a formula for amount of resin required per area of cloth?

 

Will epoxy resin go of slower if you use less than the prescribed hardener or will it just not go of at all?

[wheels 543]

Is there a formula for amount of resin required per area of cloth?

 

Yes and no. It's purely volume, So easy to work out by width x length x height. BUT!!! there are 2  things that will make this incorrect. What the substrate is. As in, if it is virgin Timber, it will soak up some resin. If it is already solid glass, it won't. The second is how efficiently you can get the glass cloth against the substrate and get excess removed. The resin on itself is not strong. The Glass itself is useless if you can not bond it. So the most efficient is to have the Glass held as close to the substrate as possible with just enough resin to fill it and bond it. Extra Resin is actually just wasteful and adds no strength. So this is why vacuum bagging is so popular.

 

Will epoxy resin go of slower if you use less than the prescribed hardener or will it just not go of at all?

No. Epoxy requires just the right amount of hardener to resin. In fact technically, Hardener is the wrong word. It is Part B rather than Hardener, because it is simply a component rather than an additive.

The following is very very basic, because Epoxides are a complicated heard of beasts.

With epoxy, you can think of the Resin as being a bunch of Molecules with lots of open links. Part B is a bunch of Molecules with a whole lot of bits that want to fit into the open links. The two link together and become one new molecule. If you have too much of one component, then there are molecules that have no where to link up to and that means the molecule remains liquid. You may not see or feel the liquid, but it is in there and that means the hard epoxy s not as strong as it could be. So you need just enough to ensure there is a good bond and no unbonded links. As the Epoxy hardens, the ability for links to meet up slows. By heating the epoxy, you can cause the links to continue to form for longer and hence that increase in strength with post curing.

      With Poly/Vinyl Ester resins, it is completely different. The Resin itself wants to change and in fact is slowly changing right from the day it was made and placed in the Tin. The "part B"is a Catalyst. It causes that change to happen in a much faster rate. You can control the speed of the reaction by the amount of catalyst you put into the resin.

 

[Black Panther 1,591]

Slow it down by putting it in the beer fridge - you have one of those right?

[wheels 543]

 

Slow it down by putting it in the beer fridge - you have one of those right?

Yes, but don't do the silly think I know one guy did. He mixed up too much Epoxy undercoat and decided that he could put it in the bottom of the Freezer and keep it for far longer. In fact he thought it such a great idea, he also put the brush in with it. All in a plastic bag of course. The idea worked well. He took it out the next day, a whole 24hrs later and gave the Hull another coat. The Hull was dry and hard as rock, the Brush and undercoat was still soft. In fact, as the Undercoat warmed up on the Hull, it went off quicker.

Then he heard a yell from his Wife inside the House. Hi Name was uttered clear and loud. The smell of the Solvent was throughout the freezer. Ooops. So he stuck the sucky end of the Vacuum cleaner in the freezer and sucked all the fumes out. Thankfully nothing tainted the food in the freezer. But I learned never to do that again.

Epoxy Resin should not be a problem because it is usually Solvent free.

[SloopJohnB 322]

Normally 50%/50%

 

Bit of reading here

https://www.compositesaustralia.com.au/wp-content/uploads/2011/12/Composite-Fibre-Volume-and-Weight-Ratios2.pdf