Crosslinked PVC vs Balsa Core for Foils

Discussion in 'Materials' started by CatBuilder, Jun 1, 2010.

    Joined: May 2010
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    I'll weigh in a little bit here. As far as wood I personally like the Paulonia we have noticed that it does get a little off color when it abosrbs the epoxy. Kinda like a green hue not to noticeable (unless it is on a cedar strip canoe.. and its extreamly pale in compairison....doh.....) as far as mixing epox. Again I can only speak from our epoxy view. We formulate our epoxy to me exactally 2:1 (or others for our special hardeners) BY VOLUME. If you go to do epoxy by weight it WILL NOT be 50g:100g (just an example). For example off the top head I remeber 1 harder mixture(our 631 5:1 epoxy) now if your mixing by volume its a perfect 5oz of resin to 1oz of hardener for any resin. now if you go by weight. Its more like 18g hardener to 100g of our THIN(127) resin, whereas you would be closer to a 20g hardener to 100g of our THICK(1500) resin. That works out because of the volume difference in the liquids and the slight amount of diluants in the thinner resins. I do my testing when I make new formulations first by weight to see what the exact properties are like with PURE untouched resin(which closely resembles our THICK 1500) and the new hardener chemical. After I find something I like and get the checmical companies numbers figured out(their numbers are horrible I had 1 that claimed to be 40:100 even at 30:100 I still had way to much hardener. after a week of curing it was still able to be bent inhalf by my bare hands) then I will add chemicals to bring the volume side to the closest even volume that I want to make the mixture(ie 2:1 4:1 5:1 ect.). If you ever plan on mixing epoxy by weight weather it be from my company or another PLEASE be sure to get ahold of someone with enough tech information to get exact weights of the epoxy so you dont end up ruining a project.

    Now that my crazy looking rant is done. if you have anymore question just keep in contact. Give me a call before you start heading down to Florida and we can see what kinda turn around time we will need for the materials to get started with.

    Kyle Dunn
    Raka Inc.
  2. Herman
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    Herman Senior Member

    The epoxies I sell (Sicomin, Hexion, sorry, no Raka. Is it available in EU anyway?) all state the mixing ratio in both volumetric fractions and by weight. These figures are also on the containers, together with the working time, which saves a lot of phone calls.

    Indeed specific weight of resins and curing agents can be way different, making the 2 mixing ratios also very different.
  3. Herman
    Joined: Oct 2004
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    Herman Senior Member

    I realise I have not responded on the "what should I use for getting the mixing ratio right" question, although Richard already gave a hint.

    There are basicly 4 options:

    Very large batches:
    If needed continuously, a piston pump machine could be an option. This is what the windmill manufacturers use. 2KM and Composite Integration are potential suppliers.

    Alternatively, cut open a 1000 liter container (IBC), put that on a scale (we have a pallet mover that has a scale built in) and measure from there. Good to measure the occasional 800 kg (1800 lbs) batch.

    Large batches:
    gear pumps could be an option. Resix is a manufacturer.

    Occasional: Do the same trick as above, with a scale and a large container. For hand laminating boats I recommend a white or transparent bucket, weigh in the desired amount of resin, take a marker and mark the level, weigh in the curing agent, and mark again. Some tape over the marks will protect them from being washed away. Mix in that same container, then pour into the buckets that the workers use during the lamination. Reuse the mixing container for the next batch.
    DIY boatbuilders use this when hiring an (experienced) laminating crew, where the owner mixes the resin this way.

    Normal amounts:
    Some options are viable:
    -Install a scale, pour the resin from a container (our 20 liter containers have nice taps for that) and pour the curing agent from a plastic oil can (these come in various sizes, from 5 liters (1 gallon) to perhaps less then 1 liter (1 quart)). Do keep in mind that the curing agent can oxidise, so a certain amount of throughput is needed to keep things fresh.
    -Use plastic pumps to dispense from the container. Works great, but DO CHECK THE MIXING RATIO on a regular basis. Do not expect top of the bill accuracy from a $2 pump. Alsi check just after installing, perhaps the limiter of the pump for curing agent needs adjusting.
    -Gear pumps can do a very nice job here, especially when you need small or normal batches many times a day. These will save you a huge amount of waist, and save time. Resix is a brand name, West has similar ones.

    Small batches:
    -either use scales to weigh very small batches. Use an accurate scale. Mine does 1/100 of a gram (more useful for polyesters, with their 0,05% mixing ratios of some additives)
    -or cut the top off a syringe, and use that as an adjustable measuring cup. Works great, and is reusable.

    This is just an overview of what I see most. I am more then happy to learn about other options.
    Joined: May 2010
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    Hermon, as of right now we dont have anyone that resells our stuff basically anywhere but 2 places here in florida. We can esailly ship to EU but haven't put time or effort into getting ourselves on someones self.
    But anyways, what we do around here is the clear mixing pots we carry. they are graduated marked in customary/metric and they have some fancy markings for goofy mix ratios so you dont have to have the math figured out. (Im still a little confused cuz there's a few of them that also have a %ed delution marks also, so yeah.) I stick with Ounces or mL when I do surfboards or anything around the shop. Pumps are great but airbubbles can mess it up. we have the clear pots from 1oz size to 5qt size.
    Something one of our customers told us they used a 5gal paint mixing bucket and had a drill mounted with a paint mixing blade and were mixing up 3gals at a time. mix for about 5 mins then pour into another 5gal bucket and mix another min. He had helpers and poured it all out into a bunch of paint trays. (he was happy that he had plenty of time to do the job) Matter of fact that customer is on this forum. Charly if I'm not mistaken. lol.
    Hermon I understand your liking of the exact mix rations for both ways right no bottle I have run out of room on my lable and 99% of our customers say screw the weight lets just dump x ounces of resin in a mixing pot and 1/2x ounces of hardener. lol If people wanted the weights I could pull them up I have alot of them saved in a file on my computer somewhere. (gotta love being a computer programer by schooling but a expoy worker by trade.)
  5. apex1

    apex1 Guest


    thats one of the main advantages for the homebuilder, Epoxy is a very forgiving material. Even a rough mixing ratio can give a good result. Trying that with Poly or (worse) Vinyl leads into a perfect desaster.

    Thanks Kyle.

  6. M-Sasha

    M-Sasha Guest

    And for the pro too!

    no worries in a wide range of ambience conditions, stable when storing over years and years.

    And predictable properties in almost all conditions.


  7. Herman
    Joined: Oct 2004
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    Herman Senior Member

    That is absolutely true. Still I do tell my customers to follow the mixing ratios as accurate as possible. Guess what happens if I say they can "guesstimate" the amount needed....

    On weight vs volume: we both agree that it does not matter at all, as long as the right figures are given. Here people seem to mix by weight more often. Perhaps this is a regional thing.

    The good thing about epoxy is that no matter how small the batch, as long as it is properly mixed, it will cure. So different with polyester, where you can tune for a nice cure in thicker parts, but lose the cure in thin areas. (which is a pig in RTM moulds: nicely cured product, a sticky mess on the seals.) And that is just one thing that can go wrong. I also have to admit that polyester pays my bills...

    We have the graduated cups as well, the diluent part is for mixing paints. These cups come from the automotive industry. We carry them in 350, 700, 1350, 2250 ml. (roughly from 1/12 gallon to a generous 1/2 gallon, sorry, I am not good in imperial)
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