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martin.langhoff

Managing epoxy cure times

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So far I've patched up some holes, strengthened a few pieces and fabbed some other little bits and pieces, so I'm slowly getting better at Epoxying the tips of my fingers together :-)

Initially I used the West Systems sachets, I now have WS 105+205 jugs with pumps, peel ply, CF, Fiber Glass and Carbon Kevlar Fiber cloth, and bunch of quick questions.

I work in small 8oz batches as delivered by the WS pumps; usually my pieces are small or tiny. Environment is Miami, FL, so warm+humid. Work happens on my balcony with a view of the bay where I pine to sail. Therefore I don't have much patience, I want to be in the water and not mucking about with glue! :-)

  • How short can you reasonably wait for one coat to be 'tacky' and ready for next layer?
  • How long can I keep epoxy in liquid/gel state by cooling down in a wide-bottomed pot? How cold does it need to be? Is there overlap between those, so I can get two coats out of one 8oz batch? :-) (Edit: for example, can we put rough numbers to the fine graph in this WS article? https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/ )  
  • When I'm working on strengthening a piece, layering on top... if I patiently wait for the base coat to get tacky and apply the first layer of cloth... is it reasonable, safe, sound to apply a couple more layers of cloth? (assuming a flat/simple surface, laid out flat). All these "wait two hours" bits pile up :-)
  • Is there any rough cure time "calculator"? I know it's hard with all the temp, batch size, pot shape variables...

And finally -- what's your favorite home DIY composite technique (link to writeup or video...)? I'm specially interested in tips and techniques for low-effort decent finish. So far my pieces have been plenty strong, but hairy/spiky and ugly as sin.

 

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Wet on wet ?   The cotton ball test....if it sticks , its wet...green stage ..and you may bond to it without fear of blush

if you try to apply to many coats of resin to a poece of fabric ....you end up with poor resin to fabric ratios or fabric that is floating on the substrate 

not sure your project...but peel ply is your friend.  

To use...

Rapidly Load the resin onto fabric....apply  peel ply , squegge off excess resin...let cure...job finished 

get some peel ply...learn how to use it 

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6 hours ago, martin.langhoff said:
  • How short can you reasonably wait for one coat to be 'tacky' and ready for next layer?
  • How long can I keep epoxy in liquid/gel state by cooling down in a wide-bottomed pot? How cold does it need to be? Is there overlap between those, so I can get two coats out of one 8oz batch? :-) (Edit: for example, can we put rough numbers to the fine graph in this WS article? https://www.westsystem.com/instruction-2/epoxy-basics/epoxy-chemistry/ )  
  • When I'm working on strengthening a piece, layering on top... if I patiently wait for the base coat to get tacky and apply the first layer of cloth... is it reasonable, safe, sound to apply a couple more layers of cloth? (assuming a flat/simple surface, laid out flat). All these "wait two hours" bits pile up :-)
  • Is there any rough cure time "calculator"? I know it's hard with all the temp, batch size, pot shape variables...

1) immediately. Don't wait. Multiple layer laminations are typical/normal! No need to wait.

2) use 206 slow hardener in Miami (or for any beginners unless working in really cold climates). shallow pan is good. ice water bath for pan in real tropical climates. 

3) see 1)

4) West usually does give pot life for 100 gm batches (~4 oz) in their literature. Too lazy to search it for you.

Yes, peel ply is awesome. Even fabric store light ripstop nylon works very well but may leave contaminents so use at own risk or solvent wipe afterward.

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Not what you are asking but here goes.

I had good luck with pumps... till I didn't. Now I weigh the epoxy & hardener.

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2 hours ago, Zonker said:

1) immediately. Don't wait. Multiple layer laminations are typical/normal! No need to wait.

:-) well that's what I have been doing, but then results are not all that good. 

I do wet-on-wet, and I mostly layer cloth on top of something. The video (below) shows the kind of ease-of-work-vs-quality I'd like to get -- cutting out the multiple layers of sanding and finish. This chap makes it seem easy! My parts (and cosmetic needs) are simpler; I would have stopped at the first or second 'clear layer'.

As I (currently) don't wait-for-it-to-get-tacky before first layer, cloth doesn't stick well and sags. I'll probably experiment a bit with a strategy of...

  • mix epoxy batch, pour to wide-base container
  • apply basecoat quickly
  • chill remaining epoxy
  • heater/hairdryer on basecoat :-)

Once basecoat is at or approaching "ideal tack point", remove epoxy from chiller, and lay several layers of cloth. Either on the part, or on a flat surface, letting them cure to 'gel' before transferring to part.

 

 

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2 hours ago, Zonker said:

Yes, peel ply is awesome. 

I agree it's awesome, but I don't fully connect to how it'll address these questions. Where's what I know:

 - I can use it to hold things in place, so less sag, so awesome. Still, it seems much better to "wait until it's tacky" to avoid sag.

- Can squeegee bubbles out, even out epoxy, so awesome.

 - I can use it to apply some layers of cloth today, and others tomorrow, because the texture ensures good bonding even if earlier layer has cured fully. 

Am I missing something that would help me control cure (and general work time) better, with Peel Ply? 

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1 hour ago, Autonomous said:

Not what you are asking but here goes.

I had good luck with pumps... till I didn't. Now I weigh the epoxy & hardener.

Anything in particular to learn/watch out for?

I would probably f it up 1:5; are the pumps worse than that? Or did they break?

 

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That video really only applies to vertical layups.

For the typical horizontal layup, I usually use the dry method as per WEST: https://www.westsystem.com/instruction-2/epoxy-basics/applying-woven-cloth-tape/

You can lay up pretty much as many lams as you want in one session, or make a dry stack of several layers of glass and wet out in one go, although you can't do too many at once or you risk insufficient fibre coverage.

For vertical and up-side down layups, I used to use the wet method, which has problems of sagging cloth as you mention.  I've since learned to do it using the dry method with a light spritz of spray adhesive either to the dry glass or the lay up surface.  Then offer up the glass to the surface and wet out.  The main drawback is you tend get a lot of epoxy drips which have to be cleaned up . Only thing is you can only do one lam at a time.  Also, this method only works with epoxy - do not try it using poly or vinyl ester as those dissolve the adhesive very quickly.  

For anyone concerned about contamination by the adhesive, keep in mind dry stack with adhesive is done in resin infusion too.

The spray adhesive is like an aerosol version of rubber cement.  3M sells it - something like 777.  I use Airtac2.

One last thing, for cleaning up wet epoxy, white vinegar works much better than acetone - plus much cheaper and healthier.

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1 hour ago, martin.langhoff said:

Anything in particular to learn/watch out for?

I would probably f it up 1:5; are the pumps worse than that? Or did they break?

 

Statistically you are OK with the pumps. In my case they quit metering accurately and wasted quite a bit of cloth and resin in the middle of a project. I just won't give the pumps another chance.

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No Peel ply doesn't change epoxy cure times. Simply gives a nice finish, ready for further bonding, fill/painting.

To get that glossy clear carbon look you need good technique and a nice shiny mold finish. Or lots of layers of clearcoat, not epoxy.

Brown mylar packing tape makes an excellent smooth mold release for flat surfaces.

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For vertical or overhead applications I lay up horizontally on peel ply or polyethylene sheet from Home Depot, then transfer to the site.  For a mainsheet traveler backing I did 6 layers of 17 oz biax at a time .  I was done in two cycles.  And the polyethylene sheet was big enough between folds that it worked as peel ply.

(Polyethylene sheet doesn't work as peel ply for polyester resin, by the way.  The styrene expands the polyethylene.)

As for epoxy speed, when I mix up a lot I set the mixture on ice packs in a  six-pack cooler.

 

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11 hours ago, martin.langhoff said:

Anything in particular to learn/watch out for?

I would probably f it up 1:5; are the pumps worse than that? Or did they break?

 

Those pumps are handy for small stuff.  They last a long enough to get jobs done 

If you are laminating then use mixing cups. Even better , mixing  cups plus a scale 

that west is a pain in the ass to measure .....in future stick with systems that use 2 to 1 ratios. Hard to make ratio mistakes.   Choose no blush type epoxies.

 

i always use SLOW hardener...nothing worse that kick off stress , hurry, hurry  when working . Go slow, be precise , 

fast stuff is only for obvious fast type jobs 

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18 hours ago, Autonomous said:

Not what you are asking but here goes.

I had good luck with pumps... till I didn't. Now I weigh the epoxy & hardener.

I use a scale for small batches  up to a couple of ounces..

 

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18 hours ago, 12 metre said:

One last thing, for cleaning up wet epoxy, white vinegar works much better than acetone - plus much cheaper and healthier.

+++ on the white vinegar. 

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11 hours ago, Islander Jack said:

For vertical or overhead applications I lay up horizontally on peel ply or polyethylene sheet from Home Depot, then transfer to the site.  For a mainsheet traveler backing I did 6 layers of 17 oz biax at a time .  I was done in two cycles.  And the polyethylene sheet was big enough between folds that it worked as peel ply.

(Polyethylene sheet doesn't work as peel ply for polyester resin, by the way.  The styrene expands the polyethylene.)

As for epoxy speed, when I mix up a lot I set the mixture on ice packs in a  six-pack cooler.

 

I've heard of others using this method, but never had any luck with it myself.  The devil is in the details I suppose, and would like to know how this is done exactly. 

My experience trying this method was the following:

It was a bit less messy than straight transferring a wetted out piece.  However, one problem I had was getting it positioned properly and it could be because I was glassing over a vertical/overhead surface (inside edge of cabin/deck).  Not quite as easy as it may sound because you're trying to focus on two surfaces on two different planes.  Plus the sheet didn't support or stiffen the piece much or at all, so I still had a floppy piece to deal with (kind of like pizza dough - except it can't be spun or thrown up onto the surface.

The second problem was peeling the sheet off without peeling off the freshly laid up glass as well.  I suppose if you wait until it gels you could do it, but how do you do multiple lams at a time (you mention 6 lams in 2 cycle, so 3 at a time I would assume).  I would think if you wet out 3 at once and tried to lay up, the weight of 3 lams would be too much too allow it to adhere in an overhead application.

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1 hour ago, slug zitski said:

And learn how to dispose of exothermic chemicals like epoxy and combustible solvents .

they will bite you 

One thing you may be able to do with regards to exotherm is pour a bit of vinegar in  with the unused epoxy and give a quick stir if possible.  Acetone or other solvents thin epoxy, but vinegar (or any mild acid IIRC) kills the reaction immediately - which is why you have to be a bit careful not to slop even a drop of vinegar on an uncured epoxy layup.

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When glassing overhead taping, I wet out each layer on a flat table covered with plastic sheet. Then sprinkle (literally) with a small amount of colloidal silica. It thickens the resin and makes it stick to overhead surfaces better, just like using a pre-thixotroped resin but wets out the glass easier than mixing it into the resin beforehand. 

If you're laying down a layer of tape, you roll it up and apply a bit at a time, gently does it.

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With lightweight selvage edge tape you can roll up a section dry, place it into a ziplock bag , pour the appropriate resin in...squish around a little to intregnate the tape..the remove and apply .

if you want to learn all the millions of tricks  for working with composites you should google homebuilt aircraft ...some very good builder blogs that doument Construction . They alway strive for optimum  hand layup resin to fibre ratios and waste reduction 

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West system do an extra slow hardener 209  see http://westsysteminternational.com/en/hardeners/west-system-209-extra-slow-hardener

Really useful when working in the summer months in the tropics. I only would mix enough for the current work and would discard any left over rather than going the fridge route  and I learned to measure by weight using a cheap electronic scale.

Learn to use peel ply. It is magic at giving a pro look to inside work. See Youtube vids for guides. eg https://youtu.be/3cTrKlzK0rw

Here is one of the jobs where extra slow hardener will useful. 28c here just now, more in the sun. [Martinique] 

1-DSCN0307.JPG

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On 1/4/2018 at 10:32 AM, 12 metre said:

... one problem I had was getting it positioned properly and it could be because I was glassing over a vertical/overhead surface (inside edge of cabin/deck).  Not quite as easy as it may sound because you're trying to focus on two surfaces on two different planes.

That does sound more difficult.  I've done overhead and vertical but not both simultaneously.  And my areas were about 1 square foot or less.  Maybe area is a factor or success.

On 1/4/2018 at 10:32 AM, 12 metre said:

Plus the sheet didn't support or stiffen the piece much or at all, so I still had a floppy piece to deal with (kind of like pizza dough - except it can't be spun or thrown up onto the surface.

Good description!

On 1/4/2018 at 10:32 AM, 12 metre said:

The second problem was peeling the sheet off without peeling off the freshly laid up glass as well.  I suppose if you wait until it gels you could do it, but how do you do multiple lams at a time (you mention 6 lams in 2 cycle, so 3 at a time I would assume).  I would think if you wet out 3 at once and tried to lay up, the weight of 3 lams would be too much too allow it to adhere in an overhead application.

I did 6 lams twice for 12 lams total.  Yes, between applications I waited until it gelled very well.

I was using Apex epoxy, which is more viscous than West, so maybe viscosity is also factor.  Harder to wet out but easier to paste up.  By the way, I really like Apex, even though it's a bit thicker.  Cures super hard.  But I keep West on the shelf because it has long life.  Edit: long shelf life.

Another thing to worry about with this method is trapping big air bubbles between the substrate and the lay-up.  I attach the stack to the substrate along one side and roll it on from there, then roll more for assurance.

Regarding vinegar clean-up:  Whenever I try it I'm left with a thin slime.  Yes, it's inert, but I find I have to remove it with acetone.

Mixing 5:1... I measure out the small volume first, then calculate and match the large volume to it.  I may end up with more or less total batch than I want, but the ratio comes out better than if it were a 2:1 mix.

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On 1/5/2018 at 3:43 PM, TQA said:

Learn to use peel ply. It is magic at giving a pro look to inside work. See Youtube vids for guides. eg https://youtu.be/3cTrKlzK0rw

Can you explain a bit more @TQA? I use peel ply, but it leaves a patterned look. Useful for other things but... not a nice finish. Is there a trick that follows after using peel ply?

I get much nicer neutral finish from oven/baking paper covered with hair spray. After it dries, I am layering some thin epoxy and/or Krylon UV clear coat on top of that. Experimenting.

For example, I made a mounting piece for a Velocitek Makai, a flat, two-layer twill carbon tear-drop shape, on a baking sheet, plus a wristband for my son adding glow-in-the-dark powder to the epoxy. (I was fixing boat parts alongside, so making good use of the already mixed epoxy, and experimenting with finish...). The finish on the baking sheet was decent, matte, and on top was glossy.

 

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You have been given a lot of good advice.  If you get a digital scale and make a resin/hardener spreadsheet your consistency  will no longer be a concern, also if you cover the scale with saran wrap it will last a lot longer.  I also love my BIG thermometer in the shop.  If you use UV stabilized epoxy you can flow coat the final finish and not need to sand.  Just keep the surfaces to be flow coated horizontal and gravity will do the work.  Check out the Videos by Fiberglass Hawaii of master glassers at work.  Aloha, Guerdon.

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On 1/4/2018 at 1:19 AM, Islander Jack said:

For vertical or overhead applications I lay up horizontally on peel ply or polyethylene sheet from Home Depot, then transfer to the site.  For a mainsheet traveler backing I did 6 layers of 17 oz biax at a time .  I was done in two cycles.  And the polyethylene sheet was big enough between folds that it worked as peel ply.

(Polyethylene sheet doesn't work as peel ply for polyester resin, by the way.  The styrene expands the polyethylene.)

As for epoxy speed, when I mix up a lot I set the mixture on ice packs in a  six-pack cooler.

 

 

thanks for that , I was looking for a better way to do that ..

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On 1/4/2018 at 11:09 AM, wick said:

+++ on the white vinegar. 

also rubbing alcohol..   i go to the dollar store and buy a bunch of the 16oz bottles..  I like to change out the caps to ones like on shampoo bottles that have the flip lid, that way i don't have to keep unscrewing the lid off and if I forget to put the cap on , the whole bottle won't evaporate off..   I use vinegar too, but then I end up smelling like a salad.. 

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1 hour ago, Grande Mastere Dreade said:

also rubbing alcohol..   i go to the dollar store and buy a bunch of the 16oz bottles..  I like to change out the caps to ones like on shampoo bottles that have the flip lid, that way i don't have to keep unscrewing the lid off and if I forget to put the cap on , the whole bottle won't evaporate off..   I use vinegar too, but then I end up smelling like a salad.. 

I used Denatured Alcohol (recommended by the guys at Fiberglass Hawaii) to thin out epoxy thus making Penetrating Epoxy.
I needed to make my slide board waterproof. 10% DNA to the epoxy mix and then the hardener.
Holy shit did that stuff kick off quick. Just enough time to coat the board and let it soak in. I suppose that doing it in direct sunlight on the patio was the issue.
After first coat, some light sanding and a second coat, it looked Fng awesome. Nice clear coat like a new surf board. I got a photo somewhere.

saw a friend use Peel Ply, that is some cool stuff. If I ever make a slide board out of foam and carbon, that shit will be the ticket.
 

 

 

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Solvents such as DNA, acetone, and lacquer thinner help reduce the viscosity, but have several effects such as reduced strength and colouration (with acetone).

Epoxyworks has a good article on the topic: https://epoxyworks.com/index.php/thinning-west-system-epoxy/

In summary, if you are going to use a solvent, lacquer thinner is probably the best because:

- it won't discolour like acetone, and

- although compressive strength is reduced by 35% at 5% which is similar to acetone, that is much less than the reduction using DNA

Although 10% may be okay for surfboards, it causes too much of a reduction in mechanical properties to be of much use for a structural item.  

I'd say 2-3% and no more than 5% max.  Even then, heating the epoxy is the preferred method of thinning, although it has practical limits to how low you can get the viscosity

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