The pouring urethane sidewall thread

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mammuth
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Post by mammuth » Thu Nov 19, 2015 12:21 pm

I think this nozzles are good if you have a 1:1 ratio with your mix. A different ratio like 1:20 will not mix well enough ... dunno if there are nozzles for ratios like that.
Tom

IslandRider
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Post by IslandRider » Thu Nov 19, 2015 3:34 pm

This is genius, wish I'd thought of it.

Tubes are ~$5-10 a piece, reusable

http://g01.s.alicdn.com/kf/HTB1mcydGXXX ... XFXXX7.jpg

Put it in one of these

http://ecx.images-amazon.com/images/I/4 ... SX342_.jpg

Add a $1 static mixing tip. No more urethane going off in the cup, no more spilling all over the place trying to get it in the channel. Will pay for itself after a couple uses in reduced waste, just mix and use exactly how much you need.

Or ready made for $80.
http://www.ebay.com/itm/Manual-two-comp ... Sw5ZBWPAWn


I've ordered some shit, will report back on how it works.

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Akiwi
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Post by Akiwi » Fri Nov 20, 2015 12:27 am

Looks sweet. I hadn't seen those mixing tubes before
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falls
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Post by falls » Sat Jan 02, 2016 12:48 am

Poured my first polyurethane sidewalls today. Didn't really go well.
I was using smooth on smoothcast 305 as gozaimas has used (full disclosure is that I bought it 3 years ago and hadn't opened it - probably not ideal for polyurethane, but the air tight seals were still intact on top of the bottles).
Temp according to local weather station was 30C and humidity 29%.
Routered a trench stepped at 3 heights. Bamboo.
Sealed channel with one coat of a penetrating wood sealer (largely turpentine with some white spirit and synthetic polymers). Had left it to dry 24 hours (recommended 12hrs) and has been pretty hot so drying wasn't as issue I don't think.

Anyway mixed up the part A and B for 1 minute. Let is sit for 1 minute then poured it into the channel. Visually looked clear and bubble free as it ran out into the channel. Then as goz described as it heated up many bubbles started coming from the bottom of the liquid and rising up. It may have even foamed a bit as the liquid was level with the top of the channel but when set was higher than the channel.

Interestingly the unused stuff in the mixing pots cured virtually bubble free and glossy. Also at one end in the first channel it was a little low so I added a bit extra on the second pour and this cured bubble free and glassy (where it was added on top of already cured polyu rather than into the primed channel).

So my synopsis is:
1. It was capable of bubble free curing so the long time in storage probably didn't make it junk from the start.
2. The timber primer is incompatible with the smooth on 305 and induced the bubbles (one thing I was noting was that it does get very hot when it cures and whether this did something to the primer)
3. A single coat on primer still left the wood that has some moisture exposed and this is where the bubbles came from.

Anyway have been meaning to give this a go and rather than spending another $50 on a new pack I thought I should use what I had.
I will post a few pics
Interested to know if gozaimas reads this whether you junked your atmospheric pressure poured core blanks or whether you laid them up.

I will plane the core blank flat to remove the excess and see what it looks like before giving up. Might try pouring the other ski without the timber sealer.
Pressure chamber looks like it is necessary from my first impression.

Cured smooth on 305
Interestingly on the far channel end the furthest out overflow has cured pretty glossy and bubble free.
Image
Looking a bit foamy
Image
Glossy cure when poured over the cured bubbly under-layer
Image
Don't wait up, I'm off to kill Summer....

pmg
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Post by pmg » Sat Jan 02, 2016 2:00 am

falls wrote: Pressure chamber looks like it is necessary from my first impression.
Exactly my result when trying :) That's why I gave up. Wish you more luck.

gav wa
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Post by gav wa » Sat Jan 02, 2016 4:13 am

I've always had more issue with smooth-on that with other brands like Era, which is heaps cheaper too plus can add colors.
I seal my channel with a thin coat of epoxy resin. It's the same as what's going in the lay-up later so I know it won't effect the finished product. Plus it seals quite nicely, just takes 24hrs to dry. I've also used plain old wood glue with good results.
The temp and humidity where pretty good so it isn't that, plus like you said the left over in the pot cured fine. That exact point is the reason I started sealing my channels since my second board.
Keep a little heating torch (like a plumbers torch) handy if you can, after pouring give it a few minutes to start to react and cure and then quickly wave the flame along the poly and it will drag out most of the bubbles.

gav wa
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Post by gav wa » Sat Jan 02, 2016 4:51 am

Just so you don't think I'm full of it, here are a couple I did 2 weeks ago.

Image

[/img]Image

It is possible to get decent results with channel pouring, it just takes a bit of practice and a warm dry environment. Don't give up too quickly. Do small test pieces. Get a piece of timber you use for cores and router a heap of 6 inch long channels in it. Seal each channel a different way, try multiple coats in some, etc. Then you don't use heaps on poly trying to get it right.
Well that's the way I practiced anyway.

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chrismp
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Post by chrismp » Sat Jan 02, 2016 10:37 am

From your description this sounds and looks a lot like a reaction from too much moisture. As gav suggested, try different methods of sealing your channels with small samples until you find something that works. Generally epoxies or PU based paints are a good tip.

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falls
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Post by falls » Sat Jan 02, 2016 3:59 pm

thanks for the tips.
I used a torch on the second pour and it did pop all the surface bubbles, but they just kept bubbling up from the depths after the flame moved on.
I think it is either an incompatible sealer or poor sealing.
I also blew the channels out with compressed air a few minutes before pouring (but over 30 minutes on the second one) which could have added moisture?
Which product from Era are you using Gav? I had a look at their range and just came away confused!
Don't wait up, I'm off to kill Summer....

IslandRider
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Post by IslandRider » Mon Jan 04, 2016 10:25 am

Def looks like a moisture issue to me. There will be water in your compressed air supply, but I doubt that's the issue. You need to create a completely inert barrier between the wood and the urethane and it will work the same as it does in the pot.

gav wa
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Post by gav wa » Tue Jan 05, 2016 5:28 am

I use the Erapol CC60D.
They do a full range and the title is the shore hardness.
CC60D = shore 60D
CC95A = shore 95A

They are a fair bit thicker than smooth-on so you have to move around the groove as you pour the mix out. It can work to your advantage though as you can pour more along the sides and less at the tips if you want. It's thinner than honey but you can still pour a little more in spots and it levels nicely but stays in that zone a bit.

One thing with it is that you want to mix it thoroughly. A lot of people shy from mixing too hard as they don't want to add too much air, but the only issue I've ever had with the stuff is when I went a bit shy with stirring it and I ended up with sections of it that just didn't set. So I had to router it back out and do it again.

the stuff takes pigments really well. it has a shelf life just like all polyurethane. I use their Era-purge which comes in a spray can, which you use to purge out air when you are closing the tin after use. It still goes darker in tint color after about 4 months though.

Fresh polyurethane is always the best.

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falls
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Post by falls » Wed Jan 13, 2016 2:21 am

thanks gav
I didn't get that far down the list - kept reading about having to heat part A to 65C and part B to 80C and then keep it heated to cure and it all seemed too hard.
It looks like it is available from Adelaide casting/moulding supplies so i might check it out and have another go.
Are you using a heated cure epoxy in layup?
Just wondering about the polyu melting at the 80C I press at.
Don't wait up, I'm off to kill Summer....

gav wa
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Post by gav wa » Fri Jan 22, 2016 6:07 am

I press at 80°c and haven't had any issues. I've also never heated either part of the polyurethane. I might have to read up on their website more, the instructions on the product itself doesn't mention any of that.

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falls
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Post by falls » Sun Jan 24, 2016 3:49 am

the one you are using says 20-30C is appropriate for both part A and B. It recommends 24 hrs at 20C for a full cure.
Don't wait up, I'm off to kill Summer....

gav wa
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Post by gav wa » Wed Jan 27, 2016 5:12 am

Yeah I leave it a day after pouring before machining it.
It's never had any troubles in the press tho.

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