The pouring urethane sidewall thread

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Dimitar
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Post by Dimitar »

Looks like almost everybody have troubles with those bubbles.

We made some tests with smoth-on products. Our final result is more than excellent.

You don`t need any pressure/vacuum chambers.

All you need is sanded and impregnated channel surface.

We use cheap high speed rotation tool for sanding the channel with very fine sand paper head. All small swarfs shall be well sanded.

http://www.skileurope.com/gb/en/diyocs/ ... ion-tool-/

Then we seal the channel with wood impregnator and we wait patiently to dry.

The channel is prepared for pooring.

The last test was with Smooth-cast 320. No vacuum, no pressure. No bubbles at all.

The environment temperature is quite important. Just keep it 23 celcius degrees and everything will be ok.
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chrismp
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Post by chrismp »

Thanks for the update! What exactly is this wood impregnator you're using?
Dimitar
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Post by Dimitar »

chrismp wrote:Thanks for the update! What exactly is this wood impregnator you're using?
It is not something special. We bought it from local hardware store.

Image

Drying time is not as short as we would like - 3 hours in room temp....

First time we did not wait enough and the Smooth-cast mixed with the impregnator. The result was something like a foam.. :D

So patience is important.
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dbabicwa
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Post by dbabicwa »

Balkan wrote:
chrismp wrote:Thanks for the update! What exactly is this wood impregnator you're using?
It is not something special. We bought it from local hardware store.

Image

Drying time is not as short as we would like - 3 hours in room temp....

First time we did not wait enough and the Smooth-cast mixed with the impregnator. The result was something like a foam.. :D

So patience is important.

Nah, it is not that. The temperature is not so relevant as moisture in the air and a core.

SM 320 has 3 mins pot life. That is more relevant than anything.

If you get a 30 sec pot life PU, there is less chance to form the visible bubbles.

Faster PU = less bubbles (without vac/press chamber). The Industry is using ultra-fast resins.

You might not seal it and still get a good result with 320.

Been there, done that.


PS

Careful with your primer: the two-part PU normally does not bond well with 1 part...
Dimitar
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Post by Dimitar »

dbabicwa wrote:
Nah, it is not that. The temperature is not so relevant as moisture in the air and a core.
I agree. Moisture in the core is the main trouble. The PU contacts with the water and bubbles appear. We can`t remove that water, so next option is to seal it inside the core.

Sanding the channel - IMO this is the point. When you sand the channel, you reduce the specific surface area of the wood.
The primer closes wood pores and keep the water into the core.

The temperature is important, because when it is colder, the pot life is longer, and the chemical reaction is different than it should be. Different chemical reaction = side effect = bubbles...

The PU bonded very well to the impregnated wood.

For now, this method works for us. However, we have to make a complete board with this type of sidewall, before any conlcusion. We will keep you updated.
gozaimaas
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Post by gozaimaas »

Until you have profiled the core you cant tell if you have bubbles or not.
For me the pressure box is easier than controlling temp or humidity and my pu looks like glass when it comes out of the box. You can see your reflection in it.
Dimitar
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Post by Dimitar »

gozaimaas wrote:Until you have profiled the core you cant tell if you have bubbles or not.
For me the pressure box is easier than controlling temp or humidity and my pu looks like glass when it comes out of the box. You can see your reflection in it.
We already profiled one core and there are not bubbles. We will upload some pics soon.

Obviously, your pressure chamber works well.
We just try to find easier and cheaper method, because Smooth-cast is designed for atmospheric pressure at 23 celsius degrees.
camhard
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Post by camhard »

Here's a not so great photo of the
vacuum chamber. Black 1/2" acrylic on the bottom, clear on top. Routed 1/8" deep channel in each and filled with silicone. First used leftover from heat blanket, but decided cheap bathroom stuff in a caulking tube actually did a better job, hence the bits of red on top of the white.

Using DTrain's product, degass until the bubbles stop (approx. 5 mins). As I mentioned before, temperature in the room is still pretty crucial; basically, you want it as hot as possible, to make the reaction nice and snappy. The trick is to not make it so hot that it goes off in the pot...

Image
Dimitar
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Post by Dimitar »

Some pictures of our sidewall...
We use smooth cast 320 - no pressure, no vacuum, just sanded and sealed channel.

Image

Image

Image
skidesmond
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Post by skidesmond »

How well does the Smooth-Cast 320 bond to the wood when fully cured? Does it stay in-tact when profiling the core?
Dimitar
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Post by Dimitar »

skidesmond wrote:How well does the Smooth-Cast 320 bond to the wood when fully cured? Does it stay in-tact when profiling the core?
It bonds really well. We already profiled 2 cores and everything was ok.
ben_mtl
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Post by ben_mtl »

Oh nice !
What's the difference between the Smooth-Cast 300 serie and the 320 serie ?

What product do you use to seal the wood core before pouring the PU ? I tried with one coat of polyurethane varnish with not much sucess (I was using Smooth-Cast 326 and had some bubbling, not much.. but too much)

Also I have a mail from Smooth-On where they strongly advise on not using their products on snowbaord/skis since their PU resins/rubber quicly becomes brittle when the temperature drops... I've used the PMC790 and it seems OK though... + other SkiBuilders have used those products sucessfully.
A bad day skiing is always better than a good one at work...
Dimitar
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Post by Dimitar »

ben_mtl wrote:Oh nice !
What's the difference between the Smooth-Cast 300 serie and the 320 serie ?

What product do you use to seal the wood core before pouring the PU ? I tried with one coat of polyurethane varnish with not much sucess (I was using Smooth-Cast 326 and had some bubbling, not much.. but too much)

Also I have a mail from Smooth-On where they strongly advise on not using their products on snowbaord/skis since their PU resins/rubber quicly becomes brittle when the temperature drops... I've used the PMC790 and it seems OK though... + other SkiBuilders have used those products sucessfully.
320 is off-white and it is designed for adding color pigments. It has very short pot life (~3 minutes).

There are some scratches on our sidewall after 1 full day shredding, but it is still solid.

Scroll up this page for details about the primer, that we are using.
gozaimaas
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Post by gozaimaas »

The 305 is not brittle when cold.I have had no probems with cracking or scratching
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chrismp
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Post by chrismp »

"Cold" usually refers to -20°C to -30°C for most PU...so it's likely that you haven't encountered such low temperatures yet, but it could happen and then the PU might become brittle.

That's the reason why we are using Adiprene LF 950. It has a brittle temperature of -70°C.
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