West 105 is really easy to sand

[Jon Matcho]

I was working on sand-and-fill using the West 205 105 epoxy system, which is just a mix of micro-balloons ("micro") and epoxy.  I can now confirm these statements:

• Sanding after the MGS epoxy system cures is like sanding a rock.
• Sanding after the West system cured is much easier.
• I still don't like finish-sanding.

 

Edited September 16, 2018 by Jon Matcho
Changed reference to the correct West 105 epoxy system.

[macleodm3]

I can tell West 105 with 205 or 206 is easy to sand when I have small glob (9 sq inches or less) to sand down.  Yes, it does sand OK and its evident with small spots.  You wouldn't know its easier to sand when using a 36" x 4" 3M sanding board for hours and hours on a wing surface.... my Gosh I can't imagine what MGS must be like!!!

I REALLY DREAD sanding the vertical surfaces... winglets and fuselage sides.  With a strake or a wing you can lean in to the sanding board... not gonna be as easy on the next several surfaces which are vertical.  I do have a used Ingersoll Rand IR315 air file arriving here Friday....  This will help knock down the high spots and give me a fighting chance.

As mentioned by others.... you can do 3 hours worth of sanding in 1 hour if you catch the West 105 before it cures.... my timeframe is spread it out (better be quick), then try to get back to sand in 3 to 4 hours (using fast 205).

[Kent Ashton]

Yes, sanding is no fun.  Getting the mixture right is a factor.   An epoxy-rich mixture spreads easy but is harder to sand.  A micro- (or West filler)-rich mixture is hard to spread but easier to sand.  When I have prominent low spots and defects on a glassed wing, will spot-fill and sand those first.   I buy a big box of West filler from boat supply dealers--an airplane will use most of it.  For the first full coat I usually start with a straight epoxy wipe followed by a stiff mixture and not-so-stiff for the next coats.

I try to get the mixture on the surface pretty quickly with the squeegee, then use a 6" dry-wall mud spreader that I heat up with a couple of passes with a propane torch.   The warm metal helps to move and level the mixture.

When the sanding has got things pretty flat, I use a stiff aluminum bar about 18-20" long, mark it up with a wide Sharpie and rub it perpendicular to the chord.  The bar will leave Sharpie and oxide smudges on the high spots which you can lightly sand.

When it looks good to prime, spray a light rattle-can guidecoat of sandable primer and sand it all off to see the defects you missed.  They are lurking there!  ?

[Jon Matcho]

On 9/11/2018 at 12:13 PM, macleodm3 said:

As mentioned by others.... you can do 3 hours worth of sanding in 1 hour if you catch the West 105 before it cures.... my timeframe is spread it out (better be quick), then try to get back to sand in 3 to 4 hours (using fast 205).

I'm actually using West 105 Resin with the 209 Extra Slow hardener.  The properties for 209 are slightly lower than the 205 Fast hardener, but the window before cure is MUCH longer.  I like going to bed sometimes. ?

On 9/11/2018 at 12:57 PM, Kent Ashton said:

A micro- (or West filler)-rich mixture is hard to spread but easier to sand.  

Ah, I just learned about the line of West Filler products.  Cool, I'll have to get some and try them out!  

On 9/11/2018 at 12:57 PM, Kent Ashton said:

When I have prominent low spots and defects on a glassed wing, will spot-fill and sand those first.   I buy a big box of West filler from boat supply dealers--an airplane will use most of it.  For the first full coat I usually start with a straight epoxy wipe followed by a stiff mixture and not-so-stiff for the next coats.

I try to get the mixture on the surface pretty quickly with the squeegee, then use a 6" dry-wall mud spreader that I heat up with a couple of passes with a propane torch.   The warm metal helps to move and level the mixture.

When the sanding has got things pretty flat, I use a stiff aluminum bar about 18-20" long, mark it up with a wide Sharpie and rub it perpendicular to the chord.  The bar will leave Sharpie and oxide smudges on the high spots which you can lightly sand.

When it looks good to prime, spray a light rattle-can guidecoat of sandable primer and sand it all off to see the defects you missed.  They are lurking there!  ?

Thanks for the tips -- my next question coming in here today was going to be about when/how to transition from epoxy/filler to primer.

[Jon Matcho]

I feel like I have a chance at dealing with the Finishing process when I get to it (which I've been told is 33% of the entire build).

West is your friend and there are a lot of good guides out there, such as this one:  

 

 

[Kent Ashton]

21 minutes ago, Jon Matcho said:

my next question coming in here today was going to be about when/how to transition from epoxy/filler to primer.

Everytime I rush things, it is a mistake.  Get the surface filled, leveled with the aluminum bar and all the sanding scratches sanded out and defects filled or removed.  Then spray the thin rattle-can primer and sand it all off; it will reveal additional scratches and defects.  When those are fixed you are ready to fill pinholes (yes, they are still lurking there) with the "Cory Bird" method of straight epoxy wipes.  Wet-sand that smooth and you're about ready for a primer-surfacer.

[Voidhawk9]

I've made more dumb mistakes with filling than probably half a dozen of any of you!

I found it really hard to sand when I first started out on some educational pieces. It took me quite a long time to discover that I was using a micro-BLEND, not just micro. Blended with colloidal silica, the stuff that makes it cure really HARD!

Then later when I switched to my 'production' epoxy, the sanding was pretty hard too... because I am using a TOUGHENED resin! 

Once I switched to micro and a non-toughened resin for filling, it got a LOT easier!

[Kent Ashton]

11 hours ago, Voidhawk9 said:

Once I switched to micro and a non-toughened resin for filling, it got a LOT easier!

Yep and if you switch to West's plastic filler it will be even easier.  The only real data point I have for that opinion is that strakes filled with micro glass balloons seem to be more resistant to dents and dings from the car-keys-in-the-back-pocket.  I use micro balloons there and also on the wing and canard leading edges.

[Jon Matcho]

Another thing to keep in mind is that if you start sanding too early when the epoxy is in the "bubble gum" stage.  This will end up making a mess of your sandpaper and you won't get much done.  I just found this out after sanding on West's extra slow hardener (209) from a session last night (~9 hours ago -- my shop is getting cool these days so that didn't help).  I haven't had much of a problem when sanding after fully cured, but then again it's never fun sanding drips away.

In general I have been happy with the sandability of West 105 with glass micro-balloons.  Otherwise this foray into finish-sanding could have been thoroughly discouraging.

[macleodm3]

 

3 hours ago, Jon Matcho said:

Another thing to keep in mind is that if you start sanding too early when the epoxy is in the "bubble gum" stage.  This will end up making a mess of your sandpaper and you won't get much done.

I keep a compressed air nozzle close at hand to clean off the sandpaper.... 30 seconds sanding, 10 seconds cleaning the paper, back and forth.  You get SO MUCH progress at this stage, its worth it.

I have a bunch of cured micro that needs to be sanded (had company over the weekend and got no sanding done).  I LOVE my Ingersoll Rand 315 air sander.... $40 with free shipping (used), but I don't think it would work well with a smaller compressor.  Its making the sanding easier... but I still use the 36" sanding boards too.