oddball peel-ply application?

Will peel-ply (or taffeta, or ripstop nylon) readily 'vent out' trapped air? If yes, what's the heaviest (easiest to keep flat) format of the stuff I might scrounge up somewhere?
If it's ALL too floppy, would it make sense to stretch it around a flat form like plywood, hoping for it to allow bubbles to vent out somehow?

Gory details:
I'm grappling with a filled-epoxy application that's got nothing to do with boats, but I'm guessing there's some good advice available here. My guesstimate at adequate slope for drainage on a new balcony wasn't great, so I've been adding some slope to it using heavily filled epoxy. I've done a number of batches using a large (55" square, 1" thick) HDPE "flattening form" lowered over the wet, troweled mass of filler. I first trowel the filler out with a heavily-vee-notched trowel, knowing I'm going to end up with defects/furrows between the perfectly-planar peaks (where the HDPE flattens them). The idea was they'd be perfect guides to let me make the whole thing planar with my new added slope once all is done.
But from there, it doesn't go as I'd like, mainly because there's nowhere for air to escape in subsequent applications. So the best I can do is eyeball-trowel back over the surface. Then inevitably it's going to take another application...then that turns into two more...etc. ENDLESS. And not-so-perfect results, especially when micrometer-thin bubbles of epoxy form in places, trying their best to evade my detection until I think I'm done - at which point they'll break through after I put the UV-resistant coating over the top...

So as I asked at the top: does peel-ply have a place in this process that would release me from some of the endless batching, troweling, sanding events?

 

No.

 

Sorry, no.

the way to do this better would have been to make the angles you seek with a piece of wood or 8 of them sawn to the desired angle, make sure there is no reverse curve on them, tape them well woth ship tape all around, infill thickened resins no thicker than half an inch at a time to avoid fire and use a wide piece of aluminum angle woth wood handles on each side. Then pull tight. After the first batches have stopped heating, say two hours, follow with more batching until it is done. Then pull up the wood slats and fill (again no more than 1/2" thick, 3/8" is safer). Anyway, your hdpe caul idea is not the way to go here and could also be a way to burn the place down, not to mention it won't come out too even.

Your kinda past the point of my method. Ditch the hdpe caul and start laying it up the hard way by hand and with a grinder and straightedges.

 

I normally use polyester for this type of shaping, it's easier to work with, and far less expensive but...

Screed it just like you would concrete, the first few batches don't need to be touched, just keep them lower than the forms, only the final layers need screeding.

Micro spheres make sanding and shaping the epoxy mixture much easier.

 

Thanks, Fallguy.
I'm seeing I missed some explanatories, and should have posted a photo of typical problem area - will do so when it's light here, after work...
My required added thickness is no more than 3/8", so no worries about overheating of batches.
As to regulating the slope, I'm doing that using flathead screws driven along a single 'contour line' a foot or so down from the high point. The low point is just the factory-produced aluminum flashing corner at the low end of the balcony, so no guide needed there. I use the screws like miniature jacks, in conjunction with a couple of levels, to raise or lower what will be the finished surface, with the jack-screws left within the mix.
Laid over the screw-heads, the HDPE slab does a fantastic job of giving a factory-smooth surface at a slope that's very well-controlled - but only where it makes contact with the filled resin, of course. The problem, as described, is those low spots, the furrows between the glossy flattened ridges.
So if stretching a peel-ply-like fabric over plywood is a non-starter for air-release, what about stretching the stuff like a window-screen, say over a 1x4 frame, then squeegeeing that from the back side, spanning over the nice flattened ridges?

 

Ondarvr - thanks for the input. I've not priced polyester for a bunch of years now, but it's almost unseen in our go-to resin supply location (Fiberglass Hawaii) and I had the idea it was only used for rare purposes anymore. I'd have thought it would be much more expensive, actually. I've been buying epoxy by the gallon via Amazon in recent times, and filling to the extent possible for purposes like this.

Speaking of which - I've used q-cel (until I last ran out) and then wood flour as filler. The q-cel certainly sands more easily, but it's not free, as is the flour. What filler alternatives might be good in this setting, where if any strength is required, it's simply compression, against something like a sharp heel or a table-leg?

 

Why the fixation on epoxy?
Concrete products for such uses are commonplace, most of which can be epoxy-enriched for strength in thin areas.
the surface can be troweled to a variety of surfaces without needing a peel ply.
Use tapered metal screeds to break the area up into easily workable sizes, and design them to be left in as control joints.
OP doesn’t say what subfloor he’s working on top of, concrete? Plywood?
Subsurface may be easier to modify in the long run.

 

Yes, there are many traditional products that cost less and are commonly used for something like this.

 

Correction
The texture left from pulling off the peel peelply will obscure the microbubbles.

And leave a surface ready for the next coat without sanding.

 

Yeah, I concur about the cementitious options, but this is a cantilevered and palpably-flexible wood-frame balcony. Also, making tapered metal screeds would be much more time-consuming than just adjusting the screw-heads (as described above) to give me the high-end guides. It's fairly long, and since I'm just now getting into a zone that requires a little more thickness than where I started off (in order to maintain the same pitch) I'm thinking I might economize a bit by embedding some hardibacker to displace some resin, but that'd probably be the extent of deviation from the filled-epoxy approach. I'm paying about $110 for a two-gallon kit, which gets stretched a lot by the filling, so though not cheap, it seems a worthwhile investment in terms of durability and assuring watertightness.

My investment in TIME, however, is ridiculous, as always.

I hadda give up on uploading photos - can't even get them out of my phone right now due to some network problem. But the HDPE-flattened ridges are perfect screeds, I would have shown. On the next application, though, to fill in those lows, it seems by nature, the epoxy rakes out of the valley a bit when troweled, or is slightly proud of the surface. To get a flatter surface, I'm envisioning overlaying the freshly-troweled surface with peel-ply on a stretcher-frame, then squeegeeing the entire surface to flatten across the high-points. This would, in my imagination anyway, release air-pockets, and come close to flattening the newly-filled areas to the same level as the adjacent ridges. Since the epoxy isn't the finish coat (which will be an elastomeric UV-tolerant coating) I just need to get within, say, the 40-grit range of "flat" to feel like no waves or sanding scratches will pop through later.

 

I use 20-25% aerosil for a harder finish than just microballoons.

There is little reason to mess with peelply.

Sand the area to no or almost no shine.

Run your trowel in different directions each time. I use a 14" concrete trowel for this kind of infill. Fill one way, then 45 degrees, then the other way. Low spots are part of the work. The reason your valleys come out low is trowel flex or a bit of shrinkage.

 

To clarify, I use 20-25% aerosil and 80-75% sil32 spheres or balloons, by volume for a harder mix. Typically, about 10-15% the weight of the epoxy or about 2.2 times in powder the epoxy by volume.