Fiberglassing with waterbased polyurethane (Varathane)

[Malain]

Hi Guys,

I read a couple of days ago in a UK model magazine that scale guys over there currently use waterbased polyurethane (the new stuff guys now apply on hard wood floor in houses) for bounding thin fibreglass layer on balsa and ply structures. Since I'm working in a rather close workshop and that I hate the chemical fumes typically associated with resin, I'd like to know if some of you have tried this method and what kind of results were attained. Thanks!

Marc

[lenb]

I ran some tests with some products a few years ago. I used 3/4 oz cloth and waterbased poly,I'll have to look to see which one, I still have it.
It worked ok, but was no way near as hard as resin, either Epoxy or Polyester.


Len

[Malain]

Hi Len,

I gave it a try the other day on a sample, and you're quite right: it works, but it does'nt look as rigid and solid as resin... I'll go with the traditional method for the fuselage of my actual building project. By the way, it's a "replacement" for my defunct Topaze (lost this fall at the September Soar in Vermont 😢), it's the 4.5 m wingspan version of the Slingsby Skylark, a pretty cool design from the mid-fifties. I'll post some pictures for a short building post in the coming weeks 😎. Thanks for the advice,

Marc

[lenb]

That was a beautiful plane Marc, so sorry to see it crash.

[nichda]

This is a topic I am familiar with re the different approaches of epoxy resin versus water based polyurethane, so happy to share my experience.

Recently I completed two identical sports power models.
One was finished with West Systems Epoxy, and the other using Deluxe Products Ezikote
(https://www.deluxematerials.co.uk/en...243900746.html)
Both were finished using the same 3/4 oz cloth from the same roll.

Water Based Resin (Ezi-Kote or other single pack polyurethanes):
Easy to apply, and very easy cleanup with water and virtually no odors in the shop.
Can easily achieve two coats of resin in the one day as it dries quickly (2-4 hours).
Covers well but must be block sanded (as usual) to get a good flat base
Not as hard or as durable as Epoxy but still suitable.

West Systems Epoxy:
A little more prep required to apply the 2 part resin but if you use electronic scales for measurement you will be precise each time (and will know exactly how much is being added as weight).
Definitely stronger odors in the shop with the cleanup needing acetone.
I also used a peel ply fabric over the top of the resin to soak up the excess, which is then peeled off when its all dry.
Takes probably an extra day or two to allow for the epoxy to dry thoroughly.
A bit more sanding is also required compared to the Ezi-kote resin, but the resulting base for the finish is more durable and accepts the final finish better.


So what to use? which is best?
If you want a fast finish and are not looking for that super deep gloss finish, then go with the water based resin approach.
If you are chasing the best and most durable finish you can get, and are not afraid of putting in the effort with plenty of block sanding, then the 2 part epoxy finish remains the way to go.

For me, I am happy to use the water based on a sports models but for a scale glider or scale power model it is the West Systems Epoxy finish all the way.


I hope that helps

Dale Nicholls

[lenb]

Good report Dale.

[ARUP]

I have used the Minwax Polycrylic brand water based polyurethane for finish glassing. It is inexpensive, easy to apply, dries fast between coats, levels well and sands well without loading the paper. It is lightweight compared to an epoxy or polyester finish. Because of that it won't resist hangar rash as well. I can easily push a fingernail into it and leave a mark. Because it is soft the same 'fingernail test' can break the cloth encapsulated by it. I would never use it to finish a wooden floor even though that is one of its marketed applications!