Finishing wooden tube advice

[Rod]

Hi

I am refurbishing an old scope I built a long time ago. I just finished this octagonal tube. The wood is Russian Birch and the darker strips have a Jarrah laminate.

I went to the paint shop and they suggested Integrain Ultraclear Exterior - a water based polyurethane. I have only used oil based polyurethane before. I wondered if anyone had experience of this kind of product and could tell me how you found it.

Thanks

Rod

[Kunama]

Love the tube you made !!
Not a fan of waterbased PU varnishes.
I use oil based PU as they give a better, harder finish and with proper sanding between coats, they give a very much smoother surface.

Edit:
Clear Cabothane is easy to come by and does well, a quality brush should be used, don't overwork the stuff (once it is brushed on fairly evenly don't go back over it if it has had even a minute to cure)
sand between coats, 3 coats will give you a really nice finish

[jenchris (Jennifer)]

I've used oil/water emulsions, they're convenient but not that clever.
I'm a great believer in epoxy coatings. They add a huge amount of strength too.
West system make some excellent products.

[glend (Glen)]

Absolutely if you want it to last for decades, be waterproof, and add impact resistance then a good boat building expoxy system is the solution. It's not cheap, and has to be mixed correctly and applied by foam roller and tipped off with a foam brush. I've built six boats using the stuff and they all still retain their hull integrity. West System is a good one but hard to find in Australia, International HT9000 resin and hardeners are resdily available from Whitworth's Marine shops, BCF outlets, etc. HT9000 is also cheaoer per litre than West System. However, working with epoxy and producing a smooth finish is not a good idea if you have no experience with two-part paints, and their surface preparation. A good novice alternative is a spray on polyurethane, but make sure it has UV inhbitors or else it will yellow and become cloudy over time - it's also pretty cheap.
My 10" carbon strut tube imaging newt was built with HT9000 epoxy. You can see how it finishes wood if you check my refractor and newt build threads in the ATM forum here.

10" imaging newt tube (in progess) here:

http://www.iceinspace.com.au/forum/a...1&d=1415688633



127mm iStar Sturt Refractor (in progress) here:

http://www.iceinspace.com.au/forum/a...1&d=1397213498

[Rod]

Thanks for all the advice.

I live on the coast and I think can get west systems products but not having used them before I am more inclined to try the spray on polyurethane Glen suggested. I don't have a spray gun but saw this aerosol can is available at Bunnings:

http://www.bunnings.com.au/british-p...thane_p1400040

It looks to be UV resistant. The tube is small (6 inch F5 scope) so two cans might be enough.

What do you think?

Thanks

Rod

[glend (Glen)]

Consider what you will do to the tube internally, it's hard to spray inside a tube, you may need to use a brush and you can get the same polyurethane in small tins. Most people would think about flocking the interior of the tube, or painting it flat black, or adding baffles; all of which are easier while it is being built. You could seal the interior with the polyurethane and then paint it black but realistically just painting it flat black inside might be enough. I assume the tube is glued up with an adhesive, just make sure the adhesive is not going to be attacked by your choice of finish.

[Rod]

Thanks Glen

I have plenty of leftover flat black paints. I was planning to seal with one of those and then line at least the section opposite the focuser with some self adhesive velvet I have.

The tube is glued up with polyurethane adhesive. There are no internal baffles.

So you think that spray on poly would be suitable?

Thanks

Rod

[glend (Glen)]

Yes Rod, polyurethane adhesives rely on moisture in the air to cure, and the glue would obviously be cured by now. There will be a solvent propellant in the can with your spray polyurethane finish, but the glue should not be bothered by it and it will evaporate quickly. If your worried about it just test it on a glue line inside the tube first.

[Dealy (Kev)]

G'day Rod,

The marine epoxy is definitely the best, but there is a product called 'Wipe-on Poly', available at Bunnings and other hardware shops, that is applied as the name suggests. I do a fair bit of woodwork and have used it many times, and it has produced very good results for me. Oil based does give better results.

It will be easy to apply to the inside as well.

The general rule when coating timber is whatever you do to one side, do to the other. This ensures you won't get uneven expansion of the timber.

Once the timber is sealed you can blacken the inside with flat black or flocking.

Your tube looks great

Kev

[Rod]

Thanks Kev

I like the epoxy finish very much. I looked up a video on how to do it. Looks great on Glen's scopes. I might try it one day but at this point I could see myself making a terrible mess with that process.

The wipe on poly sounds great but Bunnings only seems to stock the interior variety. I could mix my own. I saw suggestions on the net for mixing 50/50 mineral spirits and polyurethane. Sounds simple enough.

Rod