plywood - how to hide wood grain?

[Florin Andrei]

I'm doing a small plywood-based project - it's a telescope mount, the plan is here:

http://stellafane.org/tm/dob/

I want to paint it in such a way as to hide the wood grain - it should look like plastic, or metal, or some "generic" unspecified material. But I'm not sure how to accomplish that.

One way I can think of is to apply several layers of primer, just keep painting primer over primer until it's smooth enough, then paint it the final color (flat black) with a paint spray or something. Would that work? Would a primer spray be ok?

Are there better methods?

What should I do with the edges? Should I apply a thin layer of "plastic wood", to hide the way the two pieces are joined at the edge?

I'm not entirely sure yet whether I'm going to use plywood, or whether I'll use poplar or pine or oak or something nicer. But in any case, I'm going to use good-quality wood, free of large uneven knots and gaps.

[Russell Sansom]

Decades ago an industrial arts teacher told me about "Furzite," a "wood stabilizer." I used it on some plywood furniture I made from the nomadic furniture book that was floating around in the "hippie" days. I still have a few pieces of that plywood around the shop and it is still like plastic or metal. Unfortunately, I never saw furzite or "firzite" again and I don't know what its chemistry was. This is the stuff if you can find its equivalent. Just DON'T sand with a rotary sander or with a soft hand pad ... it will erode the soft parts of the plywood more than the hard parts.
Anyway, I have successfully used gesso ... kind of a mixture of plaster and varnish. Artists use it to fill canvas so it is is like paper in texture. Acrylic Gesso dries very quickly and you can put on 3 - 4 - 5 coats in an afternoon.
On the matter of wood for your Dobsonian mount, I am a very big fan of poplar. It can still be had from Home Dep. in good widths. It's one of the best painting woods in existence. It works easily but is a stiff hardwood that is very stable. While all hardwoods shrink and expand in width, the poplar will be very stable in length. I doubt that a nice square tube in poplar, painted white outside and black inside will move enough to shift your collimation or focal length any significant amount. I'd say a 12" width will move 1/8" or so from summer to winter. multiple coats of varnish will retard this.
p.s., an excellent way to hide end grain on plywood is to laminate a thin strip of wood to it. You can attach it with finish nails and white glue. Any thickness will work from 1/8" up.

[Kent A Bathurst]

What should I do with the edges? Should I apply a thin layer of "plastic wood", to hide the way the two pieces are joined at the edge?

1] Sand it well - I'd go to 150 grit. Then, use the Minwax Hi-Performance 2-part stuff - much, much easier to get good results than the "plastic wood" - just be sure to mix up only a small amount, so it stays "apply-able". Then sand smooth after 30 - 45 minutes. Easy to work with.
2] Or - Edgebanding. There is stuff with pressure-sensitive adhesive, but I use the stuff with hot-melt glue. It is like "iron-on" wood tape. [You won't mess up the iron - just be sure to do it while the S.O. is out of the house, or you will have to run out to WalMart for the cheapest iron you can find. DAMHIKT. "What in the SAM HILL do you think you're doing with my clothes iron??"]. You will have to take some time and care to trim the edges. Since you are painting, plain-old birch will do just fine. Stuff's available everywhere on-line, or at any woodworking store.

[Chris Fournier]

Perhaps you could use your plywood to construct the base and then contact cement a laminate or even HIPS (high impact polystyrene) to the plywood? If you glued the HIPS to the plywood you would have a plastic looking base. You could use .060 thick or even thinner stock. You can machine it with woodworking tools. You can help it form around complex curves with heat (it's used in thermoforming processes). You could even go for "haricell" texture which looks pretty cool but then you'll have to be careful about flush trimming.

As a bonus it's very inexpensive from a plastics supplier in your area.

Neat project.

[Florin Andrei]

I was told to use marine grade plywood and then encapsulate it in epoxy, to stabilize the material - this is due to the fact that the telescope is going to see a lot of dew and humidity. If I do that, I assume the epoxy will pretty much cover the grain altogether, is that right?

[Rob Sack]

1] Sand it well - I'd go to 150 grit. Then, use the Minwax Hi-Performance 2-part stuff - much, much easier to get good results than the "plastic wood" - just be sure to mix up only a small amount, so it stays "apply-able". Then sand smooth after 30 - 45 minutes. Easy to work with.
2] Or - Edgebanding. There is stuff with pressure-sensitive adhesive, but I use the stuff with hot-melt glue. It is like "iron-on" wood tape. [You won't mess up the iron - just be sure to do it while the S.O. is out of the house, or you will have to run out to WalMart for the cheapest iron you can find. DAMHIKT. "What in the SAM HILL do you think you're doing with my clothes iron??"]. You will have to take some time and care to trim the edges. Since you are painting, plain-old birch will do just fine. Stuff's available everywhere on-line, or at any woodworking store.

I would probably not use iron on tape for a painted project. I would glue and nail solid wood edge banding instead. If you haven't started the project yet, have you considered MDF, either regular weight or exterior grade? Dopn't use the light weight version, the edges are too fragile. MDF paints great, and after two coats of primer, the edges come out like glass. The Minwax 2-part wood filler is a good idea, but it is extremely expensive, especially if the project is going to be painted. In this case, I would go down to the nearest auto parts chain and buy a large container of Bondo and a full box of dust masks.

[David Jones]

I was told to use marine grade plywood and then encapsulate it in epoxy, to stabilize the material - this is due to the fact that the telescope is going to see a lot of dew and humidity. If I do that, I assume the epoxy will pretty much cover the grain altogether, is that right?

Yes epoxy will hide the grain, this is how many boats are built: plywood with epoxy and you can't even tell that most boats and the structures (cabins, etc...) are built using this method which is also very water resistant. The only downside with epoxy is it's resistance to sunlight, it will need to be covered to protect it from the sun-might not be a problem though if it's only out at night.

Aloha,
Jonesy

[Howard Acheson]

The trick is to start off with a small pored wood veneer plywood. Stay away from pine, fir and oak. Birch veneer plywood is readily available and the small pores are easily filled with the first coat of an oil based finish or a alcohol based primerfd. Thin the paint slightly, apply it, let it dry for a three days and then flat sand it with 320 paper on a flat sanding block. For the edges use Bondo and press it firmly into the edges. It cures and hardens quickly. Once hard, use 220 paper to sand it flat.

[Tony Bilello]

Yes epoxy will hide the grain, this is how many boats are built: plywood with epoxy and you can't even tell that most boats and the structures (cabins, etc...) are built using this method which is also very water resistant. The only downside with epoxy is it's resistance to sunlight, it will need to be covered to protect it from the sun-might not be a problem though if it's only out at night.

Aloha,
Jonesy

Paint the epoxy...Duh

[Florin Andrei]

Paint the epoxy

Yes, all the plywood will be painted flat black. That was the plan from the beginning.

[John Coloccia]

If you fiberglass it instead of just using straight epoxy, you'll have a much more durable structure that will better survive all the travel your telescope will be doing over the years.

[Prashun Patel]

What's the construction? I too vote for MDF if you've not already begun building. It'll paint smooth with less effort.

[Henry Ambrose]

I was told to use marine grade plywood and then encapsulate it in epoxy, to stabilize the material - this is due to the fact that the telescope is going to see a lot of dew and humidity. If I do that, I assume the epoxy will pretty much cover the grain altogether, is that right?

Yep, this will do the trick. Two coats of resin and then paint it. If you want super moisture resistance then a layer of glass cloth will help you build a film that is waterproof - really waterproof.

Another thing to think about is using MDO (Medium Density Overlay). The paper face will paint as it is so all you'd have to worry about filling and smoothing are the edges.

[Curt Harms]

Yep, this will do the trick. Two coats of resin and then paint it. If you want super moisture resistance then a layer of glass cloth will help you build a film that is waterproof - really waterproof.

Another thing to think about is using MDO (Medium Density Overlay). The paper face will paint as it is so all you'd have to worry about filling and smoothing are the edges.

This might be the easiest if you can find it. MDO is used for highway signs so I'd imagine it's quite water resistant/waterproof. Bondo on the edges, sand and paint.

[Florin Andrei]

I found some really nice epoxy resin that appears to be designed for the purpose of making a flat, transparent, glass-like surface on top of plywood, but it's pretty expensive. As long as I'm going to paint it anyway, I guess I could use generic epoxy, which is somewhat cheaper. I wonder if the generic one is less fluid, though (the transparent one claims to be very fluid and easy to spread).

Oddly, the most expensive was the epoxy glue at Home Depot. More expensive than the fancy epoxy "glass coating".