Problems with plywood

[brandon26]

I am about to start making a chair for a school project from plywood. I have limited knowledge about plywood, but there are a few things I hope you guys can help me with:

1) I want a smooth surface, how can I achieve that?

2) Shall I smooth the surface before or after actually making the final product?

3) What finishes do you recommend I use for the plywood?

I need help urgently.

Thanks

[Shedhand]

I am about to start making a chair for a school project from plywood. I have limited knowledge about plywood, but there are a few things I hope you guys can help me with:

1) I want a smooth surface, how can I achieve that?

2) Shall I smooth the surface before or after actually making the final product?

3) What finishes do you recommend I use for the plywood?

I need help urgently.

Thanks G'day
If you have a choice of plywood I'd go for what we here in Australia refer to as Marine Ply. Its probably the best quality in terms of finish and unfinished durability. Without knowing what design the chair is i'd cut the components, finish then put it together. Others here would be better qualified on what type of finish to use.
Cheers and good luck with the project.

[bsrlee]

If you are going to finish (paint or stain) the surface, remember to mask off the areas where glue is going to go - use the special masking tape that can be left of for several days - here its blue & made by 3M. Paint & stain can reduce or stop glue from adhereing properly.

Again, being in the UK rather than in Oz, you may/will have access to different grades & types of ply. Do you want something with a waterproof glue line (usually Urea-Formaldehyde, but shows a black glue line) not water resistant (melamine based)? Hard wood or soft wood plies? You may be able to get ply with a voidless construction such as 'Marine' ply mentioned above, or 'Birch' ply - much beloved of Yank woodworkers & coming from Finland (best) or ex-USSR (sometimes very poor).

Again, depending on the exact parameters of your design & the exam criteria, you may be able to get away with a cheaper ply & fill any surface defects (or glue laminate 2 thicknesses together with the 'bad' faces in).

Concrete formwork ply is also very strong, waterproof & voidless, but it usually has a resin impregnated suface - which you can use as a surface finish by itself or as a base coat if you use the right paint. It also only comes in 1 or 2 thicknesses.

[brandon26]

Hi,
I think I am using a very cheap version of plywood, I am not too sure which type it is though, because I stole it from my dads workshop.

Can I use a sanding machine to first of all, achieve a smooth surface on that plywood? Or is that not possible, because the plywood is made fom several layers of veneers.

What can I do to mark out the visible veneers on the edge of the board?

[brandon26]

Could someone take me through the process of finishing plywood please.

That would be very helpful

[graemet]

G'day Brandon.
Even if you are using cheap ply. it will help to start with a smooth surface, so do some sanding before you assemble. The only ways you can hide the glue lines on the edges are 1. paint over them, or 2. cover the edges with a veneer or edge banding. As it is crummy plywood, you will probably need to paint it anyway.
Cheers
Graeme

[Tex B]

Brandon,

To finish plywood, I would:

1. Sand with 120 grit sandpaper (either by hand with the paper wrapped around a block of wood or sanding block, or with a handheld sander like a random orbital sander using light hand pressure. If by hand, five to ten 'strokes' over everything is probably enough. For finish sanding, do not use a belt sander.)
2. Sand with 240 grit
3. Sand with 320 or 400 grit (whatever you have)
4. Wipe it down with a clean cloth, then with a tack cloth or a cloth with a bit of turpentine. This will pick up any dust left from sanding.
5. Apply the finish

If you want to paint, just paint it. Depending on what it will be used for you can put on a coat of primer/sealer or whatever. But for a school project, a couple of coats of paint should be fine. I'd recommend water based paint, makes the cleanup a lot easier. If the paint is too rough when it dries, use a fine sandpaper (320 to 800 grit, whatever you have) with light pressure and then another coat with a good brush. This process will take a couple of days depending on the drying time of the paint and the temperature.

If you want a 'natural' looking finish, and have more time, use one of the products designed for that - polyurethane, danish oil, shellac, etc. There are plenty around, but I'd recommend not using a brush with them, even if the can says to. Most of the polyurethane or other 'clear' finishes look better if you rub them on. So get a cloth, make a ball that fits in your fist, put on some rubber gloves, put some finish on the ball of cloth, and rub it on. When the cloth gets a bit dry, put some more finish on and keep going until the whole project is rubbed. Let it dry a day, and rub on another coat. You can put some finishing wax on this for a really nice shine. This process will take several days since you usually need 24 hours between coats. Some poly products will only need 8 hours.

Plywood edges look OK if they're painted along with the rest of the piece. For unpainted pieces, most people will cut a small strip of wood and 'frame' the ply. Usually the wood is wider than the ply, so there is a lip. This is called a 'design feature'.

This is how I would do it. Many others will take some objection to this and have other ways, but as long as you have a smooth clean surface to start with, most finishes will look pretty good.

Hope this helps. Good luck with your project.

Tex

[brandon26]

Thanks a lot guys,

I am going to start the project as soon as school starts after xmas.

Merry Xmas guys