Finishing Plywood

[STAR]

I have purchased some cheap plywood from Mister Ply and Wood. It is CD grade but does have a clean C face.

It is only for the workshop and associated cabinets but one problem I seem to be having is that the good face is very soft and absorbent which means that any finish I put on it is inconsistent and sometimes absorbs and other times seems to hang around which then gives it a pooled effect with blotches .

I had thought about a sanding sealer like Feast and Watson what are the recommendations.

Is the problem the cheap absorbent plywood. If it is, then it is suitable for the workshop and I might have to go upmarket for better quality if required.

Peter

[RufflyRustic]

Hi Peter,

I kinda think you've answered your own question. :rolleyes:

However, you could try a sanding sealer on it, or even a light coat of white shellac before applying your finish of choice.

One other suggestion for consideration is that you veneer plywood like this.

cheers
Wendy

[Tex B]

Peter,

I've found that sanding very fine makes a big difference on plywood finish, particularly if you stain it.

Try going up to 800 or 1200 grit. Then use a sanding sealer or a thin coat of shellac. This will cause some fibers to stand up, so go back over that with your fine sandpaper.

should come up a treat.

Tex

[STAR]

Hi Peter,

I kinda think you've answered your own question.

cheers
Wendy

Yep. Thanks Wendy. I was hoping I was wrong. I was once. but I was mistaken. :rolleyes:

Peter

[Harry72]

Before sanding and sealing it hit it with some thinned out filler(Timbermate is good), sand through the grits up to 240g then seal it.
What type of cabs are you going too make, framed or ply boxes?

[soundman]

The problem with CD ply as such is that it can be quite inconsistent.
Even knowing what spicies is a big start.
It could be hoop pine, slash pine, radiata pine or meranti.

All behave very differently, but remember one thing, it is a structrual product and realy isnt intended for painting or clear finishing.

It will be made from rotary cut veneers ( as is most ply) whick means it will be full of tiny cracks.
If it is made of pine particularly radiata or slash, there will be hard and soft portions of grain that will both sand and absorb finish at different rates.

You can with work achieve a good finish on it but it can break your heart.
If you achiece fully choked "piano" finish there will always be the risk that the material will move and open up a crack right in the middle of the sheet.

I have learned my lesson, do not spend too much time or expect too dood a finish from low grade plywoods.

That said
this is waht I have learned.

Do not sand raw plywood too much particularly with a random orbit sander, because the soft parts will sand more and the hard parts less ending up with a grain rippled finish. restrict your self to a once over of the sheet with 120grit at first. that will remove any factory fuzz and clean the sheet.

If you are going to fill with timber mate do it now. However the problem I find with timbermate on ply is that if you machine sand, particularly a random orbit with dust extraction you can pull most of it back out of the grain, the more you sand the more you have to fill again. If you are going to use timber mate you have to keep sanding to an absolute minimum.....I have given up on timber mate in ply except for filling holes, then I would rather use bog, plastibond or epoxy.

Using a sanding sealer or a chalky high build primer is esential if you want anything like a good finish on ply.
A sanding sealer will even out the softness and hardness and will bind the surface. A thinned first coat of sealer or primer is the go.

I would go as far as to say give the whole sheet a first coat of sealer before you cut it...it will make the ply cut a lot cleaner. Please yourself if you sand now or later. Think about if this causes you gluing problms first. I have been known to seal both sides and rebate away to facilitate gluing.

once you have done what you need to do and are heading on with finishing, sand it to no more than 180gritt and put on a full coat of sealer, and repeat till you have the surface quality you want.

Remember to do as much work in sanding sealer as you can before you go for top coats.
Make sure you use a sanding sealer compatable with the top coat.

If you are thinking about staining plywood, I would recommend not, you are better getting your colour in a coat of finish.

I am convinced that fine sanding ply is pointless, particularly prior to sanding sealer.
The finest I would go would be 240 gritt. You are wasting your time trying higher order finishes on low grades of ply, so you will be using relativly thick film forming finishes. With these fine sanding is more than pointless it detracts from the performance and adhesion of the product.

you might rubb out the final finish with 800 or 1200... but not between coats.

One big lesson I have learned on ply is not to over sand.
Another is not to try a fully choked finish on cheap ply in nitro laquer.

cheers

[STAR]

Thank you for your replies. I appreciate the time, thought and effort in your wording.

It all adds to my thinking bank and helps provide me of a clearer picture of the problems to be faced with the cheaper CD ply.

The cabinet is a portable turning gauges holder that I can safely store my turning equipment and safely take them to my wood group without cutting my self.

So the finish does not have to be pristine but naturally I would want it to be ok even if only to protect the ply from the elements.

ps.

I have to get myself able to put up photos. When the traveling gypsy ( Neil, aka Dai Sensai )gets back in town I am booking a photo posting lesson. The problem of going over to Neils is I get sidetracked when we go into his shed as he is always doing something new and interesting and that's were we stay and run out of daylight.:C

[Old farmer]

A note only to thank Peter for raising this thread and all who have contributed so much helpful information.