Scraping plywood?

[Kaa]

Newbie question: I have some plywood surfaces (marine okoume plywood) that got a couple of coatings of epoxy (no glass) and a couple more coats of, I think, something like polyurethane varnish. The whole thing is cracking and peeling. I am pretty sure I have to get to bare wood and do it properly.

Now, if it were wood, I'd heat-gun it and scrape it. But since it's plywood, I'm not sure that scraping is such a good idea. Can/should I scrape plywood, or I'm risking various unpleasantness and it's better to stick to sanding?

Kaa

[Ron Paro]

I'd go ahead with the heat gun and scraper. Remember that you are scraping the varnish and epoxy, not the plywood itself. You may not need to get all the way to bare wood, if you can get to a solid layer that is not cracking or peeling. Start in a less-conspicous spot and see how it goes.

Good luck! - Ron

[Dave Gray]

I learned that heat is a wonderful way to remove unwanted epoxy. That and a scraper beat sanding hands down, and you will save several days of effort and elbow grease.

[Whitedog]

Does that amount of heat on the plywood compromise the integrity of the bonds between the layers? I am about to start sanding away at polyester resin on the bottom of my plywood boat. I assumed heat would be a no no.

WD

[Lewisboats]

Does that amount of heat on the plywood compromise the integrity of the bonds between the layers? I am about to start sanding away at polyester resin on the bottom of my plywood boat. I assumed heat would be a no no.

WD
The glues have a higher heat threshhold than the epoxy. You should only need to get to a softening stage...probably 140-150 deg or so...but it depends on the epoxy. The wood will also act as an insulator so the glue won't see quite that high a temp. I don't know about Polyester tho...do you have some available...if so do a bit of an experiment and coat some plywood, let it cure for a couple of days then heat it to see how hot it needs to be before it goes soft.

Steve

[Vernr]

I have just finished stripping all the paint and epoxy from my plywood Hartley using a head gun and scraper........could not recommend a better method!!!

It is quite surprising just how little the ply (actually) heats up.....I think the timber acts as insulation for the underlying glue layer. It takes very little heat to make the (surface) paint and epoxy soft enough to remove with a scraper.

http://i168.photobucket.com/albums/u185/Vernr/Hartley005.jpg

[JimD]

Kaa, are the cracks and peels right down to the plywood or is it just the poly topcoat doing all the cracking and peeling as some of them seem to like to do? And do you want to refinish it bright or paint it? If its just the topcoat that's causing the trouble there's no need to remove the epoxy down to bare wood, and if you try to remove the epoxy with a scraper keep in mind how thin the top finish veneer of the plywood is likely to be if you scrape into it and then try to sand the scrapes out with the random orbital. If you're going to paint otoh it all becomes a lot less problematic. Even if it is the epoxy cracking, if you want to refinish bright I wouldn't try to remove it all and risk scratching up the ply. I'd take about half or so of it off with the random orbital and then re-epoxy. Then do some topcoat reseach to find something less prone to peeling

[Kaa]

Kaa, are the cracks and peels right down to the plywood or is it just the poly topcoat doing all the cracking and peeling as some of them seem to like to do?

It's ALL peeling. Pictures:

http://i296.photobucket.com/albums/mm161/kaa_photobucket/Varnish1_20080419_0002.jpg

http://i296.photobucket.com/albums/mm161/kaa_photobucket/Varnish2_20080419_0006.jpg

http://i296.photobucket.com/albums/mm161/kaa_photobucket/Varnish3_20080419_0008.jpg



if you try to remove the epoxy with a scraper keep in mind how thin the top finish veneer of the plywood is likely to be if you scrape into it and then try to sand the scrapes out with the random orbital.

Yeah, that's what I'm worried about.

Kaa

[Ray Frechette Jr]

Revarnishing may not be terribly viable anyway.

The ply is weathered, to get the color back you will need to sand to fresh wood, which is going ot mean you have a serious divot.

And there is not a whole lot of thickness to the veneer to sand into.

So, you may end up with fairing and painting in the end or coldmolding a veneer layer on the top if you want bright surfaace again.

IN any event, I would sand the weathered areas first and evaluate before going to far.

Then you might opt for an overall sanding and painting.

On the plus side, 6 coats of quality Marine Varnish will last about a year or two while 3 coats of cheap paint will last about 5-6.

[JimD]

Having seen the photos I'll toss my two cents worth in with Ray. Choose a test area so to speak on one of the badly peeled and weathered areas and see if you can come up with new wood without sanding deeply into the top veneer. Good chance you won't have much success and then your decision will be made for you - there won't be any practical way to restore it to a bright finish without adding new wood.

[Lew Barrett]

Could try bleaching it. Try a small area and see how it goes. The ply will easily survive oxalic acid, and it should return the color. Light scuff and you're off.

[Paul Girouard]

Ya he might get lucky that ply looks pretty checked :eek:.

Hopefully he's got to it soon enought to have gotten to it BEFORE it starts to de-laminate.

How old is the plywood? Older veneer was a LITTLE thicker , not much , but a little.

The stuff today is wafer thin , almost (if not) un-sand-able without going thru to the core materials.

Good luck.