Okume and epoxy

[Howard]

Maybe now is a little late to worry about it, but everytime I coat a new piece of okume with epoxy, I'm left with a very rough surface....presumably a bunch of little air bubbles coming out of the wood. Probably a good thing, as the epoxy is being deeply absorbed into the wood. The downside being it's a real pain to get sanded back smooth. Anything I can do to avoid this?

[Guest]

Thats what is known as outgassing. If I understand it correctly, you are precoating your plywood? I will wait for further comment before a comment session. This has nothing to do with satuation.

[Howard]

Pre-coating and coating in place. But due to the rough texture that's left, sanding is a chore and in tight areas, would be next to impossible to get smooth. So I'm trying to pre-coat as much as possible. It's also easier to get a smooth finish when it's laying flat.

Yes....I'd say this is a variation of outgassing. I've seen large bubble outgassing on other woods, but okume...with it's porous surface, seems to be different. Not quite a froth...more of a gritty feel to it... and reminds me of a raised pebble finish. It would be an effective non-skid if left as is.

Not too bad sanding down the few pieces for building a dinghy, but if you were doing a bigger boat, this would take the fun out of it.

[JEM]

Couple of tips:

-Do not let epoxy cure in direct sunlight. That will cause bubbling.

-West system recommends you coat when the temperture is decreasing. That minimizes outgassing.

-When I coat, I stay with the boat, or I come back and check after, 20 minuntes or so. I pop the bubbles with the tip of a chip brush.

[Howard]

These are being coated indoors, in stable temps.

I think it's a function of okume. I've coated fir and luan plywood in the same environment and don't get the same response. Fir stays pretty smooth when coated. Luan (at least the stuff I have) really soaks up the juice and has an almost dry looking surface after the first coat. Funny how they seem to react differently.

[kydocfrog]

Just finished putting two coats on most of Charlie Girl II, pretty much in the sun. I didn't get too much bubbling, but then her okume has cured for a couple of years at least. Did get some pinprick size bubblies in some places that I attribute to too vigorous appliciation of roller.

Did find some serious delamination along keel similar to what has been described on some other threads. Poured in a lot of epoxy and put a single sheath of 4" fiberglass tape along the keel. We'll see. Need a year out of the keel before I bob the whole thing anyway.

DocA

[Charlie Jones]

I don't think he's getting outgassing. I think the Okume is having the grain raised. I've found much the same thing.

The answer is - don't sand- scrape.

Also, if you are pre coating, you can get a second coat on as soon as the first is tacked. But a scraper is the real ticket on precoated flat panels. I can scrape the entire hull of a 16 foot canoe in 15 - 20 minutes where sanding would take several times that long. I usually don't even touch a panel with sandpaper til I'm up to the third coat or so, depending on what's happening to that panel later. If it's gonna be glassed over, then the scraper is ALL it gets.

The scraper will also make really short work of drips and runs, although those are far easier to get rid of while the epoxy is still uncured.

Oyster- your take on the subject?

[Guest]

presumably a bunch of little air bubbles coming out of the wood. I've coated fir and luan plywood in the same environment and don't get the same response. Fir stays pretty smooth when coated. Luan (at least the stuff I have) really soaks up the juice and has an almost dry looking surface after the first coat. Funny how they seem to react differently.

I don't see no writings about raised grain. It says air bubbles from where I see it. Now, in my opinionated opinion, you cannot compare coating fir plywood, which in most cases carries a different face grain and different satuation across the face that does not allow for the resin to float on top. Luan, in most cases, is what can be described as vertical grains on the good face of it alllowing the resin and initial coating to soak in unlike the okume plywood, by nature is more dense and close grain.

I will venture out on a limb and say that in the different temperatures of the plywood, and the temperatures of the resin, dictated by the location of storage and exciting it by stirring it, pinholes or air bubbles is very common in higher ambient temperatures. I would also suggest the slowest hardener,[a problem that has multiple consequences this time of year with conventional 5 to 1 mixes or even 3 to 1 in the cheaper brands] even if it means switching brands.

As a side note, after coating with epoxy and some settling time has occurred, keep tabs and even use a very short nap roller and use denatured alcohol, sparingly, after the coat is tacky, rolling it across your surface, if you see this problem, and this normally will make most if not all of it to go away.

[Charlie Jones]

I've seen large bubble outgassing on other woods' date=' but okume...with it's porous surface, seems to be different. Not quite a froth...more of a gritty feel to it... and reminds me of a raised pebble finish. It would be an effective non-skid if left as is.

[/quote']

Here's why I said grain raising- the part where he was talking about Okume. Agree - fir, lluan and Okume all are very different animals when it comes to reaction to the epoxy coatings.

[Howard]

Texture is easier to feel than to see, but I made an attempt to photograph it. I never considered just covering over this, assuming perhaps it was small bubbles (but doesn't look or feel like bubbles when you study it closely). I'm going to give Charlies scraping trick a try, and also do a sample with Oyster's roller trick with D-N-A. I've got several large panels to go and would really like to avoid all that sanding.

However, once that first coat is on and smooth, the subsequent coats are easy. Only bubbles in those are the ones I whip into the epoxy when mixing, and I'm getting better at that. BTW...I'm using RAKA with slow hardener.

[/img]

[Guest]

No problem Charles, I had replied to his original comment and read the second comment as to believe the little fisheyes were coming into the finish. The photo shows a bit different on my screen as if the epoxy is a bit heavy in just one coat, leading me to believe that a heavy nap roller is being used too, causing the rough texture that seems apparent here, which is normal. Tell us more about your roller head.

There shows some white spots, on the right, as if you are getting some of those in the coating, too.

[Howard]

I'm using a nylon bristle chip brush. I spread on enough to get it evenly wet....making the dry spots go away. I then try to drag off the excess so that it dries to a smooth, even surface. On the sample, I don't see any white spots. I also got out a magnifying glass, and I don't see any bubbles. It's more like gritty granules.

I'd be glad to make up some samples and mail them to anyone who would like the examine them in person.

Send address to:

haudsley@tranquility.net

[Guest]

Don't know what to tell you, Howard. :?

[capt jake]

It appears to me to be some sort of contamination; maybe some dust left in the pores that is getting pulled out with the epoxy?? I whole heartedly agree with the scraper for working cured epoxy, it gives a nice finish.

FWIW, I use a 'Bondo' plastic spreader to apply epoxy. It moves it around well and leaves a smooth finish to begin with (or as near smooth as I think you will get).

I have also seen a trick used with Kevlar thet may work here; lay plastic sheeting over the epoxy and then use a brayer (smooth roller) to press the sheeting to the epoxy. When the sheeting is removed it leaves a glossy smooth finish only in need of light sanding.

[Barry Pyeatt]

What I'm seeing here doesn't look like bubbles to me either, it looks like textured epoxy. I've not seen that by applying with a chip brush, only with longer nap rollers, but obviously it happens. But then, thinking back, I've never tried coating a larger panel with a brush. I've not had grain raise like that either. I'm wondering if the epoxy is beginning to gel and the brushing is pulling it a bit as you go over it.

We used a lot of "Poor man's peel ply" in finishing out large plywood panels with epoxy. As Capt. Jake just stated, it is heavier gauge polyethelene plastic. The clear stuff for construction sheeting. 4-6 mil generally works good. Sometimes referred to as "Visqueen." Commonly used for ground cover under concrete slabs, etc.

We rolled the epoxy on the panels, (they were generally hardwoods for decorating) with a foam roller or as Capt. Jake stated, with a plastic spreader. Then laid the poly film over the panels and rolled it out with a smooth rubber roller to give a complete contact with the surface. Once cured, the poly just peels off leaving a completely smooth surface. Using actual peel ply fabric will leave a slight texture to it which is great for laminting or applying glass later on.

This technique is also used by some glass shops (Boat builders included)that do a lot of layups over plywood to give them a really smooth surface that doesn't need much to get a really nice finish on it.

We knocked any ridges or high spots off with a scraper first and then used a long board to sand it completely smooth. Like Charlie, I'm a strong advocate of using scrapers rather than all that sanding. Lots faster and less work for a smoother finish.

[Guest]

Ah, a scraper in the hands of a freshman scraperholic, can be worse than a textured finished piece of wood. The safest way to learn scraper 101, is to begin by grinding the edge or end of your blade to a rounded corner, just a wee little bit, to insure you do not end up with a random pattern of self inflicted deep artifical grain lines at random angles sometimes to the running surface area. :wink: Thats my only drawback with this recommendation without a warning label. But then again, in this setting, we have a lot of unknowns, that maybe knowns in other associated fields of enjoyment, like refinishing mamma's kitchen cabinets and piano stools.

[Barry Pyeatt]

True wisdom spoken there Oyster!

[Barnacle Jim]

Hi Howard,

The orange-peel appearance of your epoxy coating appears to be identical to what I encountered as well. Like yourself, the wood I used was Okume. Unfortuantely, I was not able to solve the problem. In fact, I ended up scraping all the epoxy from the panel, and then applying polyurethane. It was a long and arduous job.

Here are a couple of suggestions

[Howard]

Tried a test panel yesterday. Actually, 4 of them. They were: Okume; marine fir; luan (actually...underlayment for vinyl flooring); and some birch veneered particle board crap that came as backing for a set of cabinets. Interesting response, as the okume did exactly the same thing...rough pebbled finish. The fir and birch were also slightly bumpy, but not anything like the okume. The luan, true to form, sucked up the first coat and had a mostly dry surface, with little "streams" of slick epoxy where it was put on thicker. Interesting that the run-off that was drug off to the side and puddled on the plastic sheet below and to the side of the panels was clear and smooth. No bubbles or pebbles in that.

So I still thinking this problem is somehow related to okume and epoxy, and may be something like a raised grain response. But once you get rid of the grit, it's "clear sailing". Subsequent coats go on as smooth as you make them. Charlie's scraping worked, as does my original method, which was waiting for the stuff to harden enough to sand, then knocking down the tops with 60 or 80 grit sandpaper on a random orbital sander. It's just more work.

As I only have 3 panels to go (6....if you count both sides), I'll do what I've been doing. If I was to build a larger boat, with many more panels, I'd have to consider switching to a different plywood; covering with the plastic sheets, or see if something like a drum sander would work to knock down that first coat.

If it's perfectly smooth, that release film sounds good. The plastic sheets always seem to have wrinkles in them, and that leaves ridges and valleys that are very hard to sand back to smooth.

Thanks to all for your comments and advice.

Howard

[Guest]

Lightbulb moment.... What you may have going on here is two things. In most of the hardwood plywoods that are imported, treatments for pests , required by the government takes place.

Here is a good article for idle reading.

http://www.usconsulate.org.hk/beetle/1999/0120.htm

Also in most of the hardwoods, they contain a bit of natural oils that rise overtime even when you, yourself will cut solid timbers and see a nice change of colors, mostly lighter than the original piece of lumber. Overtime you will notice a darkening of these raw cut pieces, if left about in your shop.

You could be getting some release, not measurable or unsafe, but a bit of orange peel effect for lack of another analysis, such as noted in natural oils from the body transfered to wood products coated coated with paints that goes imporperly prepared for a finish product.

One practice that I have always done on most all plywoods and all hardwoods, is to sand smoothe and wipe down with denatured alcohol, or in the case of teak with acetone before coating with any barrier coat, whether it be paint, sealer coats of epoxy or varnish.

My new opinion and thoughts on this problem.