how good does polyester and glass really bond to wood? wanting to make half glass half wood fins for a fishy fish i just shaped…i will make the fins from a old skate board with good curves…i got the idea from taylor o…thanks taylor
Howzit tjd, The only problem is the oils in the wood. When working with wood I always put a lam resin coat on it first to seal in the oils, You can thin the resin with styrene, but not to thin. The heat from the kicking resin when glassing sucks the oil out of the wood to the surface and it can cause delamination of a foggy look. Aloha,Kokua
Hey up!
I’m by no means experienced in these things but have built two hollow wood boards and a few sets of wood fins (not quite as many as Mr chip fish) and have only used poly, so far no worries with bonding. Like Kokua says some woods are oily and may cause problems so just choose your timber carefully…avoid pre-oiled cherry and the like, experimented with this cos it looked nice…didn’t work.
Good luck
Jase (MMM)
Hey up Kokua
is that what causes that fogging of the resin. I’ve had that when I was glassing part of the bottom of my last board, the oak was fine but parts of the sapele were a bit wierd. Luckilly it went clearer as it dried, not noticable at all now.
Jase (MMM)
hi tjd !
when you say ‘half glass, half wood’ fins …I assume you mean you have the glass on the outside ?
Or, were you going to do what a mate of mine did …sandwich fibreglass between ply layers ?
This worked nicely for him …on his latest keels , he tinted the glass , to help him with foiling .
I also assume yours will be curved fins , then , if you’re using an old curved skatedeck ? …good stuff !
Please post some shots when they are made , eh ?
ben
Howzit Fatbas, Is the sapele wood dark colored? When doing haubush tail blocks I found the darker wood was more of a problem. Yes I would say that is what causes the wood to fog, which could also mean that the glass didn’t bond well there. They didn’t have to much problems with this years ago when they were cutting old growth trees but todays young growth lumber doesn’t have a chance to force the oils outward from the heart wood. The issue of S.J. with the Curren wood board projects explains it and how they dealt with it, but they stripped the poly and reglassed with epoxy due to a longer colder cure which doesn’t draw the oils to the surface.Aloha,Kokua
Hi Kokua
Yes the sapele is quite dark, is this a common thing with darker woods? Do darker woods generally contain more oils than lighter woods? There doesn’t seem to be any problems with the bonding so far but the board was only finished about three weeks back and has only been used for a few short sessions. Fingers crossed from now on then! Oh well if it messes up I’ll just have to build another one…Oh hardship!
Cheers
Jase (MMM)
Howzit Fatbas, Can’t say for sure that all dark wood will have more oil, just that dark haubush is a problem and I precoat any wood that is going to be glassed with poly. This could be a good project for some one who has access to a lot of different wood types. They could do some tests, could be very informative results. Aloha,Kokua
i glassed a 6’4 hollow with poly no problems , and because the wood is already brown you can get away with the cheap home depot resin ( it does the job but its a brown color) it rides great and doesnt leak.
Hey JG
you must get better GP resin over there than the crap they sell to us schmucks in the UK. The stuff they sell over here is very green, gloopy, stinky, cloudy and generally shite in every way. I have to use the more expensive clearer suff (I love wood) Still, I have found someone who can supply some nice, dead clear resin for the same price everywhere else charges for GP res, if only he could get me epoxy at the same price I’d be stoked!
Jase (MMM)
Hey Chipfish, How did you get that picture of me for your avatar? That’s what I see in the mirror every morning before my cup of coffee. You could have at least asked my permission. This is so embarrassing.
Now, regarding wood: Some dark woods are fine to glass over. I’ve done it with the darkest of the dark…Ebony, with no problems. It’s definitely dependent on the chemistry of the different species. Redwood can have problems,(delam) as well as Tulipwood (bubbles). But, as we know, Cedar, Basswood, and Balsa are fine. It pays to experiment with scraps: a little time now may save a lot of time and headaches later. Doug
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Now, regarding wood: Some dark woods are fine to glass over. I’ve done it with the darkest of the dark…Ebony, with no problems. It’s definitely dependent on the chemistry of the different species. Redwood can have problems,(delam) as well as Tulipwood (bubbles). But, as we know, Cedar, Basswood, and Balsa are fine. It pays to experiment with scraps: a little time now may save a lot of time and headaches later. Doug
Hey Doug - great name 
You probably mean wood characteristics and physical (aka working) properties, rather than chemical. IRT characteristics I think porosity and oil content are the most important in boardmaking. With physical properties it’s probably density, workability and permeability.
Is anyone interested in discussing the role timber plays in sandwich construction? I’ve read a few comments about compression vs tension, but little about some of the other critical factors in timber use (e.g., strength IRT width vs thickness, sub-surface tensioning using sheer ala the Perry Principle).
Anyway, just interested 
-doug
PS. Thanks to everyone who’s posted so much on here regarding sandwich boards (Bert, et al).
Quote:
Hey Chipfish, How did you get that picture of me for your avatar? That’s what I see in the mirror every morning before my cup of coffee. You could have at least asked my permission. This is so embarrassing…"
…the same place fatbassy got his ! We’re triplets , REMEMBER ?? Only our mother can tell us apart . …ben
Hey People
One thing you are overlooking is the humidity factor, any moisture in the wood will lead to delams and fogging. I found this out the hard way on my first HWS.
Didn’t delam though, hit the wood with a hair dryer or in an oven at 120 deg C, nice and dry then…
Yep - the hydroscopic nature of wood means that we need to be very aware of how it will always equalise with the moisture in its environment. Wood typically comes out of the kiln at somewhere around 9%MC. Sometimes more, sometimes less - depending on where it will be delivered.
Timber thickness impacts how quickly wood will equalise its MC to it’s environment (assume unprotected timber). Think wood takes a long time. Thin wood (like 2-4mm laminates take a matter of hours). MC directly impacts wood’s ability to bend. More importantly, from the perspective of this thread, it affects how it might “sweat” under a layer of epoxy/polyester resin.
Which is going to bother epoxy/polyester resin more? Water or oil? Every timber varies in how oily it is. Every piece of timber can vary in MC.
Blather, blather 
-doug
Hey tjd,
Kokua and some of the others are the “go-to” guys on glassing. I’ve done several balsa boards with various wood skegs, nose/tail blocks, and stringers. Though I’ve been a furniture maker and wood guy for over 30 years, I always have a pro glasser do the glass job. The successes and problems are always researched back to what we feel may have been the culprit (wood dryness, type of wood, etc.). I’ve also made hundreds of wood fins with various woods in recent years which has sent me through this learning curve we’re discussing here.
Many of the comments made so far seem right on the money. I would summarize my experience by suggesting the following:
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The moisture content of the wood is critical. A 2x4 from home depot is loaded with moisture vs a piece of previously kiln-dried walnut stored in an attic in tucson) I agree with Doug’s comments about thickness and dryness. You can’t “dry” a thick board (1/2" or more) with a hair dryer or by zapping it in a micro-wave. Moisture content is a technical measure of it’s internal cellular content or “trapped moisture” and has nothing to do with how it feels to the touch. I always allow my newly purchased kiln dried lumber to sit stickered and stacked in my shop for weeks or more (months) depending on thickness, to “acclimate” to the environment. I’ve had many “dry” boards cup and bow once resawn or cut open on the saw to expose the internal cells. If I rip or resaw a piece of hardwood I always sticker and stack the pieces for several days before final cutting and assembly in order for the wood to “acclimate”. Newly milled lumber requires a minimum of roughly 1 year per inch of thickness IF properly stacked and stickered in correct environment. Nuff said, just make sure your wood is properly dried or you’ll have problems.
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Woods commonly classified as “oily” are the rosewoods and teak, which can cause problems with glue-ups and especially with glassing. Even oils from your hands when handled on hot sweaty days just prior to glassing can cause eventual delam problems.
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No need to prejiduce against dark woods as color doesn’t know resin. I’ve never had glassing problems with black walnut or ebony or wenge. The single biggest problem I have ever encountered with glassing over wood is when I have used burled or “highly figured” redwood. I’ve had experience with both thousand+ year-old “old growth” and young “plantation grown” woods and haven’t noticed much difference due to the actual age, but I suspect it is the age that causes the core cell dryness. Trees add new growth to the outside diameter of the tree or log, and the tree decays from the center or earliest wood (plinth). The thousands of microscopic air pockets and cells within burled wood release that air when the hot resin hits causing bubbles and problems.
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Don’t sand too fine. I used to sand my balsa boards to 220 grit or more for that “pristine” look, however, the glass doesn’t like that smooth surface. I now sand to 8o gt. for better “stick”. I was told that Velzy used to sand his balsa boards to 60 and often bring in boards with rasp marks with instructions not to sand before glassing. You’ll still get that super high gloss finish with poly if that’s what you’re after.
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Bottom line: Use most any properly kiln dried wood you want, don’t over sand, and seal it very good prior to glassing. Prior to taking my fins to the glasser, I brush on thin coats of slow-kick resin to seal the wood. Once dry, if you see any “flat” looking areas it usually means the resin sucked into the wood and you need to keep adding sealer until all the wood has a gloss look. Then it’s time to glass it.
This is a long-winded response, but I think back to when I began experiementing with glassing wood, and desperately wished for advice. I hope this helps. Enjoy the ride!
Richard
Hi Richard,
I’d be interested to hear your thoughts on the “modern speed drying” techniques. Which basically amount to artificially elevating the temperature and lowering the humidity of the timbers’ environemnt - the wood thinks it’s heading for a lower MC than it really is. That’s oversimplifying a bit tho… 
I have had really good results with this on timbers up to 1" x 3" - from dripping green timber to cured wood in 4 weeks or less. Done properly there’s minimal checking (in some cases less than stickering and drying) and no structural damage.
To take this back on topic…
I would think that pinholing/bubbling is from timber with low absorption characteristics and maybe even slight oiliness. The timber doesn’t absorb fluids well (so doesn’t absorb your resin of choice) but it will still quite happily release air into an encasing fluid as it warms up. If that’s right (quite possibly it is not!) one solution might be to seal the outside of such timber after rasing it’s temperature. The wood will be cooling and trying to suck in more air. But since its resin encased it will be force to suck in a small bit of resin instead. As for slight oiliness… Maybe a wipe down with acetone? Better/simpler to use different wood in that case, tho.
Fogging is an interesting one. I’d guess at wood that isn’t at it’s final MC (so it still contains some moisture). As it warms up to its usual use environment’s temperature it tries to release water vapour - but that’s trapped by the layer of resin. That’s probably more plausible for timbers that don’t absorb fluids as readily. In any case my experience has been that “internal fogging” is usually associated with MC issues. Here’s an easy way to make sure your veneers are at ambient MC - keep them inside with you for a few days. If it’s too hot for you it’s too hot for them. If it’s too cold for you its too cold for them. Even the thickest veneers (at least, those that we’d us on boards) should have equalised by then. If you are really dedicated you could weight them every day - when their weight stabilises to within a 10% shift their MC has equalised.
Too much? Lemme know 
-doug
Howzit Hicksy, I keep a hygrometer in the shop for humidity readings and it’s usually between 75% and gets a high as 110% ( go figure ). This another reason to precoat the wood with just resin before glassing the board. It’s really hard not to think about humidity when you live in 1 of the wettest places on earth, annual rainfall is around 400" a year.Aloha,Kokua
Hey kokua!
That sounds like our tropical north You know, if you can get MC down to something like 20% you’ll get better strength and liughter weight. And it shouldn’t pick up more moisture once its embalmed in resin.
-doug
Hey Kokua,
You guys definitely reside in a saturated environment, though isn’t it pineapple juice not rain? You mentioned relative humidity readings above 100%, which some may contest, but a little known fact is that fresh cut wood can also have a moisture content (mc) above 100%, due to the fact that certain sapwoods can actually be more than half water by weight. Also on the topic of wood and moisture, it’s amazing just how much lumber can be saturated with water when you might think it’s “dry”. Lumber loses roughly half it’s weight from freshly cut to kiln dried to around 8% moisture content (mc). To put that in perspective, a piece of timber that weighs 60 pounds when cut will weigh around 30 pounds once kiln dried to 8% which is equivelant to well over three gallons of water being lost from the wood - an amazing amount of water contained in a board.
To bring this all back toward topic, I agree it’s important to keep humidity levels in mind not only for you guys that glass, but for the guys who deal with wood boards (stringers, blocks, wood fins, etc.). I actually keep three hygrometers located at different places within my shop and have a dehumidifier going full time in my finish room where I keep wood ready to work. We’re humid here on the south coast (gulf).
Doug, I think you are right on with your comments. I’ve been told, and Kokua would likely agree, that the ideal time to glass is just at the time of day when the highest temp has been reached and the temp then begins to fall, pulling the resin in.
I mentioned earlier the issue of “acclimating” wood within your own environment even when purchasing kiln dried lumber. The following guideline may be of some generalized help to those who care about this kind of stuff: The average annual relative humidity in New England is about 75% while the average in the southwest is about 35%. Therefore, if two identical boards are kiln dried to 8% and one is sent to each local, each board will slowly “acclimate” to a new moisture content relative to that geographic region. That 8% dried board sent to New England will eventually reach about 14% mc, while the similar dried board sent to the southwest will eventually stabilize at about 6% mc. The wood equalizes itself in its new environment and is referred to as (emc) or equilibrium moisture content.
Sooooo, suffice to say that all this mindless chat is simply to convey that even kiln dried doesn’t mean it’s locked at that dryness forever. Wood will either draw in moisture from the environment or dry further based on surroundings which is a good to keep in mind when receiving lumber from other areas. I recently had a small amount of undried koa wood shipped from Hilo and actually left it stickered and stacked on my covered porch outside for several months before bringing it inside the shop so that it wouldn’t dry too quickly and risk cracking. Who got me started talking wood? Anyway, I hope some of this is useful to you guys dealing with wood boards.
Enjoy the ride!
Richard