View Full Version : The Mysteries of Douglas Fir

01-24-2010, 08:10 PM
I am wondering if anyone has advice on how to avoid visible glue lines when working with Douglas Fir? I have a pile of beautifully tight-grained, quarter-sawn fir that I am planning to use for interior trim. The detail of the interior hatch coaming pictured below is my first experience working with this wood and it presented a few surprises. You can see a dark line in the corner gussets (1) where I laminated up two pieces to get the thickness I needed. I purposely used Titebond for this joint thinking that would provide the most invisible seam. Clearly the wood had other ideas. The photo shows the part rough-sanded after the first of what will be three coats of epoxy was applied. Is there another recommended adhesive to make that glue line less visible?

The sealing coat of epoxy revealed another surprise. The darker coloring along the sides (2), compared to lighter top, is actually in the wood, not in the lighting of the photo. The original lumber is quite old, and the planed surfaces had the opportunity to oxidize over years, waiting for me to get to them. Even though I sanded all surfaces of this part thoroughly before coating, it is possible that the darker color is oxidation that penetrated the original surface of the lumber deeper than I sanded, only to be revealed by the epoxy. Or is there a chance the various grain structures of Doug Fir really take finish that differently? Right now the finished part appears oddly mottled. I guess my real question is if I can expect the patina to even out over time?

These are simply aesthetic questions, but I have a lot Doug Fir to work in the near future and I am hoping if I can tap into the collective wisdom, I will end up with a more beautiful boat down the road. Any thoughts/suggestions would be greatly appreciated.

Thanks, Collin


Bob Smalser
01-24-2010, 09:17 PM
..... interior trim

.....Is there another recommended adhesive to make that glue line less visible?

.....(do) the various grain structures of Doug Fir really take finish that differently?

After hot hide glue, which wouldn't work well in a yacht interior, Urea Formaldehyde Plastic Resin glue has the best glueline, besides other advantages over aliphatic glues like Titebond. That said, your gluelines don't look bad from here. What's more noticeable is the change in grain between lams, and the only way to improve on that is with artificial veining of the finish, which is difficult on small stock and not usually worth the trouble.

Doug Fir is known for its texture inconsistencies, even in old growth. This is especially true in Interior as opposed to Coastal DF, because of less consistent rainfall patterns.....and much old growth available today is coming from the interior region. More rain produces a higher percentage of earlywood, and softer earlywood than in drier years.

General Notes on Glues and Goos

Resorcinol: The marine standard. If you can get 70 degrees F or higher for an overnight cure and consistent and high clamping pressure with no gaps, you won’t go wrong using it. (Throw an electric blanket over it to be sure.) Likes wood at 10-15% MC, according to Navy tests. Long open time. Repairable with epoxy. Ugly red glue line.

Marine Epoxy: The repair and restoration standard. Bonds well to a wide variety of materials, and usable in almost all flexibility and temperature conditions. Needs no clamping pressure, only contact. Fills gaps well....but easy to overclamp, starving the glue joint when pulling in thick stock. Likes wood below 12% MC. Repairable with itself; joints can sometimes be broken apart for repair using heat. Clear, relatively thick glue line and can be dyed to match the wood. Controllable open time with different hardeners. Slightly permeable to water vapor and there are many reports of failures in fully saturated wood and with White Oak. Very sensitive to UV, requiring protection.

3M 5200: A rubbery, polyurethane sealant in various colors with adhesive properties sometimes used as a glue. Fails as a glue under water saturation without high clamping pressure, and without the proper strength testing I couldn’t do here, it’s not recommended as a stand-alone marine glue. Repairable with epoxy.

Liquid Polyurethane: Gorilla Glue, Elmer’s Probond, Elmer’s Ultimate, and others. Versatile in temperature and bonding wet wood with moderate open time, these glues aren’t rated for below waterline use but initial use shows potential as a marine glue. Likes high clamping pressure and fits similar to resorcinol…it won’t fill gaps. Will successfully glue green wood at 30% MC, but the wetter the wood, the weaker the bond. Repairable with epoxy. Noticeable, yellow-brown glue lines.

PL Premium Construction Adhesive: This polyurethane goo shows promise as a marine glue with further testing and use. Works like 3M 5200 but cures and behaves like liquid poly. Appears to bond well to everything epoxy does, and more where epoxy and liquid poly won’t, perhaps because of a higher isocyanate content…it bonds to difficult surfaces only cyanoacrylate super glues will bond to. The only general-use glue I’ve found that will bond difficult aliphatic-contaminated surfaces. Appears flexible to temperature and moisture content with gap-filling ability, but as a construction adhesive, its open time is shorter than liquid poly. Appeared to like high clamping pressure, and unlike other glues, wouldn’t bond at all without at least some. Repairable with itself and epoxy. Glue line as in liquid poly.

Urea Formaldehyde Plastic Resin Glue: Weldwood, DAP and others. The old interior furniture standard, and in older marine applications that required well-blended glue lines. Still preferred by many, as it is a no-creep glue easily repaired using epoxy. Long open time, it needs tight fits and 65 degrees F or higher for an overnight cure…it doesn’t fill gaps. Best glue line among them all and moderate water resistance still make it useful for interior marine brightwork applications. A relatively brittle glue and UV sensitive, it requires protection….but its brittleness is an aid to repairability, as joints can often be broken apart for repair. An inexpensive powder with a short, one-year shelf life.

The Titebond Family of Aliphatics: Convenient. No mixing, just squeeze. Short open times, fast tack, and short clamping times. Fast, and an acceptable long-grain layup glue…in heated, commercial shops, I’ve had rough-cut Titebond panel layups in and out of the clamps and thru the planer inside of an hour. Flexible in temperature and to a lesser extent in moisture content, but the bottled glue can freeze in unheated shops, and glueups require 55 degrees or warmer to cure. A flexible glue, it has been reported to creep under load, sometimes several years after the joint was made. The latest “Titebond III” appears to be a stronger glue than its two predecessors. Difficult glues to repair, as they won’t stick to themselves and no other glues will except cyanoacrylates, which are too brittle for general use. Epoxy and fabric aren’t bonding to aliphatic glue lines in marine strip construction, compounding repair difficulties. While not definitive, the new PL Premium appears to bond well to Titebond III residue and is worth pursuing by those repairing old white and yellow aliphatic joints.

Eric Hvalsoe
01-24-2010, 10:13 PM
nice summary

01-24-2010, 10:17 PM
That's Douglasfir?

01-25-2010, 06:35 AM
Hmmm... I suspect my original post may have been unclear. The glue staining that is particularly curious to me is the diagonal line across the corner gusset. I've updated the image to make it clearer (a reload might be required). When the part is held in your hand, these dark lines are VERY prominent.

Mrleft8, the wood is definitely Doug Fir. I think my limited skills as a photographer make it appear more like teak... now if only I could carry that alchemy off in the real world!


01-25-2010, 07:07 AM
I like using stains - Firstly do a neat job, then stain before coating - I suppose there are purists that aren't into stain, but personally I'm into it - I love some of the depth of colour and highlights of grain that can be brought out in timbers with the right type and number of coats of stain (use a good cloth though). Protects against UV damage and discoloration etc too - I'm a bit of a Sikkens junkie


Lew Barrett
01-25-2010, 11:50 AM
This question is sure to annoy (or maybe it is naive) but I have to ask why you are laminating trim rather than just cutting and shaping it from solid stock? I can't guess what the dimensions of your gusset are from here (and it does look fine to me in the photo as Bob said) but would it be that much harder to just shape it from one single piece?

David G
01-25-2010, 12:43 PM

No, it's not at all common for doug fir to have those sorts of random streaks of darker wood. It is possible that the surface oxidation of your salvaged timbers was not completely removed - esp. if you did not joint or plane them, but instead simply sanded. Could that also be the case at your glueline? The colors seem similar. It looks like something leeched into the wood. Could be the result of surface discoloration of an old, exposed, stick. Or... You didn't, perchance, add colorant to the glue in an effort to make the glueline color match the final color??

Your doug fir will, indeed, darken over the years. It reacts to UV exposure. I doubt that the bulk of the pieces will get as dark as your existing streaks appear to be. Also... the photochemical reaction in doug fir tends to result in a different color - orangey, red, brown. Your streaks appear to be more chocolatey.

Tom Robb
01-25-2010, 08:00 PM
My first thought was that this is wood after all and fretting over the uniformity of the grain for me would be beside the point.
Plastic is nice and uniform.
But if it bothers you, scrap it and try some other bits. Also those color matching ideas may serve you.

01-25-2010, 08:04 PM
I have to ask why you are laminating trim rather than just cutting and shaping it from solid stock?

Lew- The corner radiuses I will be fabricating will require stock from 2" to 3-1/2" thick. The stock I have available is all 1". From past experience (with other species), I had no reason to believe the glue lines from laminating up the stock would be so prominent, so I forged ahead. Live and learn. In the end, your suggestion may prove the most pertinent. Getting some 12/4 would solve all my problems, but I must admit that none of the Doug Fir I've seen on the lumber yard racks over the past several years matches the tight-grain, old-growth fir I stockpiled for this project years ago. Compromise is such a sweet sorrow.

Best regards,

01-25-2010, 08:37 PM
It is possible that the surface oxidation of your salvaged timbers was not completely removed.

David, the more I think about it and listen, the more I think this is exactly the issue. The stock I am using is salvaged 1" stair tread that was surfaced on four sides and used unfinished as shelving. I came across 100s of board feet of this stuff in an abandoned building. Several of the boards were 18' to 20' long. It was in perfect condition but probably exposed to light for 40-50 years, so the oxidation is deep and rich. No simple surface sanding penetrates it, and the application of glues and sealers just highlights the varying patinas, once I mill it to my specs. My experience is in working much hard woods, so I am not use to patinas that penetrate so deeply. With a little forethought, I suspect I can learn to take full advantage of the character of this fir.


01-25-2010, 08:44 PM
fretting over the uniformity of the grain for me would be beside the point.

For me too. I prefer to spend my time fretting over ugly glue joints that distracted from the beauty of the wood.

01-25-2010, 09:21 PM
Collin...if you dunno need that old, oxidized fir, please bring it to me...and I'll buy you a nice cuppa coffee and a piece of your favorite pie....and you'll have my warmest thanks.
Best regards,

Lew Barrett
01-25-2010, 09:31 PM
Collin your work looks plenty fine to me as it seems to do to everybody else here (and among the fussiest have commented so far). I think you're good with however it turns out!

That stuff in the photo sure does look like teak.......has me shaking my head.