I have a situation where a glulam beam is exposed on the outside of the building and on the inside of the building. How do I handle putting a clear coating the beam? Can I use one paint product instead of an interior and exterior paint product?
Treat it the same as a piece of sawn lumber
Okay then I guess I will use nitrocellulose lacquer. Thanks!
try ZAR by UGL.
I’d be antsy about using nitrocellulose lacquer for exterior use, due to its only moderate water resistance, and also its tendency to yellow as it ages, which shows clearly on light-colored woods.
Also, assuming it’s field-applied, will there be VOC issues if this is a LEED project?
The only exterior clear coating for wood that I’ve found to be durable is spar varnish–if someone is aware of other clear-coat products with a good track record for exterior use, I’d be glad to hear of it. Again, VOC content could be an issue for interior use of spar varnish.
Is there a limitation on VOC for the coating? There’s an indoor air quality issue that now (at least in California) applies to non-LEED, etc. projects. There are considerations for local air quality management authorities as well as the indoor air quality czars.
I agree with Dave about the Spar varnish for the exterior. Don’t forget to have the treatment done after all fastener holes are drilled, so that the inside of the holes gets the treatment, too. This can be shop done, actually with field touch up – but there shouldn’t be any field touch up if all cuts are done in the shop. In the northwest, these coatings work the best if they are shop done and protected until installation is complete.
as to Mr. Regener: the Puget Sound Air Quality guys are strict, but its not like California where there are “Washington versions” of various finish projects. You can still get solvent based coatings that actually work.
lacquers and related finishes are a specialty area I deal with daily, a real problem, and tied to both my consulting and hobby - so I’ll be happy to provide any info or research you need. This specific subject is a “pet peeve” so I take off the consulting badge (and shove invoices in a bottom drawer) and provide all the advice I possibly can. I’ll have a few questions, so if nothing’s been decided hopefully I can help.
I have to run to an appointment but will post when I get back.
OK, I’m WAY late!
Anne, we still get solvent based coatings that actually work; it’s really the applicators having to re-train themselves every time there’s a change that’s the problem. Manufacturers do little to notify users of formulation changes and keep the same product name even when the application characteristics are quite different.
OK - First, everyone is right about spar varnish on the outside, although it will yellow as much (if not more) than some modern lacquers. It really depends on individual products. As far a “nitrocellose lacquer” goes, I don’t like it on any laminated product. Even though almost all modern lacquers are nitro/acrylic blends (whether they say so or not, and an MSDS doesn’t tell you either) with improved flexibility they’ll still crack eventually.
When it comes to lacquers and related finishes, I wear two hats - one my “work” hat, the other refinishing guitars as a hobby. There is a lot of interest in duplicating instruments of the 50’s and 60’s, especially “relic” finishes, where the finish is artificially aged, worn, discolored, cracked etc.
Here’s somebody’s random example (not one of mine - I don’t usually post pics of my work):
http://www.josephmind.com/TeleRelic.jpg
This has caused a huge resurgence of wood finish debates, overflowing into wood finishing of any kind - furniture, architectural etc.
It’s also caused a huge amount of confusion and disinformation, some specific to the guitar world (some claiming they can “hear” differences between nitrocellulose lacquer, acrylic lacquer, polyester and polyurethane finishes…which is nonsense) and some applicable here.
When you specify “nitrocellulose lacquer” you could end up with pure solvent-type “nitro”, acrylic/nitro blend or water based lacquer. Some products labeled “lacquer” are not really lacquers as we think of them, but conversion varnishes or other clear (or in some cases pigmented) coatings. What John mentions regarding VOC’s is important almost everywhere, though - because if it says “lacquer” on the label that’s how it’s classified under air quality regulations.
Some jurisdictions have exemptions for 1-liter and smaller containers…some don’t. But the general rule is that it’s illegal to sell, apply or specify products that exceed the upper VOC limit of their classification. And some local rules differentiate between interior and exterior applications.
So before you decide what to specify, you need to know, of the possible product types you can think of, what the air quality rules are for both the application process(es) and each “candidate”.
It gets stickier. Shop-applied finishes fall under another set of rules, so if that’s a possibility it needs to be considered. To make the pile even higher, if shop application is to be done (or is an option) you need to be sure the system can be touched-up in the field.
Then once you have all that info for all possible candidates, you need to know the location of the application(s). You may have a system that can be legally applied in the shop and touched-up in El Paso but if the shop finisher is in Phoenix he may only be able to apply products that can’t be touched up in El Paso…
Ergo - unless you can control the location of the application you might need to include some language that requires bidders to ensure such products can be used in both locations if necessary. It still may be tangled up in the submittal process but at least the burden is clearly on the contractor to provide a workable solution.
And that’s without even getting to what’s specified vs what’s used.
Some are very insistent they want “nitrocellulose lacquer” and not “acrylic lacquer”, insisting the latter is inferior and that the two are also incompatible (especially when acrylic is applied over nitro).
I want to make sure there’s a clear understanding of one important fact that seems to cause confusion every other day - “acrylic lacquer” DOES NOT mean it’s water-based.
The fact is that with a few exceptions sold in small quantities (and not suitable for larger projects) almost every solvent-type lacquer made today (actually in the last 40 years) is a blend of nitro and acrylic. Acrylic resins were added initially to automobile finishes (which were nitro) to improve flexibility - and eventually almost all “lacquer” became “acrylic lacquer”.
The two are usually compatible - there are some highly-pigmented acrylic lacquers (in neon-like colors) that are not compatible with anything but themselves, but those are very isolated conditions not likely to be encountered.
But to make this very clear - unless you specify “water-base lacquer”…you’ll likely get acrylic lacquer (meaning a blend) or possibly pure “nitro”, which is fine too. But there are often problems with submittals of “acrylic lacquer” where “lacquer” is specified. There shouldn’t be. I avoid it by specifying “nitrocellulose or acrylic-nitrocellulose blend lacquer”. Then things won’t get bogged down later on.
But I generally go with water-base lacquer in architectural applications as VOC levels are generally lower, chances of early yellowing are lower, they’re more apt to be in use by shop finishers and they’re usually less expensive while providing performance equal to acrylic lacquer.
Most paint reps know far less about lacquers than the woodworking folks; I usually refer to the Woodwork Institute of California’s finish systems when I’m looking for a generic type for a specific application - then go to the MPI list for approved products.
Hope that helps - If anyone has a specific question shoot me an email!
David,
Glulam is not the same as a piece of sawn lumber contrary to what Mark advises you to do. Be careful with exterior glulam beams. I dont know where your project is located, but we had a case where the architect used exposed glulam beams (they were used as beams/railings on bridges between low rise residential towers) on a project located within a stones throw of the ocean in SoCal.
The glue formulation may have changed since, but at the time it was an organic-based adhesive. It turns out that in a humid environment tiny creatures got in the glue line and ate most of it causing a major failure of the beams/railings. What we had were pieces of unbonded wood and fat bugs.
Since then I believe AITC has changed the formulation of the adhesive, but we always recommend a sheet metal cap on glulam beams exposed to the elements to keep most of the water off the beam.
As for finishing the members, we specify that a first coat of finish be factory-applied so that even in transit there is some protection against wetting. I dislike spar varnish; it yellows quickly, is a hard finish, and has to be re-applied too often, especially on the West and South exposures, as anyone whos ever owned a wooden sailboat knows. Sikkens has a good line of exterior finish products with UV inhibitors although they are translucent; their Cetol SRD and Cetol 1 + 23 Plus have worked well for us in the past. You might want to give them a call.
Hope this helps.
This is the first time I have heard about bugs eating the glue in glulams in over 38 years dealing with glulams and other engineered wood products. I will offer a couple of facts that might provide another explanation for the reported problems.
Any glulam used in an exterior environment or where there is high humidity should be made using exterior glue as opposed to interior glue. If interior glue is exposed to high moisture levels it will loose strength. It is my impression that most manufacturers are now regularly using exterior glue for all glulams but I would still explicitly call out the use of exterior glue for members that will be exposed to moisture.
The code requires that glu laminated members that are not shielded from rain be treated or protected by a metal cap. Reference IBC Section 2304.11.3. While the code only addresses this issue for laminated lumber the same problem applies equally to sawn lumber that is similarly exposed. This has nothing to do with the fact that the lumber has been laminated. Because the laminations are not treated before laminating and because of problems associated with treating the members after fabrication the treated wood option is typically not viable for laminated lumber.
The wood that you are applying the coating to is the same as a piece of sawn lumber. I will admit to not knowing if the coating will interact with the gluline in some way but I would suspect that if it was a likely problem that we would have heard more comments about this on this thread. Suggest that you contact AITC.
Mark,
The project I mentioned with the glue eating bugs was designed in 1977 or 1978. AITC standards have changed since then. We asked AITC for advice at the time and their finding was as I stated.
Even if the wood is treated, I would recommend a metal cap for beams exposed to the elements.
If you put a metal cap on glulams then do the same for sawn lumber because the issues are the same.
I have still not heard anything that causes me to modify my original recommendation that the coating applied to a glulam should be the same as applied to a piece of sawn lumber. In both cases you are interested in protecting the wood from the effects of high moisture content.
Okay, let’s end the guess work here.
I spoke with a friend of mine who has done glulam projects here in southern California, and near the ocean, with the beams being both interior and exterior.
His recommendation based on what he has used is the West Epoxy System, either 105 or 106, with the 207 hardener. The finish is “water clear”
This product also complies with SCAQMD (South Coast Air Quality Management District) requirements for VOC’s for field application.
If you need more info, please e-mail me at richard.matteo@stvinc.com
West epoxy is by the Gougeon Brothers and is a marine epoxy intended to stand up to marine conditions:
I have them listed in the wood repair section and not general coatings.
That may be true, but two of the projects the product was used on were glulams on high end homes, at least one of which is in Laguna Beach, right near the Ocean. It was used as a general coating for glulams on at least 2 projects and there have not been any issues.
Richard,
I’d like to see the result. How long ago was the epoxy coating applies?
We’re always looking for compliant products in SoCal. Do you have an address? You can send it to me at the email address below.
Epoxy coatings will yellow and/or chalk when exposed to direct sunlight/UV. I doubt that westsystems has an epoxy that defies this basic law of resins.
Is the epoxy rigid or can it accommodate dimensional change in the wood due to changes in moisture content? While glulams are made of “dry” wood there is still some moisture adjustment that will occur during use especially if the epoxy does not totally encapsulate the member.
I agree with anon. I thought that epoxies yellowed very easily.