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bcanuck
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# Posted: 3 Dec 2023 12:06
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I am hoping to do a 3 ply 2x10 or 2x12 beam 20’ long. I need it to be pressure treated. I understand that warping and twisting is an issue as the lumber dries. Would it be less likely to warp or twist if i did the nailing or bolting together when still wet, and let them dry together, or try to dry them out first and try to force them straight afterwards?
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ICC
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# Posted: 3 Dec 2023 13:09
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Assemble it wet if that is the way the PT lumber gets to you. S/S or hot dipped galvanized or other fasteners approved for the type of PT you get. No adhesives.
-izzy
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Brettny
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# Posted: 3 Dec 2023 15:49
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Wet is fine. I would definitely get 20' lumber.
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Irrigation Guy
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# Posted: 3 Dec 2023 21:42
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You can get pressure treated LVLs
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spencerin
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# Posted: 4 Dec 2023 19:26
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Assemble when wet, and get 20' long pieces if you can.
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travellerw
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# Posted: 5 Dec 2023 00:28 - Edited by: travellerw
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IDK.. I'm in a different camp. Built up beams gain a ton of strength from adhesive. Even though construction adhesive is "moisture cured", too much moisture reduces or even eliminates the bonding strength. Some of the boards at my local suppliers are absolutely sopping wet and I'm sure adhesive would not adhere properly. It would cause the adhesive to skin too fast and not bond.
I think this is one time where you have the luxury to build it better than industry. Personally, I would pick the driest boards I could, or in my case I went with white lumber and instead coated it after the beam was constructed. White lumber also has the advantage of a higher load rating than pressure treat. Of course the downside is maintenance (a recoat every 5-7 years).
Of course if you are building without access for a recoat, then you are between a rock and hard place. Pressure treat is your best bet, but I would spend the time picking out the driest, straightest boards. Even if it meant going to 10 different suppliers.
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Aklogcabin
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# Posted: 5 Dec 2023 10:01
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I would also try to get the driest boards I could. And use adhesive between them. Probably titebond 3. And spread an even coat across the entire surface. Trying to insure I apply some pressure and get the glue down into the grain the best I could. Might even stick some plywood in the lumber sandwich.
The suggestion to use LVLs is a good one. You can be certain that you will have a straight strong beam and order the lengths you need. I used them for rim joists on our cabin along the BCI laminated beams.
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Brettny
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# Posted: 5 Dec 2023 10:17
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Quoting: travellerw too much moisture reduces or even eliminates the bonding strength. Some of the boards at my local suppliers are absolutely sopping wet and I'm sure adhesive would not adhere properly
Polyurethane subfloor adhesive or great stuff construction adhesive that you need the pro foam gun for actualy wants moisture to cure. I believe it says you can use it on damp wood. That stuff also works great for a subfloor adhesive. It helps with a rock solid floor.
I didnt use any adhesive on my 32' long tripple ply 2x12 beams. I used headlock screws from fasten master. 2 or 3 rows every 16in. Theres a manufacturer suggested pattern to that. There no cheap but re doing a girder under a cabin is not something I want to do when I could have just spent an extra $100 to begin with.
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Brettny
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# Posted: 5 Dec 2023 10:19
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https://www.amazon.com/Great-Stuff-343087-26-5-Ounce-Floor/dp/B0045LPK2S/ref=mp_s_a_1 _3?crid=31NX00LYTEUWS&keywords=great+stuff+construction+adhesive&qid=1701789454&spref ix=great+stuff+con%2Caps%2C199&sr=8-3
https://www.amazon.com/FastenMaster-FMHLGM412-50-Heavy-Duty-Flathead-Fastener/dp/B001 OELZ0U/ref=mp_s_a_1_3_mod_primary_new?crid=17WTEUOB4FDD7&keywords=fasten+master+headl ock+screws&qid=1701789499&sbo=RZvfv%2F%2FHxDF%2BO5021pAnSA%3D%3D&sprefix=fasten+maste r+%2Caps%2C387&sr=8-3
Brand dosnt really matter. Theres alot of manufacturers selling this polyurethane foam glue and large head structural screws.
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spencerin
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# Posted: 5 Dec 2023 19:42
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Asking for my own knowledge - why would adhesive matter in this situation? The fasteners are what hold the boards together. To me it makes more sense to fasten the boards together when wet as they may wrap some as they dry, potentially making it harder to line them up to fasten.....
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ICC
Member
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# Posted: 5 Dec 2023 20:59 - Edited by: ICC
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Personally, I don't use adhesives when making a built-up beam. I'll either use spiral or ring shank 16D nails or as Aklogcabin did, use Fastenmaster Headlok screws. Those are an excellent product, that are safe for any PT wood. The washer-like head adds to the pull-out resistance.
I do use adhesives for sunflooring as that is where squeaks can occur and properly gluing eliminates the squeaks. Proper use mainly means applying the adhesive and laying the subfloor sheets on top below the open-time expires.
Properly glued layers of a built-up beam may add some strength, but it is not a huge increase. An engineer does not count such glue in the calculations, as there is no guarantee the glue will be properly used. That is what the engineers I have talked to over the years have all said. Factory-applied glues, OTOH, are applied in a controlled environment and are a totally different thing. Poorly applied glue (too much) can also prevent the layers from fitting closely and could be detrimental.
When the built-up beam is correctly supported with a pier under each and every splice, all the fasteners really have to do is keep the wood sandwich layers together
-izzy
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KinAlberta
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# Posted: 6 Dec 2023 15:00 - Edited by: KinAlberta
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The adhesive might fill any gap and prevent the trapping of water or moisture.
Depending on exposure and what might get screwed or nailed into it, I’d consider caping the beam with a strip of butyl tape.
Also note that there’s different types of PT 2X_s. “In ground†has far better treatment. Possibly a lot wetter when new.
I read somewhere years ago that the lighter treated lumber was essentially downgraded from say on-ground to use some distance above ground.
Found this:
Different Types of Pressure Treated Wood - WoodCritique
Excerpt:
In-Ground Contact for Critical Use
Pressure-treated lumber for in-ground or critical use comes with a greater retention level than the one in the above or ground contact. I advise that you use in-ground type lumber in areas with a greater risk of deterioration or critical structural uses, such as the foundation posts exposed to fresh or groundwater.
In the above case, the best pressure treated wood should be the UC4B and UC4C; UC4B comes with a higher retention level than the lower graded types. The UC4C has even more retention levels.
Marine Grade
Wood treated using water-based chemicals for saltwater immersion comes with significantly higher retention levels than the other categories. The UC5A contains almost double the weight of preservatives as the UC4C. The UC5B and UC5C have more than…â€
https://woodcritique.com/blog/different-types-of-pressure-treated-wood/
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spencerin
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# Posted: 6 Dec 2023 22:42
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"I read somewhere years ago that the lighter treated lumber was essentially downgraded from say on-ground to use some distance above ground."
If that happened, that probably coincided with the change from CCA to ACQ 20 years ago. CCA performed/s better than ACQ.
FYI - you can still get CCA treated lumber. You're just not supposed to use it in residential structures. Like if you're building a pole barn, you can use it for the foundation.....
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