Gluing up treated lumber

[lilranch2001]

Has anyone ever done glue ups on treated lumber?
I am wanting to build a 10-12 foot bridge across one of my creeks for my tractor and utv to cross, and I would like to glue up arched 2x4's as the main stringers.

I thought a urethane water activated glue like Gorilla Glue would work

Just thought maybe one of you guys may know better than me

 

[k0ua]

Hmm.. I have never done that.. Of course as you know Pressure treated lumber is "wet" for some time." and wants to shrink. I will be watching this to see if anyone has experience and wants to weigh in on this. Maybe I can learn something too!

 

[Gary Fowler]

As KOua has said, most pressure treated is saturated with water/chemicals and needs to dry in the open air preferably in the sun for 6 months or more before painting or staining so I would think the same would be true for glue even the water cure type. Lots of shrinkage going to happen and that would likely pull the wood away from the glue since you couldn't count on both sides shrinking the same amount at the same rate. But this is just my opinion as I have never tried to glue together PT wood.

 

[sparc]

I've never tried what you ask, but a couple years ago the local electric utility installed some new poles. They were not your normal round poles made from tall, straight tree trunks, they were glued up laminations of 2x12 and used to form poles over 50 foot long. They may have some bolts or large lag type screws also, can't tell just driving by. They have been in place for over 2 years and I go by almost every day on my way to work and have seen no signs of delamination or other degradation. Next time I can I will snap a pic and put it up here.

You might search on line and see if you can uncover something about how they are made.

E-LAM® Structures | Laminated Wood Systems

 

[k0ua]

I've never tried what you ask, but a couple years ago the local electric utility installed some new poles. They were not your normal round poles made from tall, straight tree trunks, they were glued up laminations of 2x12 and used to form poles over 50 foot long. They may have some bolts or large lag type screws also, can't tell just driving by. They have been in place for over 2 years and I go by almost every day on my way to work and have seen no signs of delamination or other degradation. Next time I can I will snap a pic and put it up here.

You might search on line and see if you can uncover something about how they are made.

E-LAM® Structures | Laminated Wood Systems

We have some of those here too. They seem to work.. But they may be glued up kiln dried wood, and then treated.

 

[s219]

Construction adhesive works on dry PT wood. If you are gluing up the 2x4s in a way that the glue carries a structural load, you need to use something with known properties for that use. Not just any glue can be used in structural applications. Maybe show a picture of how you want to do the layup and we can figure how critical the glue is.

 

[jel1988]

Gluing lumber together to form structural members is best left to engineers and truss manufacturers. You would be further ahead to look at standard construction methods to support the loads you require.

 

[9fingers]

A Few years ago the University of Maine did research on using a layer of unidirectional fiberglass tape embedded in epoxy in laminating wooden beams. oNly one layer on the bottom lamination was needed to increase the strength of the beam by more than 50% . Doesn't apply to PT Lumber but using this method along with KD lumber and then waterproofing might work.

 

[EddieWalker]

Gorilla glue likes water in the wood, so that might be a good thing. I'm not a fan of gorilla glue. It's too expensive and there isn't any advantage to using a glue that is rated for stronger then the wood itself.

I would use 2x12's and exterior grade construction adhesive like liquid nails or one of the other name brands. To make it really strong, I would sandwich half inch treated plywood between the beams and screw it all together ever 12 inches, top and bottom.

I'm not sure of what the 2x4 stringers are for? Since this is something you plan to drive your tractor across, I would make sure you have the beams supported by concrete on either end and I would space my joists 12 inches apart. Since it's only spanning 12 feet, I think blocking the joists half way should be sufficient. I wouldn't use nails, they tend to work their way out once the wood dries out and then even more so with movement. Screws and bolts would be the only type of fastener I would use.

Eddie

 

[BHD]

at one time I bought some treated plywood, I do not know if it was treated before the glue up or after, but was designed for wood basements, that they were pushing 30 or so years ago,

I use for a craw hole entrance, and has been doing good for 20 years,

I know some of the stuff is hard on hardware, but consider bolting it together, (find some SS steel tubing and make some rings for greater grip) normally called split ring construction, basically use a hole saw to cut a ring area and matching on the other and put in the ring and bolt through the center, ,
TECO Split Rings (Timber Rings) On Cleveland Steel
Installation Tools On Cleveland Steel
http://www.clevelandsteel.com/PDF/Timber_Conn_print.pdf

the split rings were pushed back in the 70's when trusses were more of a DIY projects, companies would give a set of plans a set of plans and build you own truss, instead of using ply wood gussets, some AG universities have plans for split ring trusses as well,