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Forum topic by MrRon posted 08-12-2017 09:49 PM 1794 views 0 times favorited 34 replies Add to Favorites Watch
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MrRon

4352 posts in 3026 days


08-12-2017 09:49 PM

I want to fabricate a built-up beam comprising (2) 2×8’s and a 2×4. I will nail them together , but want an adhesive to develope the beam strength. The catch is; the wood is pressure treated, ground contact. I don’t know if the preservative used will prevent the adhesive from bonding. My thought would be to use PL-3 or an epoxy. What say you?


34 replies so far

View Loren's profile

Loren

9432 posts in 3431 days


#1 posted 08-12-2017 09:50 PM

I think something like liquid nails would stick.

View jonah's profile

jonah

1265 posts in 3082 days


#2 posted 08-13-2017 12:18 AM

I’d use a polyurethane construction adhesive. Liquid nails or similar.

View josephf's profile

josephf

170 posts in 1879 days


#3 posted 08-30-2017 04:30 AM

i have had a few failures with liquidnails . they have alot of products though . Pl premium has held up very well ,have never seen it fail . I have seen a tube/contruction adhesive for treated wood . do not recall brand .
recently used a liquid nails product and 3 days later it hadn’t set ,still runny .
oh -another thing , tried to use there big tubes for setting floor sheathing .tubes failed . had to stop the job ,drive to town for more .happened twice .
also use good [like GRK] screws to assemble the beams .clamp and screw . went back to a job i did 8 yrs ago .the treated wood had dried out and some of the nails were popping and most were loose .the places i used screws were still tight

View Rich's profile

Rich

1714 posts in 372 days


#4 posted 08-30-2017 04:45 AM

Ron, I think this is a similar situation to wood finishing. Do some test boards. It never hurts to wipe down with naphtha for a clean glue surface. If you’re concerned about flexing, then PVA glues might be a problem, since they do creep. DAP Weldwood is a good alternative to that in that it dries rigid and helps keep its shape. Crazy, I think this is the 3rd or 4th time this week I’ve recommenced DAP…lol

Again, I’d do some test glue ups and see what adheres the best and is the most rigid.

-- No matter how much you push the envelope, it'll still be stationery.

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Madmark2

352 posts in 371 days


#5 posted 08-30-2017 04:46 AM

The key to good gluing is 100% coverage and good clamping no matter what the adhesive.

m

View AlaskaGuy's profile

AlaskaGuy

3420 posts in 2092 days


#6 posted 08-30-2017 07:08 AM

May I ask the size a use of the beam? Is it structural?

-- Alaskan's for Global warming!

View Logan Windram's profile

Logan Windram

341 posts in 2245 days


#7 posted 08-30-2017 12:49 PM



The key to good gluing is 100% coverage and good clamping no matter what the adhesive.

m

- Madmark2

id add open time to this astute post…

View jonah's profile

jonah

1265 posts in 3082 days


#8 posted 08-30-2017 01:42 PM

I would nail the pieces together temporarily, but when framers make beams, they bolt them together. Nails alone will probably not suffice since the PT is likely ~25-30+% moisture content and will shrink significantly.

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MrRon

4352 posts in 3026 days


#9 posted 08-30-2017 03:55 PM


May I ask the size a use of the beam? Is it structural?

- AlaskaGuy


The beam will be 16’ long and form an inverted “U” . There will be a 4×4 post at each end and one in the middle, secured with 1/2” carriage bolts, 2 per post. Each side of the beam will have joist hangers. The beam divides a 16’x16’ deck in half. I tend to over design everything; must be my naval shipbuilding background. It has been raining every day for the past 2 weeks and is projected to continue into next week, so I haven’t made much progress on this deck project. I am spending this down time making sure everything will go together as planned. I would post a drawing of the deck, but it wouldn’t show details. I hope my explanation will be adequate.

PS. The wood is sitting outside in the weather and is pretty wet.

View josephf's profile

josephf

170 posts in 1879 days


#10 posted 08-30-2017 05:03 PM

right off shrinkage will kill you . 99% percent sure anything but a butt joint will give you trouble .
I could sujest biscuits /or dominos [festool] and tb111 ,though as wet as the wood is i do not think miters have a chance .you’ll end up with bad miters which is way worse then a good butt joint.

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jonah

1265 posts in 3082 days


#11 posted 08-31-2017 03:03 AM

You’re going to want to bolt it together, probably with stainless steel bolts every couple feet. Adhesive is fine, but you need a rock solid mechanical connection. Through bolts with fender washers and nuts.

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josephf

170 posts in 1879 days


#12 posted 08-31-2017 03:16 AM

Pulled some treated ,brown and green stuff apart from 8-10 yrs .no problems on the galv bolts . I think ,based on my calif , bay area galv is fine .actually bolts probable waist of $ .Good screws .
I have not seen the plans . Not even sure what he is building .but it is outside .If the beams are exposed to weather on top use a membrane of some type to shed water .
I could see stainless if you have salt water nearby or it is a high end project . For a 100yr type build .

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jonah

1265 posts in 3082 days


#13 posted 08-31-2017 09:28 AM

It’ll be outside in the weather, so I’d spring for stainless bolts unless the cost difference is prohibitive.

View MrRon's profile (online now)

MrRon

4352 posts in 3026 days


#14 posted 09-01-2017 09:05 PM

Here is a sketch of the beam for my deck. Dimensions shown in inches. The adhesive will be between the 2×4 and the 2×8’s. Decking will go on top of this.

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josephf

170 posts in 1879 days


#15 posted 09-01-2017 10:37 PM

oh i see .only bolts on the end/through 4×4 posts .2×4 are spacers stacked on the flat ? when you say decking are you referring to flooring or roof decking . i might have a chance to copy that . pretty simple,very sturdy and all material easily handled by one person .

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