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Forum topic by Stanley Coker posted 07-30-2019 10:29 PM 628 views 0 times favorited 14 replies Add to Favorites Watch
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Stanley Coker

263 posts in 3707 days


07-30-2019 10:29 PM

Topic tags/keywords: question

I have a project that I need to glue two whole sheets of plywood together. I was going to use wood glue, but was wondering if contact cement would be a better choice.
Any advise would be greatly appreciated.

Thanks

Stanley

-- Stanley, North Georgia


14 replies so far

View hairy's profile

hairy

2934 posts in 4044 days


#1 posted 07-30-2019 10:35 PM

When 2 pieces coated with contact cement touch each other, you can’t move them. Wood glue will give you a chance to align the pieces, contact cement won’t.

-- Genghis Khan and his brother Don, couldn't keep on keeping on...

View Ocelot's profile

Ocelot

2356 posts in 3150 days


#2 posted 07-30-2019 10:42 PM

[double post deleted]

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Ocelot

2356 posts in 3150 days


#3 posted 07-30-2019 10:49 PM

Assuming that you are talking about gluing them face to face to make a thicker piece of plywood, I believe the standard thing for that is called “construction adhesive”. I have used “Locktight PL”.

Staple gun with appropriate length of staples helps hold pieces together while adhesive sets.

View pottz's profile

pottz

6383 posts in 1496 days


#4 posted 07-30-2019 11:01 PM

i have always used titebond applied with a roller but as ocelot said construction adhesive will work.i would not recommend contact cement though for the reason hairy stated.

-- sawdust the bigger the pile the bigger my smile-larry,so cal.

View ArtMann's profile

ArtMann

1435 posts in 1328 days


#5 posted 08-01-2019 01:46 PM

I assume you realize that if you follow the normal guidelines for clamping pressure of PVA glue, you will have to apply many tons of pressure. A few sacks of sand or concrete blocks is nowhere close to enough. It is very hard to do a glue up like what you are describing without getting a lot of voids between the sheets. Just be warned. My current favorite way of laminating large pieces of plywood or MDF to each other is to use epoxy that has been thickened with wood flour and spread on onto one sheet with a toothed trowel. Epoxy will maintain strength between surfaces with a significant gap due to low clamping pressure.

View DS's profile

DS

3301 posts in 2932 days


#6 posted 08-01-2019 02:14 PM

I’ve glued large panels together using a vacuum bag press and PVA adhesive. I basically made my own curved plywood 9 feet long on a form. The results were outstanding.

I used a homemade press and bag and it wasn’t very expensive at all.

https://www.lumberjocks.com/DS251/blog/28597

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View DS's profile

DS

3301 posts in 2932 days


#7 posted 08-01-2019 03:48 PM



I assume you realize that if you follow the normal guidelines for clamping pressure of PVA glue, you will have to apply many tons of pressure.

- ArtMann

Atmospheric pressure is about 14 PSI at sea level. A panel this size, (approx. 30” x 108”) has 3,240 square inches.
Assuming 80% efficiency draw against atmosphere at 1200 ft above sea level, (11.2 PSI) the pressure on the panel was about 36,288 lbs, or 18 tons.

Not bad for a tiny venturi and fabric store vinyl.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

View therealSteveN's profile

therealSteveN

3902 posts in 1086 days


#8 posted 08-01-2019 06:29 PM

I’ve used the dirt cheap Elmers white in the Gallon Jug, and used screws into the non show side. Usually 1 1’4” drywall screws are great. After 24 hours you can remove the screws if it’s for something like a workbench, or router table top, and you want to cut, or drill into it. Make sure to do it on a flat set of saw horses, or something you can make flat, large enough to hold 4×8 sheets. I let it dry 24 hours before putting it into use.

Been doing that for over 40 years, never a problem if you use glue enough to lightly cover the back. I say lightly cover, as in all surfaces. Lightly as in too much and you will have puddles running out. Just glue one side, when you clamp it together with screws set every 6” you will make contact at all points.

-- Think safe, be safe

View sras's profile

sras

5200 posts in 3641 days


#9 posted 08-01-2019 10:44 PM

I’ll echo the previous “keep it flat” comment. I did something like this several years ago for my workbench (3’x8’). I had a sag of just over an 1/8th of an inch. I used 1 1/4” thick plywood and that bend was LOCKED in.

-- Steve - Impatience is Expensive

View ArtMann's profile

ArtMann

1435 posts in 1328 days


#10 posted 08-01-2019 10:49 PM

Using screws is a great idea if you can tolerate the holes after you remove them. Screws produce tremendous clamping pressure and you can use lots of them.

I think there is a little more to vacuum bagging than DS said but that would be good too if you are set up to do it.

I just wanted the OP to realize that there is more to getting a reliable lamination than what you see most people doing, especially with sizes like whole sheets. I discovered this principle the hard way. I cut out a pattern in my lamination and observed obvious voids in several places. I bet I used 300 or 400 pounds of weight. I don’t think there is any way to prevent gaps in the glue with just random weights. It is much easier if you use a thicker layer of thickened epoxy.

View Stanley Coker's profile

Stanley Coker

263 posts in 3707 days


#11 posted 08-04-2019 01:52 PM

Thanks Guys for all the advise on gluing up large panels. I have been thinking on using screws on the bottom side that is not going to be seen. This going to be a long table top for a conference room. The picture that they gave me looks to be hickory wood, they want it to be 8 ft long and 42 in wide. My worry in gluing up boards that long is having a bow. If I had access to a large belt sander, no problem. My thought was to glue a sheet of hickory plywood to a sheet of birch and trim it out with hickory. They already have metal frame legs that it will be attached to. The screw holes on the bottom will not be seen. Gluing them together on a flat surface should insure a flat top.

-- Stanley, North Georgia

View Lazyman's profile

Lazyman

3977 posts in 1899 days


#12 posted 08-04-2019 02:10 PM

Don’t know your table design but another approach would be to use a single sheet and use battens on the bottom to stiffen it and keep it flat. That might be easier. If you will have aprons, those will help as well. You could add edges to give it a thicker look on the sides if necessary. You will want to add edging (veneer at least) anyway to cover the plies along the edges.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View splintergroup's profile

splintergroup

2929 posts in 1734 days


#13 posted 08-04-2019 02:15 PM

A flat layer of glue is critical no matter what method you use for clamping (with a vacuum bag being the most forgiving). Use a fine tooth mastic spreader (from the tile aisle of your local HW store). This ensures an even layer so your clamping method doesn’t fight thicker blobs of glue.

View therealSteveN's profile

therealSteveN

3902 posts in 1086 days


#14 posted 08-04-2019 06:09 PM

If this is to be a conference room desk, table or whatever you call it. I would only consider solid wood for the top. Glued properly, and of sufficient thickness (think 5/4 minimum through 6/4) for something that size, and depending on what you did on the bottom edge to reduce the bulk, Generally a large chamfer bit will udercut to make it look much sleeker, while still retaining rigidity. I can’t imagine the grain lines of a plywood top for a presentation type piece. Plywood grains are so Formica like, repeat, repeat, repeat.

Go solid wood. When you said “I have a project”. My mind was seeing a shop benchtop, or similar.

-- Think safe, be safe

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