Tabletop Mystery...

[Kurt Swanson]

I recently built a dining table for a client of mine and the top has developed some cracks. One area is even starting to buckle upwards slightly. Here are the facts:

1. The top is made up of (6) 4" wide flat-sawn white oak veneers 1/8" thick, glued (Titebond 3) to a 3/4" plywood base.
2. The top has a single finish coat of Rubio Monocoat.
3. Humidity in my shop is 40% (radiant floor heat). The client has forced-air, so I'm sure it's less than that.
4. The underside of the table has been sealed with polyurethane.

So I'm not sure if it's the Rubio Monocoat allowing the wood to dry out,that's the problem or maybe I should've use quarter-sawn white oak, or maybe the veneers were too thick or too wide and that is causing the issues.
Thoughts?

[Bradley Gray]

Likely the white oak wasn't fully dry.

Bad luck to only veneer the top - the bottom should be veneered and finished the same as the top.

[Frank Pratt]

1/8 is thickish for veneer. It is done, but is about the thickest that's recommended and in this case it was obviously too thick. I would only apply it that thick over solid wood the same grain direction. Veneering both sides would help prevent cupping.

Can you post some pics? I can't make sense of what you describe. If the veneer is buckling upwards, that would indicate that the wood was in a dyer state when you built the table & now is in a more humid environment. Am I understanding correctly?

[Dave Sabo]

The issues is almost certainly related to the naked bottom. The other factors helped conspired against you too.

I think the 4” is waaaay too wide for that assembly. But, that’s my opinion or gut feeling rather than something from empirical data or testing.

Wouldn’t have used plywood as a substrate either.

[Patrick Kane]

By 'buckling up' does the end of the table top look like a frown or a smile? If the middle is higher(frownie face) then your top took on more moisture than the bottom. If the ends are higher than the middle(smile) then the top dried out faster than the bottom. I agree with others than things should always be finished the same, and most importantly, you have to balance your veneers.

The cracking is very weird to me. Did you allow for the table top to expand and contract a smidgen? How much did the piece cup?

[Richard Coers]

The issues is almost certainly related to the naked bottom. The other factors helped conspired against you too.

I think the 4” is waaaay too wide for that assembly. But, that’s my opinion or gut feeling rather than something from empirical data or testing.

Wouldn’t have used plywood as a substrate either.

Fairly certain the naked backside is not causing the top veneer to crack.

[Kurt Swanson]

Likely the white oak wasn't fully dry.

Bad luck to only veneer the top - the bottom should be veneered and finished the same as the top.

I purchased this lumber from a trusted source. I measured the moisture content at 6%.

[Kurt Swanson]

By 'buckling up' does the end of the table top look like a frown or a smile? If the middle is higher(frownie face) then your top took on more moisture than the bottom. If the ends are higher than the middle(smile) then the top dried out faster than the bottom. I agree with others than things should always be finished the same, and most importantly, you have to balance your veneers.

The cracking is very weird to me. Did you allow for the table top to expand and contract a smidgen? How much did the piece cup?

Several areas show cracking, which I assume is from going to a drier atmosphere. The area that is buckling upwards acts as though it's expanding form excessive moisture.

[Kurt Swanson]

I don't have the option of posting pics, so here's a description of the project. The table is 6' long and 4" thick. I made it by cutting 1 sheet of plywood into 5 pieces, 1 top, 2 sides and 2 ends. All 5 pieces were cut with 45 degree bevels and then glued back together to form a 5-sided box. The veneers were glued to the plywood before it was cut into 5 sections.

My suspicion now is that I should have used narrower, thinner veneers and made them from more stable quarter-sawn white oak.

[Mel Fulks]

I purchased this lumber from a trusted source. I measured the moisture content at 6%.

But was it kiln dried?
Never read any thing good about Titebond 3

[Tony Shea]

I would tend to agree with the choice of glue for veneering as well as the veneers being a bit too thick. I also agree that both sides of the plywood should be veneered especially when applying that much glue to one face of the plywood. There is a ton of moisture in glue which would then eventually dry out during the cure which then causes all sorts of movement if the other side is not treated the same. I'm not 100% sure the cracking is caused by the cupping but it certainly could be if the cupping is bad enough, especially if the veneers are 1/8" thick. The thinner veneers would certainly bend much easier without splitting which is my opinion of why you're getting cracking. Without seeing pictures this is only a guess though.

The cracking could also be from oak that has been dried too quickly. I have seen this many times in white oak specifically.

[Stewart Lang]

1/8" veneer is definitely on the thicker side. So that could add to the problem.

I doubt it's the glue. Titebond III is good stuff. Their cold press veneer glue would have been better though.

I doubt it's the width either. 4" is on the narrow side for veneer, so I doubt that's causing a problem. I veneer much wider around 6" if I can.

I have a feeling it probably didn't get enough pressure when gluing. Did you use a vacuum press? That's about the only good way to get enough pressure to veneer an entire dining table top, especially when using thicker veneer.

If there wasn't enough pressure to properly adhere the veneer, combined with thicker 1/8" veneer, you'll definitely have some lifting/cracking problems down the road with normal humidity changes.

[Mel Fulks]

yes, the veneer is thick , but other moderns have used thick veneer . I've worked with old timers who made it and used
it. But they always called if "facing " ,not veneer. They bragged about making it, and had no failures. I have a friend
who owns a 17th century table with a marquetry top with pieces 3/32 to a little over 1/8th. Had a lot of loose veneer and
some missing veneer. He reglued and made patches, used hot hide glue on all. He has had it at least 40 years,and it's
been stable. Veneers have gotten thinner in my lifetime. Twice.

[Kurt Swanson]

1/8" veneer is definitely on the thicker side. So that could add to the problem.

I doubt it's the glue. Titebond III is good stuff. Their cold press veneer glue would have been better though.

I doubt it's the width either. 4" is on the narrow side for veneer, so I doubt that's causing a problem. I veneer much wider around 6" if I can.

I have a feeling it probably didn't get enough pressure when gluing. Did you use a vacuum press? That's about the only good way to get enough pressure to veneer an entire dining table top, especially when using thicker veneer.

If there wasn't enough pressure to properly adhere the veneer, combined with thicker 1/8" veneer, you'll definitely have some lifting/cracking problems down the road with normal humidity changes.

No, I didn't use a vacuum bag, so inadequate pressure during glue-up makes the most sense with the results I'm seeing. Looks like I'll have to make a new top. Thanks for the help Stewart.

[Patrick Kane]

Kurt,

For what you are doing here, i think a torsion box would also do you some good. If you need help in that regard, google/youtube it. It is a very stable way to make a thick, light, hollow structure.