# Can you use biscuits with 1/2" plywood?



## nostrildamus (Feb 24, 2009)

...or will the biscuit swell, deforming the surface?
Maybe I'd be better off using a spline of regular wood.


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## tonyuno (Jan 5, 2013)

What grade of plywood are we talking about here?


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## BernieL (Oct 28, 2011)

Do you have extra scraps of the ply... experiment and learn - and tell us. I have my doubts.


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## Oneal-Woodworking (Apr 14, 2013)

nostrildamus said:


> ...or will the biscuit swell, deforming the surface?
> Maybe I'd be better off using a spline of regular wood.


Not going to swell to the point you would notice...

Especially if you cut the biscuit pockets with the correct size cutter for the buscuits you are using...

If you are doing some painted project and are looking for an 'invisible' joint after it is painted that will be 'invisible' FOREVER - You don't want to be using plywood for your project and trying to join it together...

Just my opinion... :thumbsup:


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## tonyuno (Jan 5, 2013)

Reason in asking the plywood grade is that I have biscuit joint 1/2" Baltic birch with no problem, good both sides I don't know about and any grade less shouldn't matter tat much.


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## nostrildamus (Feb 24, 2009)

This is quality 1/2" plywood, 7-ply plus the two face veneers. I could do a test run, but what if the problem doesn't show up for a few weeks-months? The final finish will be high-gloss and any defects will definitely be visible. I have the proper sized slot cutter for the biscuits but I know that the biscuits are compressed and are meant to swell with moisture from the glue, creating a strong bond.

As a separate issue, when we say "Baltic Birch," doesn't that just refer to the face veneers? Home Depot and Lowes sell "Baltic Birch Plywood" but it's not very good.


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## tonyuno (Jan 5, 2013)

No, real Baltic Birch is seven ply and has no voids. It is used good quality furniture and shop use, i,e. torsion boxes etc. the "Baltic Birch


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## tonyuno (Jan 5, 2013)

Sorry wrong button. The "Baltic Birch from HD is actually made in Asia ( mainly Korea) and is a not so cheap copy. It is unusual to find true Baltic in bigger than 4' square sheets.


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## Al B Thayer (Dec 10, 2011)

I understand your concerns. It could swell enough you wouldnt be able to sand out. Are you actually cutting the slots with a biscuit jointer? If your bound for one reason or another to join with biscuits. I would make the biscuits from wood and give them a not so tight fit. Biscuits can make 3/4 hardwood "bubble" and require extra work in getting them flat.

Al

Friends don't let friends use stamped metal tools sold at clothing stores.


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## Al B Thayer (Dec 10, 2011)

BernieL said:


> Do you have extra scraps of the ply... experiment and learn - and tell us. I have my doubts.


Do you have your doubts it will swell or doubt they should be used because it will swell?

Al

Friends don't let friends use stamped metal tools sold at clothing stores.


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## Steve Neul (Sep 2, 2011)

The biscuit is only 1/8" thick. If you put it in the center of the plywood there would be 5/32" to 3/16" of wood over it so it wouldn't show through.


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## woodnthings (Jan 24, 2009)

*butt joints here?*



nostrildamus said:


> ...or will the biscuit swell, deforming the surface?
> *Maybe I'd be better off using a spline of regular wood.*





nostrildamus said:


> This is quality 1/2" plywood, 7-ply plus the two face veneers. I could do a test run, but what if the problem doesn't show up for a few weeks-months? The final finish will be high-gloss and any defects will definitely be visible. I have the proper sized slot cutter for the biscuits but I know that the biscuits are compressed and are meant to swell with moisture from the glue, creating a strong bond.
> 
> As a separate issue, when we say "Baltic Birch," doesn't that just refer to the face veneers? Home Depot and Lowes sell "Baltic Birch Plywood" but it's not very good.


If so, I go with a full length spline of hard wood. It should be a more predictable slip/tight fit than the biscuits in my opinion.
Make a practice piece or 2 to get it just right. Getting a full length slot for the spline will be an issue IF you don't have a router with a slot cutter. :yes: Then biscuits may be your only choice.

I slotted and splined the entire sub floor for the lower story of my house using a router and slot cutter, because I didn't want any deviations from the joints with adhesive tile on top. It worked very well, but it was labor intensive. :laughing:


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## GeorgeC (Jul 30, 2008)

OnealWoodworking said:


> Not going to swell to the point you would notice...
> 
> Especially if you cut the biscuit pockets with the correct size cutter for the buscuits you are using...
> 
> ...


Very good answer.

George


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## Al B Thayer (Dec 10, 2011)

Biscuits can go either way.

Now that I've dyed, finished and polished all my raised panel cabinet doors, I see shallow but distinct oval depressions every 6" or 7" along every edge joint, exactly where I cut slots for biscuits before gluing up. I centered the slots in the 3/4" birch stock and glued up before thickness planing to 5/8" for flush panels. What happened, and is there anything I can do about it?

Talk about depression... Unfortunately, all you can do about this particular disaster is to tell your customer the dimples in your panels are custom design details, and charge a little extra for them. Then make sure it doesn't happen next time.

As you know, biscuits are compressed during manufacture in order to insure they'll expand when moistened by wood glue, guaranteeing a very tight fit in the slots cut by your biscuit joiner. This expansion, abetted by increased moisture content in the surrounding wood, creates enough pressure to distort the solid wood on either side of the biscuit—rarely if ever enough to cause problems through more than 1/4" of wood, but often visible as raised biscuit-shaped ovals if the biscuits are less than 1/4" from the surface. If you plane or sand a joined panel while such moisture-induced swelling is present, it's easy to imagine what will happen when the wood finally returns to its dry dimensions: you'll see permanent biscuit-shaped depressions where you removed the temporarily swollen wood.

There are three ways to avoid the problem. First, be sure your biscuits are always more than 1/4" below the surface. Second, when that's not feasible (as in the case of your 5/8" panels), give the joined wood several days to dry before planing or sanding. Third (perhaps most practical), don't put any glue on your biscuits. If they don't swell, there won't be any pressure to telegraph through to the surface, and you'll have nothing to worry about. In joints like those in your panels, you use biscuits for accurate surface registration rather than for strength, since clean edge butt joints are plenty strong enough to need no reinforcement—so the biscuits don't need to be glued. Installing them dry keeps adjacent surfaces aligned while you apply clamp pressure, which is all you're trying to accomplish.

Copyright © 2002 Highland Hardware, dba Highland Woodworking

Friends don't let friends use stamped metal tools sold at clothing stores.


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## TomC (Oct 27, 2008)

tonycan said:


> Sorry wrong button. The "Baltic Birch from HD is actually made in Asia ( mainly Korea) and is a not so cheap copy. It is unusual to find true Baltic in bigger than 4' square sheets.


I've only found it in 5' x 5' sheets.
Tom


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## tonyuno (Jan 5, 2013)

Yes, thinking back the sheets probably are that size. I of course meant four x four not four square.


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## nostrildamus (Feb 24, 2009)

OK, well, I couldn't resist doing some experimenting. 
First, to see how much a biscuit can swell, I soaked one in glue for 30 minutes, then let it dry. These are Porter-Cable 20 biscuits and Titebond Original glue. Dry, the thickness is 0.156" (see photo, on bottom). With glue, the thickness is.... 0.163" (photo, on top), a difference of only 0.007" or less than 1/128". Interestingly, the biscuit seemed flatter, with an even thickness after gluing. Perhaps the biscuit is really only compressed around it's edge.

Second, I used the biscuit to attach solid walnut edging to 1/2" plywood. This is the best quality plywood I could find, it does have some voids, but you can see in the photo it's much better than what the Borg sells. Slots were cut with a router and a Carb-Tech Biscuit cutter. The cutter is 5/32" wide (0.156), same as the biscuit thickness. It's been dry a few days now and there's no noticeable deflection of the surface.

I might repeat the experiment with cheapo plywood to see if there's any effect.


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## Oneal-Woodworking (Apr 14, 2013)

nostrildamus said:


> OK, well, I couldn't resist doing some experimenting.
> First, to see how much a biscuit can swell, I soaked one in glue for 30 minutes, then let it dry. These are Porter-Cable 20 biscuits and Titebond Original glue. *Dry, the thickness is 0.156" (see photo, on bottom). With glue, the thickness is.... 0.163" (photo, on top), a difference of only 0.007" or less than 1/128".* Interestingly, the biscuit seemed flatter, with an even thickness after gluing. Perhaps the biscuit is really only compressed around it's edge.
> 
> Second, I used the biscuit to attach solid walnut edging to 1/2" plywood. This is the best quality plywood I could find, it does have some voids, but you can see in the photo it's much better than what the Borg sells. Slots were cut with a router and a Carb-Tech Biscuit cutter. The cutter is 5/32" wide (0.156), same as the biscuit thickness. It's been dry a few days now and there's no noticeable deflection of the surface.
> ...


 
If I may ask - What sort of micrometer did you use and are sure that you were not measuring the added 'thickness' of the glue on the surface?

Just curious... 

Our shaper is current set up to with the biscuit cutter and I would be happy to sink a few into some scraps for you and take before and after measurement of the 'swelling' (or lack thereof) in both half inch plywood and some hardwood planed down to half inch... 

Talking about measuring the thickness of the plywood (right at the buscuit) and the hardwood after the buscuit is glued, installed, and glue has dried...

I got a good mic and can give accurate measurements of any swelling if you like. 










Your 'experiment' is getting cool now! LOL!


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## cabinetman (Jul 5, 2007)

I wouldn't use biscuits for anything. Oh wait...my grandson likes to play with them in the bathtub. He makes little fleets of boats with them. It certainly is a sight to see.:yes:









 







.


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## Midwest Millworks (Nov 20, 2012)

cabinetman said:


> I wouldn't use biscuits for anything. Oh wait...my grandson likes to play with them in the bathtub. He makes little fleets of boats with them. It certainly is a sight to see.:yes:
> 
> 
> 
> ...


Where does your grandson get biscuits from? I can't imagine you bought them considering how you feel about them. I share your thoughts regarding biscuits, so don't think I'm busting your chops. 

Mike Darr


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## nostrildamus (Feb 24, 2009)

I have a Starrett caliper. I wiped the biscuits down before the glue dried so there wouldn't be any buildup on the surface. I'd be very interested to see what results you get measuring the plywood itself before, after, and maybe a couple weeks later. I can't imagine the biscuit is going to shrink back as it dries because it's permeated with cured glue, but who knows?


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## cabinetman (Jul 5, 2007)

Midwest Millworks said:


> Where does your grandson get biscuits from? I can't imagine you bought them considering how you feel about them. I share your thoughts regarding biscuits, so don't think I'm busting your chops.
> 
> Mike Darr


I think I bought 1K of the three sizes when I got the tool, and after using about half the biscuits decided it was junk joinery.









 







.


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## Oneal-Woodworking (Apr 14, 2013)

nostrildamus said:


> I have a Starrett caliper. I wiped the biscuits down before the glue dried so there wouldn't be any buildup on the surface. I'd be very interested to see what results you get measuring the plywood itself before, after, and maybe a couple weeks later. I can't imagine the biscuit is going to shrink back as it dries because it's permeated with cured glue, but who knows?


So you have good tools... I was guessing as much based on your post and measurements... :thumbsup:

I will be sure to get pics for your thread both before and after showing the readings I get... :yes:


I will get some using some MDF core 1/2" plywood with buscuits as well just cause I got some laying around... THAT stuff is WEAK as heck and will show any 'swelling' with ease I am thinking...

I have used buscuits a LOT over the years and like them. They make for some really strong joints in MY opinion and I have not had any of my stuff come apart as yet. Have done a metric boatload of mitred doors with them and never had any issues 'after the fact'... :thumbsup:

Great thread for people interested in buscuit joinery. :thumbsup:


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## Oneal-Woodworking (Apr 14, 2013)

cabinetman said:


> I think I bought 1K of the three sizes when I got the tool, and after using about half the biscuits decided it was junk joinery.
> 
> 
> 
> ...


 
Please share pictures of your 'failures' for others to see... 

I am curious to see pics and examples of the problems you have had with them.

THIS 'buscuit joint' is well over 20 years old with NO signs of failure... Table HAS been 'abused' along the way with no ill results...


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## Al B Thayer (Dec 10, 2011)

nostrildamus said:


> I have a Starrett caliper. I wiped the biscuits down before the glue dried so there wouldn't be any buildup on the surface. I'd be very interested to see what results you get measuring the plywood itself before, after, and maybe a couple weeks later. I can't imagine the biscuit is going to shrink back as it dries because it's permeated with cured glue, but who knows?


Nost,
I use a biscuit jointer on joints that require strength but may not be visible so I don't have any stories to tell one way or another. I do know there was an article in Fine Woodworking about someone that used them and finish sanded right away. The wood was swelled but nothing he noticed. Later when he finished there were very slight impressions visible at each biscuit. I've never used them on thin stock where they could be a problem. 

Consider this. New fresh biscuits are thinner out of the can than biscuits that have been around for a while. Fresh biscuits will expand a great deal more than the one you tested. Maybe it was old. After some time they swell some with age without glue. I've been using them almost since they were on the market. At glue up old ones fit tight in the slot and new ones are quite a bit loose. When I bought my Porter Cable biscuit cutter. One of the selling points was that the slot didn't have to be perfectly matching the adjoining slot. The slot is wider than the biscuit allowing alignment at glue up.

Al

Friends don't let friends use stamped metal tools sold at clothing stores.


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## nostrildamus (Feb 24, 2009)

Well, the verdict is in. It's been a few months now and my project doesn't show any swelling or depression where the biscuits are. I even used biscuits on 1/2" MDF, covered with veneer, and there doesn't seem to be a problem.

One factor, though, is that my biscuits are 10-15 years old (I bought that 1,000 piece lifetime-supply, too). As Al points out above, maybe these biscuits are already swollen. They still fit easily into the slot, though....


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