Help, brad nailer spliting MDF

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Forum topic by clin posted 06-20-2016 09:47 PM 2106 views 0 times favorited 10 replies Add to Favorites Watch
View clin's profile


930 posts in 1145 days

06-20-2016 09:47 PM

I’m building a torsion box from 1/2” MDF. I decided to test my 18 GA brad nailer to see how it would work. I was disappointed to see that nailing through the side of one 1/2’ piece into the edge of the other piece, split the one taking it on the edge.

Length of brad made no difference. Even at the shortest I would consider using (1” long), it split the the one on edge.

building torsion boxes from 1/2” MDF with glue and a brad nailer seems common, but I’ve seen no mention of this splitting problem.

Pretty much all the joints are glued and brad nailed butt joints. Even the most significant part, attaching the top and bottom panels to the webs.

Has anyone else done this, and is this just a case of don’t sweat it, just rely on the glue?

-- Clin

10 replies so far

View firefighterontheside's profile


19088 posts in 2005 days

#1 posted 06-20-2016 09:56 PM

If the nails are holding while the glue dries, I wouldn’t sweat the splitting. In the end, it’s the glue that holds it strong. Maybe consider pre-drilling and using screws and glue. You have to make your pilot hole just the right size. Too big and it won’t hold. Too small and it will split.

-- Bill M. "People change, walnut doesn't" by Gene.

View clin's profile


930 posts in 1145 days

#2 posted 06-20-2016 10:37 PM

If the nails are holding while the glue dries, I wouldn t sweat the splitting. In the end, it s the glue that holds it strong. Maybe consider pre-drilling and using screws and glue. You have to make your pilot hole just the right size. Too big and it won t hold. Too small and it will split.

- firefighterontheside

Ignoring the splitting seems like it may be the only choice I have. I was expecting to shoot a brad about every 5” in the top and bottom panels. That’s works out to be 120+ brads in each side. That would be a whole lot of very tedious pilot holes.

Also, even if I did get all that pre-drilled. I doubt I could drive all those screws before the glue would start setting. I figured it would be a challenge shootin’ and scootin’ with the brad nailer.

I do agree that the brads are just to help hold things together until the glue dries. But splitting the MDF, obviously weakens it. And that stuff isn’t all that strong to begin with. But if the glue stabilizes it, then perhaps it doesn’t matter.

-- Clin

View splatman's profile


586 posts in 1547 days

#3 posted 06-20-2016 11:00 PM

Would it help to nail it like this:

Alternate the angle of each nail. First nail, lean the nailer left, next nail, lean it right, so on.
The idea is to avoid nailing parallel to the faces, which leads to splitting.

View clin's profile


930 posts in 1145 days

#4 posted 06-20-2016 11:33 PM


I just ran out to the shop and gave your suggestion a try. While it wasn’t 100% effective, it definitely was an improvement. It makes sense too. The MDF seems to have a layered structure. So driving the brad across the “grain” should give it less of a tendency to split it. I did notice the brads ran a bit squirrelly. Curving and bending and popping out of line with the angle I started them. This is not a problem since all this would be internal to the structure and never seen.

After some more experiments, I found,not surprisingly, that if I stayed 3/4” or more from the end of the piece, it wouldn’t split. This is not possible for attaching the side pieces, since I have to nail into the end of the web. The web is only 3” wide. So if I put in two brads, they would typically be closer to the outside edge than 3/4”. But at least for the vast majority of the brads, going in the top and bottom panels, I would be well way from the ends.

I’m also running some experiments just driving one brad in the middle of the end of the web. This leaves 1 1/2” of space from the edge of the web. Once the glue sets, I’ll examine the joint and see how it looks. All the edges are very straight and true. So it doesn’t really need two brads in each piece to pull things square.

-- Clin

View Nubsnstubs's profile


1408 posts in 1878 days

#5 posted 06-20-2016 11:36 PM

How are you holding the gun? Sometimes when I nail stuff, if I’m shooting with the grain, most of the nails just leave a spot where they penetrated. If I position the gun in an across the grain orientation, I’ll get splits. That is mostly because of the point on the nail. Most today have a V point. If that is positioned going across the grain, you’ll get splits, but leaves a larger hole to putty. If it’s positioned going with the grain, no splits, but leaves a better looking nail hole.

I just shot 2 nails into the edge of a piece of 3/4” MDF. One across the edge and one along the edge about 3/8” from corners. What I said above is correct. The gun and nails I used is the Senco SLP20XP using 1” nail. It’s all about being smarter than the nail… Also, I think putting nails every 5” is too many nails.

3/4” MDF is made starting out as a 16” thick batt of material, then gets compressed to 3/4”. I can’t say what 1/2” starts at, but yep, it is a layered structure …...... Jerry (in Tucson)

-- Jerry (in Tucson)

View MadMark's profile


979 posts in 1601 days

#6 posted 06-20-2016 11:48 PM

Y’all have been watching Norm again. You can’t nail mdf, the stress cracks spread and even if it looks like it wall hold, it will fail quickly. Use glue for more strength than brads and use clamps, not brads, to hold while the glue dries. Alternatively don’t bottom dollar out and use better materials.


-- Madmark -

View clin's profile


930 posts in 1145 days

#7 posted 06-21-2016 12:01 AM


I played with the orientation (rotation if you will) of the gun. While the “head’ of the brad is wider in one direction, the brad wire is square and the tip of it is flat. It made no difference, because the business end of the brad is the same in both directions.

My application is just as Splatman showed in his image. I’m going through the top board which does not split. It’s the board that is receiving the brad on edge that is splitting.

I happen to be using Bostitch 18 GA brads.

5” between brads may be too many. Though some builds recommended every 3”. But it is a large area that cannot be clamped, without a bunch of large cauls. I will lay weight on it. But it is important to try to get the panels to snug up to the webbing. I’m trying to make this come out as flat as possible.

My web spacing is 5”, so centering the brads between the adjacent crossing web joints, would make some sense.

Since there would be a lot of brads in the panels, I figured I’d place every other one to start. Check things with a straight edge and see how it looks. If the panel is nice and flat, I won’t add more brads and I’ll just let the glue do it’s thing.

-- Clin

View jbay's profile (online now)


2681 posts in 1048 days

#8 posted 06-21-2016 12:07 AM

Your 18g brads are fine.
Stay a couple of inches from the edge and nail about every 8 inches and you should be fine. Use a nice bead of glue, don’t be stingy, glue is cheap and is what is going to give you the strength.

View clin's profile


930 posts in 1145 days

#9 posted 06-21-2016 12:44 AM

Only been about an hour, but I broke the glued joints I was testing. Single brad centered in one and two in the other. Both joints looked the same. And even though the glue wasn’t fully cured, the failure was the top layer of MDF peeling off.

Points is, I think I’ll just go with one brad in the end of these 3” wide webs. that will avoid splitting them. And as long as the joints look tight, I’ll call it good. As for the top and bottom skins, I can stay clear of the ends and avoid splitting that way.

If I have a joint that won’t stay tight with just one, I’ll apply Splatman’s idea of toeing in the brad when adding a few more.

I know several of the examples of building torsion boxes (like the Wood Whisperer’s) use separate web pieces and toenail about half of them. This may be one reason why they didn’t comment on splitting. Or maybe just my brads are more prone to this for some reason. Maybe some difference int he MDF. Though this MDF is from a quality supplier and they called it “grade A” and said it was better than what the BORG sell.

Anyway, thanks for all the input. While nothing was a silver bullet solution, I appreciate the comments. And Splatman in particular, that technique wasn’t even on may radar as far as a way to prevent splitting.

-- Clin

View runswithscissors's profile


2846 posts in 2174 days

#10 posted 06-22-2016 03:32 AM

Routing or dadoing shallow slots in the front piece might help both with the glue strength and splitting problem. First time I ever installed mdf baseboards, I discovered that stuff can’t stand end nailing (as in a mitered corner). I avoid it like the plague.

-- I admit to being an adrenaline junky; fortunately, I'm very easily frightened

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