Fixing tearout in particle board speaker baffle

[glebert]

I have a modernish Acoustic B450 210 combo that had a bit of a rattle. Found that one of the 8 screws on one of the 10" speakers had torn the T-nut out of the particle board baffle. It was a lateral tearout, towards the speaker opening, not straight through the thickness of the baffle. Tightening the other screws down made the rattle go away, but I suspect it is temporary. I want to put some sort of filler in the torn out area and replace t-nut, was wondering what filler works well? Since this is a pretty high powered combo bass amp my big concern is the filler crumbling or pulling away from particle board under stress. I have used water putty for this sort of thing in the past but they were for lower powered amps.

Thanks,
Greg

[xtian]

I would consider two-part epoxy, depending on the size and shape of the hole.

[J M Fahey]

Or plain wet some sawdust , add a couple drops of white carpenterīs glue, knead it into a somewhat stiff sticky ball and apply it competely filling the broken/missing area.

Wet contact surface with glue and apply quite more homemade wood putty than needed, because it contracts somewhat on drying, so you have to sand it down to shape.
Press it well so it goes inside all nooks and crannies, DEEP.

At least as good as fresh good quality chipboard, youīll have to drill a new hole, etc..

[Chuck H]

Or plain wet some sawdust , add a couple drops of white carpenterīs glue, knead it into a somewhat stiff sticky ball and apply it competely filling the broken/missing area.

Wet contact surface with glue and apply quite more homemade wood putty than needed, because it contracts somewhat on drying, so you have to sand it down to shape.
Press it well so it goes inside all nooks and crannies, DEEP.

At least as good as fresh good quality chipboard, youīll have to drill a new hole, etc..

Isn't that pretty much how it's made in the first place? Except with lower quality adhesive maybe.?. I think this is a good solution. I might even try a marine epoxy filler product too. They make the same stuff for home patching (a less flexible and faster hardening product) and I use it to rebuild rotten wood on trim, gables, etc. When it's half hard it can be shaved like a bar of soap which can save a lot of sanding for more intricate shapes. But the important thing I want to reiterate is that the area to be patched needs to have any loose material removed and whatever filler product is used needs to be worked well into the nooks and crannies of the busted out area.

[TomCarlos]

And now, I have a reason to save the saw dust when I occasionally do some cutting on the table saw, sander, and chop saw. Thanks for the great tip and Glebert, Good Question!!

[R.G.]

Good advice, all. It's all about gluing sawdust together with an adhesive. There are better and worse adhesives for a variety of conditions.

For wood in dry conditions, ordinary carpenter's glue is pretty good. It does depend critically on clamping the joint tightly together while it dries. For concretions of sawdust, to get best results, it needs to be really compressed. Epoxies and urethanes are not so sensitive to clamping.

It's worth thinking about why the particle board failed in the first place. Glue joints are regularly advertised as stronger than the base material. That's true, but the base material gives up right at the outside edge of the glued joint at places where the stress is a bit higher. Glues are also tremendously strong in compression and shear, but not so much in tension. fiber composites are so strong at least partially because the fibers are bound together along their lengths, transferring any tension stress into a shear stress on the glued joint, and relying on the tension strength of the fibers, which can be very high. Particle board doesn't get much help from the composite gluing of wood particles. So it fails easily in tension, and especially if it's absorbed water to swell the particles and loosen internal bits of the particles.

It's likely that this failed at the screw joint because the hole and tooth-intrusions of the T-nut weakened it locally and then a piece failed in tension from the main mass. Merely replacing the failed part with a plug might not help much. It would help to reinforce the whole area. I liked the reference to marine adhesives. There are some products which are water-thin epoxies that are intended specifically to reinforce loose, partly destroyed wood. "Getz-Rot" is one brand name. Soaking a similar stuff into the remaining wood could be a good idea to reinforce where the repair will go. Then putting in a plug molded of sawdust and epoxy could help.

What would really help is to reinforce the whole area the thing mounts to. A good McGuyver might be to do a good reinforced plug, then epoxy a layer or two of fiberglass tape around the entire hole, including outside the immediate area of the hole circle. That could transfer any local stresses to the glass fiber and spread them out. My boating friends would suggest something like that.

[Randall]

I would just make a new baffle out of birch ply if feasable.

[J M Fahey]

I have tried different binders, including nitro lacquer type, in fact you can find it here in little cans as "artificial wood" ... never liked it, also polyester resin, epoxy, etc.
Resins are very strong but also very hard, and if , say, you screw something there it may even crack.

Found that relatively low quality wood glue gives me a relatively elastic material which does not crack and takes screws well.

Not attempting to improve tha base material but to repair it "good enough".

Of course epoxy or even better adding fiberglass will make it far stronger if needed, but the typical problem I solve is torn speaker and specially handle holes and relatively large chunks missing along cabinet edges after years of road use.

And here plywood is expensive and as rare as henīs teeth; our de facto cabinet material is chipboard, period, not even MDF, and you all know how easily it disintegrates and loses huge chunks.

Oh well.

[glebert]

Thanks for all the ideas and input. I am leaning towards a bit of a hybrid approach, using Juan's suggestion for sawdust and glue to fill in the void, and on the inside of the baffle making a not too thick plywood plate around the repair area. I want something the t-nut can bite into without digging into the patch itself and tearing it out again.