Best Structural Wood Filler?

[Tom Watson]

I just used some Minwax High Performance Wood Filler on some blown out dowel holes that were on a chair that I'm restoring.

I've used it a fair amount before and it appears to be a typical two part epoxy where you add a strip of hardener to the goo and mix it up.

I've mostly used it in flat areas that didn't have the kind of stress placed on it that the dowel system in a chair has.

I have to say that I was a bit disappointed.

It didn't bond to the wood all that well and some of the holes blew out again when I went to insert the dowels.

I've used Bondo before, too and it seems to be about the same sort of stuff.

I'm not a chemist and there might be differences that I'm not seeing.

I've used Durham's Water Putty before too, but i don't think of it being used on a stressed area.

Does anyone know of a reliable filler that can be used in things like a chair frame where the holes are cut close to the outside of the wood?

I'd like to have a better go to product than what I'm using.

Regards,

Tom Watson

[Lew Hodgett]

Depends on how much screwing around you are willing to do.

First you need to get a good bond between the wood fibers and the filler.

You do that by mixing up some laminating (low viscosity) epoxy and brushing it on all the raw wood fibers in the dowel hole.

I'd use a plumber's acid brush for this part of the process.

Allow a few minutes for the epoxy to penetrate the wood fibers and hopefully start to "kick".

Now apply your epoxy "filler", "fairing putty", etc, and allow to cure.

Fairing putty is nothing more than laminating epoxy thickened with micro-balloons.

The laminating epoxy bonds to the wood fibers, the fairing putty bonds to the epoxy.

Make sure the dowel holes are rough so the wood pores are open and can accept the epoxy.

Take a look at the System3 web site.

Think they have just introduced some filled epoxies aimed specifically for the wood worker market.

Have fun.

Lew

[nailshooter41]

Tom - this is just my experience, and as always, just my 0.02.

When I have rebuilt/restored/refinished wooden chairs as part of a job (I usually get the damn chairs if I do a table refinish) I have had problems with ALL of my adhesives sticking from one time to the next.

At this point, when I have dowels to repair that are no longer performing, I do different things to them depending on where they are on the chair.

If in the seat area, I saw them off completely and drill new holes and use new dowels, the largest ones I can fit in. If I need a special size of dowel, I turn them out on my lathe, and put striations on them with a pocket knife, or if I have a lot I spiral the striations on the lathes while the dowel stock is mounted between centers. I can never find 1/2" dowels when I need them.

If I am repairing a splat, I drill the holes out as well and put in a new dowel. If the dowel is seen I carefully fit it in and stain it to match. It will be seen regardless, so I really don't make a lot of effort to hide the dowel. In some cases, I have added dowels that show where there were none before to pin the splat in place. The folks were pleased with the results. This of course, was not done to a priceless antique.

If I am dealing with a spreader, I drill out the holes in the legs, and sand the spreader adhesion area clean with 80 grit. I thicken the epoxy with micro balloons if I have them, with wood flour if I don't. Behind leg, out of site, I pin them with a 18 ga. brad after gluing and clamping.

I have found in my experience that the reason that glues (practically all of them are at least pretty good these days!) don't stick is residue in the area to be adhered. With that in mind, that is why I drill out the dowels and holes. I sand out all holes with sandpaper on a small round stick, then clean them out with acetone.

If a joint has been in failure for a while, there is no telling what can work its way into the joint itself or mechanical holding devices. On chairs, I find food, dog/cat hair, Pledge, soapy cleaner residue, and all manner of filmy crap that prevents adhesion.

Hope some of that helps.

Robert

[Tom Watson]

You know, Robert, this is one hell of a good precis on dealing with dowel failures in wood that is essentially sound. What I'm looking for is a filler that will work when the chair has continued to be used to the point that the dowel hole has blown out in two planes and the wood either needs to have a dutchman inserted, or it needs to have a filler solid enough to redrill the dowel hole and get back to business.

What is going on with this particular chair is that they ran the holes way too close to the end of the wood. They would have been better served by using a mortise and tenon instead of a dowel but this appears to be factory made furniture and that might not have been in their lexicon.

I guess I wasn't clear enough and you have my apology.

I appreciate your efforts.

Regards,

Tom Watson

[Tom Watson]

Thanks, Lew.

This sounds like the real deal.

Regards,

Tom Watson

[Lew Hodgett]

What you need to remember is that unlike typical wood worker's glue, epoxy fairing putty needs some thickness to obtain it's strength.

Thus it is a natural for filling worn oversize dowel holes for example.

The trick is to get a good bond to the raw wood fibers first.

When I would lay glass on plywood, would grab the ROS with 40 grit paper and sand the ply first.

Never had a bond break loose.

Have fun.

Lew

[dadiOH]

My experiences with fill & drill...

1. If the fill is enough to leave 1/8" or more of the fill around the diameter after drilling, all is well

1. If 1/16" - 1/8" of fill is left after drilling, all *may* be well

2. Any less fill left will have been messed up by drilling.

In your case, I'd probably "fill and insert"...pack the hole(s) with thickened epoxy (I prefer Cab-o-Sil to micro balloons), insert dowels, let cure. Squeeze out can be cut off after the epoxy is set but not hard or wiped off earlier. Vinegar removes it easily.

dadiOH

[Larry W]

The minwax product is polyester based and not really different from bondo or auto body filler. These products do not actually bond to wood, they really depend on simple mechanical interlocking to hold. Look for a true epoxy filler .