Need REALLY STRONG glue to fix a chair
May 24, 2007 10:40 AM   Subscribe

Need something stronger than epoxy to fix a plastic office chair arm

I've got an office chair consisting of rigid plastic armrests that are sort of rounded rectangle shape (the bottom and one side are bolted to the seat and back of the chair itself.

The armrest broke, so I put epoxy on it and wrapped a bungee cord around it so it would hold its shape. Unfortunately, the epoxy wasn't strong enough to withstand the pressure of its own shape and of me leaning back in the chair and promptly broke.

What do you recommend I use to fix this armrest that will be able to withstand the force of me leaning back on it. I'm surprised because the epoxy says it can withstand 1000+ lbs. of force
posted by beammeup4 to Home & Garden (13 answers total)
1000lbs of force? I'm going to assume that's PSI and not some arbitrary marketroid number.

The strength of your bond is largely dependent on the area being bonded. You will have to modify the broken area, by cutting a section out and replacing it, or putting the equivalent of a splint on it (on the bottom, so the top is smooth), or drilling out a hole in the middle and putting a peg in, etc. This will allow the epoxy enough surface area to bond properly, and give you the strength required.

Alternatively, if you can find an equivalent armrest at walmart or something, and find the manufacturer, you can probably write to them and they'll send you a new armrest you can bolt on.
posted by defcom1 at 10:56 AM on May 24, 2007

The problems are: (1) the epoxy has only a small area to stick to; (2) your leaning back multiplies the amount of stress on the joint; and (3) epoxy isn't very good on plastic.

You have to reinforce the joint. Straighten out several large paperclips. Go to a hobby store that has miniature drills and get one that's barely larger than the wires. Drill longitudinal holes into both sides of the broken arm, put a appropriate adhesive in the holes and on the edges and glue up the joint again. You could also make a sleeve of heavy-duty heat-shrink tubing to stabilize the joint.

Go to This-To-That to find which adhesive to use.
posted by KRS at 10:57 AM on May 24, 2007

Harbor Freight sells a very cheap hobby tool/drill, around $8.00 with some attachments. JB Weld often works well in these situations.
posted by craniac at 11:14 AM on May 24, 2007

I did a project for my 7th grade science fair where I compared different adhesives. 10 years later, the effectiveness of polyurethane glue on most surfaces still kind of freaks me out. I know I tested plastic, and I think polyurethane was pretty great.

I just remember that my testing apparatus broke the ceramic plates I was using to test before the glue joint gave out. My dad and I were like "Daaamn player".
posted by crinklebat at 11:14 AM on May 24, 2007

My guess is you didn't give the epoxy enough time to cure before you loaded it. Even the quick setting kinds require 24 hours to approach full strength. By that time the bond is stronger than the plastic you stuck it to.
posted by ikkyu2 at 11:16 AM on May 24, 2007

If you want crazy strong wrap some carbon fiber around it and then soak it with epoxy.
posted by zeoslap at 12:03 PM on May 24, 2007

Here's what I'd do....

I'd get some nice monster drywall screws and screw 'em into the chair side. Maybe 3 or so, and leave at least a good couple inches exposed.

Then I'd cut off the tips.

Then I'd epoxy around the base of where the screws meet the chair. JB Weld would be a good bet.

Then while that was still wet, I'd blowtorch the screws as hot as I could get 'em, and then push the arm onto them. Rinse/repeat until it's seated firmly and epoxy squishes out.

Let it dry, and sand off the JB weld.

Oh, and btw---this is less than likely to work, it's just fun to play w/ blowtorches and PVC fumes.
posted by TomMelee at 12:22 PM on May 24, 2007

My grandfather (who is a bit crazy) decided he was going to "fix" my chair when it broke. This involved a couple of long, fairly thin pieces of metal, bolted on, and a lot of metal wire wrapped around. It did (does) hold, but it's not exactly pretty.
posted by anaelith at 12:44 PM on May 24, 2007

If the chair arm broke from just using it or leaning on it, it's likely that it broke right at the point where the maximum force is exerted. So your repair has to be STRONGER in that area than just the plastic alone.

Plastics do not epoxy well, and epoxy is never good at joints that get torsion or flex, so epoxy was a poor choice on both counts. If you can find a solvent-type glue that is meant for the chair's plastic, that may work, in combination with some of the splinting or reinforcing options. Or you could fabricate a replacement armrest (or two) in plastic, wood and/or aluminum and bolt it on.

Reality check - Most companies would either toss the chair, or phone the supplier for a replacement arm.
posted by Artful Codger at 1:00 PM on May 24, 2007

Two words - "GORILLA GLUE."
I used to to repair a leg on an antique three-legged folding table. Works great!
posted by winks007 at 1:18 PM on May 24, 2007

A picture might help; I am personally having a bit of trouble visualizing this.

My experience agrees with Artful Codger's regarding epoxy and plastics (doesn't often work). One problem I've had with plastics repair is that there so many different types of plastics that all react differently to adhesives.

I'm not sure how you want the chair to look after it's done. Epoxy by itself isn't nearly as strong as with a suspended fiber in it such as fiberglass or (as previously mentioned) carbon fiber. You could use fiberglass tape and epoxy to "splint" the broken site, but it won't be very pretty.

When I had a similar problem with a broken pull handle in an automobile I ended up using a hidden reinforcement of aluminum that was screwed to either side, with a small amount of a flexible glue to handle the (as small as possible) gap. You may be able to effect a similar repair by splicing in a metal bracket, depending on the shape of the arms.

You could look for a differently-broken chair and scavenge it for the replacement arm. This may be difficult as it is likely that this arm is a weak point and any chairs you may come across may have the same problem.

A final possibility might be to make a replacement arm out of another material (wood? resin?).

Again, though, unless the chair has great personal or economic value, then I wouldn't bother. If you simply can't afford a new chair I'd advise simply living with it.
posted by RikiTikiTavi at 1:27 PM on May 24, 2007

I use plastic resin bonds on architecture models, mostly for plexi-glass. It chemically dissolves the two surfaces and welds them together. It may work on your chair, depending on the type of plastic it uses. Check your geeky local model store.
posted by BeaverTerror at 7:20 PM on May 24, 2007

I recommend a gap-filling cyano-acrelate glue. This brand is very reliable. I am a furniture maker and find this to be indispensable. The accelerant is handy. Time after time this has proven to be much more reliable than gorilla glue in my shop and home.

Good luck.
posted by bigsurmoon at 3:12 AM on March 9, 2008

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