DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Carpentry and Woodworking > how do you repair a doorknob hole?





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Old 12-02-2009, 08:40 PM  
diyonthefly
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the glazing putty takes a long time to harden. it's great for nail holes and even anchor holes. i painted over it and it took the paint well. i'll never work with epoxy again. it's messy, leaves a bumpy finish and tends to discolor yellowish. i guess glazing putty is better than spackle in terms of strength. i put the doorknob on and it seemed to hold up ok. i really wanted to use wood putty, the stuff that comes in a cylindrical tube, you cut and roll in your fingers to mix the hardening agent in, but i couldn't find it. also the wood putty i found was only in wood color, the glazing putty was white. guess i wasn't thinking that i could just paint over it. ka duh!



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Old 12-02-2009, 10:07 PM  
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Maybe buy yourself some water putty. If you don't, you'll forget what it's called next time you need to do a repair like this. The stuff lasts forever in a dry environment, and if you buy some, you'll have it and use it on the next wood repair project. I think you'll like it more than glazing putty for interior wood repairs.

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Originally Posted by diyonthefly View Post
the glazing putty takes a long time to harden.
That's because glazing putty is just a mixture of clay and linseed oil, and linseed oil takes a long time to solidify when exposed to air.

And, in fact, that's exactly how glazing putty is supposed to work. Wood is a natural material which swells and shrinks with changes in it's moisture content due to seasonal changes in atmospheric temperature and humidity. Glass, on the other hand, is a ceramic material that hardly expands or contracts at all with temperature changes (and is unaffected by humidity). Consequently, you don't want your glazing putty to harden up so that it won't be able to accomodate the relative movement between the wood and glass. You want it to remain a semi-solid for as long as possible SO THAT it can maintain a seal at the joint between the glass and the wood despite there being relative movement between them. Even if the exposed surface of the putty hardens up and cracks during it's lifetime, the still softer putty under that surface will continue to maintain a water tight seal between the wood and the glass. Eventually, however the putty needs to be replaced, but nowadays most people are replacing glazing putty with modern synthetic caulks which weren't available years ago when putty was most commonly used. They still use the glazing points to hold the glass in place, but use modern caulking around the glazing instead of putty.

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i painted over it and it took the paint well.
Only paint over glazing putty with oil based paint. Because it contains linseed oil, I don't think latex paints will stick well to it. If you want to paint the door with a latex paint, then use an oil based primer over the glazing putty, and when that oil based primer is dry, paint over it with the latex paint.

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i guess glazing putty is better than spackle in terms of strength. i put the doorknob on and it seemed to hold up ok.
They'd be about the same, I think. One is a mixture of clay and linseed oil, the other is a mixture of gypsum with a bit of glue. The strongest would have been water putty which is basically a mixture of Plaster of Paris and white wood glue.

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i really wanted to use wood putty, the stuff that comes in a cylindrical tube, you cut and roll in your fingers to mix the hardening agent in,
No, anything that comes in two parts that have to be kneaded or mixed will most often be an epoxy. The stuff you're talking about (where you cut a piece off a tube and knead it to a uniform colour before setting it) is an epoxy.

Next time you want to repair indoor painted wood, try water putty:

DAP Products - Repair Products - DAP® Water Putty (Dry Mix)

Home Depot should sell it.

Or, if your "Painter's Putty" doesn't last, repair it better next time with water putty. (I'm presuming this is an interior door. Glazing putty will stand up better outside than water putty. Glazing putty is more or less water proof, whereas water putty is only for interior applications.)

Water putty dries to a hardness similar to wood. When mixed it's got a consistancy that allows you to shape it well, and it typically comes in a colour that's similar to wood so that it won't stand out like a sore thumb when stained. When hard, it'll be about the same hardness as Plaster of Paris, but it's be a lot tougher (cuz of the glue in it) so it doesn't crumble or crack easily. It can be drilled, but I wouldn't trust it to hold a screw as well as wood. Here's the colour of dry water putty (but it still looks a bit damp near the bottom of the thumb:



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Old 12-03-2009, 08:30 PM  
diyonthefly
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that is a very fine thumb mold. speaking of plaster of paris... isn't that the stuff you use in paper mache. what if you added very fine particles of paper mache or other fibrous material to the water putty, wouldn't that make the end product even harder?

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Old 12-05-2009, 12:55 AM  
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Adding paper fibers to water putty might work well because the water putty has white wood glue in it, which bonds extremely well to cellulose.

Maybe give it a try. If no one else has tried doing that before, the idea might make you rich beyond your wildest dreams. And, if and when that happens, try to remember the little people who were nice to you at www.houserepairtalk.com.

PS:
Plaster of Paris and gypsum are chemically kinda similar, but also chemically kinda different. They're both compounds made of calcium sulphate and water. In one form, you have gypsum, which contains two water molecules for each calcium sulphate (CaSO4) molecule. If you heat the gypsum, you drive off the water as water vapour, and the chemical structure of what's left behind changes so that there are now two calcium sulphate molecules per water molecule. The resulting powder is called "Plaster of Paris", whereas the starting material was "gypsum". Gypsum was called "alabaster" in ancient times. In Greek, "alba" means "white", which was probably the root word of alabaster.

That chemical reaction is very important. Since you need to heat gypsum to drive off the water and produce Plaster of Paris powder, when you mix Plaster of Paris powder with water, you get an exothermic reaction that releases that heat again. And, this is exactly why drywall makes a good fire stop. Heating starts to drive the water out of the gypsum core of the drywall at about 80 deg. C. As the water is driven out of the gypsum, the temperature will rise to about 150 deg. C. But, that's still well below the kindling temperature of wood. So, instead of water that boils at 100 deg. C., gypsum converts to Plaster of Paris at a temperature range from 80 degrees C. to about 150 degrees C. Since the heat of the fire goes into converting gypsum into Plaster of Paris, no matter how hot the fire gets, the studs behind the drywall won't get any warmer than 150 degrees Celsius. It's kinda like no matter how high you turn up the ring on your stove, the pot of water will only boil at 100 deg. Celsius. It'll boil faster the higher you turn up the ring, but it'll still only boil at 100 deg. C. It's the same with drywall. That conversion from gypsum to Plaster of Paris happens between 80 and 150 degrees Celsius, so all the heat of the fire will go into converting the gypsum core of the drywall to Plaster of Paris in that temperature range. So, the wood studs behind the drywall will never get hotter than 150 deg. C. as long as there's gypsum between them and the fire, and that protects the studs so they don't burn. (Or, more correctly, don't ignite for long enough that there's time to evacuate the building.)

It's really that chemical reaction of converting gypsum to Plaster of Paris that provides the high fire safety rating of drywall. It's essentially the same as having water in the walls. As long as you have that water chemically bound up in gypsum, the wood studs behind the drywall won't start to burn until all of the gypsum has been converted into Plaster of Paris.

(In real fires, that Plaster of Paris gets hot enough that it undergoes further chemical changes so that even if you were to collect the dust that the gypsum leaves behind, it wouldn't react with water anymore to form gypsum. It forms another compound that doesn't react with water.)

Ya gotta know this stuff to get your DIY'er armbadge in drywall.

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Old 03-28-2010, 08:26 PM  
AnonaJean
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The same thing happened to me, I sprayed some expanding foam into the hole and let it cure, once it hardened, I sanded and painted, can't even tell there was ever a hole, also the foam acts as a tough backstop. Might want to cover the new area with one of those rubber doorknob stops.



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