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View Full Version : Bondo... anyone use it to repair rotten wood?



Joe Lyddon
02-06-2006, 01:23 PM
If so, can you give me some help as to:

1. What kind to buy? (Where to buy it?) (How much is it?)
2. How much to buy?
3. How to mix it?
4. How to apply it?
5. Sand it?
6. Prime it?
7. Paint it?
8. Like it?
9. Don't like it because of .......

Thank you! :)

Have Fun!
Joe

http://woodworkstuff.net/

PK
02-06-2006, 01:34 PM
I used Bondo to patch up the skirting around a deck. After painting, you couldn't even tell. Alcohol was involved at the time, so it's not like there was any careful thought about this, but I've heard of other people doing this intentionally and having good results. I'm sure there's something made specifically for this, but Bondo worked okay for me.

It's real easy to use. I used the two part stuff myself, we were actually working on a '75 Blazer, but I believe they make some pre-mixed stuff too. It's pretty cheap stuff, so I'd just buy a bit more than I thought I'd need.

mrohde
02-06-2006, 03:33 PM
1. What kind to buy? (Where to buy it?) (How much is it?)
I used Bondo brand packaged as a wood filler. I'm pretty sure it's the same stuff they sell in the car parts stores as auto body filler. I think I bought it at Lowes. I don't remember how much it was, but it seems like less than $10.

2. How much to buy?
That was easy. They only had one size. It's a volume deal. It'll fill about as big a hole as the size of the can. It doesn't expand or shrink.

3. How to mix it?
I mixed mine on a paper plate with a popsicle stick as a stirrer.

4. How to apply it?
It depends on how big the hole you're filling is. I used a small putty knife to apply mine.

5. Sand it?
Just like wood.

6. Prime it?
Just like wood.

7. Paint it?
Just like wood.

8. Like it?
It serves the purpose, I guess. It depends on what you're doing and why you're doing it. I had some rot in a door frame. I dug out the rot, sprayed in some nasty chemical (a home brewed bora-care, as I recall), and filled it with bondo. It was a stop gap measure. Had I the time I'd have done something more appropriate.

9. Don't like it because of .......
It ain't wood.

Limey
02-06-2006, 06:32 PM
Joe, I work as a Home Handyman Technician so come across this problem quite frequently.
Two products I use regularly are Min Wax Hardener which is a liquid you paint on and reinforces the surface ready for the filler...good thing is it works even if the wood is not totally dry.

They also make a grey bondo type paste which you squeeze a dab of hardener with and it works and smells exactly the same as genuine Bondo but it's more expensive...you can guess which one I use. Depending on weather ,temperature I will add more or less hardener as in cold conditions it takes considerably longer to harden to the point that it can be planed or sanded smooth..most customers won't pay for two visits??

However in the summer it hardens very quickly and so mixing large amounts is a prob as you have to work like the clappers to get it in place and fashioned before it gets too hard.

It's an exothermic reaction so it sets up and hardens evenly ..i.e. it doesn't slump too much and doesn't skin.

The other stuff I use and love can be found here but it is pricey

http://www.rotdoctor.com/epoxy/woodrestoration.html

Just dig out the rot and then use the hardener ..this way the patch stays in situ and dooesn't shrink and fall out.

Theres also another product I use indoors whose name escapes me but it sticks like the proverbial to a blanket, is base cream color rather than off white or grey and is easily tinted with powder pigments for perfect matching while you work it and hardens at the same color so you can (with a good eye)make truly invisible repairs.
I'll try and find the exact name if you need it but its something like Abutron.

Haywire Haywood
02-06-2006, 07:07 PM
I've heard that you can use superglue on rotten wood as it soaks in and actually makes the rotten stuff solid again. I've never done it tho and don't know how it would take paint and stuff.

Ian

TDHofstetter
02-06-2006, 07:17 PM
I've been plenty happy with ordinary Bondo autobody filler from the local auto parts store. Practically every car-parts place carries it, as to KMart and Wal-Mart (usually). Not the stuff with embedded fiberglass fibers - that's rough on tooling. No need for it anyway. Also not the Bondo brand fiberglass (polyester, really) resin that comes in the "hip flask" can - just Bondo in the big round can. Pint, quart, gallon.

Don't buy a whole lot more than you really need, 'cause the little bottle of hardener will crack & leak & be a general mess if it waits around a long time.

Mix according to directions on the can, approximately. It's not overly critical. Mix on some surface you do NOT care about - like the bottom of a broken plastic bucket, a paper plate, in somebody else's shoes. Mix with nearly anything - popsicle stick, tongue depressor, somebody else's shoehorn.

If ya get a little on ya, don't fret it. It'll pop back off after it's hardened. Do NOT get it in your hair or your socks.

Pretty much smear it on & in. Apply far too much. Work FAST 'cause ya ain't got much time after it's mixed right.

Use a rasp or a Surform plane to shape it pretty nearly the way you want it. An angle grinder does a good fast rough job, too. When it's nearly how you want it, break out the sandpaper. It'll take about the finest sandpaper you're willing to throw at it.

Yup. Ordinary primer works well. Paint per taste. I kinda' like the flavor of enamel, myself, but that may be an acquired taste.

:)

-- Tim --




Call me
Kaw-liga
:)

autobodyman
02-06-2006, 07:21 PM
Bondo, or plastic filler by any other brand is not water proof. As a mater of fact it will take water. It's fine to use indoors on wood, but I would go with Duraglass made by Evercoat, on anything outside. It's water proof and mixes and spreads just like "bondo" but it's water proof. It is harder to sand than bondo though so don't over build to much.

I get mine from a local Napa, but I would think you could do a google if your local place doesn't carry it. I think it comes in quarts, I buy gallons, body shop and all.

~Mike

mstens
02-06-2006, 08:13 PM
You can get clear hardener for regular bondo ya know, makes it grey instead of red ;)

mstens
02-06-2006, 08:15 PM
Sure, but if you prime and paint it's a non-issue IMO. Just like when it's skim coated on cars.

autobodyman
02-06-2006, 08:35 PM
It's not a non issue, even on cars. Haven't you ever ground off bondo and found rust? If you use to much hardner the heat created can cause condesation, hence rust. Then there are those guys that drill holes threw the metal panel for pulls and just throw bondo over the top, those little bondo boogers draw water. I quit using anything but duraglass in the bodyshop years ago. More expensive to be sure but worth it I think.

I believe on wood it would take moisture, hold it and cause rot over time.

I may not be a master woodworker but when it comes to body work I am a Master.
http://www.customers.collinscom.net/autobody/aselogo2.jpg

~Mike

garyeng
02-06-2006, 09:24 PM
If it was me going to repair something that was going to be outside I would not use plastic body filler. I would just mix up some expoy and add a little microlite and some colloidal silica and never worry about it again. It sands real well too trust me. Now maybe not as easy as bondo but it will not fall out like bondo either. The downside to it is that it is expensive and it takes 12 hours to set enough so you can sand it. There is some other stuff I use that is also epoxy based and only takes 4 hours to dry before you can sand it but it is expensive too.

If we are just taking about using it inside the house and it will never be exposed long term to water than you can use Bondo or whatever without a problem.

Gary

TDHofstetter
02-06-2006, 09:45 PM
Waitaminnit, Mike. This time I'm going to argue with you one one point. Probably nitpicking, but I'm pretty serious about physics. Heating does NOT cause condensation. If it did, every time you hit steel with a torch it'd get wet. Condensation happens when a surface is significantly COOLER than the air around it... whether that surface chilled faster than the air did or the air warmed faster than the surface.

The only time I've ever seen rust under Bondo is when either (*) it was there before the Bondo ever went on, or (*) the Bondo didn't bond right to an improperly finished surface and allowed moisture to wick into the gap.

True, Bondo isn't waterproof. I've watched a lump of cured Bondo slowly dissolve under a downspout. It IS, however, water RESISTANT. I think it's just resistant enough to be a good patch for outdoor use if primed & painted well enough to protect it and the wood around it from becoming inordinately moist. I very much doubt that the small amount of moisture retained in ordinarily protected wood is enough to significantly weaken the filler-to-wood bond.

OK, I'm done. :) No offense, just wanted to get that straight.

-- Tim --




Call me
Kaw-liga
:)

rrich
02-06-2006, 09:54 PM
Tim,
" Do NOT get it in your hair or your socks"

You're supposed to add, DAMHIKT... ;) ;) ;)

BradTheNailer
02-06-2006, 11:55 PM
Well first off "Bondo" is a name brand of body filler.
If you're using it just to "hide" the rotten wood, I wouldn't sweat it, Use it. I can tell ya the more expensive body filler (usually always) is better. It's easier to work!

Now, if you want to use it to "strengthen" rotten wood...I wouldn't recommend it.

Think about it.... It's used on automobiles to hide the crap and leave a nice smooth finish. It's not used for structural strength. If things are that bad on a car, the metal is cut out and replaced with new metal, the same should be applied to wood. If the wood is that rotten, covering it with body filler will just make it pretty, it's not going to help the structural strength of the wood. I would suggest you replace the wood.

Body filler (Bondo) is just that, a filler, not a metal or wood replacement.




"I just don't understand...
I've cut it three times and it's still too short!"

[link:www.mgsawmill.com|M&G Sawmill]. Makers of the finest sawdust in Texas. Oh, did I mention we have hardwood as well?

autobodyman
02-07-2006, 09:12 PM
Tim,
I'm no physicist but I have heated some metal in my time and I have noticed that if you hold a torch for a moment over a single spot on the metal a ring of moisture (more like a fog on the metal ) will form out a slight distance from the spot being heated, granted it doesn't last long but it is there. Like it to a wall of your house, if it's really cold outside and really warm inside at some point in your wall the temperature will be just right for condensation.

Heating or cooling in and of itself doesn't cause condensation it's the difference in hot and cold that produces a zone of condensation based on relative humidity, they call it the dew point.

I also don't believe that painting wood in an outdoor condition will last forever, at least in my experience paint on wood outside eventually fails, peels flakes off so at some point the body filler will be exposed to some moisture. In the end replacing the rotted wood would be best, but if your going to patch the wood the Duraglass will last longer than "Bondo". To each his own, you can lead a horse to water but you can't make him drink.

[FONT color=#ff0000] >OK, I'm done. :-)No offense, just wanted to get that straight.[FONT color=#000000]

None taken, I hope I don't offend you, but I think your wrong when you say this:

[FONT color=#ff0000]>Heating does NOT cause condensation.[FONT color=#000000]

And your correct when you say this:
[FONT color=#ff0000]>whether that surface chilled faster than the air did or the air >warmed faster than the surface.[FONT color=#000000]

The Bondo when to much hardner is added gets very hot, hence the cool metal and in your words "warmed" air create a zone of condensation between the Bondo and the metal. Dupont did some testing on two component polyester fillers that bore this out. They mixed their components at 1% 3% and 6% and found that the material set up faster at 6% but also generated more heat and more condensation occured. As a side note using more hardner than recommended in the end made the filler harder, and more brittle and less flexible.

It doesn't take long for bare steel to rust when exposed to moisture (you may not see it without a microscope but it's there ). I doubt anyone here cares much about bodywork, but that's one of the reasons it's recommended and I use an acid etch primer over bare steel, and sand threws.

~Mike

Joe Lyddon
02-08-2006, 12:42 AM
I thought Bondo had structural strength... like Epoxy... very strong.

Easily applied to wherever you wanted it to go... into holes, cracks, and crannies... :)

That's what started me thinking about it...
(you out to POP my balloon?) :) :)

Have Fun!
Joe

http://woodworkstuff.net/

autobodyman
02-08-2006, 02:34 AM
It will work though it's not as strong or water proof like Duraglass

http://www3.uschem.com/uscp/list_product?pass_catalog_number=1&pass_category_number=4
Click the Duraglass link to get more info, also view the tech bulletin:

http://www.uschem.com/techbulletin/Duraglas.pdf

~Mike

JCCLARK
02-08-2006, 07:09 AM
I have been doing bodywork a long time and I can tell you
for a fact regular Bondo bodyfiller is like a sponge and will
soak up water. That's why you are never suppose to wet sand it.
I learned that the hard way. Water gets down in it and it takes
forever to dry. Use the Dura-glass waterproof filler.
It says "waterproof" on the can, regular filler does not.


Jim C.

TDHofstetter
02-08-2006, 11:50 AM
Ah - time to pass on a li'l information. Cool.

Here's what happens near that torch flame.

The gas you're burning, be it butane, oxy-butane, MAPP, oxy-acetylene, or what have you... produces, as part of its normal exhaust, an amount of good ol' water. Produces aldehydes, too - that's the awful sharp smell you sometimes get when you light up the gas oven. The water comes out of the torch as superheated water vapor, and condenses on the (still relatively cold) metal. That happens ONLY until the metal's warm enough to stop condensing the superheated vapor - and then the metal dries off nice & sweet.

The whole mechanism of condensation goes like this: Water molecules as vapor form are bouncin' around pretty loose. They can (and must) run around loose because they have so much energy (from heat, probably) to make 'em bounce off each other right smartly. As you remove the heat, you rob 'em of energy - which makes 'em a little less bouncy. At a certain point, they'll stop bouncing off each other and stick to each other like shorts to the wall. Remove more energy and they'll huggle up (that's ice). Add energy (heat) again, and they'll start movin' around... they don't like hangin' with other sweaty molecules. Add more energy yet, and they'll start arguing & bickering among themselves... and turn bouncy again.

That's paraphrased, of course - but that's what happens. It's the cooling that takes energy away from the molecules, and the heating that adds it. Condensation can only happen on a surface that's cooler than the molecules - not on one that's warmer. Assuming no difference in pressure, mind ya - increased pressure makes the condensation happen at lower temperatures, less pressure makes it happen at higher temperatures.

N'matter, though. I doubt much of this whole discourse will make much diff'rence to anybody actually workin' the stuff. Fun to talk about, though. :) :) :)

-- Tim --




It's a bird!
It's a plane!
It's Supe...
...
No, it's a bird.
:)

autobodyman
02-08-2006, 12:57 PM
Very interesting Tim,

Mostly clears up the moisture halo on the sheet metal using a torch for me.

How about this though, I've seen water drops actually form when heating frozen copper water pipes with a propane torch, up the line from where heat is being applied, enough to even drip off before drying. I assumed this is condesation occuring between the heated area and the cold area ( dew point zone ).

>[FONT color=#800000]Condensation can only happen on a surface that's cooler than the molecules - not on one that's warmer.[FONT color=#000000]

But isn't that what I'm saying? The filler gets hot, heats the molecules, the metal surface in relation is cold, cools the molecules. At some point between the hot and cold the dew point is reached and condesation occurs.


>[FONT color=#800000]N'matter, though. I doubt much of this whole discourse will make much diff'rence to anybody actually workin' the stuff. Fun to talk about, though. [FONT color=#000000]

Yes it is, nice to learn and hear other peoples opinions and experiances.

~Mike

Joe Lyddon
02-08-2006, 01:29 PM
As I was at the Bondo website, I got pissed at how their website was useless and sent them an email to unload my thoughts... This is one of 3 emails I received from them:

Bondo Body Filler is not waterproof it is water resistant. However you could use Bondo Glass #272 to make all your repairs and then use Fiberglass Resin Jelly #431 to make your final coat to sand and smooth out to get ready to prime and paint. The two products that I have recommended are 100% waterproof. If you have any further questions feel free to give me a call.

Wayne Banks
Senior Technical Administrator
Bondo Corporation

Anyone used this stuff?
Comments?

Thank you.

Have Fun!
Joe

http://woodworkstuff.net/

autobodyman
02-08-2006, 02:34 PM
The reason I mentioned Duraglass is because that is what I use and am familiar with, I am certian other manufactures make a similiar product, Bondo, evercoat, etc...

The reason I like Duraglass is that it doesn't have fiberglass strands in it ( ie, like kitty hair ), it mixes and goes on like "Bondo" though heavier and harder when cured, and of course water proof. You can sand this stuff to your final finish without the use of jelly type fiber glass top coats ( I don't like that stuff either, messy though it does have it's places of use ). If you need a stronger repair you probably should use fiberglass cloth, or screening too.

I am sure there are many suitable products out there, I have used Duraglass with good results.

~Mike

TDHofstetter
02-08-2006, 04:25 PM
That works... provided the hot filler has some moisture to heat. That water's gotta' come from someplace. It won't be in the filler, it won't be in the metal... and if there's a continuous surface-to-surface contact between the filler & the metal... it ain't just going to generate water molecules. That'd be... spontaneous generation. Like flies growing spontaneously from spoiled meat.

Now - it'd WORK if the filler heated up some water molecules & air carbureted together. Such a mix can (because the air spreads out like the water does) actually take on a heavier "mix" of water molecules. Hot air absorbs more water than cold air. So then that heated air - which would have taken on more moisture from the surrounding, cooler air - would settle & condense on the cooler metal away from the filler-to-metal junction. Right at that junction, the metal'd be heated by the filler.

So, no - water wouldn't form UNDER The filler, between the filler & the metal. It wouldn't tend to condense right at the junction, either - that'd be the rim of the patch. It'd be most likely to condense slightly beyond that junction, in a pattern approximating the shape of the patch - weighted to reflect the density (filler thickness) at the rim. Thinner filler, lower latent heat.

EDIT: Now... what you may see when you're heating frozen copper pipe is this: You're in an atmosphere very near to the dew point to begin with... that's the temperature & pressure combination at which moisture begins to settle & condense... forming into larger & larger droplets instead of hangin' in suspension as an aerosol.

So now you come along with your torch. Burning a hydrocarbon, emitting an exhaust containing water. That extra water mixes readily with the heated air near the torch flame - because heated air accepts a richer mix. You keep applying heat, the plume of moist, warm air expands outward... because you keep makin' more. As it reaches outward, it encounters that cold nasty pipe fulla' ice... not very far out. That pipe is COLD, which chills the air back down... and because cooler air can't carry as much water, it drops some on the pipe. You have condensation right there.

To prove, get into an environment just like the one you described. Don't freeze your pipes to do it, but get to a situation where you're pretty sure you can make moisture form on a metal surface you're heating with a torch. OK, now find another chunk of cold metal at the same temperature as the metal you're heating. Say, if you plan to experiment with a short length of pipe - lay another length of pipe NEAR it, but don't HEAT it. What you want is to get your plume of hot air to come into contact with both pipes... but not heating the "test" piece significantly. Helps if the "test" piece has more latent heat... like it's solid instead of hollow. Like that.

So - you heat the one with the torch... and I'll give you any odds you can generate condensate on the OTHER piece of metal, the one that's NOT being heated.

There's an idea. Stick a pipe in a bench vise. Let 'em stand together for several hours so you know they're at exactly the same temperature. Now heat the pipe with the torch. Vise won't get hot, not for a long time. True? BUT... where condensate forms on the PIPE, it'll form on the VISE, too.

(pant, pant)... :) :) :)

I gotta' get out more often... :)

-- Tim --




It's a bird!
It's a plane!
It's Supe...
...
No, it's a bird.
:)

mstens
02-08-2006, 04:39 PM
Yep, I agree with Tim. I've seen LOTS of rust under bondo, in rust prone areas, under the same circumstances Tim's mentioned. I haven't seen any in Arizona, where there's a lower ambient humidity anyway ad a much lower dew point. If heat itself created moisture, there'd never, ever, be a rust free weld. I agree, Bondo's not the best filler on the market, but the finish that goes over it and the prep work before hand makes more of a difference in my experience.

Randy Privett
02-08-2006, 04:53 PM
Sigh :)

TDHofstetter
02-08-2006, 06:43 PM
WHAT? :D :D :D

We're CHATTING! :D :D :D

-- Tim --




It's a bird!
It's a plane!
It's Supe...
...
No, it's a bird.
:)

autobodyman
02-08-2006, 06:49 PM
I hate to keep this up, (fun though huh? :-) ) but, this statement:

[FONT color=#800000]>Hot air absorbs more water than cold air.[FONT color=#000000]

According to this link is incorrect:

http://www.usatoday.com/weather/wevapcon.htm

I'll give you there probably isn't enough air space between the plastic filler and the metal to allow much air ( humidity ) to condense so most of the rust I have seen under other peoples plastic filler repair is most likely do to improper procedures, wet sanding or using non catalized primers that also aren't water proof and wet sanding that or in high humidity areas, or left the exposed metal open to long to allow flash rusting.

But I also don't agree with [FONT color=#800000]>Heating does NOT cause condensation[FONT color=#000000] Look at the roof of your house, why do we vent these, to lesson condensation that can occur when the cooler temps in your house and the heated roof outside create a zone of condensation in your attic, of course it works both ways, warmer inside colder outside. Depending on your dominate weather conditions, determines where to install your vapor barrier, I think I saw Norm say that about the vapor barriers.

Any who this has been fun and interesting. What was the question again ;-)

~Mike

TDHofstetter
02-08-2006, 07:51 PM
Brad, you owe me ten bucks. :D :D :D

-- Tim --




It's a bird!
It's a plane!
It's Supe...
...
No, it's a bird.
:)

mrohde
02-08-2006, 07:53 PM
Hot air absorbs more water than cold air.

I'd have stated it more like "the warmer a given volume of air is the more water vapor it can hold".

Scientifically speaking, everything Tim has stated matches all the physics courses that I've taken.

BradTheNailer
02-08-2006, 09:32 PM
Brad, you owe me ten bucks. :D :D :D


$10????!!!! Hell that's worth $20 at least!


also..

"Hot air absorbs more water than cold air."

This has to be true....

Limey is full of hot air, and I betcha he pees his pants daily! LOL :D :D :D :D :D :D!!!!!!




"I just don't understand...
I've cut it three times and it's still too short!"

[link:www.mgsawmill.com|M&G Sawmill]. Makers of the finest sawdust in Texas. Oh, did I mention we have hardwood as well?