# Plaster vs autobody filler



## Mattsn (Nov 22, 2015)

As I'm nearing the next stage of my build I've been researching how to form realistic rocks and mountains. I am leaning towards using plaster, however I've read multiple times that plaster sometimes cracks later down the road and needs to be repaired. That sucks. 

I work in the auto body world, repair and restoration. I'm very familiar with body filler and I was wondering if anyone has experimented with it? I think I will try it. The advantage would be that it won't crack at all. You can still sculpt it the same as plaster however you'll probably have less time to do so. 

So again, I was just curious if anyone has tried it. Be testing adhesion to the foam today at the shop.


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## Lehigh74 (Sep 25, 2015)

Auto body filler won’t work for one simple reason. Your wife won’t be able to tolerate the aroma.

Seriously, there are some other options:

- If you want realistic rock formations, your best bet is to get some rock molds and make rocks using lightweight hydrocal. This is time consuming but in my opinion, it makes the most realistic rocks.

- Same as above but use Plaster of Paris. Less $ than hydrocal, but heavier.

- Sculptamold, Structolite or Woodland Scenics Mold-a-Scene for shaping terrain. All of these have a longer working time than plaster or body putty. Sculptamold is probably the best of the three to work with. Some use it to sculpt rocks, but I haven’t tried that. Structolite will crack if it’s laid on thick. With Sculptamold or Structolite, you can apply it and press hydrocal rocks into it while it is still wet. Mold-a-Scene is not as easy to work with as the other two, but yields decent results.

I’m interested to hear how you make out with the body putty test.


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## gunrunnerjohn (Nov 10, 2010)

Wallboard compound. Harry Henning buys it in bulk, and he molds all sorts of rocks with it. All the rocks on this bridge are wallboard compound as are all the carved stones. It's been transported a number of times to modular shows, nothing has cracked except where we run into things and have to fix them. The stones on the side, and all of the arches are 2" foam and then covered with wallboard compound. The stones are done using molds filled with the paste and then hot glued in place. The powder is what we use and mix it when we need it, works better than the premix and you don't waste it. Cheaper too...


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## CTValleyRR (Jul 26, 2014)

Certainly, everything is worth trying at least once. I agree though, that I wouldn't want that stench in my house (layouts are in the basement).

The most common reason that things crack is that the supporting structure isn't stable. This can be as simple as not using enough gussets / braces on your benchwork, or not sealing it so that it expands and contracts with changes in humidity.

Or people lean on it when trying to reach things that are too far from the layout edge....


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## Mattsn (Nov 22, 2015)

I understand the hydrocoal and plaster of Paris all the above. I've been reading on all of it. I can get the body filler extremely cheap. I know that isn't the case for most people. I belive It can work just as well using the rock molds. I'm not trying to re invent the wheel. Just thought of something different. I may try it just for that reason. The filler is adhering to my foam sample extremely well. I can't pull it off. As for the smell. There are brands that don't stink. 

As for the wife. If it were to stink I'll tell her to leave the house and go shopping for the day. Haha. I find it amusing that it's a fairly common theme on these forums that the wife is mentioned alot as an obstacle. My wife is very easy going when it comes to my projects


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## CTValleyRR (Jul 26, 2014)

I don't think most people are referring to their wives as an obstacle (although I have seen exceptions). For most of us, our significant other is an equal partner, and we're smart enough to take her opinion into consideration.


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## Mattsn (Nov 22, 2015)

CTValleyRR said:


> I don't think most people are referring to their wives as an obstacle (although I have seen exceptions). For most of us, our significant other is an equal partner, and we're smart enough to take her opinion into consideration.


Yes sir, I wasn't actually suggesting that your wife wasn't an equal. I was just being playful. Sorry


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## raleets (Jan 2, 2011)

My wife has been super-supportive during the past five years that I've been creating my model railroad empire.
Since it's located in a separate building, about 70 feet from the house, she doesn't see it very often, but when she does she's very enthusiastic and normally offers some great suggestions.
Soliciting her opinions and input has served me well when it comes to buying new "stuff" for the layout. 
Amazing the mileage you can get out of that with the little woman.


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## wingnut163 (Jan 3, 2013)

here is another idea. i use flower/water soaked paper put over a card structure.


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## L0stS0ul (Feb 6, 2015)

I bought a woodland scenic rock mold and used their lightweight plaster with it which worked really well. I molded probably 30-40 rocks groups with it and then broke up the pieces to make smaller parts which really made the one mold go far. The lightweight stuff dried so much faster than any other plaster or mud I tried. The lightweight plaster also took the paint wash better than the rocks molded in other plaster or mud. 

I did a base mountain form with foam to create the main structure and tunnel. Then used newspaper and plaster cloth to form the mountain curves. And finally glued the rocks on with liquid nails. I tried drywall mud but I think it was too dry and everything fell off the mountain overnight. Didn't feel like messing with it so used liquid nails :appl: Drywall mud was then used to fill in gaps and stuff. Came out really nice I think. I wish the rocks were a bit redder but that was an error in my wash combination.


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## /6 matt (Jul 7, 2015)

Here's my main concerns with your idea. 1. Bondo/body filler cracks when it's put on heavier than say about 1mm 2. Bondo/body filler releases heat and a lot of it while it dries.


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## Mattsn (Nov 22, 2015)

Yes, that looks great. You did a really nice job


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## Mattsn (Nov 22, 2015)

/6 matt said:


> Here's my main concerns with your idea. 1. Bondo/body filler cracks when it's put on heavier than say about 1mm 2. Bondo/body filler releases heat and a lot of it while it dries.


If you use the right body filler it will not crack. That's one reason why there are several types. You pick the one that suites your need. I can't imagine the heat that it creates is going to cause a problem. It doesn't get that hot. So unless the mold melt at a relatively low temp I dont see it being a problem


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## /6 matt (Jul 7, 2015)

Mattsn said:


> If you use the right body filler it will not crack. That's one reason why there are several types. You pick the one that suites your need. I can't imagine the heat that it creates is going to cause a problem. It doesn't get that hot. So unless the mold melt at a relatively low temp I dont see it being a problem


Um, there is no right filler and if you think there is than you are using it incorrectly (most people do). Body filler is designed to be a light skin coat that you sand flat AFTER you pull the dent completely out. Your layer of filler should NEVER be thicker than a mm or two. And yes, it can melt plastics while curing.


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## gunrunnerjohn (Nov 10, 2010)

Given the expense of bondo, I can't imagine why you'd have that be your first choice, even assuming it was perfect for the job.


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## Mattsn (Nov 22, 2015)

/6 matt said:


> Um, there is no right filler and if you think there is than you are using it incorrectly (most people do). Body filler is designed to be a light skin coat that you sand flat AFTER you pull the dent completely out. Your layer of filler should NEVER be thicker than a mm or two. And yes, it can melt plastics while curing.


Sir. I have worked in the autobody/collision and restoration field for 22 years and have made a very good living at it. I have a stack of I-car certification in many categories of this industry, (paint, plastic repair, metal finishing, frame, welding including aluminum) huge stack. I also have certifications from 3 major paint companies/brands for multiple paints. ( Dupont chroma base and chroma premier, sickens autobase plus, spies Hecker 293/295 solvent and hitec waterborne) 

There are multiple types of body fillers for multiple types of jobs. Yes some can be used thicker that 1mm whether you think they can or not. They are not all created equal as they are not all for the same type of job. Yes of course you should "metal finish" the substrate before you add filler. Are you an expert on today's vehicles with very thin metal alloys? I am... And it isn't the same as the thick steel of yesterday's classics. And niether are the repair process. 

I am not talking about "bondo brand" as that is bottom of the barrel. I use high end products in my collision shop as well as my other projects. 

In my 22 years I have never ever seen body filler melt plastic. Yes it warms up as it cures but you can lay your hand on it. It will not burn you or melt plastic. Perhaps you are using it wrong. I have applied a thick layer of a "finish glaze" ( that would be one of those types of body filler or... mud... ) to the pink foam and it did not melt a thing.


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## Mattsn (Nov 22, 2015)

gunrunnerjohn said:


> Given the expense of bondo, I can't imagine why you'd have that be your first choice, even assuming it was perfect for the job.


Honestly because I just want to try it because I had the idea. And my cost on it is probably very close to the cost of plasters due to my contracts with my jobber (supplier), and I don't have to drive anywhere to get it.

It was just an idea


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## /6 matt (Jul 7, 2015)

Well I've only been doing bodywork for 10 years so I guess I just don't know what I'm doing. If you are so qualified to work with the stuff then go do it instead of bickering with me about it. Sounds like you have already tried it anyway since you say it hasn't melted your foam. Good luck.


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## dsertdog56 (Oct 26, 2014)

I believe this is an awesome idea if you use a lightweight low dust filler. 

Newer products are also lower VOC than good old bondo. Bondo and autobody repair should not be used in the same sentence. ICK.

I'm sure if you progress with this you'll have your share of detractors. I tied some leftover expanding foam covered with wood putty and was told it looked like crap..literally! I thought it was perfect...and still do!

Good luck and make sure you post pictures.


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## Mattsn (Nov 22, 2015)

I am going to try it. Thanks. I may even post a video of how it won't melt


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## Mattsn (Nov 22, 2015)

dsertdog56 said:


> I believe this is an awesome idea if you use a lightweight low dust filler.
> 
> Newer products are also lower VOC than good old bondo. Bondo and autobody repair should not be used in the same sentence. ICK.
> 
> ...


I agree with your "bondo" comment. 

I am going to proceed with it. I don't know if it will work, or even if it will work as well as plasters. I can do a side by side comparison. I'm not trying to revolutionize the model train world. It was simply an idea and thought I'd share. (thinking out loud)


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## dsertdog56 (Oct 26, 2014)

Sometimes with folks in a given hobby (or industry/service) certain products become status quo once a majority of people start using them...and thinking outside the box isn't wanted nor appreciated.

Take Paper mache' or Plaster...my Dads first layout was loaded with it..all stuck to screen. Took a strong frame to hold all that up....and what a mess when we had to demolish it.
Same with Bondo. Back in the late 60's that's all we had...unless you were good with lead or fiberglass mat and stranded glass with resin.

Then came all the fancy stuff, now you don't have to hack anything out with chisels and other pointy things. You have molds you can use to make totally realistic rock. The same molds that everyone else buys...

The worst that can happen is you won't be happy with the results. Or...you'll work with it until you're happy with the results. That result will be all your doing, whether or not others like it will be moot.


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## Mattsn (Nov 22, 2015)

Funny. I had wondered if anyone had used paper mache.


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## L0stS0ul (Feb 6, 2015)

If there is anything I have learned in my years it's that there are many ways to get tasks done. This is a hobby after all and if you are learning something and having fun there is no wrong way to do it.


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## /6 matt (Jul 7, 2015)

L0stS0ul said:


> If there is anything I have learned in my years it's that there are many ways to get tasks done. This is a hobby after all and if you are learning something and having fun there is no wrong way to do it.


Exactly. Worst case scenario you're out some money and a little time.


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