Is wet sanding body filler a bad idea? One Bodyman I talked to told me to wet sand body filler, so I tried it on a fender and it worked really well, preventing loading on the surface of the sand paper I was using and just all around was a lot cleaner. But recently I read somewhere that the filler absorbs moisture and moisture contact on body filler should be avoided. Keep in mind this is filler on bare metal. Could I get away with it if i used the special primer you apply prior to the filler to seal it or should I plan on an afternoon of sanding back to bare metal? I appreciate any info guys. -Ryan-

NO, Don't try it! I got water on my filler that was cured once and I had rust bubbles in about 6 months. That goes for any filler or finishing putty. Use 36 and 80 grit good quality paper and it won't load up, if it does tha's what the compressed air is for.

Ryan, don't even think of this. If you have any doubts call the tech line for a body filler company like Evercoat and ask.

FORGET the old husbands tales of goofy crap like this, ask the MANUFACTURE of the product for guidance, not a "Junior chemist" who thinks he can do better research and development than the manufacture does.

Ryan, please, please, please don't take this personal. You asked a good question, if you didn't ask, that would be dumb. But you asked because you thought there may be something wrong with what you were told. For that alone, I give you an atta-boy graemlins/thumbsup.gif

I chopped the top on my 48 Chevy truck when I was 16 years old, you guessed it, I did a lot of the filler work on that top chop wet sanding the filler! graemlins/clonk.gif

So you have to know, I can relate with being a newbe. I remember all too well. Below is a little "editorial" I wrote a while ago on this subject of drifting from the manufactures recommendations.

If you want to see the "Basics of Basics" on body filler and many other "Basics" on auto body and paint click here for the "Basics of Basics" over at the Team Camaro site. (http://www.camaros.net/forum/ultimatebb.php?ubb=get_topic;f=3;t=005647)

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Listen, the subject of mixing products comes up here often. I put this together to clear up why I feel the way I do about the subject. I by NO means am saying this to anyone and it is not personal. In fact, I don't even remember a particular post or person saying anything. It just comes up from time to time.

Rules, rules, rules, so many rules. Use this don’t use that. Sand this, don’t sand that. These companies must think we are stupid right? They tell us to buy their products only. Of course they do, so they can make money off of us, right?

That is how many people feel. They mix and match products thinking they can out smart the chemists that created the product!

The manufacture spent hundreds of thousands of dollars, possibly even millions developing the product. They did EVERYTHING possible to make it perform it’s best. Heck, if they found it worked better if you painted it while standing on your head, THAT would be in the tech sheet!

Did you know that most of these products you use have a lifetime warranty? That’s right the manufacture will stand behind their primers, paints, and clears for your LIFETIME. Now, as a DIYer you can’t have this warranty. What makes the difference between the warranty YOU have (usually none) and the lifetime warranty a shop may have? The training, that’s what. The manufacture has classes for the painters to go to. He then takes a test, if he passes, the manufacture knows that he understands the procedures and proper product choice. The manufacture has learned that it is likely the painter will use the product properly and it will perform as expected. The manufacture puts hundreds of millions of dollars on the line with this warranty. They know they can, if the product is used EXACTLY as they have instructed on the tech sheet.

I have always been the kind of guy to follow instructions. Even before I had the training I used the products exactly as I was told to. I am sure this accounts for the very few failures I have had in the 28 plus years I have been doing this work.

Five of those 28 years I was a paint rep. If there is one singular thing I came away from that job with it would be importance of following the recommendations. As a rep I visited hundreds, possibly thousands of shops. These shops were in every shape and size. From one with seven frame machines and five paint booths doing a million dollars of business a month, to a one man shop with two stalls.

Among these shops there was a very distinct pattern, the ones who went to tech school, had only ONE brand of product on the shelves, and REFERRED to the tech sheets, had fewer problems. Most of these shops had NO problems, EVER.

They were open to hear about new products and ready to learn about how to make any product or tool perform better. Oh yeah, and they made more money.

Then, there was the “dark side”. These were the shops that would buy any product, any brand, just to save a dollar. Their shelves were covered with so many labels, it looked like the cans of soda and beer in a Quikie Mart cooler.
If, and I mean a BIG if, you could get them to a tech class, they were disruptive and later told me how they “could have taught that class”. They were quick to tell you how smart they were and how the paint company didn’t know jack about the “real world”. These shops took up about 99% of my trouble shooting time. They didn’t have little “how can I get this primer to dry faster”? sort of problems. They had TOTAL catastrophic failures! I was the first one they called because we must have put out a “bad batch” of product.

I tell you this only so you can understand where I get this passion that I have for using products properly. It was like watching a basketball came where one of the teams were wearing wet jeans and cowboy boots! After a while you wouldn’t even have to watch, you would know what the outcome was going to be.

Most product data sheets can be read in a few minutes. They are available on line, as well as in the store where you bought the products or even many are available on “Fax Back” right over your phone.

Get proper mixing containers. Be sure the solvents used match temperatures of the booth. Double check to be sure you have ALL the components (and enough of them) BEFORE you start so you don’t find yourself tempted to be “creative”.

The three most important things and the most common cause of failures are as follows:
1. Mix the proper components accurately .
2. Use the correct solvent for the temperature.
3. FOLLOW THE RECOMMENDED FLASH TIMES.

All this info is on the product data sheets, use them.

Painting can be difficult, there are things that are quite honestly out of your control. So, why not do EVERYTHING that IS in your control correctly.

I used to wetsand my glazing putty with 220 and water and it would come out sweet. On my last project i did this on i had tiny little bubbles come up all around where i had filler. I popped one with a small pin and presto,a little water came out. So i dont do it anymore. I'm sure if you let the filler dry out in the sun or dry it with a heat gun it would be ok,but not worth the risk in my opinion.

When Evercoat introduced glazecoat about 15-16 years ago they recomended wetsanding, now I notice none of the polyester products they sell mention anything about wetsanding. Fillers do absorb moisture but for years I wetsanded my fillers without any problems. Before the polyester glazing putties came out I wetsanded regular polyester fillers to 400 grit and would apply my (Laquer) primers without any problems. A heat lamp applied to the filler area helped to make sure the moisture was evaporated before priming. Now I don't wetsand polyester anymore and most of my projects have epoxy applied below any filler for extra protection. Another interesting thing to consider reguarding wetsanding is most polyester primers do recomend wetsanding as an option raising a question as to why and why not with fillers? While wet blocking a panel in primer a person often times cuts through into the underlying filler exposing it to moisture, no big deal IMO just make sure it's thoroughly dry before you reprime. Most failures in the form of water bubbling I've seen are from moisture absorbtion from the backside of the panel caused by pinholes or butcher work where someone has filled holes etc.
In conclusion I have wetsanded fillers in the past without any problems. Nowadays I apply epoxy primer before filler application and I don't wetsand any fillers. And I wouldn't recomend wetsanding filler if the product manufacturer doesn't recomend it. Sure makes for a lot less dust though :D

Thank you all so much for the info! Luckily I had only started applying filler on one fender. Thanks for the editorial martin, really opened my eyes on a few aspects of the body work realm. SO my final question is, Should I use an epoxy type primer underneath the filler to be safe? and If I do use it, could wet sanding be ok with this preventive measure?( with careful drying with heatlamp etc...)
Thanks again guys I know this probably has been covered time and again but I am trying my best to get this done right. Oh, and btw I'm doing the work on my teacher's 52 chevrolet pickup. Thanks again! -ryan-


p.s. 1972 chevelle
350 mostly stock

I'm sorry, I just don't see any reason to wet sand filler. Yes, it would keep some dust down but that is it. It would actually just create a different kind of mess, no dust but "bondo mud" all over the place. That is no trade off for me.

You can feel the work so much better with the filler dry. It just makes no sense to me at all.

Epoxy under the filler, yeah it is a great way to do but not the only way. Under certain conditions like high humitity and long exposure without protection on the bare metal, yeah, sounds great. But in my climate, spending a day or more doing body filler work on a panel inside a shop or dry garage, there just isn't a need for it.

You can sand with a finer paper without clogging. Ever sand filler with 220-320? Paper clogs quick.Wetsand it and it doesn't clog.

I'm with you but why would you need to sand the poly putty with anything finer than 180? I mean, I do very rarely sand with 320 but it really isn't that big of a deal. The 320 is not to block but only sand enough to sand out the scratches from the 180. On that subject, have you tried the 3M dry guide coat? If you like to finish off the putty with the finer paper (but it would have to be dry sanded) that dry guide coat is fabulous. It easily fills EVERY single 180 or 220 scratch. I know you can't use it with the wet sanding so it may not work for you. But if you give it a try with dry sanding you may want give dry sanding a try.

Martin,what i used to do is say you had some tiny dings in a panel that was being painted,i would sand them with 120 wipe them with glaze. I would then wetblock them with 220,then 320,dry them with a heat gun then spray a wet on wet sealer and then paint.So i would not use a primer.The 320 wet gave the glaze and surrounding area a nice surface to seal right over. Probably not the best way but for the type of vehicles we were doing it worked great.

Originally posted by MARTINSR:
have you tried the 3M dry guide coat? I know you can't use it with the wet sanding Martin, Ive used that dry guide coat for the past several months when wet sanding. In my 2003 3M product catalog it says can be used for dry or wet sanding.

You know something I dont??

Originally posted by boomhauer:
Martin,what i used to do is say you had some tiny dings in a panel that was being painted,i would sand them with 120 wipe them with glaze. I would then wetblock them with 220,then 320,dry them with a heat gun then spray a wet on wet sealer and then paint.So i would not use a primer.The 320 wet gave the glaze and surrounding area a nice surface to seal right over. Probably not the best way but for the type of vehicles we were doing it worked great. I wasn't even thinking of that, yeah, I'd say that is a super way to do that procedure. You say it isn't the "Best" way but it really isn't bad at all especially if you were to seal it before painting. Heck, polyester primer doesn't need a sealer or anything over it. That polyester putty is pretty darn close to polyester primer. We will do something similar where I work and still not wet sand, just use 400 dry paper.

Eric, LOL, goes to show you what you can learn when you read the instructions! smile.gif I just looked in the 3M catalog and sure enough it says it can be used dry or wet. I just assumed (and you know what that means) that it being dry would just wash off.