Body Filler & Banana Skins

One of the most common application questions I get asked about is with regards to body filler and how problems manifest themselves. This of course can be with or without the use of infrared. I therefore decided to write an article to cover the do’s & don’ts to help you avoid the things that will possibly slip you up, or as I call them, banana skins.

To begin, let’s first establish what body filler is and why it can cause problems if not treated correctly. The main ingredients (but not in all cases) are talc, as in baby powder, fiberglass (polyester) resin, styrene and in the hardener methyl ethyl ketone peroxide (MEKP). This is not good stuff to get in your body either via inhalation of fumes or indeed dust from sanding. A point to note is : Boiling point (decomposes): >80°C / 176°F. Another important point to note: Do not get that stuff anywhere near your eyes. It can cause blindness in seconds, so little chance for an eye wash in time. Another point to note is that body filler, or should I say the talc content is hygroscopic (readily absorbs water) so don’t leave a vehicle in damp conditions with exposed body filler. Moisture could get absorbed and give you big problems later in the repair.

Body filler is exothermic (creates its own heat when curing). You can actually feel the heat coming off it when it’s curing on the panel. It’s therefore important that it’s not applied in low temperature, by that I mean low 60o’s F / 15.5o C or below as there are major downsides. Firstly the chemical reaction slows significantly; I mean getting this fully cured (ready to sand) could now take hours. Secondly, if the ambient temperature is really low, the metal panel is most likely lower still, so the potential of creating condensation under the filler is very real. 

One of the common mistakes made with body filler is incorrect mixing of the hardener. Yes I know there are some good mixing products out there, but many will be just using a pot of body filler and a tube of hardener. The mixing ratios are really quite fine, for example 3 part per 100 or 50 to 1 etc. Judging that is really quite a challenge. There are a few suggestions to keep in your minds eye to make this judgment easier, like squeeze out a line of hardener 2 thirds across a filler pancake or cow pat. Another approximate ratio I was shown was the golf ball and small garden pea guide. Not very scientific, but it worked for me.

Over catalysation is sometimes done on purpose, especially in cold weather or the body man is under pressure to get a job out quick. Unfortunately this can come back and bite you in many ways. There is a list of problems you could experience, incorrect curing, brittle job that can crack, peroxide bleed-through on the finished paint job and increased bubble chances to mention a few.

When I am giving a clinic on infrared curing, one of my suggestions is to use infrared all the way through the process, in fact I go further, use infrared on the panel before you apply the very first product and that’s body filler in most cases.

The reason is it removes any chance of moisture causing an adhesion problem at a later date and the added heat also helps the product work properly.

I am only talking about a 2 minute application of infrared costing less than 1 cent For goodness sake!! This can avoid so many problems and cost, for example the shop does not use infrared on the filler, but does on the primer. All of a sudden, they see something starting to lift or bubble / blister on the primer surface. Yes, moisture, air or gas trapped expands when you heat it and that 2 minute application I suggested starts to make sense. If the filler is going to react i.e. has air trapped in it, at least you see it before getting into the more expensive part of the repair, top coat etc.

When mixing body filler try to spread it out, fold and repeat, rather than just stir in the hardener. To avoid folding in air bubbles, press the spreader to the palate to squeeze air bubbles out as you mix.

Also avoid using bits of cardboard as your mixing palette, although yes, most of us have done this at one time. The reason is that a lot of cardboard is treated to make it a little waterproof. That treatment includes wax, which can be transferred into your filler and onto the paint job. It can also pick up fibers, which again can effect the quality of your paint job. Mixing palettes are not expensive and worth the small expense.

The other scenario if not using infrared is the heated booth shows you the problem when the clear is baked, or it might not even show you the problem there. The job could pass quality control and get handed back to the customer. The new paint job is sitting on the customer’s driveway and Mother Nature (the sun) delivers a large dose of infrared that exposes the underlying problem. This can manifest itself in small micro blisters, pin holing or even cause the filler to bulge. Its certainly going to be a re-do, that comes off the shops bottom line, not to mention the effect on the shops reputation.

Anyway, back to using the infrared on body filler. Body fillers can be treated with varying temperatures dependant on the manufacturer. There are even variations between European and US brands, so here is a really safe starting point. If you have temperature control set it at a max of 120o F / 48.8o C. This may be increased in some cases, but first check the product instructions you get from the manufacturer of the body filler.

You can also control temperature using distance however I can only give you advice on B-TEC units as all infrared units will have distance, power and wave length variations. Our units are normally used at 24” from the panel. If you don’t have our temperature controlled version pull back to 36” and bake on full for around 6 minutes. Allow to cool before sanding. Another option is keeping the 24” distance, but only run on half power for approx 7 minutes.

It’s all about building on a firm foundation. There is no point using great paint systems if the products underneath it fail.

I hope you found this article useful and it helps you avoid some of the common slip-ups found when using body filler. If you have any questions or require advice about infrared, you can contact me at B-TEC Systems.

Written by: Peter L Phillipson, Technical Sales Manager (IR) B-TEC Systems

www.bteccleaners.com