How to use Bondo
Bondo and other polymer based body fillers are used widely by auto body shop professionals and amateurs alike. These products have been around for years and are continually improved for ease of use, durability, porosity, and environmental acceptability. Many years ago dents and automotive body imperfections were filled with Lead an extremely heavy filler which had a pension of separating when the cars went bouncing along.
As with any products of this toxic nature care must be taken to assure application in a well ventilated area. An exhaust fan or booth is recommended with sources of outside fresh air through open doors or windows. Also recommended the use of an OSHA approved mask for long term usage of compounds with concentrations of Toluene, Benzene or other toxic aromatics.To be certain consult the packaging and/or OSHA hazrdous material data sheets (MSDS), for safe handling, use and disposal. Always follow manufactures instructions for individual safety, fire prevention and environmental concerns. Not only for the product itself but for chemicals used in clean-up and surface preparation such as Acetone or Prep-Solv again highly toxic and flammable.
The first step in any repair of this nature is surface preparation. Damage repair is typically on an older vehicle involved in an accident resulting in rough or jagged surface metal, peeled paint, rust and residue of cleaners and waxes. These must always be cleaned and prepared in order for any Bondo compound to adhere forming a tight bond. Dent pullers or hammers are used to straighten and reshape the metal close to original body line for larger wounds.
Once rough shaping is done the surface can be coarse sanded using grits from 36 to 120 to remove paint, rust, waxes and primers. Surface preparation needs to extend at least one to two inches past the existing damage area. One other method to prep the surface is media blasting: using, sand, glass bead, soda or water jet. After prepping the surface remove any extraneous debris with a solvent to assure a clean dry surface.
If this is a first experience with a product of this nature the user should experiment and practice on a scrap piece of metal to see how the process goes. Duplicate the preparation on the scrap piece and proceed with mixing a small batch of the Bondo material and the "Activator". Most polymer compounds of this nature are a mixture of two parts that when joined create a chemical reaction stimulated by the activator/hardener. Usually the activator is a distinctly different color from the parent material; so the user can easily be assured by a uniform color when completed. Activators are commonly red or blue mixed with white or grey parent material resulting in a reddish/pink or blue/grey fully mixed color. Mixing is normally suggested thirty seconds to one minute time. Depending upon the amount of activator and room temperature the catalyzing chemical reaction is fast or slow. Higher temperatures and more activator speed up the hardening time. Usually recommended work temperature is seventy degrees, resulting in a working time of five to ten minutes.
The mixture is applied using various size spreaders, typically one to three inch wide plastic paddles, which can be used to apply and mix the material on a plastic flat board/palette. Mix only enough product which can be applied in the few minutes of set-up time, as once the material starts to set it can no longer be used. Start with a golf ball size or smaller amount, larger when your technique improves. This product sets up very quickly and can be sanded or re-coated in ten to twenty minutes. Thin layers of 1/8" to 3/8" thick; as specified per product work sheet, rough sand and re-coat deeper holes. Spread well beyond the the damage area with a firm wiping action, feathering, on to good metal or fiberglass body segment.
When set the hardened material can be sanded to a smooth finish from 120 to 400 grit sanding media. Imperfections can be re-filled or spot glazed prior to primer and paint finish coats. Sanding by hand or machine will create harmful dust so operators should wear applicable dust masks or hoods using dust collectors to vacuum up the potential cloud of dust.
Clean up, at once; all mixing sheets, spreaders and stirring sticks, all tools used. Again toxic chemicals are typically used; so plenty of ventilation is needed, masks and gloves recommended. Any excess material un-used and clean-up products need to be disposed of properly in approved containers. Safe storage of left over product in approved storage for flammable materials, and definitely do not mix any activator in un-used material.
