Be careful, some common fillers will fail! So what is the difference?
Here are some of my favorite fillers, an one to watch out for…it will fail if used outside.
MH or Synko Spackle: this is a very easy to use exterior spackle…it is a bit hard to sand but it really adheres and fills all those uneven surfaces on fascias, siding and exterior trim with ease. It holds up well for years. Be sure to prime raw wood before applying spackle and then prime the spackle when dry for the most durable patches.
Bondo is a catalyzed polyester filler (costs about $40/gallon) that can be mixed to dry in minutes to really move a job along. This filler is often mistakenly used on exterior wood….a big mistake as Bondo in hydrophilic…it will absorb water and expand causing the patch to delaminate and pop off your paint. It can be used on interior wood repairs but never outside.
3M Marine filler is also a catalyzed filler (costs about $190/gallon) that can also be mixed to dry quickly. This product is formulated for marine environments and so is unaffected by water. I have patches that last for years with this product….every wonder why one painter bids more to do a project….this is one reason to hire the more expensive guy as he is using materials almost 5 times more expensive and understands why it is worth it.
Most painters buy whatever is available at the paint store; a craftsman can go cross discipline and find products that will give a better more durable result (like sourcing patch materials at a marine store!)