This guide outlines in brief how to prepare MDF trim for paint to achieve top quality finishes fast with emphasis on nail holes.
Chipping factory primer, puckered holes and glue strands caused by nail gun installation on MDF trim can cost painters thousands of dollars in short time and without them even knowing it. Here are a few tips to prevent wasting labor regardless where the MDF was manufactured or who or how it was installed.
Step 1 – Identify Scope of Work
Are any or all of the following visible?
- chipped primer surrounding nail holes
- puckered nail holes
- glue strands
If any of the above are visible then proceed with Step 2 If not, I typically do not recommend pre-sanding MDF unless unusual circumstances
Step 2 – Pre-Sanding MDF Trim
In order to make certain labor is not wasted painting MDF a few steps should be followed before re-priming, painting, filling or caulking MDF trim. Factory primed MDF is not the ideal surface to produce top quality fine finishes.
- sand puckered areas around holes
- ensure any necessary exposing of bare MDF is revealed before applying primer
- re-priming may be necessary if sanding puckered areas after primer or paint exposes bare MDF
- remove any glue strands by sanding
- glue strands can accumulate in nail putty or patch fillers if not removed creating difficulties producing flush patching by putty knife or by finger using nail putty
- remove chips of primer by sanding
- sanding ensures primer chips break-off entirely prior to filling with nail putty or patch compounds
- if avoided, sanding after re-priming or the 1st coat of paint may expose bare MDF requiring additional re-priming or breaking-free more chips of primer not necessarily visible to the eye
Step 3 – Shop-vac All MDF
Shop-vac all trim to ensure powdery sanding dust residue is removed. Removing any dust film will assist with filling nail holes and caulking efficiently
- use a short bristle round brush attachment
- sanding dust accumulates in the nail holes, it is important to remove the dust to ensure efficient patching or filling holes
Observations working with MDF
There are many variables associated with producing nice results on MDF, many of which can consume labor filling nail holes on MDF. Avoid the common scenario below
- re-priming or painting over chipped primer, glue strands or puckered areas will require unnecessary sanding and/or re-priming
Various ways to complete the above tasks to maximize efficiency include:
- type of sandpaper and abrasiveness to cut through dense MDF puckered areas fast while not scratching factory primed surfaces
- type of sandpaper used to quickly remove glue strands effectively with little effort
Not following the above steps can lead to unwanted surprises after the first coat of finish paint is applied. Sanding the puckered area around the nail hole seen below will expose bare MDF and the 2nd coat of paint will not likely fully cover the exposed bare MDF.