How to Sand Primer on a Front Door [Repaint/Refinish]
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Sanding primer on my front door, followed by cleaning it off with a tack cloth (pictured).
This article covers the basics and finer details on how to sand primer on a front door when refinishing / repainting. Specifically, this documents how we completed this step on our fiberglass front door, but it applies to any wood, fiberglass or any material exterior door (or furniture) where priming is recommended. These tips will make your paint job smoother and the final product will look more professional.
As for the tools and materials involved…I did some comparison shopping. Here are the best prices as of 6/3/2020 just comparing between Amazon and Home Depot (all affiliate links, but hey, this is where I spent my money for this project too!):
Tools and materials to sand primer on a front door.
MATERIALS:
- DAP Dynaflex 230
- Denatured Alcohol –you probably won’t need a gallon even if you are at the stripping paint off the door stage, but if you think you do, check out Home Depot (link to the 1 gallon).
TOOLS:
- 220 Grit Sandpaper
- Shop Vac
- Tack Cloth
- Saw horses or anything nice enough not to scratch the other side will do. We used 5 gallon buckets.
- Shop Cloths / Old T-shirts
- Gloves or Aveeno –most sanding projects dry my hands out–nothing like a day of tile–but even after a day of tile, this Aveeno lotion is magic!
- Your elbow grease
- Patience –This is not the most glamorous step, but it is better than stripping the old paint off!
You’ve got this!
The main tool for sanding primer is 220 grit sandpaper.
We chose to sand the primer with 3M 220 grit sandpaper.
By hand.
There isn’t a lot of paint on the door at this point. A power tool, such as a random orbital sander, can quickly grind down to the original surface (or beyond) and land you back where you started (or worse).
Hand sanding the exterior door is the way to go so you have instant feedback.
Careful cleaning!
There will be some sizable chunks of gunk that you’ll want to shop vac up from time to time during the sanding process. They clog the sandpaper and give you an uneven surface otherwise.
Said gunk coming off the sandpaper. You can see some white spots on the sandpaper too.
When you shop vac the bulk of the dust and debris I recommend putting your fingers in front of the nozzle as a buffer. This way you are less likely to make contact with the door, creating a mark from the plastic nozzle on the fresh primer.
No contact marks here!
Detailed cleaning!
We used tack cloths to get the finer dust and debris off the door.
We used HDX tack cloths. If you haven’t used one before it is a cheesecloth like fabric with linseed oil and other ingredients giving it a waxy, tacky feel, with a light scent.
Tack cloths easily pull the fine dust and debris left behind from the sandpaper.
Work in a controlled-light environment or do a final review at night with a flashlight or shop light.
You have a better chance at spotting imperfections when you can control the light. A sharp angle with a bright light will cast shadows when a small imperfection sticks out or drops below the surface of the surrounding paint.
While we worked in a garage, a shop light at night made spotting last blemishes so much easier.
If you have cracks, for instance, between the face of the door and the side, you can fill it in with a caulk.
The gaps in our door were between the outside framing and the door face–on both sides. The white primer only made the problem more obvious.
NOTE: We also prepped the surface by cleaning it with denatured alcohol before caulking.
Klean Strip Denatured Alcohol
We chose DAP Dynaflex 230 for this gap for a few reasons.
- It is 100% waterproof and this is an exterior door that will experience weather.
- The door and caulk will also experience extreme temperatures in a dry environment so the caulk needs to remain flexible and crack proof, both of which are listed first on the label.
- The DAP Dynaflex 230 is ideal for multiple surfaces including fiberglass.
- The 2-4 hour dry time is nice, but I wasn’t planning on painting until the next day anyway.
DAP Dynaflex 230 is good stuff!
We chose to caulk these gaps in the door after applying both layers of primer and sanding.
We could have done it just after stripping the paint, prior to primer. However, it will bond better to the primer.
Likewise, we could have done this step between primer layers, allowing one layer of primer after the caulk for the paint to attach. We didn’t sand between layers of primer because there just wasn’t enough paint on the door so the risk of taking off too much paint was high. As I mentioned before, sanding allows for a better, grippier surface and that seems ideal for caulk as well. This is a paintable caulk so the Alkyd paint in the next step will go on just fine.
Caulking the unsightly gaps in the door with DAP Dynaflex 230.
Sanding primer is one of those mulligan steps too.
During the priming phase and subsequent drying phase anything could get missed or lodged in the primer:
- paint boogers,
Technically named “paint boogers” from our little booger picking at the paint tray…
- places where paint is obviously thicker along an edge,
The primer built up along the bottom edge of this panel. It was easy to see in the evening with a shop light.
- a bug flew into the attractive shiny wet paint. No picture proof here because we kept the garage door shut during this step and thankfully I didn’t trap any flies inside (unlike when I was painting the first layer of the color coat).
This is your chance to smooth them all out.
Huzzah!
If you don’t, the next layers of paint will only magnify the problem.
It is a good idea to lay the door flat when sanding primer.
If you choose to sand the door while in place, the only good positions are
- all the way open (bad if it is not a temperate day)
- or closed (bad for uniform sanding all the way to the edges).
In addition–speaking for my own abilities here–I know I am better at applying even pressure on a flat surface rather than on a vertical surface.
Please add any other tips you may have on sanding primer on an exterior door in the comments below.
To see these tips for yourself in action:
Related posts:
11 Tips for Priming a Fiberglass Door [No Paint Sprayer]
Stripping Paint Off a Fiberglass Door
10 Unusual Tips on Repainting a Front Door
Why Every Smart Lock Needs a Gasket!!! <– Spoiler alert: because you don’t want it digging into your newly primed (and painted) door!
Related videos:
FAQ to Sand Primer on a Front Door
Can you sand primer on a front door?
Yes!
Sanding paint is most commonly done when painting furniture. Sanding a front door is no different than painted furniture!
Do I really need to sand primer on a front door?
Hey! At least you are past the “do I even need to prime” question! High five!
Just in case you are on the fence whether sanding primer is absolutely necessary here are a couple arguments:
- Sanding primer roughs up the surface of the primer, creating a better bond with the paint layer.
- You can remove any imperfections embedded in the primer.
- It smooths out the paint brush strokes, so they won’t be as obvious and allows the original texture of the door to shine through. This is especially true if you are salvaging an old door. Having stripped off the old paint, you worked hard to expose the old texture. Covering it with brush marks is somewhat of a downer.
The original texture of the fiberglass door is clearly visible after sanding the primer.
What is the best grit sandpaper for sanding primer on a front door?
220 grit sandpaper is a great starting point and you can move to finer grit sandpaper as desired.
Can you use a random orbital sander to sand primer on an exterior door?
Sure, but it is not recommended.
There is very little paint covering the surface of the door if there is only paint. A random orbital sander, while fast, can quickly eat away at the thin layers of primer.
Side note, this is why we only sanded the primer after two layers, not between the first layer and the second.
Hand sanding is best at this point in the project.
