How to sand weatherboards for re-painting?

kez6

I'm starting to sand back the existing paint from a weatherboard house in preparation for painting.

What size grit should I be using - particularly on areas where the existing paint is in good condition (no flaking).

(I should also say, painted previously within the last 20 or so years, so we think we're safe from lead!)

Thanks

MitchellMc

Hi @kez6,

The grit you use really depends on how much material you need to remove and how quickly you want to get through it. For example, if you have several layers of old, flaking, cracking, or bubbling paint, you might start with a coarse grit, like 60 grit, on an electric sander to quickly remove the bulk of it. The downside of such a coarse grit is that it can leave deep scratch marks, so once you’ve removed the majority of the old paint, you’d want to progressively move up to 120 and then 180 grit to smooth the surface. At 180 grit, the scratch marks are small enough that two coats of paint will cover them without issue.

If you only need to remove a single layer of paint or just want to slightly scuff the surface, 120–180 grit is usually sufficient. Finer grits take longer to sand through thick layers but need less finishing work afterwards. However, they can clog quickly if there are multiple layers of paint to remove.

For areas where the paint is in good condition, sanding is often unnecessary unless you’re dealing with a gloss finish. Gloss coats should be lightly sanded with 180–240 grit to “knock back” the shine so the new paint can adhere properly. Otherwise, for most exterior paints (like Dulux Weathershield), as long as the paint is sound and clean, you can simply wash it down with sugar soap and paint straight over it. Sanding is mainly required if you’re removing damaged paint or preparing a glossy surface for repainting. 

Here's a helpful guide: How to choose the right sandpaper for the job.

Please let me know if you have any questions.

Mitchell