How to paint over Spakfilla Rapid Gap Filler?

Question

I was filling some drill holes on my walls using this product

https://www.bunnings.com.au/selleys-180g-spakfilla-rapid-gap-filler-180g_p1231864

it's very easy to work but it never sets completely. Even if you leave it for months you mix some water and then it becomes soft again

by the same token I fill a shallow hole and sand it down perfectly.

as soon as I paint over it the water in the paint dissolves the filler and it is no longer the surface that I had prepared

how are you supposed to deal with this?

MitchellMc · Answer

Thanks for the additional information, @bara3.

The product is water-soluble, but there's a significant difference between adding water directly to reconstitute it and painting over it. Even with a water-based paint, you're not applying pure water to the filler. You're applying a formulated coating containing binders, pigments and other components, and only a relatively thin film is applied. Your brush or roller is also only in contact with the surface momentarily, so I wouldn't expect it to reconstitute properly dried filler in the same way as directly adding water.

Given you've experienced this issue more than once, I'd recommend switching to a different filler.

Mitchell

bara3 · Answer

my product is a few years old. And I literally picked it yesterday it was more or less all dry I added some water and then within an hour it was soft as new

I like this product because it seems easy to use, whereas with other fillers when I use a straight edge to spread it sticks to the edge and comes off the wall.

in the past I've also used it to try and smooth out a curved plaster wall which had imperfections, and the thickness of this material must have been less than 1mm max. after sending and everything was completely perfectly smooth to the touch, I left it for more than a week before painting and then after the paint dried there were channels like before I did any work on it. I've even used a hair dryer to make sure

to me it appears this is water soluble even when completely dried?

MitchellMc · Answer

Hi @bara3 ,

I use this product quite often and can't say I've experienced it dissolving when painted over. It will typically set hard after a few hours in warm, dry conditions, although it can take longer during periods of high humidity.

If the filler is distorting when you paint over it, the most likely explanation is that it hasn't fully dried. Sometimes the surface can appear dry while the filler underneath is still soft, and the moisture from the paint can then disturb it.

I'd allow it more time to dry completely before sanding and painting. Alternatively, if you're not happy with the product, you could return it and try a different filler such as

https://www.bunnings.com.au/uni-pro-500g-multi-purpose-interior-filler-500g_p1210281

.

Here's a helpful guide: How to fix a hole in a wall.

Please let me know how you go and if you have any questions.

Mitchell