My worry is Rapid Spakfilla will dry up once I open the tub, over a night or so?

I use Selleys Permafilla. Stays useable for ages if you replace the paper cover in the tub.

Selleys Ready Mixed Filler - Fillers | Mitre 10™

larknz: As long as you put the lad back on properly it will stay usable for weeks

timmmay: The soft filler sometimes goes moldy after a while, but it takes months or years.

Do you mean in the container or on the material to which it is applied?

I’ve tried lots of different brands over the years and this is the single-pot one I have come to like best. Soft and creamy to apply and sands really well.

https://www.mitre10.co.nz/shop/pal-patchfilla-500ml/p/370628

M10 sell it, Bunnings don’t - not sure about elsewhere. I usually shop at Bunnings but go to M10 to get this.

Sold in many different pack sizes. It does dry out in the container if the lid is not properly on. I try to buy a size that suits what I’m doing now or soon, so there’s not a lot left that can dry out.

timmmay: I tend to use a two-part builders fill, it dries incredibly hard and is not at all flexible. It is not good for joints it is better for flat areas. One advantage is it dries incredibly quickly and can be sanded about 20 minutes later.

The two part stuff can shrink when it dries tho, so it can take another touch up after the first lot.

I've never used it on GIB though.  I find if all the materials in use on the surfaces are the same type then you can sand them more consistently. 

eracode:

 

timmmay: The soft filler sometimes goes moldy after a while, but it takes months or years.

 

Do you mean in the container or on the material to which it is applied?

 

In the pot.

If the stuff does go black or icky, just scrape off the top layer and bin it. Worse it if it has started to dry out - then you'll get lumps in your work and it's very hard to get a good finish.

If its started to dry out in the pot, also scrape and bin.

mdf:

larknz: As long as you put the lad back on properly it will stay usable for weeks

I've got a tub in the garage that is a couple of years old and its fine. Put the plastic sheet on and the lid and keep it out of the sun and it will last ages.

Selley's spakfilla is the stuff to use alright.

Bought some last year just before the lockdown and worked my way around the top floor and half the bottom floor of our house - fixing up bumps and knicks and then painting.

Got to the point of re-doing the kitchen in the last month and I fished out my container of spakfilla and its still fine to use.

Just keep those plastic sheets that are under the lid. If you keep these on top of the filler and keep the lid on when not using, it should last for a long time.

Dries quickly and sands easily too.

elpenguino:

The two part stuff can shrink when it dries tho, so it can take another touch up after the first lot.

mdf:

larknz: As long as you put the lad back on properly it will stay usable for weeks

I've got a tub in the garage that is a couple of years old and its fine. Put the plastic sheet on and the lid and keep it out of the sun and it will last ages.