All you need is PVA glue and fine sawdust.
I use a small yogurt tub to mix it in, and a plastic gift-card cut into a thin strip to spread the filler. This reduces the tidy-up time. (We were doing number-words today and I had a limited amount of time in which to work... Home-Education + DIY = Never enough time)
The PVA can be the kids craft stuff and the sawdust is best if it is from the wee bag of a sander - it is really fine and there will be no other debris in it.
A little goes a long way, and it does start drying within about 30mins. So start small, pop about a tbsp of glue into the tub and add a little sawdust on top.
Mix it well, it should be about the consistency of peanut butter.
Once you get the filler into the gaps make sure you give the surface a good scrape to get off any excess as it dries really hard and it is a bitch to sand down.
Anywhoos, we have nearly finished sanding the stairs (I've been saying that for weeks haven't I?) and I WILL get painting sometime soon. So we just had a few more holes to fill and then.... you guessed it... more sanding *head/desk
|The filler you can see here was made using much larger sawdust,|
it was hard to put on and really difficult to sand back (this bit hasn't been sanded yet)
So use fine sawdust instead.
Small was in charge of the photography today, so excuse the photos.
So yes I am still working on the staircase, and progressing just a teeny bit at a time.
I've not had anytime this week to check out the other girls progress on the Staircase Challenge, so I'm off for a blog wander.