Filling phone extension back box hole

A dry sand and cement mix should be fine, but bulking it up with pieces of broken brick would be even better at avoiding shrinkage. John

Irrespective of what you use its not going to be a one off application.

To avoid the possibility of cracking, especially around the perimeter of the hole, seal it with a 50:50 PVA:water mix and allow to dry. Unsealed Old brick or plaster surrounding the infill will suck the water/moisture out of whatever you use and its liable to crack at that point during the drying process.

A thin layer over a reversed back-box in unlikely to be satisfactory.

As suggested in another answer a bit of brick or stones or similar to bulk out the infill means that you can use much less filler.

You could use mortar or your polyfiller to secure your infill - whichever is more convenient, handy, cheaper. Make sure that the infill is a few mm below the finished surface. Let it dry.

Even when you fill flush the filler may shrink back slightly when it dries requiring another light skim over the top. It helps if your trowel you are using for the final layers is wider than the hole you are filling.

- Paint inside of hole with dilute PVA.

- When PVA is dry (about an hour) fill hole with bonding plaster (may be called undercoat plaster in the sheds), leave surface slightly (about a mm) below wall surface.

- Next day (or later) use your polyfilla to fill the remaining shallow depression, get it as flat as you can.

- When polyfilla is dry (next day?) sand it flat by wrapping 120g sandpaper around a piece of wood that's long enough to bridge across the hole.

- Repeat the last 2 stages if the result isn't as good as you want.

- paint with diluted finish paint, then a couple of undiluted coats.

I have many methods E.g. (if you have some handy) use a piece of plasterboard wedged in the hole below the surface of the finished wall and skim. There are many other ways to do the wedging. Simply get ANYTHING that will support the first bodge coat of plaster - scrunched newspaper newspaper, a blown up balloon, used condoms, expanding foam, and old bit of expanded foam packaging, or PU insulating foam.

All it has to do is support the plaster till it sets. And don't use polyfilla - its way quicker to use several coats of fast setting plaster.

But often the best material for speed of setting (curing or air drying) doesn't come in small packs at a reasonable price, especially if being used for a one off small job.

I agree that polyfilla is not the best but the chap said he had some, and it will do the job. What won't work well is to fill the whole hole with the stuff.

But I keep an out-of-date bag of Wickes multi surface filler for small, quick jobs like this.

PS, why bother to remove the back box ?.

As long as it is not sticking out above the surface, just fill it with whatever old filler is to hand or mix some old filler with sand/cement for first fill.

It comes in small enough packs.

And is cheaper than polyfilla.

Thats why people dont skim walls with polyfilla

Just what I used last week for a much bigger repair but now I have probably 20kg left that will go off before I need it again.

What I've always found in the sheds that the outside of the bags are always covered in plaster dust which will get on you clothes :)

The excess will now be sprinkled on the lawn :)

Previously I did manage to keep some, and usable, for nearly two years packed very tightly to the top of an airtight container. After partially filling the container was vibrated to remove air pockets and to pack down the plaster powder. This was repeated until I couldn't get any more in.

I've also kept old plaster for fixing in back boxes but I've had to work fast as it will go off within 5 minutes.

What do you do with the remaining 24.9 Kg?

I find it lasts years if wrapped - but it goes off quickly and is only useful for basic filling.

I dug a bag of O-O-D bonding coat into my back garden to improve the clay and the drainage. Gypsum seems to be useful for this problem and unlike Lime is doesn't alter the Ph (AFAIK).

Bonding also contains some sort of granular material which is also useful for heavy clay soil.

The 10Kg and 5Kg bags of Wickes fine surface filler were more useful to keep. Unlike gypsum plaster it can be scraped smooth if it goes off too fast with a stiff steel ruler and then sanded flat.

This product might be better to keep dry for those small jobs long after it has expired

What he said. I've generally tossed it in the bin as well. Probably a good thing to add to landfill

Andrew snipped-for-privacy@btinternet.com wrote in news:vqc4ri$2us3r$ snipped-for-privacy@dont-email.me:

New to me so thank you.

Wickes do a smaller pack too (5) but disproportionately more expensive at £15.50:

Going rate appears to be around 2quid a sachet.