Fragile plaster


I trying to fix some wood to a wall, but the plaster is old and friable so when I start to insert a screw into the "cheville" or dowel it just doesn't hold as the plaster crumbles.

OK I can cut out a large area, re-plaster with something more durable but that is just a load of work.

Does anyone have any idea of an alternative?


Peter S

That's how the old skirtings were fitted in my place, Peter, with bits of wood buried in the plaster (b). Couldn't be bothered doing it that way meself, so replastered the height straight and used those cheville-tap screws :)

Hi Ian

Thanks and no as I have never come across them but interesting idea and much easier though I do not think they will work with my problem.

Two ideas that I have recalled since going out.

a) Not sure the name,, but they are long screws with a "cheville" already fitted. Drill thru the wood into the surface and then hammer in the screw with aforesaid cheville. Works fine on a floor but not with this wall.

b) Best thought so far. Cut out a space and deep enough to find a stone. Fit a piece of wood of sufficient size to provide stability and depth, Re plaster and then fit the skirting to the wood. Doable, just boring waste of time.

This trivial job, which was to finish off the top floor of the house with new oak floor boards, all the bedrooms being done, has turned into a bit of a marathon but then I am retired. And people still ask what to you do with your time???

Peter S

Have you thought of these "clips de fixation", Peter?

Hi Suze

As I posted, I am putting in skirting boards, so there is no downward pressure, only lateral pressure as the wall is not flat or straight.

As you say, this approach would not work if I was trying to fit heavy duty shelving for example when I constructed the bookcases and cupboards for the library/TV room. when I used a different technique.

Peter S

You seem to have a solution already

but if you put up anything heavy with this system you will find the ... ( you still havn't told us )

on the floor with a large gob of cement on the end of a raw plug !

Hi Suze

Well you are of course right. It is an interior wall that has been entirely covered by plaster, so not pierre apparent, but the plaster, which I assume but do not know is lime plaster, crumbles very easily.

I am replacing old pine "cheap as chips" skirting with oak skirting to match the floor I have just laid. The old wall needless to say makes the proverbial "hind leg of a donkey" seem quite straight, which of course places tension on the wall when fixing.

I have not encountered this problem with any other walls in the house with the same procedure, the same quality plaster and the same degree of "hind leg".

One trick I came across some years ago, when filling an irregular space, was to use a mix of cement powder and plaster of Paris. This provides a combination of strength and speed of drying (about 15 minutes). It is very useful when fitting new power sockets into an existing wall. So you can place the "box" and fill in around it, hold it by hand for a few minutes when the compound will have become hard enough to leave though not hard enough to work. Or if you are trying to drill at a very precise spot, for example putting up a display of say 8 pictures on a wall, and you hit a stone and the drill goes off centre. Make the hole bigger, fill with the compound and you can then drill a very process (millimetre accurate) hole.

When I solve the problem, then I will let you know if anyone is still interested.

Peter S

Bit confused as you talk of pierre apparentes and lime plaster and plaster hardeners !

If you have pierre apparente with a lime and sand MORTAR, no amount of plaster hardener will help...

But you can drill into the stone with no problem ( not percussion)

You still havn't mentioned what you're hanging :)

"removing a largish area of plaster, back to the stone work," ??? pierre apparentes are not covered !

Hi all

Very useful input and thank you.

James, the position of the wood is set by what I am trying to do as the whole wall suffers from the same problem, so moving it is not an option, though I have dome that elsewhere.

I seem to recall using something like Chemfix some years ago but that seems best for an irregular hole caused by "poor" drilling. I ma not sure this will work, though I will try with holes that are now up to 2 inches across and 1 inch deep. Pits, rather then holes, might be a better solution.

Some form of plaster hardening solution might work but I doubt it will soak in far enough, though again I will try.

I have considered constructing a small wooden frame, fixing it to the floor and using that for support but that creates a fairly ugly result.

So far, I think I am stuck with removing a largish area of plaster, back to the stone work, refilling with "colle-ciment" and going from there.

I was hoping there was an alternative but well absence of your ideas working then that is the last resort.

Well the really last resort is to sell the house.

Peter S

The reason for suggesting a chemfix compound is the screw is secured into the chemfix WITHOUT causing expansion in the mortar (hence cracking it out) and a decent lump of chemfix won't be inclined to fall out. Sleeves are also used to increase the surface area of the holding chemfix. If it does fall out then your wall is very poor a re doing the mortar is your next job but fixing up whatever elsewhere is probably a good idea.

There a fair bit on luck involved as you could quite easily miss a stone and just be into the mortar in any case no matter how deep you go. Best bet is to put it up somewhere else!


Thanks it is old, very old "pierre apparent" with ancient, I guess lime plaster covering up the large gaps.

What I am drilling into is anyone's guess, but maybe if I drill deep enough I will find stone and with the right depth of plug that might work. But if the plaster is over 1 inch in depth and that is what is crumbling then I am not sure the plug will hold as it will be too flexible where it is exposed. Still I suppose get the plug fixed in stone and then re-cement around it.

Drill deeper (100mm), and hammer the plug in to the depth of the hole using a punch or the longer screw you will then use to reach it, assuming it's a stone wall?

You could use some chemfix or the french equivalent Cartouche resinee or cartouche scellement ciment or epxoy.

Baring in mind we can't see what your trying to hold onto plaster