Please help me! I recently had some skimming done by an amateur diy
bloke, and as the skim has dried it is cracking. These cracks start off
as being like light pencil lines on the wall, but over a few weeks they
grow in length and width. Any ideas about why this has happened?
My house is over a hundred years old, but base plaster is no more than
10 years old i'd say and looked reasonably ok (to me - a complete
know-nothing of diy!!) when the wallpaper came off.
My amateur re-did one area believing he may have forgotten to bond it!
But as other larger areas have begun to crack too, and his re-done bit
has gone again too, he is less inclined to get involved! I guess you
really do get what you pay for!!!
But if anyone could tell me possible reasons for these cracks i would
be very very grateful!
Many thanks, Lisa x
As the house is over a hundred years old, it will have been built
with lime mortar and lime plaster originally. Lime doesn't set hard
like cement mortars and gypsom plasters used today. This means that
lime houses routinely move around, and the lime is tollerant of this.
However, modern gypsom plaster is hard and will not flex as the
house moves, so you will get hairline cracks. Usually this is not
enough to matter and the cracks are small enough to vanish when
painted. The correct way to do this would have been to use lime
plaster, but that's rarely done nowadays unless required for a
listed building, and it takes weeks to set.
If the cracks are of any significant width, you may have some other
Thanks very much for your reply Andrew, sounds like you really know
The plaster that i found under the wallpaper, before the skim, didn't
look as old as the house and i think it was probably done by the people
who owned the house before me, within ten years. Judging by some of
their other DIY i wouldn't think they had taken the trouble of using
lime as the base plaster but it seems to be just the skim that is
cracking. As the cracks are developing they look too deep to cover
with paint alone. Any ideas how i can get the smooth walls i'm after
Andrew? Thanks again, Lisa x
It all depends on what the backround was. I have skimmed over old limewash
paint with great success, you just have to prepare it properly 1st.
Normally, cracking like you describe is because the backround has'nt been
prepared right. It sounds like you had a high suction surface and the way
to do this is to apply a good coat of pva to the area, let it dry and then
apply another coat and whilst it is still wet, apply the new plaster. But
how to get over your problem now. You either scrape it off and start again
or hang lining paper, filling the cracks 1st.
They start off looking like pencil lines, but it was done about 2
months ago now and some cracks are as wide as if a pencil was dragged
through the plaster (best way i can think of describing it) and this is
still growing. So paint would go over but you would still see the
crack underneath it, and i don't know when it wll stop cracking.
Thanks again, Lisa x
Andrew - my pencil example may not be very good! I don't mean the
entire thickness of the whole pencil, but a couple of mm into the
sharpened end - so maybe 2 or 3mm wide. I'm not very good at this
measurement thing - well i am blonde as we've already established :o)
If it was a bonding issue as others have suggested, plaster must
be loose to have moved that much, so much so it would be falling
off which you have not said is the case. If it was some other fault
with the plaster mix or application, cracks would have formed within
a couple of hours as the plaster set, not months afterwards.
So I'm left thinking it's either excessive movement in your walls,
or the scratch (base) coat has lost key and come away from the
wall, so it can move by itself. Does the plaster sound hollow if
you tap it? Does it noticably move if you push on the plaster?
Sounds like it wasn't bonded. Generaly to do this kind of job the
plasterer generously paints the area to be plasterd with PVA glue
slightly diluted with water then he plasters that wall while its still
wet and sticky.
The bit he re-did, he scrapped off the old skimming right? Which means
you wont have too hard a job rip away all of his poor work. If he just
plastered over the bit that he said he *may* have forgoton to bond
then where is the sence in that?
Hi Marble, i think it points to the bonding too. But when he re-did
the bit he "may" have forgotten to bond, he did bond the second time
(after scraping the 1st skim from that section) and cracks are still
appearing there 2nd time around. I'm wondering if he "may" have
forgotten to bond the rest too, where cracks are at their worst. But
he must also have done something wrong on the re-done bit? I am
wondering if, as Kev said, he didn't follow the right process for
bonding being a novice. Perhaps the dried coat of pva first would've
made the difference - or perhaps he didn't use enough pva? or too
much? Really appreciate your help! Lisa x
It should be very difficult/ impossible to scrape off a properly
bonded re-skim ,and as you've said there are no cracks in the old base
plaster, I think that settles what the problem is. The only thing you
can do is scrape it off and get a better plasterer in. Either he could
try the 2 coat PVA method Kev mentioned or consider using the more
expensive bonding agents like Bond-It from British Gypsum or the Knauf
equivelent from Wicks.
What was the colour of the area that was platered over? if was pink I
would say it was recent( within 10 years plaster). If it wa white-ish
and had a thick grey powdery backing then I would say it was original
Lath and plaster.
What was the reason for plastering over? Was the background loose or
Basically I would start from what the condtion of background surface
was/is and move through to materials used and method of application.
I have walls that have been rendered and platered 4 months ago and are
showing new cracks evey day ( haven't been painted yet). I put this
down to shrinkage nd the fact that there is no heating in the house and
its often left open to drafts and cold weather. Thats my particular
circumstance so you see every situation is different.
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