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chipmunk
Junior Member
Joined: 30 Jan 2008
Posts: 4
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 Posted: Wed Jan 30, 2008 9:45 pm Post subject: How do I cure crazy pattern cracking in paint? |
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I have just put a coat of paint on a wall that was previously replastered (some time ago) and have several places where the paint has now cracked in a crazy paving pattern.
Grateful if someone could tell me why this has happened and what I need to do to fix the problem.
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paintycait
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Joined: 21 Nov 2005
Posts: 300
Location: Scotland
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| Posted: Wed Jan 30, 2008 11:06 pm Post subject: |
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I am going to lift a post I put on another board about this problem...so apologoes to those who visit both biards and get a feeling of deja vu
The most common crazing problems with water based paints are caused by differing drying rates and often referred to as "mud crazing", this looks just like it sounds...like dried up cracked mud, is caused by one coat of paint being put over another that isn't fully dry but can also be caused by a sudden drop in temperature straight after applying the paint, too thick a coat in this situation might cause the same thing too. The high humidity just now might man that
Another term - crocodiling happens when a hard drying material goes over a soft drying material or the coat underneath is reactivated and stretches then dries faster than the coat on top...this can happen if the paint you're painting over has had PVA added to it (another reason for me to hate PVA). This looks similar to the mud crazing but producing a pattern resembling the crocodile or alligator hide but the lines are less like cracks more like indentations
Grease or other contaminants could possibly cause interrupted drying rates or adhesion causing cissing or wrinkling or on the surface etc.
The solution depends on the actual situation and without knowing what they've got on the surface there's not much point in saying much more. What was on the plaster before you painted? What type of paint did you use? Just one coat or 2? Is it a kitchen or bathroom? Has anyone been smoking in there? How big are the areas of crazing?...more details required
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chipmunk
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Joined: 30 Jan 2008
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| Posted: Wed Jan 30, 2008 11:26 pm Post subject: |
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The wall was initially just bare plaster ( it was a repair job - fireplace removal - under wall paper that I had removed) and I put an initial thin coat of white B&Q contrators paint on followed (2 days later) by a thicker coat of SuperMatt Magnolia (Dulux - I think). It seemed fine with the white piant but cracked when I put on the Magnolia. I have subsequently put another thin coat of the Magnolia on in the hope that it would cover the cracks but it cracked through again.
The room is a dining room and not sure about the smoking but it was under wall paper previously. The patches of cracking are smallish - around 6 inches long by 2 wide but randomly placed and mainly around the joint area between the "new" repair plaster and the original wall on either side. No other areas of the room have been affected - all of which were previously covered with wallpaper. |
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tim'll fix it
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Joined: 18 Jan 2006
Posts: 2137
Location: Leicestershire
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| Posted: Wed Jan 30, 2008 11:47 pm Post subject: |
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i bet its where the PVA for the bonding is on the face of the plaster
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paintycait
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Joined: 21 Nov 2005
Posts: 300
Location: Scotland
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| Posted: Thu Jan 31, 2008 12:17 am Post subject: |
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Could well be PVA...good possiblity that there might be wallpaper paste left on the surface ...listening to you talking about it being by the joins. Paste will throw the paste off...is there any curling to the edges of the cracked paint?
How thick a coat of paint did you apply after the mist coat? In this humidity if you lathered on too much paint you could have drying issues.
Sounds like you need to get a hand sander and get that stuff off IMHO...too many variables. Then I would maybe line the wall to be safe....sorry, it's not good news is it?
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chipmunk
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Joined: 30 Jan 2008
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| Posted: Thu Jan 31, 2008 12:27 am Post subject: |
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No, no curling - the cracks are more like indends in the paint.
The 2nd coat was pretty thick as I was trying to cover the marks on the wall in one coat  - if this was the the problem though wouldn't I have found this issue in other places in the room?
I think your suggestion to sand down and line the wall is probably the way to go. What would I line the wall with? |
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fordy
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Joined: 21 Jan 2008
Posts: 79
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| Posted: Thu Jan 31, 2008 3:25 pm Post subject: |
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Sounds like youve put the paint on too thick and too quickly after the last coat.
Id personally undercoat, leave to dry and recoat. If that doesnt work then cosider lining. |
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Kernel32
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Joined: 14 Jan 2008
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| Posted: Thu Jan 31, 2008 3:35 pm Post subject: |
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It's paste thats at fault.
Not pva. |
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Wood Magnet
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Joined: 07 Feb 2006
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Location: sunderland
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| Posted: Thu Jan 31, 2008 3:51 pm Post subject: |
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fordy
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Joined: 21 Jan 2008
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| Posted: Thu Jan 31, 2008 4:01 pm Post subject: |
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He hasnt lined the wall though, so why would paste be a problem?
Am i missing something? |
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Telmay
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Joined: 09 Mar 2007
Posts: 2469
Location: Worthing, West Sussex
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| Posted: Thu Jan 31, 2008 4:32 pm Post subject: |
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It's paste thats at fault.
Not pva.
There is no paste, the wall has been re-skimmed and not wallpapered.
Could be too thick a paint with mud effects or plaster is contaminated.
Personally would rub it down and give it a coat of zinsser bullseye or rub it flat and line it. |
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chipmunk
Junior Member
Joined: 30 Jan 2008
Posts: 4
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| Posted: Sun Feb 03, 2008 7:24 pm Post subject: |
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Thanks everyone. I appreciate the help and advice.  |
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bobbie-dazzler
Senior Member
Joined: 26 Oct 2007
Posts: 1533
Location: Greater london
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| Posted: Sun Feb 03, 2008 7:45 pm Post subject: |
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| fordy wrote: |
Sounds like youve put the paint on too thick and too quickly after the last coat.
Id personally undercoat, leave to dry and recoat. If that doesnt work then cosider lining. |
I have done this in the past and it has worked for me, the UC must be oilbased, and thinned with white spirit.
Leave it for a day or so, then emulsion again, but thin down the emulsion slightly.
Try it on the one wall first, the worst one, and if it doesnt work for you, then go down the lining paper route.
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handyman
Senior Member
Joined: 16 Jan 2006
Posts: 2863
Location: Alderley Edge, Cheshire
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| Posted: Sun Feb 03, 2008 7:48 pm Post subject: |
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| chipmunk wrote: |
| The wall was initially just bare plaster ( it was a repair job - fireplace removal - under wall paper that I had removed) . |
So, there could be hard paste thats got wet around the patch plaster.......hence the different reaction when painted later?
or, it could be pva when the plastering was done.
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