DIY Doctor

Plaster problem

Postby America119 » Wed May 11, 2011 12:59 pm

I had a new front extension and back extension last year. The new rooms as well as the old walls of the house were plastered/replastered. They were not all plastered at the same time and the plaster was bought at different times from different suppliers. I waited a couple of months until the plaster was dry and then bought Wickes matt emulson and watered it down 4 parts paint to one part water and emulsioned all the walls and ceilings. When I painted a top coat the paint left rough marks all over the ceilings and walls. I contacted Wickes paint maker in Germany who tested the paint and there is nothing wrong with it. The paint manufacture told me that Wickes paint is not suiltable to water down and I had taken all the bonding out of the paint and basically there was nothing but white powder on the walls. I sanded a room down with an electric sander and applied two coats of Zinser paint followed by two coats of Dulux matt paint. The same problem appeared again. I tried to rub down the rough patches and painted the wall again. I also tried Polyfilling the rough patches/rubbing them down and then painting the wall. None of these things worked. I sanded another room down, applied one coat of Dulux plaster sealer for dry plaster/powdery surfaces and applied three coats of Dulux matt paint. The problem is still there. Can anyone please suggest what to do? Does anyone know of a plaster consultant who might know why the patches are appearing? I have also tried a short haired roller and a matt paint from a paint shop, which apparently the professionals used. I followed their instruction, but that didn't work either. Before trying the Zinsser and Dulux plaster sealer I painted a small patch on a wall to see how quickly it absorbed it. It absorbed very quickl. I tried it today on the wall with Dulux sealer and it didn't absorb it very quickly at all so probably the wall is sealed.
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Gorilla Glue heavy duty grab adhesive

Postby JRS » Thu May 12, 2011 8:20 pm

Any pics? New plaster should absorb the thinned paint very very quickly, Hens why its thinned and a full coat wouls just lye on the surface. It will also look very patchy but its normal. 2 coats should clear that up no problem. Other than that i really cant understand what else could have gone wrong. Also i wouldnt use an oil bases paint as primer,
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Postby toplondonchef » Thu May 19, 2011 9:43 pm

Hi America 119

I recently had a nightmare painting new plaster as well which may be similiar to your problem, or at least may help

Had a large ammount of building work done at home over a couple of years and decided to decorate all rooms once the building works had been completed
Used three different plasterers (due to problems with initial builder) and some walls were skimmed, some boarded over and some stud walls created

I too used Wickes trade emulsion and watered down approx 25% to use as a mist coat. Several walls formed strange patches where the paint wouldn't stick or soak into the raw plaster and the more coats applied just made the patches worse. They ended up forming a crater with the edges getting more raised and still no paint sticking onto the wall

Posted the problem on this site and spoke to several decorators and paint shops but got various advice and ended up spending more and more money on different solutions. Tried the Zinnster which didn't work so sanded down back to plaster areas I had mist coated

A guy in the Dulux Trade Centre reckoned problem was down to the plasters spalshing around PVA solution after walls were plastered and also over polishing of the plaster can leave the walls lovely and smooth but can be a problem to paint. He recommended Dulux Trade White Undercoat, which is an oil based paint. Obviously more expensive than Wickes emulsion and seems a bit over the top to seal plastered walls but it did the job brilliantly and stopped me stressing out

Just a light sand of the walls and a wipe down and applied the undercoat, without thinning down, with a short pile roller. Allow plenty of ventilation as oil based is a bit smelly, especially when used on large areas, ie. walls
This covered all the walls with a solid white base coat which then took the emulsion top coats really well giving a great finish

Can't gautentee that this will sort out your problems but if your as stressed as I was then it's worth a go and good luck

PS. Have used Wickes Trade Emulsion White on ceilings probably 6 or so times before and had no problems with it, also watering down first to use as a mist coat but on the walls always use Dulux

Let us know how you get on !
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Postby America119 » Sun Jul 03, 2011 5:53 pm

Just picked up your lengthy and detailed response, which described perfecrtly my experiences. Still do not have one room finished yet, but will try out your suggestion. Many thanks.
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