sealing painted walls
- Thread starter norwich9
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'Sealing' it wont make any difference the patchyness is more then likely down to either the way you put it on or the plaster absorbing it in some places more than others.
Just give it a light rub down and re coat..
Theres no benefit mixing PVA with matt
Just give it a light rub down and re coat..
Theres no benefit mixing PVA with matt
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Paint absorbation is a good thing.
It means your Vinyl Matt sinks/adheres well to a new/bare surface.
Worst thing to do is is use PVA as an sealer/primer on new/bare plaster to "help" kill paint absorbation. This practice can lead to blistering of emulsions etc..It looks great at first but lonterm it can cause problems.
Also, by mixing PVA to Vinyl Matt can make the Vinyl Matt dry flexible which can probs aswell, when used over bare/new plaster.
What type of material are you applying the Vinyl Matt on ?
What is the instructions on the Vinyl Matt tub, in terms of thinning ?
It means your Vinyl Matt sinks/adheres well to a new/bare surface.
Worst thing to do is is use PVA as an sealer/primer on new/bare plaster to "help" kill paint absorbation. This practice can lead to blistering of emulsions etc..It looks great at first but lonterm it can cause problems.
Also, by mixing PVA to Vinyl Matt can make the Vinyl Matt dry flexible which can probs aswell, when used over bare/new plaster.
What type of material are you applying the Vinyl Matt on ?
What is the instructions on the Vinyl Matt tub, in terms of thinning ?
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How do you mean 'patchy'?..
Patchy as in differnt sheen levels, lighter and darker areas that are noticable especially when you look down the wall?
Or patchy as in it hasnt covered?
If you have overlaps in the paint on the first coat it will appear patchy because they will have slightly more paint on them and be slightly smoother..the light bounces off smoother surfaces differently to rougher ones..that gives the appearance of a 'patch'
It can also happen when you paint up to a dry edge with a fresh coat..thats called flashing and also looks patchy.
What are you using to apply the paint with?..and what technique are you using?
What 'Macphersons' is it?..vinyl matt?, contract matt? (eclipse) vinyl silk?
And how long are you leaving it before you decide its patchy?..paint takes a lot longer to dry properly..and will appear patchy when its drying..especially in the later stages..ie after about half an hour.
Forget about PVA its an old wifes/builders/amateurs tale...you wont find it mentioned on any of the paint companies sites..
And the reason they make primer sealer..
There are many different surfaces out there, primer sealer is meant for those..read the back of the can.
The standard trade practice for applying emulsion to basre walls is..
One mist coat...which is normally a thinned coat of either vinyl or non vinyl matt depending on the thickness of the plaster followed by two coats, which can also be thinned slightly of the same.
A 'mist' coat in any shape or form be it on bare plaster walls with emulsion or exterior rendering is NOT a 'sealer'..it primes the surface making them ready for subsequent coats
Patchy as in differnt sheen levels, lighter and darker areas that are noticable especially when you look down the wall?
Or patchy as in it hasnt covered?
If you have overlaps in the paint on the first coat it will appear patchy because they will have slightly more paint on them and be slightly smoother..the light bounces off smoother surfaces differently to rougher ones..that gives the appearance of a 'patch'
It can also happen when you paint up to a dry edge with a fresh coat..thats called flashing and also looks patchy.
What are you using to apply the paint with?..and what technique are you using?
What 'Macphersons' is it?..vinyl matt?, contract matt? (eclipse) vinyl silk?
And how long are you leaving it before you decide its patchy?..paint takes a lot longer to dry properly..and will appear patchy when its drying..especially in the later stages..ie after about half an hour.
Forget about PVA its an old wifes/builders/amateurs tale...you wont find it mentioned on any of the paint companies sites..
And the reason they make primer sealer..
There are many different surfaces out there, primer sealer is meant for those..read the back of the can.
The standard trade practice for applying emulsion to basre walls is..
One mist coat...which is normally a thinned coat of either vinyl or non vinyl matt depending on the thickness of the plaster followed by two coats, which can also be thinned slightly of the same.
A 'mist' coat in any shape or form be it on bare plaster walls with emulsion or exterior rendering is NOT a 'sealer'..it primes the surface making them ready for subsequent coats
Primers/Sealers for new/bare plaster are made for certain emulsions that cannot cope with being applied directly onto new/bare plaster.norwich9 said:
Most of the cheap & retail emulsions cannot be applied directly to new/bare plaster. Though it can be "done" but it makes the surface dodgy for future decoration and/or wallpapering over. Even by applying a primer/sealer when it is not ment to be can cause flaking of paints also.
You see, the thing about primer/selaer for new/bare plaster is a con. They are directed specifically for the DIY man.
It is to make money for big companies. Example is say the primer/sealer is £30 needed for new/bare plaster. Then you buy more retail emulsion than you really need, say about £60, as it has poor covering power etc. This totals to about £90.
Therefore, say you apply the sealer and it takes one day. Then say you apply the emuslion and it takes you two days. This is now three days. In my opinion, this is two days wasted. But the company does not care how long it takes you. Just as long as you buy there product and they can make maximum money from your project.
However, by using Vinyl Matt then you cut out the need for a sealer/primer, meaning one day saved (do the garden instead, hehe) and £30 saved for not needing to buy a sealer/primer.
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Nope..not really the only thing that will stiop that is by having a dry wall..
No amount of paint will hold effloresence back (salts)
If what you have been told doesnt suit you, carry on with the PVA..its virtually impossible to answer the question without some pointers about application and what 'macphersons' your using.
No amount of paint will hold effloresence back (salts)
If what you have been told doesnt suit you, carry on with the PVA..its virtually impossible to answer the question without some pointers about application and what 'macphersons' your using.
Not all primer sealers stop salts.norwich9 said:
Though, it can be dodgy using Oil based primer/sealers on plaster walls as they can contribute to trapping miosture and causing damp like conditions in certain conditions.
Therefore it is bad practice to use certain primers/sealers when they are not needed. It is only when after years of surface painting that if there is a problem with salts then only then should you use special primer/sealer. Also, the usual busy painter will only come across efflorescence (salts) in about 0.01% of surfaces of there decorating lifetime. So, it would be waste of materials and money to seal every surface with Alkali Resisting Primer, as it is not needed. Hence percentage.
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