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Hi all. Any advice on what amount of thinning needed (if any) for water based primer when applying with a brush and roller to new gyprock or drywall. Seems to be a ton of different approaches, ranging from no need or anything from 20% to 5% to make sure the primer bonds well to paper faced plaster. Will be using Wattyl acrylic sealer undercoat. Any thoughts much appreciated.
 

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Hi all. Any advice on what amount of thinning needed (if any) for water based primer when applying with a brush and roller to new gyprock or drywall. Seems to be a ton of different approaches, ranging from no need or anything from 20% to 5% to make sure the primer bonds well to paper faced plaster. Will be using Wattyl acrylic sealer undercoat. Any thoughts much appreciated.
Wow, Haven't heard the name of Wattyl since I worked for them in 1995. All manufacturers have a variety of interior primers. a universal rule of thumb would be, the cheaper the primer, the less the resin, the more the pigment Thinning a cheap primer more than 5 percent would not be good. I would not suggest thinning Quik Dry whereas the Pro Block could take up to 10%. As stated below, a primer is not meant to be thinned by the manufacturer. More water = less resin, means less adhesion.
 

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Wow, Haven't heard the name of Wattyl since I worked for them in 1995. All manufacturers have a variety of interior primers. a universal rule of thumb would be, the cheaper the primer, the less the resin, the more the pigment Thinning a cheap primer more than 5 percent would not be good. I would not suggest thinning Quik Dry whereas the Pro Block could take up to 10%. As stated below, a primer is not meant to be thinned by the manufacturer. More water = less resin, means less adhesion.
Seemingly a weird UK practice (since I'm bored and like reading their stuff) is thinning their paint by up to 20-30% on their first coat on plaster, then the second coat use it unthinned. The idea is the thinner the paint is for the first coat, the more it will soak into fresh plaster (though their plaster is more gypsum based than our plaster, which is usually more lime based) compared to unthinned where it would sit on top but not absorb deeply in. But they also don't tend to use a primer first, just the thinned normal paint for the first coat instead of primer.

But yeah, for drywall (drylined, as they say in UK, as in, sanded while dry and just the lines between sheets) I think just any normal drywall primer at full strength is probably ideal, and an even higher build is probably more ideal than something thinner, as drywall's main problem is the joints telegraphing through if the primer coat doesn't seal it fully enough. There's a few super thin primers like Gardz that fully seal and are designed that way, but if you just thin a normal primer it's not going to seal as well due to less solids, I'd guess.
 

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Seemingly a weird UK practice (since I'm bored and like reading their stuff) is thinning their paint by up to 20-30% on their first coat on plaster, then the second coat use it unthinned. The idea is the thinner the paint is for the first coat, the more it will soak into fresh plaster (though their plaster is more gypsum based than our plaster, which is usually more lime based) compared to unthinned where it would sit on top but not absorb deeply in. But they also don't tend to use a primer first, just the thinned normal paint for the first coat instead of primer.

But yeah, for drywall (drylined, as they say in UK, as in, sanded while dry and just the lines between sheets) I think just any normal drywall primer at full strength is probably ideal, and an even higher build is probably more ideal than something thinner, as drywall's main problem is the joints telegraphing through if the primer coat doesn't seal it fully enough. There's a few super thin primers like Gardz that fully seal and are designed that way, but if you just thin a normal primer it's not going to seal as well due to less solids, I'd guess.
Those were the days when plaster walls existed. In days of old, late 80's early 90's new construction was rampant in South Florida. Rule of thumb was 45 gallons on an exterior and 80 gallons on the interior of a 2500 square foot house. Paint was cheap, slightly over $7 to $12 a gallon for the exterior. Even with those extraordinary prices, contractors would try to save money by buying Mistints and spraying them on the stucco as a skim coat. Worked well as suggested by the UK practices, until they used an interior paint on the exterior. The curing stucco had a high PH of well over 8 and the interior paint was @ 7 on the ph scale. thus causing stucco failure. Thus the hot stucco primers and interior drywall primers were invented. Enamel undercoats were okay for woodwork, but left a blemished finish on drywall.

The average price of painting a new house in the early 90's was slightly over a dollar a square foot "under roof". Not until the early two thousands did the commercial painting price rise into $1.50 a square foot range. Try competing with a price point of over $20 a gallon and be competitive with the big guns in the industry. Inequitable pricing still exists, but you must be in the Million dollar a year price club.

To answer your question, its fine to heavily thin the primer on stucco or plaster finishes, it gives greater paint penetration. Thinning on an interior drywall primer leads to loss of adhesion. The cost of materials put into a can of paint is closely measured. disregarding recommended application results in loss of implied warranties. Continue to have a great weekend.
 
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