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cart 06-23-2008 03:43 AM

Paint,heat and moisture
Hi All,
A question on painting,heat and moisture.

Our daily temp here is about 11 deg celsius or 52 fahrenheit,its been wet and cold for weeks now.

I am soon to put a coat of preplock stain sealer (shellac based) on the ceiling and proceed to painting the rest of the walls ( water based), on previous coats of undercoat I have come across some paint blisters( they have been repaired) should I have a small bar heater going in the room when or prior to painting?The most noticable blisters where above the window,which I have partially open when painting and around the holes in the wall where the power points are removed.

When I breath, when in the room, there are times that my breath is like condensating and even though the paint is dry it still feels dampish and very cold, also should I lengthen the required of waiting times between coats.

As I said prior it is pretty damp here at present.

Thank you


Nestor_Kelebay 06-23-2008 06:04 PM


A shellac based product forms a film strictly through evaporation of the solvent (alcohol) in it. So cold temperatures will merely slow down the evaporation of alcohol from the ceiling sealer, making it take longer to dry to the touch. However, the shellac product will stick properly; it'll just take a lot longer to dry.

Latex primers and paints are a whole nuther kettle of fish. Cold temperatures and high humidity can each wreck the film formation process in latex products, which is probably what resulted in your paint film blistering before. So, your shellac product on the ceiling will dry properly, just more slowly than it would at warmer temperatures, but your latex primer or paint might not even stick or "dry" to the right colour.

What you need to do is provide artificial heat in that room for the latex paint to form a film properly. You need to warm up the room to a comfortable temperaure before you apply your paint, while painting and during the film formation process. You can tell when the film formation process is over when you start smelling that "freshly painted smell" in the room. What you're actually smelling is something called a "coalescing solvent" that helps the paint resins form a proper film.

Once you smell that "freshly painted smell", it means that the coalescing solvents are evaporating from the paint film, and once they do, no more changes can occur in the paint film, so film formation is as complete as it's ever going to be. At that point, I'd leave the heat on until that freshly painted smell begins to dissipate, and then turn the electric heaters off. The return of cold temperatures and high humidity won't affect a properly formed latex paint film.

The artificial heating will also speed the drying time of the shellac based product on the ceiling.

Post again if you want to know how cold temperatures and high humidity affect the film formation process in latex primers and paints.

slickshift 06-23-2008 08:37 PM

Your temperature is within specs...but barely
I'd recommend extra drying time or some added heat
Please make sure the paints (and walls) are also up to room temp. before painting
Cold paint can fail pretty quickly

cart 06-24-2008 02:48 AM

Thank you Nestor and slickshift I warmed the room this morning, mainly to dry out some patching up on these blisters,I cut in with the stain blocker on the ceiling and found that to go tacky very quickly with the warmth up there.

I hear what you are saying about the latex paint,so thats why when I repair a blister I can peel the paint off in strips? I think I may have found some cause of the blistering above the window,apart from the coldness coming in the window I have an aircon unit above the window and about 75mm down from the ceiling,when I fitted the new cornice I had to cut some of the cornice away to enable it to sit above the aircon unit.

I did not cement under that area and I had about 3mm gap that was not filled, I was surprised on the amount of cold air that was coming in through there and that air was flowing around the area I was/am having problems with.

Tomorrow I hit the ceiling with the stain blocker,the small area I cut into, when that had dried I applied a very small amount of ceiling paint in a small spot,it actually stayed white,so heres hoping.

Thanks again for the replies they where very informative I now know something about different paints and how temp can effect both on the walls and in the cans:thumbsup:



Nestor_Kelebay 06-24-2008 08:27 PM

Well, I believe I can explain why you can peel off your paint in strips.

Latex paint is basically a mixture of clear and coloured particles (called "pigments") and clear hard plastic particles (called "resins") suspended in a solution of water and a water soluble solvent called a "coalescing solvent".

When you apply the paint to the wall, the first thing that happens is that the water evaporates from it. Those clear hard plastic resins find themselves surrounded by the coalescing solvent at a steadily increasing concentration. That coalescing solvent dissolves (kinda) in the plastic resins and makes them mushy (by lowering the glass transition temperature, Tg, of the plastic). The result is that the resins are much softer and stickier than before. That softness allows the relatively weak forces of capillary pressure and surface tension to cause the soft mushy resins to stick to one another and fuse together into a solid film of soft mushy plastic. Then, the coalescing solvent evaporates out of the paint film causing you to smell that "freshly painted smell" in the air. As the coalescing solvent evaporates, the plastic hardens back up again to it's original hardness.

That's at least how things are supposed to happen.

However, if you're painting in cold conditions, the plastic will tend to remain hard just because of the temperature, and the coalescing solvent will be less effective in making it mushy. As a result, the plastic resins won't get as soft and sticky, so they won't stick to each other or the substrate as well.

I think the fact that you are able to peel off that paint in strips means that the plastic resins in it didn't get as soft and sticky as they should have, otherwise the paint film would be stuck properly to the wall.

cart 06-25-2008 12:05 AM

Thank you Nestor I see how important tempature is for the problems I have encountered.

I have applied one coat of the stain sealer on the ceiling it dried to a beige colour/fawn and wow what a transformation of the ceiling it actually makes me want to leave it as is,compared to how it looked prior.

Application was great with a roller seeing how sloppy it looked in the paint tray,I do intend giving the ceiling another coat just in case.

Throughout this room I have had to patch up walls and the ceiling,in some cases large cracks as well as replacing sections of plaster that had to be cut out of existing plaster and fitted in,very old house here.

I did notice that where I had done these repairs to the ceiling where I had joined up and bogged up large areas,the one coat of stain sealer hid all of these,the ceiling looks so flat.

With any sealer left could I apply some over these type of bogged up areas on the walls,allowing I would be only doing these areas and not the whole wall.
At present the walls are of a white colour from the undercoat I have already applied.

Would the beige colour of the stain sealer applied only where required on the white sealed wall conflict with the colour I want to paint the walls, which is Crushed Rock, which will be a low sheen to assist in hiding these repairs.
I suppose I mean if i was to paint crushed rock on a wall which has a normal type sealer which finished white and the same colour on a wall finished in this stain sealer which finished in this beige colour, would there be a difference in the one colour on the two walls?

Thank you for your time and input into my questions,every thing is being taken on board here:)


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