Thinning Paint.........Advise Please

[WhaleBat]

I have never thinned paint before.

Can anyone advise me of the reasons for thinning paint, advantages / disadvantages. I have always just used emulsion straight from the tin on walls and ceilings and undercoated wood before glossing straight from the tin.

Are there any general rules of thumb that can be used when thinning paint? Does it have to be accurate ratios, and what is it best to thin the paint with?

Thanks again to anyone kind enough to answer.

 

[Zampa]

There are two types of paint, trade and retail, in general retial paint doesnt need thinning...trade formulations sometimes do.

There are various reasons for thinning paint, some paints are 'sticky' when your trying to appy them, especially oil based glosses...so you need to add a drop or white spirit to them (not turps substitute, which can have an effect on the sheen of the paint)

Sometimes the paint is two thick...this is often common with some undercoats, if its too thick it will leave brushmarks..so it need thinning

It is also hard work using a paint thats too thick...again a little thinners makes it easier for the person putting it on

Another reason is to allow a paint to semi penetrate a surface, I have just done an outside job, new rendering, the first coat which was an oil based masonry paint needed to penetrate the surface, this enables it to 'lock' on the surface and provides a good based for subsequent coats...so I used 15-20% white spirit

Some surfaces like rendering are porous, which causes the paint to suck into them...thus making it hard work to apply and youl end up using to much paint (which doesn't penetrate or prime and just sits on the surface)

The other and maybe most obvious reason it to help make the paint go further...(hence white spirits nickname...'doomore') it will help to a certain extent but the type of surface will have a bareing on this, imagine a gallon of water and a gallon of slightly thinned paint on a plaster surface...the paint allthough thicker will go further becasue the water being thinner will be absorbed more into the surface....so thinning paint paint purely to make it go further in order to save money doesnt always work plus, by thinning it you are reducing its covering power.

Most painters beleive that it far better to give something two decent coats than having to give it three because the second one has failed to cover.

When you thin an oil based paint you are breaking down the carrier oil and resins..remember that the highest percentage of gloss paint is this oil....think of it as a varnish with with powder in....if you break the oil down in gloss paint to much it will go flat

Too much thinners can also have an effect on the binder in a paint...the binder holds the pgments together...it this happens the surfac of the dried film will become chalky and powdery

Water based paints acrylics, masonry etc...thin with clean water

Oil based, gloss, undercoat etc...thin with white spirit

There are also some speciality paint that have their own types of thinners...hammerite for example

Hope that helped.

 

[Paintbrush]

There are two types of paint, trade and retail, in general retial paint doesnt need thinning...trade formulations sometimes do.

There are various reasons for thinning paint, some paints are 'sticky' when your trying to appy them, especially oil based glosses...so you need to add a drop or white spirit to them (not turps substitute, which can have an effect on the sheen of the paint)

Sometimes the paint is two thick...this is often common with some undercoats, if its too thick it will leave brushmarks..so it need thinning

It is also hard work using a paint thats too thick...again a little thinners makes it easier for the person putting it on

Another reason is to allow a paint to semi penetrate a surface, I have just done an outside job, new rendering, the first coat which was an oil based masonry paint needed to penetrate the surface, this enables it to 'lock' on the surface and provides a good based for subsequent coats...so I used 15-20% white spirit

Some surfaces like rendering are porous, which causes the paint to suck into them...thus making it hard work to apply and youl end up using to much paint (which doesn't penetrate or prime and just sits on the surface)

The other and maybe most obvious reason it to help make the paint go further...(hence white spirits nickname...'doomore') it will help to a certain extent but the type of surface will have a bareing on this, imagine a gallon of water and a gallon of slightly thinned paint on a plaster surface...the paint allthough thicker will go further becasue the water being thinner will be absorbed more into the surface....so thinning paint paint purely to make it go further in order to save money doesnt always work plus, by thinning it you are reducing its covering power.

Most painters beleive that it far better to give something two decent coats than having to give it three because the second one has failed to cover.

When you thin an oil based paint you are breaking down the carrier oil and resins..remember that the highest percentage of gloss paint is this oil....think of it as a varnish with with powder in....if you break the oil down in gloss paint to much it will go flat

Too much thinners can also have an effect on the binder in a paint...the binder holds the pgments together...it this happens the surfac of the dried film will become chalky and powdery

Water based paints acrylics, masonry etc...thin with clean water

Oil based, gloss, undercoat etc...thin with white spirit

There are also some speciality paint that have their own types of thinners...hammerite for example

Hope that helped.

This is such a helpful post - thanks for taking the time to impart your knowledge.

I have spent a lot of time rubbing out brush marks from primer and undercoat.

Today I tried thinning the undercoat with w/s - what a difference!

No more brush marks and the paint goes on so much easier.

If this is used with a gloss foam roller will it leave a good finish or will I still have to lightly drag a brush across afterwards?

Cheers.

 

[Zampa]

Thanks..

Its nice to know I didnt write all that in vain, especially as the original poster couldnt be arsed to reply!! ...god knows how you found the thread though..its five years old!

Re the roller....on a large flat area like a door it makes sense to use a roller, especially if your a novice.
A lot of painters do this do if they have a lot of them to paint..many roll then pull a dryish brush over them to remove the roller stipple..but if you are careful and put a nice even amount of paint on then theres no harm in leaving it as it is..the stipple effect of the roller can be a finish in itself

That said, if the area already has brush-marks in it from previous coats then it would be a good idea to brush it out after you roll..doing a manageable section at a time...roller stipple over brush marks or vice versa really looks ugly.

Dont roll the whole door then run the brush over it...it will probably drag..do it in quarters or thirds

If your using a water based gloss then id say using a roller is essential to the untrained hand...and you probably wont have time to brush it out as the water based stuff dries very quickly

Hope that helps..

 

[Paintbrush]

I am sure it's had tons of views, and tbh no one really needs to ask anything else as it's all there

I see what you mean about the stipple effect on the roller.

It leaves an almost satin finish on the undercoat that I have done so far, very easy to apply the right amount too.

I thought maybe the stipples might disappear as the gloss skin dries?

Will try roller with undercoat tomorrow using thinned paint as today, see how it looks.

Thanks again,

 

[joe-90]

I thought it was the 'Ghost of Christmas Past' when i saw the name.

Are you back for good Zamps?

 

[Zampa]

I thought it was the 'Ghost of Christmas Past' when i saw the name.

Are you back for good Zamps?

On and off Joe if/when someone replies to a thread..

How you doing fella?

 

[joe-90]

I'm still here 24/7 - so they tell me.

 

[Paintbrush]

Ahh slight problem encountered.

All was going well when painting gloss onto an under coated surface. Thinning the paint worked well giving a mirror like finish with one coat of Dulux non drip b/w.

The front door (hardwood stained) has been rubbed down and primed twice, togther with two coats of white under coat. I have rubbed down between coats which left a very smooth finish ready for the gloss - here comes the problem.

Added a bit of w/s to the Crown non drip (Oxford blue) and apply as before. Finish isn't too bad but coverage shows the undercoat and leaves the paint a lighter shade of blue.

Not to worry, will add another coat today. I tried flatting it down with 400g but stopped after a while as the paper couldn't get a hold of the paint (it seemed to slip across the surface).

I took a chance and went on the paint a second coat, this was a different ball game. The brush didn't want the leave any paint behind so I have to put it on way toooo think which is just about passable (drying now).

Should I have waited maybe a week before sanding for the paint to cure or used a different colour u/c?

Thanks,

 

[joe-90]

I use mid grey for that colour.

 

[Paintbrush]

I use mid grey for that colour.

Doh!!

Double Doh!!

I didn't think to get a different colour u/c - that's the difference between a professional and rank amateur.

What do you do about painting gloss on gloss, oil based - brush doesn't seem to want to leave paint behind?

How long before I sand back this errrmm....mess

 

[vibrobullit407]

I think the problem here is that you were unaware of the correct undercoat for your top coat. If you are applying a coloured gloss and don't know what undercoat to use just ask. It is common for some DIYers to just use white undercoat as they are unaware that you can get it in many colours to suit the top coat.

 

[Paintbrush]

Shall I plough on and just keep painting Oxford blue until it covers ?

I keep popping out to have a look at it but no improvement -

 

[joe-90]

If it's dragging then you need to thin more. Do it in a kettle (thin that is not piddle).

 

[dcdec]

Probably dragging because the previous coat hasn't cured. By the way non drip gloss is a thixotropic paint, i doubt your supposed to thin it because your not supposed to stir it.

You need to wet abrade fresh gloss, drying times on post 2010 OB paints seem to be longer as well, use a high grade of paper and plenty of water and be sure to clean off the slurry thats left behind