TGIF Solvents and Thinners

 

In finishing, we can use a number of solvents and thinners.  We need to know what  & when to use.  I’ll try to keep this at HS chemistry level or below.  But to understand the products it helps understand some of the basic properties.   Things are changing due to VOC (volatile organic compound) and HAP (hazardous air pollutant) laws in many states.

 

First, I like to remind people there is a difference between a

• solvent -  something that dissolves something
• thinner -  something that dilutes something to change viscosity or evaporation rate (flash off)

 

A possible point of confusion is that the same product can be either or both.  For example, mineral spirits will thin oil-based varnish but dissolve wax. Lacquer thinner is a solvent for lacquer and adding it to lacquer will thin it or possibly alter its evaporation rate.  Alcohol is a solvent for shellac but a thinner in lacquer.

 

To really find out what’s in a product, you need to look on the label.  More often you need to look up the Material Safety Data Sheet (MSDS) now also known as Safety Data Sheet (SDS).   And you may need to decode the names by CAS (Chemical Abstract Service) number.   Many chemicals have multiple names but there will be a unique CAS number.  For example “aromatic petroleum distillates," "cyclic aliphatic hydrocarbons", "distillates (petroleum), hydrotreated light” or “volatile hydrocarbons”  may be mineral spirits, or something else entirely (see distillates, below).  But if you get the unique CAS number, you can determine what it is.  For example, the CAS number for water is 7732-18-5 (who'd have thought that?)

 

Safety:  In general, with the exception of water, avoid contact with skin, eyes, and use in a ventilate area to avoid excesss fumes.   For some products, you should also wear a hydrocarbon respirator (not just a dust mask).  Also, assume most are flammable.

 

Mostly, we use three different products – petroleum distillates, lacquer thinner, and alcohols.  But these represent more narrow component groups.

 

Major categories

 

Water

 

Water, in chemistry, is known as “the universal solvent”.   Technically, H20 is a “polar solvent” because it has a positive side and negative side.   The first rule of solvency is “likes dissolve likes.”   So water tends to dissolve things like it.  This includes a lot of foods and dirt.  But it’s not really a good solvent for finishes (because we don’t want finishes to dissolve if we spill water on them.)  But we can use it as a thinner.   In small amounts, we can use it to thin waterborne finishes.   In order to comply with VOC laws (especially in strict areas like California), manufacturers are adding into things like “green paint thinner.”   Because oil and water don’t mix, it’s an emulsion and white (like milk, another emulsion).  I have not tried these, and would do trials if thinning varnish.  But it would work OK to clean brushes, etc.

 

Distillates

 

These are usually petroleum based products, but I will include others chemically similar.  When petroleum (crude oil) is distilled, various volatiles come out at different levels and give different products (fractional distillation).   From fastest evaporating to slowest, these are some of the products

 

• Gasoline - don’t use this in finishing
   
• VM&P Naphtha   -- VM&P stands for varnish maker’s and painter’s.  This is a good fast-evaporating thinner for varnish and also a good solvent for cleaning and removing wax.  Also known as benzine  (i as in alive)
   
• Mineral spirits –aka White Spirits,  what we normally see in “paint thinner”    Slower evaporating and oiler than naphtha.  To make “odorless mineral spirits”  or “odorless paint thinner” the following are extracted from mineral spirits, and  may also be extracted from naphtha

            o   Benzene aka benzol – a carcinogen and generally not available any more (e as in dead)

            o   Toluene aka  Tolulol – thinner used in many lacquer thinners

            o   Xylene aka Xylol  thinner for conversion varnish, used in some cleaner type products. 
                  It can clean off paint splatters, but can damage some finishes (waterborne). 

                  You can also use it to remove dried on glue (chemically similar to paint)

 

• Kerosene (story: my brother-in-law said his dad used to use kerosene to thin varnish.   It smelled so bad for so long that his mother would not let the piece in the house for months.)
   
• Mineral oil aka Paraffin Oil– used for cutting boards, furniture polishes, baby oil
   
• Paraffin - wax
   

Paint thinner is a generic name and can be mix of several chemicals or chemicals with some components extracted.
 

Turpentine is distilled tree sap and works much the same as mineral spirits.   It is more expensive, smellier and slower evaporating.   It has a higher solvency factor (KB value, see below). Except for special applications like oil artists, it has largely been replaced by petroleum distillates.
 

D-Limonene is another distillate product.   It is a mild solvent that is used in hand cleaners, Goo-Gone, and “Lemon Oil” furniture polishes (that are mostly mineral oil). It is obtained commercially from citrus fruits through two primary methods: centrifugal separation or steam distillation.

 

“Green Paint Thinner” or “Paint thinner substitutes”   In order to comply with VOC laws, sometimes distillates are diluted with water.  If you thin varnish with one of these, you can raise the grain quite a bit.  To avoid this either use pure mineral spirits, where available, in the first coat.  Or let the grain raise and sand off after the first coat (burying the grain).   “Paint thinner substitutes” can be anything.  Some contain chemicals that will damage an existing finish if you just want to clean or wipe off the wax.   Read the label and put on your Dick Tracy decoding ring and looking at the MSDS/SDS.   Trials are always a good idea to avoid surprises after you’ve just spent a month in construction.

 

 

Alcohol

 

Alcohol is the solvent for shellac.   It’s also used as thinner in lacquer thinner.  The most common types are

• Ethanol – grain alcohol – what’s in liquor, wine, beer, moonshine, etc.
• Methanol – wood alcohol – poisonous to drink
• Isopropyl – rubbing alcohol – usually contains too much water to use in finishes

 

While we could dissolve shellac in “everclear” (180+ proof (90%+) grain alcohol, ethanol), it is heavily taxed as a beverage.  Manufacturers add methanol to make it non-potable and thus cheaper.   The result of this is denatured alcohol aka methylated spirits in Britain.    We could use pure methanol to dissolve shellac but it would be more hazardous, more expensive and faster drying.  Shellac already dries in just a few minutes so there’s not too much a need for this approach. 

 

Alcohol is also good to remove markers like Sharpie from finishes that are not shellac. 

 

Alcohols are miscible in water, meaning they blend and are not like “oil and water.”  Most alcohols have at least some water left in them as it’s impossible to distill out all the water.

 

Ketones

 

A ketone is an oxidized alcohol.   Acetone is a familiar one.   Acetone is a very strong and fast-drying solvent and will damage most finishes and plastics..   So it’s good for stripping.   Acetone is also a major ingredient in lacquer thinner.  Methyl-Ethyl-Ketone (MEK) aka butanone, 2-butanone is another example that you might see at a paint store.  MEK is slower evaporating than acetone (but still fast) and can be used for some of the same purposes. 

 

 

Glycol ethers

 

You are not likely to see a can of glycol ether in the paint store unless you see a strange can of something called Butyl Cellosolve (trademark for Ethylene Glycol Monobutyl Ether).   Glycol ethers are a broad class of hydrocarbon compounds with long names and long chemical formulas*.     Glycol ethers are either "e-series" ethylene glycols or "p-series" propylene glycols. GEs are the solvent in waterborne finishes (softening the resins, then evaporating and letting them coalesce together).   They are also use as a solvent in lacquer thinners.  I use propylene glycol to make waterborne glazes and to retard the drying of waterborne wiping stains.  It's also used in inks and some cleaners.

Glycol ethers are miscible in water and other solvents, evaporate slowly, soften many resins and dissolve lacquer.  It is common in lacquer retarder, making lacquer dry more slowly to avoid blush.

(* example Diethylene glycol mono-n-butyl ether CH3CH2CH2CH2OCH2CH2OCH2CH2OH -- See what I said)  And why did they misspell this label??

 

Lacquer Thinner

 

Where does lacquer thinner fit in this classification?  We haven’t covered it yet, but seen it referenced. Lacquer thinner is a mix of maybe 5-10 of a group of 25 or so distillates, alcohols, ketones, and glycol ethers.   Some act as a solvent, some as a co-solvent (aka latent solvents, only work well when another primary solvent is present) and some as a thinner (dilutent).  The exact formula and proportions can vary by manufacturer, cost considerations, and desired evaporation rates.  Trial and error or a graduate degree in organic chemistry would be a way to tell what works when.

 

Lacquer thinner makes a good final rinse for brushes used for oil-based varnishes.  First, get out most of the varnish with mineral spirits or paint thinner.   Then rinse in lacquer thinner to pull out the rest and remove the oiliness of mineral spirits.

 

More Reading

 

Green solvents and their use   https://www.woodshopnews.com/columns-blogs/its-a-struggle-working-with-new-compliant-solvents

 

K-B value – the measure of a hydrocarbon solvent https://electronics.microcare.com/resources/faqs/kb-value-tell-solvent/

 

Things change and they don't always tell you: https://www.popularwoodworking.com/woodworking-blogs/goof-off-has-changed

Edited September 26, 20178 yr by kmealy

Great general information, as always.

 

Thanks, Keith.

Thanks Keith . When thinning water based paints, I've been told that water should not be used as a thinner. What product is made for thinning water based paint? I've found water based paint difficult to use in a spray painter without thinning.

Edited October 2, 20178 yr by It Was Al B

For thinning w/b products, check with the manufacturer or your particular product.  Some make a thinner specific to their offering.  While you can add mineral spirits, naphtha, paint thinner in any proportion to an oil-based varnish, the chemical balance of the dozen or so ingredients in a w/b finish is more sensitive.  You can't just add in a bunch of water and expect it work work right.