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With Chris Curwen & Expert Auto Painter - Dave Gage (Car Cosmetics)

November 20th, 2007 - Issue 30

In this issue:

• Paint Support Chemicals: Paint Thinner, Use of Auto Paint Reducers and Paint Retarder.

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This week let's continue with our Paint Support Chemicals series and focus on paint thinner, reducers and retarders.

The liquid parts (the solvents) of each paint mixture have to evaporate if the paint pigments and binders are going to cure and harden into a solid unified substance.

In order to refresh your memory on the Basic Paint Ingredients (Paint Pigments, Binders and Paint Solvents) please refer to Issue 25 of the Auto Painting Tips newsletter (Oct 16th '07) in which we cover this topic area.

As previously mentioned, those agents used to turn solid paint pigments and binders into spray-able liquids are grouped and generically referred to as paint solvents.

Paint Thinner, reducers, and retarders all fall into the category of paint solvents.

The chemical make-up of the various paint solvents used in the automotive paint industry, although similar in design and purpose, varies according to the type of paint pigments and binders used in particular paint products.

Paint Thinners & Reducers

In brief:

• Lacquer thinner is designed to work along with lacquer-based products.
• Enamel reducers which contain different chemical blends are required by enamels.

Lacquer thinner is not compatible with enamel products and reducers are not generally compatible with lacquers.

• Paint Thinner is associated with lacquer (paint thinner = lacquer).
• Reducer is associated with enamel paint and urethane paint (reducer = enamels/urethanes).

Paint thinners, reducers and retarders all essentially do the same thing, however, it is extremely important that you use them with the correct product, please remember this.

Retarders

A retarder is either a paint thinner or a reducer but with an extra-slow evaporation time. You would use a retarder for a paint job that is sprayed in an exceptionally hot climate, typically above 35 degrees C.

The function of a retarder is to evaporate more slowly than other paint thinners and reducers so that the paint won't dry too fast - which may cause checking, crazing, cracking or other surface finish problems.

The importance of climatic and temperature conditions:

Paint solvents are designed to be used under specific climate and temperature conditions. They are classified depending on the rate at which they evaporate, those being slow, medium or fast.

You might also have to use a particular solvent depending on the level of humidity in your area, being either very heavy or very light.

In principle:

• Fast evaporating paint solvents are used during paint projects in cooler temperatures,
• Slow evaporating paint solvents are used during paint projects in warmer temperatures.

If you were to follow opposite rules, so for instance if say a reducer designed for hot weather (evaporates slowly) was used in a cooler climate, the paint would not cure properly.

Conversely, if you were to use a cool temperature reducer (evaporates quickly) in a warmer climate, the paint would blush (a condition in which moisture is trapped in the paint after the fast evaporating solvent has evaporated), fade or experience other problems.

It's also very important to understand that using a fast evaporating solvent in a cool but very humid climate could cause blushing too.

In this situation, a medium paint thinner or reducer is required to allow the moisture time to evaporate along with the solvent so that the resulting paint film dries completely and evenly.

What are ideal climatic spraying conditions?

All paint products are designed to be sprayed under climatic conditions of 22 degrees C and 30% humidity. These are the same conditions used in the lab during product testing.

In order to achieve these perfect spraying conditions every time you apply paint would be a rather difficult task especially to any novice home DIY auto painter.

Professional auto painters can quite easily achieve these conditions at any time through the use of their professional spray booths equipped with a dehumidifier and a heater, something not in the possession of the home DIY auto painter understandably.

The solution for any home DIY auto painter.

Fear not because to help you compensate for your lack of such a professional facility which can easily cost in excess of $100,000 plus, auto paint chemists have designed the various paint solvents to react differently under the various atmospheric conditions.

To assist you with your painting project, there are labels on all paint thinners, reducers, and retarders that include the temperature range in which they were designed to be used.

This will help you, if you're an inexperienced auto painter to choose the correct one for your specific task at hand.

Your source of local knowledge.

Your nearest auto paint supply store worker should be familiar with the atmospheric as well as the climatic conditions in your area, consult with these experts if you are at all unsure of the correct solvent to use.

This knowledge will help you to achieve a paint job with the best finish possible. After all, auto paint supply stores want you, their customer, to be satisfied with the products you purchase and therefore continue to buy from them again in the future.

You can therefore trust that their advice on the various products and application techniques will be reliable.

Correct Mixing Ratios

Available at auto paint supply stores will be definitive information sheets and application guides which will list specific paint-to-thinner and reducer mixing ratios. Be sure to ask for this type of material when buying whatever paint products you need.

A good reference table for you to learn from would be the following:

• Etch Primer = 1:1 ratio (1 part paint to 1 part paint thinner)
• Primer = 2:1:1 ratio (2 parts paint to 1 part hardener/paint thinner)
• Base Coat = 1:1 ratio (1 part paint to 1 part paint thinner)
• Clear Coat = 2:1:10% ratio (2 parts paint to 1 part hardener and then add 10% paint thinner).

Calibrated Mixing Sticks

Paint has already been mixed with an amount of solvent when it is in the tin, but you will need to add additional solvent for it to be sprayed. Mixing sticks are used for this. Always make sure you follow the product label instructions for proper use.

Mixing sticks are calibrated to be used with a particular base and paint solvent. It is important that you use a mixing stick that is designed for the brand of paint product you are using.

You can of course pick up calibrated mixing sticks at any auto paint supply store.

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That's all we have for you this week. Thank you very much for reading. We both hope this issue has been of valued interest to you.

Coming In Our Next Issue: We take a closer look at Paint Removers.

Happy Painting!

Chris Curwen & Dave Gage
www.LearnAutoPainting.com