Solvents and recoating....
Successful recoating of one type of sealer or finish over another takes some consideration of the products being used. All floor sealers and coatings contain solvents to some extend. Solvents are often referred to as VOC’s. Most of the solvents used are specific to what solvent will cut or reduce the resin or base of the product … Volatile Organic Compounds (VOCs) or how much solvent is used in the product … Volatile Organic Content (VOC).
Hot solvents are generally those that have a high evaporation rate or evaporate quickly while milder solvents are those that evaporate slowly. Many different solvents can be used in the same product but the performance is usually linked to the predominant solvent used. The hottest solvent used in sealers is lacquer thinner which is in lacquer sealers and some wood filler products (nitrocellulose) while the mildest are mineral spirits and/or some of the glycols (mild alcohols) used in waterborne products. Solvents would range from lacquer thinner being the hottest, denatured alcohol, xylol, mineral spirits (paint thinner) down to glycols for waterborne being the mildest.
The first consideration in recoating is how long has the coating been down or cured? Next should be how thoroughly has the floor been cleaned? Then, what kind of a profile do we have, screening or abrading? What solvent is in the recoating product, will it be applied with ventilation to dry as quickly as possible and how heavy or thick will the coating be applied? If unsure, make a test sample in an inconspicuous spot.
Generally speaking, products containing lacquer thinner should never be applied over any finish except nitrocellulose or other lacquer products while waterborne and oil modified products will go over any coating. The ones that create questions are shellac products, acid cure and moisture cured products. Sealers such as Universal Sealer and Sealcoat, which are two pound cut, contain about 80% denatured alcohol and are dewaxed shellac while other shellac product at three and four pound cut will have a little less alcohol. Dewaxed shellac can be recoated without screening (hot coating) while regular shellac must be abraded for any other coating to stick because of the wax. As sealers these products should be applied very thin and with ventilation so that they dry an about ten minutes.
Acid cured products, which are conversion varnishes, are not urethanes. They come in two forms; two component products such as Glitsa Bacca, Glitsa Sealer, Synteko, Precision Swedish Finish, Lenmar and others that take an acid hardener; and single component products such as Glitsa Gold Seal, Lite Scent and Precision Swedish Crown. The two component products are often a blend of denatured alcohol and xylol which are more forgiving to use and less hot than the single component types. These are all usually applied at 350-450 square feet per gallon and with minimal ventilation. The single component products are all 80% denatured alcohol and dry faster and will attack other types of finishes, even when fully cured. This is because of the amount of material put down. These are best applied over themselves.
All of the products mentioned so far will eat into, to some extent, the coatings they are applied over since the solvents are hot. This is a “chemical bond” but is determined by how much is applied and how long the previous coating has been down. Surface preparation is still very important. This chemical contact is what causes strong solvents to “eat into” weaker coatings and wrinkle them.
Moisture cured urethane is often 50% xylol and should only be applied over itself since a heavy coat will usually eat into OMU or waterborne products.
OMU and waterborne coatings will adhere to any product which is cleaned and screened well. These scratches produce a “mechanical bond” to which these coatings will adhere. Both OMU and waterborne urethanes have a habit of not adhering well if the surface is not prepared properly and sufficiently.
The most important things to consider in recoating are, what solvent is in the product, how much solvent it contains and how long it will lay there before it is dry. Think through the process because that inexpensive recoat for the customer can become an expensive resand for the finisher if done incorrectly.
Good luck,
Bill
Successful recoating of one type of sealer or finish over another takes some consideration of the products being used. All floor sealers and coatings contain solvents to some extend. Solvents are often referred to as VOC’s. Most of the solvents used are specific to what solvent will cut or reduce the resin or base of the product … Volatile Organic Compounds (VOCs) or how much solvent is used in the product … Volatile Organic Content (VOC).
Hot solvents are generally those that have a high evaporation rate or evaporate quickly while milder solvents are those that evaporate slowly. Many different solvents can be used in the same product but the performance is usually linked to the predominant solvent used. The hottest solvent used in sealers is lacquer thinner which is in lacquer sealers and some wood filler products (nitrocellulose) while the mildest are mineral spirits and/or some of the glycols (mild alcohols) used in waterborne products. Solvents would range from lacquer thinner being the hottest, denatured alcohol, xylol, mineral spirits (paint thinner) down to glycols for waterborne being the mildest.
The first consideration in recoating is how long has the coating been down or cured? Next should be how thoroughly has the floor been cleaned? Then, what kind of a profile do we have, screening or abrading? What solvent is in the recoating product, will it be applied with ventilation to dry as quickly as possible and how heavy or thick will the coating be applied? If unsure, make a test sample in an inconspicuous spot.
Generally speaking, products containing lacquer thinner should never be applied over any finish except nitrocellulose or other lacquer products while waterborne and oil modified products will go over any coating. The ones that create questions are shellac products, acid cure and moisture cured products. Sealers such as Universal Sealer and Sealcoat, which are two pound cut, contain about 80% denatured alcohol and are dewaxed shellac while other shellac product at three and four pound cut will have a little less alcohol. Dewaxed shellac can be recoated without screening (hot coating) while regular shellac must be abraded for any other coating to stick because of the wax. As sealers these products should be applied very thin and with ventilation so that they dry an about ten minutes.
Acid cured products, which are conversion varnishes, are not urethanes. They come in two forms; two component products such as Glitsa Bacca, Glitsa Sealer, Synteko, Precision Swedish Finish, Lenmar and others that take an acid hardener; and single component products such as Glitsa Gold Seal, Lite Scent and Precision Swedish Crown. The two component products are often a blend of denatured alcohol and xylol which are more forgiving to use and less hot than the single component types. These are all usually applied at 350-450 square feet per gallon and with minimal ventilation. The single component products are all 80% denatured alcohol and dry faster and will attack other types of finishes, even when fully cured. This is because of the amount of material put down. These are best applied over themselves.
All of the products mentioned so far will eat into, to some extent, the coatings they are applied over since the solvents are hot. This is a “chemical bond” but is determined by how much is applied and how long the previous coating has been down. Surface preparation is still very important. This chemical contact is what causes strong solvents to “eat into” weaker coatings and wrinkle them.
Moisture cured urethane is often 50% xylol and should only be applied over itself since a heavy coat will usually eat into OMU or waterborne products.
OMU and waterborne coatings will adhere to any product which is cleaned and screened well. These scratches produce a “mechanical bond” to which these coatings will adhere. Both OMU and waterborne urethanes have a habit of not adhering well if the surface is not prepared properly and sufficiently.
The most important things to consider in recoating are, what solvent is in the product, how much solvent it contains and how long it will lay there before it is dry. Think through the process because that inexpensive recoat for the customer can become an expensive resand for the finisher if done incorrectly.
Good luck,
Bill
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