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    Home > Coatings News > Paints and Coatings Market > Problems and prevention measures that may occur in the application of polyurethane waterproof coatings!

    Problems and prevention measures that may occur in the application of polyurethane waterproof coatings!

    • Last Update: 2022-09-20
    • Source: Internet
    • Author: User
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    Because of its superior waterproof performance, one-component polyurethane waterproof coatings are widely used in indoor and roof waterproofing, occupying a considerable share in the market, and there is also an upward trend
    in recent years.
    So how to use one-component polyurethane waterproof coatings? And what are the precautions? Let's take a look!

    01 Advantages of one-component polyurethane waterproof coatings

    Can be directly constructed on a variety of wet or dry substrates, direct construction on various substrates, strong adhesion to the substrate, polymer substances in the coating film can penetrate into the micro-fine seams of the substrate surface, strong follow-up, good flexibility of the coating film, strong adaptability to the expansion or cracking of the base layer, high tensile strength, green environmental protection, non-toxic and odorless, non-polluting environment, no harm
    to the person.

    Good weather resistance, high temperature does not flow, low temperature does not crack, excellent anti-aging performance, oil resistance, wear resistance, ozone resistance, acid and alkali erosion resistance, dense coating film, complete waterproof layer, no cracks, no pinholes, no bubbles, water vapor penetration coefficient is small, both waterproof function and air insulation function, simple construction, short construction period, convenient maintenance of paint online coatingol.

    02 Construction process of one-component polyurethane waterproof coating

    Process flow:

    Inspection of construction preparation→ the construction of the sub-layer treatment and cleaning → the construction of the detailed additional waterproof layer→ the construction of the large-sided coating waterproof layer→ the closing head, the edge sealing→ the quality inspection, the acceptance → protection, and the isolation layer construction

    Grassroots treatment:

    The waterproof base layer should be flat, strong, dry, no sharp bumps, honeycombs, hemp surfaces and peeling, no oil stains, cracks, deformation seams of the base layer, the groove left in the pipe root should be embedded with sealing materials and do additional waterproof treatment, for a flat and solid base layer without applying the base layer treatment agent

    Additional waterproof layer:

    Yin and yang angle, pipe root, deformation seam and other basic details, should first carry out additional waterproof layer construction, strengthen treatment, increase the groove 1mm thick coating film, painted in 2-3 times, if you need to clamp the carcass reinforcement material must be impregnated, horizontal deformation seam part should first be laid a layer of polyester non-woven fabric to form an additional waterproof layer, empty paving structure

    Construction of waterproof layer with large surface coating:

    Can be used roller brush, brush, scratch or spray, should be divided into 2-3 times coating, can also be coated once, when the first time coated, the first time after coating should be fully cured to the finger touch basically non-stick when the coating is applied twice, generally interval 24h, the second time should be perpendicular to the direction of the first time of coating, if you need to lay carcass reinforcement material, you should apply paint, while laying reinforcement material

    The amount of paint used is: thickness 1mm coating film 1.
    4kg/㎡ (1.
    5mm about 2.

    Closure and edge sealing treatment:

    Check the tip area and apply additional brush to the edge.

    Construction of protective isolation layer:

    After the coating waterproof layer is finally completed and accepted by the quality inspection (if necessary, the closed water test is carried out), the construction
    of the protective isolation layer is carried out according to the relevant specifications or design requirements.

    03 Polyurethane waterproof coating common problems and prevention

    First, the problem of precipitation

    Cause: Precipitation is the most reflected problem in the use of polyurethane waterproof coatings
    Precipitation is formed
    when the filler in the paint is more dense than the density of the polyurethane glue, moves downward under gravity, and accumulates at the bottom of the barrel.
    There are two types of precipitation: hard precipitation and soft precipitation
    Hard precipitation means that the filler has been mixed with the glue liquid into a solid, and can no longer be dispersed into a liquid, becoming a waste
    Soft precipitation means that after redispersation (stirring) the filler can be evenly returned to the glue solution and is still a qualified product

    Measures to prevent sedimentation: inverted measures are used during storage; Regularly flip the barrel once, that is, reverse and change to positive, positive and upside down, which can prevent the occurrence of hard precipitation; Stir well with machinery before use, and use up the whole barrel of paint in a short time

    Note: The application temperature of polyurethane waterproof coating should be 5 ° C to 35 ° C, the mixed slurry should be used up within 1 hour, and the antifreeze storage of the product should be paid attention to in cold areas or low temperature conditions;


    Cause: The root cause of polyurethane conjunctiva is that the packaging barrel is not well sealed and leaks.

    After the packaging barrel is leaked, the solvent in the paint gradually volatilizes through the air leakage site, and the air outside the bucket containing water vapor enters and reacts chemically with the liquid material in the barrel, and the result is the liquid conjunctiva
    Even in the case of a complete seal, if the storage time is too long, there will be a small amount of conjunctiva, but the film layer is very thin
    That's because the liquid in the barrel is not full, the upper part is air, of course, there will be water vapor, which will still react
    with the liquid.

    Prevention and control method: the sealing between the lid of the packaging barrel and the barrel body should be good; Inverted storage; Avoid exposure to the sun and store
    in a cool place away from the rain.
    In addition, the polyurethane packaging barrel should be used up as soon as possible after opening, and the surface conjunctiva phenomenon
    will occur if the exposure time is too long.

    Third, the bond with the grass-roots level is not good


    1) Poor treatment at the grassroots level, which does not meet the requirements of
    the specification.
    Floating paste, floating ash, dust particles and other substances on the base layer will form an isolation layer, so that the coating film and the base layer are poorly adhered, and the coating film is peeled and bubbling
    Unevenness at the grassroots level can also make poor bonding worse

    2) The grassroots is not dry, and the moisture content is too high
    Two-component polyurethanes will react chemically when exposed to water, forming gases and forming bubbles; The one-component polyurethane itself needs to react with moisture in the air to form a film
    However, if the base layer is too wet, the moisture is much greater than the chemical reaction is required, after the coating is formed into a film, there is still a lot of moisture under the coating film, which is vaporized by heat and expanded, and the film layer will be lifted up to form an empty drum

    3) Improper
    construction operation.
    The previous paint is not dried, that is, after the coating, or too thick at one time, the surface paint is first conjunctival, and the liquid below or the moisture in the base layer volatilizes, so that the coating film adheres poorly, or even empty drums

    4) Indiscriminately add diluent.

    In order to apply scratch quickly and labor-saving, construction workers like to add some thinner
    to the polyurethane waterproof paint.
    The thinner foams
    the coating film during the volatilization process.
    Some diluents purchased at will will seriously reduce the quality of the coating film, and even make the paint unable to form a film


    1) Ensure that the quality of the grassroots is qualified before construction, and the grassroots is flat and free of floating ash

    2) The base layer should be dry
    The base moisture content of the two-component polyurethane should be less than 8%.

    The moisture content requirements of one-component polyurethane on the base layer are theoretically not as strict as those of two-component, but some construction personnel sweep away the stagnant water and work immediately after the rain, which is wrong
    For details, refer to the instructions on the manual

    3) Add the diluent
    Except for the first scratch can be added to the production plant with a small amount of diluent, the subsequent times must not add diluent
    Polyurethane coatings have a large viscosity and are suitable
    for scratching.

    4) Scrape and apply in parts
    Polyurethane paint can not be painted too thick at a time, and the previous coating is basically dry before it can be painted again

    Fourth, the coating film has no strength

    The coating film is not fully cured and dried without strength, polyurethane surface dry does not represent the curing of the coating, to be fully cured after the coating film has strength, or the paint added inappropriate additives, resulting in the film curing after the loss of the original material properties

    Fifth, slow drying, dry or non-condensing


    1) There may be a problem with the formula, or it may be an improper production process, and it may be that the construction operation is not standardized, and there is fraud and cutting corners

    2) The two-component coating is not strictly metered, not mixed according to the proportion, more B material is added, and the mixture is not stirred evenly, which will cause the coating to be partially dry or slow dry

    3) The construction environment temperature is too low, which will also cause the coating to dry or dry

    Prevention and control measures:

    1) During construction, the mixture is strictly according to the proportion, and the mechanical stirring is used to mix evenly

    2) Polyurethane coatings are reactive coatings, in accordance with the provisions of the "Roof Engineering Technical Specifications" and "Underground Engineering WaterproofIng Technical Regulations", the construction environment temperature of the reactive coatings should be 5 ~ 35 ° C

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