Smelly tar glue under the wooden floor

Smelly tar glue under the wooden floor

Renovation of an old apartment turns into a lottery game

Marlene Sandner (Germany) wanted to replace the worn wooden floor in her old apartment in the city center with a new parquet floor. To her surprise, demolition work revealed a smelly old linoleum floor underneath the floorboards, which was obviously glued to the screed. The adhesive was already crumbling and showing signs of dissolution. After the linoleum was removed, remnants of the adhesive remained stuck to the screed. The flooring installer suggested sealing the surface twice with epoxy resin and smoothing out any remaining unevenness with a leveling compound. The new parquet was then to be laid on top. Marlene Sandner is still hesitant and is therefore seeking advice from the environmental consultancy.

Adhesives containing tar were widely used between 1920 and 1960

Until the end of the 1960s, tar-containing adhesives were used in the installation of parquet or linoleum flooring. In schools, on the other hand, only a few cases have come to light in which such adhesives were used. A broader public learned of the problem through press releases about the use of tar-containing adhesives in barracks and apartments, mainly in the Frankfurt area. The cause of the pollution was imported coal tar pitch-based adhesives. Polycyclic aromatic hydrocarbons (PAHs) thus became known at a stroke. PAH concentrations of up to 300,000 mg/kg were found in the soldiers’ quarters. The material was valued by builders for its good waterproofing properties against moisture.

PAHs are composed of many individual substances

Polycyclic aromatic hydrocarbons are not a homogeneous product. The entire product group can comprise several hundred compounds. The U.S. Environmental Protection Agency (EPA) has compiled the 16 most harmful substances from all the compounds, which also differ in their volatility. These substances are therefore referred to as EPA PAHs. Since July 1, 2012, two additional PAHs have been included in the EU in addition to the previous 16 EPA polycyclic aromatic hydrocarbons. These are the substances benzo[e]pyrene and benzo[j]flouranthene, which are classified as carcinogenic. In 1998, the Expert Commission at the Federal Environment Agency in Germany selected benzo(a)pyrene (BaP) as the lead substance from the 16 individual substances, since this substance is considered to be particularly harmful to health.

The following guide values should be observed

Recommendation values developed by the Expert Commission for Schoolrooms (Germany) apply to BaP. According to these, house dust tests should be carried out for concentrations above 10 mg/kg BaP in the glue. If the BaP content in fresh dust exceeds 100 mg/kg, exposure-reducing measures should be taken in schools. In the field of occupational safety, materials with benz(a)pyrene contents above 50 mg/kg are to be classified as hazardous substances (TRGS 905). For room air analyses, different guide values I and II apply for the 16 EPA PAHs, e.g. for phenols Reference value I = 20 µg/m³ and Reference value II 200 µg/m³, for naphthalene Reference value I = 2 µg/m³ and Reference value II = 20 µg/m³. Naphtalines and phenols are very odor-sensitive. For example, the odor threshold of naphthalene is only two micrograms per cubic meter. PAHs are classified as carcinogenic, mutagenic and mutagenic. Tar adhesives may also be contaminated with asbestos fibers. Supplementary analysis is recommended.

Protective measures as required for asbestos abatement

If the contaminated material is removed properly, a site-specific remediation concept with a hazard assessment in accordance with the Hazardous Substances Ordinance must be drawn up. A certified remediation company must be commissioned to carry out the work. The occupational health and safety requirements of TRGS 524 “Working in contaminated areas” must be complied with. After removal, a fine cleaning is to be carried out, whereby the smooth surfaces are to be wiped with a damp cloth and the rough surfaces are to be cleaned with a class H12 vacuum cleaner. The amount of work required for protective measures is the same as for asbestos abatement. Particular care must be taken to ensure that the work areas are sealed off dust-tight from neighboring living areas (keyword: separation of black and white areas).

Complete removal of the screed as a sustainable measure

The tough black adhesive normally adheres very strongly to the screed substrate. Scraping it off is therefore time-consuming and associated with high dust generation. The requirements for protective measures are correspondingly high. If the adhesive remains on the screed for years, secondary contamination and a permanent odor nuisance can be assumed to be very real. The safest solution would be to completely remove the screed and rebuild the flooring. In the case of buildings that are decades old, the thermal insulation and the impact sound could be renewed in the same course as the screed installation.

Sealing surfaces with epoxy resin as a quick-and-dirty solution

Daily practice looks different. Hardly any floor layer suggests complete removal of the screed, but instead offers surface sealing with epoxy resin. Even with this method, there are better or worse versions. For example, the Ulm-based company Uzin offers a three-layer sealing adhesive system that is applied to the old parquet. It consists of two elastic polyurethane layers (2-K-PUR parquet adhesive) and a special laying fleece in between as a decoupling carpet pad. In conjunction with elastically sealed wall connection joints, the fleece prevents further escape of contaminated dust from the airtight enclosed substructure. The method requires intact old parquet permanently bonded to the subfloor and a sufficient build-up height for the new construction. If the parquet is too damaged, it is removed. The adhesive residues remaining on the screed are sealed by applying a chemical-resistant 2-component epoxy sealing primer.

Critical view of the surface sealing with epoxy resin

The material is made up of two components, with the base coat containing the epoxy resin. The hardener consists of polyamines, polyamides and poly-isocyanates. These components make the finished coating particularly resistant to solvents and chemicals, give it high elasticity and water resistance, and make it particularly acid-resistant. Caution is advised during processing. The vapors from the polyamine epoxy resins that have not yet set are harmful to health, and the polyamines themselves have a strong corrosive effect. Exposure to monomers (epichlorohydrin) is likely. Often not known, polymerized bisphenol A (BPA) is present in epoxy resin as an intermediate. In individual cases, unbound bisphenol A may be released into indoor air, or BPA may be released via aging and wear processes over the course of use. Bisphenol A is a substance of concern due to its reproductive toxic properties and hormonal effects in humans.
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