ᐅ Replacing Hardwood Flooring Over Asphalt-Based Screed: Is Sealing Necessary?

Hello everyone,
we have a house from 1962 with mastic asphalt. Unfortunately, the parquet flooring has been so severely damaged by water that it needs to be replaced.
To our surprise, the flooring installer told us that extensive work is necessary to first seal the floor. The total cost for preparation and installation is now 100€ per square meter.

- Removing remaining adhesive by milling
- Priming the subfloor with epoxy resin
- Applying and vacuuming off quartz sand
- Filling the subfloor up to about 5 mm (0.2 inches) thickness
- Priming with multi-purpose primer
- Parquet adhesive

Reasoning: Toxic substances could be released from the mastic asphalt or old adhesive. Also, looking at the old parquet, the adhesive had completely lost its grip (it really doesn’t stick at all anymore).

My question to you experts: Is this effort really necessary and justified? Who has experience with parquet over mastic asphalt? The alternative would be to renew the screed. We are talking about a total of 70 square meters.

Hello questioner.
It seems either someone did not understand the core issue of this type of floor renovation, or, which I suspect more, someone wants to build their business on the basis of FEAR and ignorance.
Regarding the individual points:
> Removing the remaining adhesive by milling <
This is necessary!
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> Priming the subfloor with epoxy resin and broadcasting and vacuuming quartz sand <
This is necessary!
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> Filling the subfloor up to about 5 mm (0.2 inches) <
This thickness will cause the asphalt screed to crack into a thousand pieces. After sanding and priming, no filling is needed if the correct (water-free) parquet adhesive is used!
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> Priming with multi-primer
Parquet adhesive <
It is unclear why an additional primer should be applied here.
Once the parquet is installed and sanded, you should have it treated with an oil/wax mixture.
You will never achieve a more beautiful floor through a sealing!
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Good luck: KlaRa

KlaRa schrieb:

>Level the subfloor to about 5 mm (0.2 inches)<
This thickness will cause the poured asphalt to crack into 1,000 pieces. After sanding, if the correct (water-free) parquet adhesive is used, there is no need to level the floor any further before priming!

Thank you very much for this expert answer! What are the consequences of it cracking into 1,000 pieces? Will this damage the parquet flooring? Did I understand correctly that you can also glue the parquet directly onto the quartz sand? Many thanks!

holz_parkett schrieb:

What are the consequences of it breaking into 1000 pieces? Will this damage the parquet flooring? Did I understand correctly that the package can also be glued directly onto the quartz sand?

As a tip, such work should only be carried out by companies that can guarantee and maintain the warranty for you.
Once the poured asphalt screed has been ground, it is no longer suitable for bonding anything. The surface becomes too smooth to achieve a strong adhesive bond with the subsequent layers.
For this reason, it is absolutely necessary to prime with a reactive resin and broadcast sand onto it.
The excess sand is removed after the resin has cured (sweeping and vacuuming).
By embedding the quartz sand firmly into the resin, the parquet adhesive (for example, a PU adhesive) can grip onto the surface of the poured asphalt. This is how it works.
However, poured asphalts are sensitive to tensile stresses. These stresses become significant if a cement-based leveling compound, a (thicker) synthetic resin coating such as epoxy resin, or similar is applied.
After 2 to 3 days, this type of screed breaks apart into hundreds of thousands of hand-sized fragments. It’s a pity I no longer have pictures from 2002 to show you what a builder can expect.
At that point, the poured asphalt screed can only be completely removed.
An experienced (and trained) flooring and parquet installer knows this. A maintenance service that might also do such installation jobs as a side task definitely does not.
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Warning: This can result in a total loss of the screed!!