Builder wants to use liquid DPM....


Thanks again for your input.

I think it suits the builder to wrap the job up asap so as to employ resources elsewhere - I really do think its as simple as that!

I am happy with them returning in a couple of months to lay the tiles/wood.

Of course, I need to be happy with his actions, and hence my posting. I think the best course of action is to identify which dpm he wants to use and then check with the manufacturer.
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In the past I have carried out the task you/your builder is looking to do.

A conservatory floor had been down for a little over two weeks and I applied a coat of acrylic screed, two coats of dpm and a final coat of water based screed.

This was using products from F.Ball but I rang their technical dept. and discussed in detail what the situation was. The final covering was Karndean which is more susceptible to failure in these circumstances than either wood floor or tiles. I did it only because the customer was impatient and would certainly NOT recommend it as a normal course of action.

It may be convenient for the builder but you are the customer after all!!
Thanks flooringman,

Did the flooring cause any trouble later?

Unless the manufacturer positively confirms their product will work in my specific circumstances, I will be instructing my builder to leave the screed to dry for 8-9 weeks.

There is probably 4 weeks of other work to occupy him in any case, so it may be a case of being offsite for only 4 weeks or so before returning to finish.
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Thanks FlooringMan,

Out of interest, why do you say you would not recommend doing this as a normal course of action, if the product is intended for use in these scenarios?
Because it's a solution to a problem and with a little patience there wouldn't actually be a problem.

I think it's really intended for a sub floor that has inherent damp but can be used in your circumstances.

If you do use it make sure the builder does so within its limitations.
Just spoke to FBall technical, and they say 'no problem'.

Apparantly the DPM is designed to release the moisture at a slow controlled rate (over many months at least), and so at any time there should not be significant moisture in the floor covering (e.g. wood) to cause any problems.

He also said you want to retain some moisture in the screed as otherwise it will turn to dust!

I asked why everyone does not use this product (as spending a few hundred pounds to speed up the work should be worth it in most scenarios) - response was that it actually is quite widely used (maybe more in commercial settings than residential).
Apparantly the DPM is designed to release the moisture at a slow controlled rate (over many months at least), and so at any time there should not be significant moisture in the floor covering (e.g. wood) to cause any problems.
As long as the "moisture" released does not exceed 2 - 2.5% moist then wood would not have problems. Still doubt - no offence - if this will be the case.
only skimmed over the post but your builder knows what he is talking about. I think the first i have heard of!

Epoxy dpm can be used upto 98% rh in a two coat system. british standard is 75% rh max before you can install a floorcovering. . However for wood flooring it needs to be lower than this.

When you apply epoxy to a wet screed (98% and below) the concrete/screed will still dry but at a very ruduced rate. Maybe even years!

However, the slower the concrete dries the stronger it will become. Force drying concrete with air/dehumidifiers etc will make it weak! Infact, new concrete should be covered up with plastic for a few weeks to trap the moister in it (like the epoxy dpm does)

Also all wooden floors fitted on concrete/screed should have a dpm (epoxy) applied to the surface before there installed. Unless your floating and then you could use a vapiour barrier instead ONLY if the subfloor has a moister content below 75% rh.

You may be confused now as i read woody's post saying below 4% etc. Woody uses a meter to read moister that reads on a diiferent scale to the British Standards 75%rh (Relative Humidity) There is nothing wrong with the meter woody uses, it just reads on a different scale. (like temperature - C & F )
1. Theres is a liquid DPM by F-ball (F 75, which is compliant with Brtish Standards 8203) that allows the installation of the membrane after 7 days on a new concrete sub-floor. It should cover the whole floor and up to the DPC.
The moisture you are all talking about!! some will enter into the wall cavity and disperse, the remainder does actually release through the memrane at a very slow rate, so slow it won't cause any problems.

Still, the membrane will allow for fast track floor installations with an RH of up to 98% (just short of saturated) which is about the moisture content after 7 days drying, subject to conditions !!

Your builder sounds like he has fairly good knowledge of what he is doing.

Go ahead !!

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