How to install a surface DPM ! (liquid dpm)

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30 Jan 2007
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West Midlands
United Kingdom
First of all you dont need to install a surface dpm if your floor reads less than 75% relative humidity on a hygrometer flooring meter. You may choose to buy one to try and miss the costs of installing dpm when its not needed after all. If not on with the info.

1- Subfloor should be cleaned and as dry as possible.

2- Prime floor with neat p131 on non absorbent floors and water down on absorbent sand cement etc (approx 1-3 mix)

3- Next self level the floor with an acrylic levelling compound.

4- When dry (24hrs+) you can give first coat of dpm (F75)

5- Second coat of dpm (f75) when first is dry. I like to put this down when the first coat has a very slight tacky surface on it but not wet of course. Depending on temp about 12 hours or so later but within 24hrs.

6- Leave second coat for a full 24hrs to cure and then prime again with neat p131 primer.

7- Self level the floor now with leveling compound of your choice. I would use a water based product (red bag) or acrylic levelling compound

You will need-
Primer - P 131 neoprene primer
Dpm - F75 ( you need 2 coats and cant part mix tubs)
Levelling compound - acrylic for base and your choice for top finish

These are basic instructions to give you an idea of what you have to do. Full instructions will be on the products and available to you where you purchase your products. You can leave a post for me if you want any more info.
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Thanks for this sticky but a quick question please.
I'm slightly puzzled by the need for two coats of self-levelling suggested. What is the purpose of steps 6 and 7; is it just belt and braces?

I've got an old concrete floor (kitchen in rear extension) beneath small lino tiles that have started to lift in places and a pretty high damp/moisture reading. Plus the floor is slightly uneven. I don't want to spend too much time but want an improved floor finish. I was thinking that steps 1-5 would be plenty with new vinyll finsh on top?
The first coat of smoothing compound is to cover up contaminates etc and to also reduce the amount of dpm you use. Some floors really suck it in and you end up using lets say ' 10 tubs instead of 2' It will work out cheaper in the long run.
As for the second lot of smoothing compound, well this is needed. You cant just lay new flooring on top of the dpm. If you want to miss one out, then miss the first one out. But not advised!
thanks for the reply
I know your advise is good and I'm being a stupid amateur but why can't I just lay some vinyll roll (or even backed carpet) on the dpm after step 5?
I'm not clear what the extra prime and leveller coats will do other than make it extra level?
I do understand about the first leveller coat containing contaminates and preventing too much soaking up of DPM.
Surely the floor finish (roll or carpet) won't damage the DPM?
Thanks for your patience.
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1- The surface of the dpm will not be protected from damage. If you damage the surface you have just wasted your time putting the stuff down

2- The surface will not be smooth enough to lay vinyl.

3- If laying lino/wood/ carpet etc you will not be able to glue to the dpm. It dries like glass so nothing on the market will stick to it!
Hi Mattysupra.......i may have come in part way thru a thread but...............would this method be appropriate for damproofing an old quarry tile floor where the tiles are not worth saving but are stable and level. They were probably laid before King Harold ruled the roost and laid on , probably ash,.
If this system works what manufacturer does the spec refer too.??

Would it then be ok to lay a 2/3" screed on top of the liquid DPM??
it is not recommended to use over quarry but you can do it if you use a acrylic based smoothing compound first. But remember there is no guarantee

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