another 1 asking for advice

[shakie1973]

Hi guys,

I have just had a new conservatory bulit. It has a dwarf wall, 3.5 square. I am really pleased with the finish but just noticed a day or so ago an area about 200mm by20mm on the reveal leading upto the french doors. It is a kindo of white powdery residue coming through the paintwork. I dont think it can be damp as the guy had good founds down and it had a good DP membrain. Once it was boarded, dot and dabbed and skimmed i let it dry naturally for about a week before applying a good coat of PVA (5-1) as it said on the container. I then gave it a further couple of days before applying 2 coats of good quality scrubable emulsion.
Any ideas please??

cheers

 

[Alastairreid]

hygroscopic salts.

http://www.buildingpreservation.com/Moisture and salts.htm

 

[Richard C]

before applying a good coat of PVA (5-1) as it said on the container.

Which container? You should never, ever PVA new plaster before painting .

I then gave it a further couple of days before applying 2 coats of good quality scrubable emulsion.

Scrubable emulsion; please say that you didn’t put vinyl emulsion straight onto new plaster, over PVA

 

[shakie1973]

No t
he emulsion isn't vinal. The pva was recommended at shop by the assistant for sealing new plaster prior to. Painting. I am just wondering if it could have came through since the builder applied some screed to the door cavity which it is next to, as he only done that about 10 days ago, and this patch has only appeared in the last day or two. I have left this to dry before putting the floor down, and its almost dry now. If it is due to the adding of the screed will this be ok once dry and touched up?

Cheers

 

[Richard C]

The pva was recommended at shop by the assistant for sealing new plaster prior to. Painting.

The assistant is a dick & you should tell him so; that’s the worst piece of advice they could have given you.

Any new building works will take at least a month to dry out, even longer this time of year & with the weather we’ve been having, it’s going to take an age, possibly until spring!

The newly laid screed may well be the cause of local damp but I would have advised leaving the plaster a lot longer before doing any painting. It may look dry the next day (light pink or grey) but the residual moisture content will still be quiet high. Paint it too early using the wrong materials & you will trap the moisture, you can then get the white powder you current see &/or micro blistering in the paint itself as the residual moisture tries to escape. It should eventually stop but will have slowed the drying out process down considerably & you may have remedial works to paint decoration; the use of PVA also means it probably won’t be stuck to the plaster very well.

For priming new plaster, use either a proprietary plaster primer or all I use is ordinary cheap white matt emulsion, thinned 25-30%; apply 2-3 coats in quick succession then laeve to dry min 24 hours before finally decorating but not before the plaster has fully dried out.

What type of floor are you having laid; don't lay anything until it's fully dried out or you will be having more problems.

 

[wozza56]

Richard c i couldn't agree more and you saved my fingers from all that typing

 

[shakie1973]

Thanks for the reply guys.

The brickwork went up around the end November . The builder then put the concrete in for the floor. It stood for about 2 weeks until the window fitter could get the framework up and glass in Soon as that was in i got the rad fitted as i thought this would help the drying. So really it was drying out from the beggining/middle of December. I then had electrics ran in and dot and dabbed. Once it was skimmed it dried for a good week or so more, prior to putting a heavily diluted coat of the pva on( a few days after Christmas, painted new years eve.....i think, and it has been fine.Then like i said the builder came back about 2 weeks ago and put the screed down, and this was visibly wet for a while, you could even see there was water forming ontop of it. Its now almost dry and its now the patch has appeared, so like i say i think its that which has lead to the white patch appear. If i let the screed fully dry for maybe another week then scrap or lightly sand the patch, then re-paint will it then be ok?
im putting down a decent laminate floor. I have the damp proof membrane and the decent underboards I still havent fitted the floor yet but baring in mind the concrete has been down now since the beginning of Dec, its only the screed section (which is about 1m x100mm) which has only been down a couple of weeks...........im no expert but it seems too much of a coincidence that this has only appeared since the screed was added in the immediate area.

thanks again

 

[Richard C]

If i let the screed fully dry for maybe another week then scrap or lightly sand the patch, then re-paint will it then be ok?

Maybe, who knows!

You picked the worse time of year & probably the worst year of many to build a cons/extension. Everything you have there is still saturated with water; do not do anything more until it’s had a chance to dry out which will take several more weeks this time of year. Don’t put a damp proof membrane on the floor, you will trap moisture that's in the screed above the DPM & don’t lay your laminate floor or it will probably start to smell & be totally ruined. Your rushing things far too much & repeating the same mistake you made on the walls. It’s understandable you want to get into your new cons but this really isn’t cons weather & before you do any more work, LET IT DRY OUT.

An unscientific but fairly good test is to lay sheets of dry newspaper on the floor before you go to bed & check them the next morning; you will know if you still have damp!

 

[mac391]

If the damp patch is local to just one area it's possible that the dot n dab finish has bridged the dampcourse. The dampcourse is only a few mm above floor level, so if you remove the skirting below the damp area and see the plasterboard toching the concrete/screed floor then thats prolly your answer.
One problem, is that your screed should not have been layed on top of new concrete, the moisture released from the concrete will stop the screed from sticking unless a liquid DPM was applied first.
You should delay any new flooring until march /april at least and check that the screed is solid and attached.

Rule of thumb!! new concrete dries out at a rate of 1 inch per month so 4 inches = 4 months,, ask your builder how deep the concret slab is so you can estimate. Remember, it's rule of thumb, in summertime drying will be slightly quicker, and winter time, slightly longer...

Even then, if you're laying a laminate, regardless of the quality you will still need a DPM, you can buy this as a foil backed underlay or use visqueen and insulation boards.

Hi guys,

I have just had a new conservatory bulit. It has a dwarf wall, 3.5 square. I am really pleased with the finish but just noticed a day or so ago an area about 200mm by20mm on the reveal leading upto the french doors. It is a kindo of white powdery residue coming through the paintwork. I dont think it can be damp as the guy had good founds down and it had a good DP membrain. Once it was boarded, dot and dabbed and skimmed i let it dry naturally for about a week before applying a good coat of PVA (5-1) as it said on the container. I then gave it a further couple of days before applying 2 coats of good quality scrubable emulsion.
Any ideas please??

cheers