Is there a place for a dehumidifier in every building project?

[Adsibob]

A more accurate title for this post would be:

 

Is there a place for a dehumidifier in every building project that involves large quantities of water, used on site in the construction process, whether it be in cement, plaster, screed, adhesive, grout or other substances?

 

In this post, @LA3222 made the point that on a relatively recently built passive house that given the amount of water used to build a house, a dehumidifier should be used as a matter of course.

What is standard practice with this? We have a combination of old walls and newly built extension (bricks and (wet) mortar) and a new loft conversion (which was all timber and tile, so not really any water). But we also had about 86m2 of concrete slab poured and about 86m2 of a 70mm to 80mm screed poured. We then re-plastered the whole five bedroom house and are now tiling three bathrooms. So there must be a lot of moisture in the fabric of the building, albeit the slab was laid some 6 months ago and the screed was laid exactly 3 months ago. 

There is still some tiling and some plastering to go, but otherwise we are pretty done with water (albeit we haven't painted yet and that must contain a fair bit of water).

 

I think there are two schools of thought on whether to speed up the natural drying/curing processes:

• On the one hand, dehumidifiers will speed the drying process up which is good.
• On the other hand, if a chemical process is rushed, it can lead to unforeseen consequences. 

 

Thoughts?

 

[TonyT]

Buy a humidity meter first if all, to determine  the % in the house, then decide if dehumidifiers are

needed.

 

 

 

[CotswoldDoItUpper]

We had 3 rooms plastered mid-December, no heating in them at all and had windows open a crack since to help dry out but plaster still wet in places (mainly where the bonding was thick underneath). Thinking a dehumidifier might be the only solution - chemical process surely must have finished by now!!

 

I think allowing the generally respected time to allow a process to complete (7-10 days max for plaster) then giving it a helping hand so you can crack on decorating or similar should be ok. 
 

Happy to be corrected if I’m wrong! 

[ProDave]

We have one but never used it for the build.  Timber frame so not much wet trades other than plaster skim, done in the summer, lots of windows open to dry it out quickly.

 

We bought it when we had a previous 1930's house that was always damp, due to poor build methods of the time and no insulation.

[Adsibob]

10 minutes ago, ProDave said:

we had a previous 1930's house that was always damp, due to poor build methods of the time and no insulation.

Did you have my house per chance?

 

[Roundtuit]

7 minutes ago, ProDave said:

We have one but never used it for the build.  Timber frame so not much wet trades other than plaster skim

Same here, but skimmed in December.  Never used a dehumidifier, but called in at site every morning to crack a couple of windows upstairs, and left a couple of fans running downstairs to try and push air through the house.  Cant recall how long it took to dry, but it wasn't holding anything up.  We get a fair bit of solar gain though, so expect that helped.

[Adsibob]

20 minutes ago, TonyT said:

Buy a humidity meter first if all, to determine  the % in the house, then decide if dehumidifiers are

needed.

 

 

 

I'm sure its quite damp as the cardboard on a a box of tiles that had been on the floor for a couple of weeks was almost soggy when I picked it up the other day to return it. Lucky Topps Tiles are so good about returns. But curiosity as to the level of humidity and whether it is improving during this humid period has got the better of me so I will buy one or two. Probably quite usseful for monitoring living conditions once we move in.

Any recommendations for a humidity sensor. Amazon seem to have too many to choose from: https://www.amazon.co.uk/s?k=humidity+meter&sprefix=humidity%2Caps%2C72&ref=nb_sb_ss_ts-doa-p_1_8

[saveasteading]

41 minutes ago, Adsibob said:

there must be a lot of moisture in the fabric of the building

If the concrete was not adulterated with extra water, then there is very little surplus water left to evaporate, as most becomes chemically bonded.

 

I think plaster is much the same but would I have to check the chemistry.

 

So, yes the place is damp after the plasterers but the whole fabric of the building isn't (shouldn't be) as wet as it might seem. With lots of air flow there should suddenly be  a big improvement and you will wonder why you were worried.

[Jilly]

I'm finding it really damp here in the east. The humidity as been >90% nearly all the time so I've used a small household dehumidifier after plastering and screeding. Seems to be ok. I found opening the windows was insufficient as the humidity is so high outside. 

[Brickie]

23 minutes ago, Jilly said:

so I've used a small household dehumidifier after plastering

@nod look away now ?

[LA3222]

My experience - albeit from a single build is that the house was out of control with excess humidity. My build.is 280m2, 2.5m Ceiling downstairs, 2.7m upstairs so there was a hell.of a lot of plastering going on. God alone knows how many of them massive tubs got filled with litres and litres of water everytime a room got skimmed. There was a hell of a lot of water went in. I also did a pug screed upstairs for the UFH, more water. Then whatever moisture is knocking around in the timber that goes in etc, it will all add up. 

 

When the humidity were 70% and below I weren't too fussed, it started climbing and was sat at 90%plus day on day over Xmas 2021 so the only way I could gwt it under control was to get a dehumidifier. Two times during the build I had dehumidifiers, once when the pug screed went down and then after plasterer had been long gone. First was a couple of weeks, second was three weeks. I was emptying it twice a day for the duration, can't recall how much it held but I bet I got rid of the best part of 1500l of water.

 

Absolutely no issues now but last Xmas the windows were drenched to the point I had to go around with tea towels morning and evening to dry them as much as I could.

 

The air test for my house was 0.24m3/m2/hr so it doesn't breathe on its own at all. The MVHR is the vent axia plus, fine for day to day but to purge all that excess moisture - no chance and I weren't leaving windows open in December. 

 

Using a good sized dehumidifier worked a treat and I would reccomend doing so to others. Why waste forever and a day trying to purge a little bit at a time, get the big boy in and get it done then you can move onto the next issue.

[Radian]

2 hours ago, Adsibob said:

Any recommendations for a humidity sensor

 

I recently bought a 3-pack of these <£5 each. They took a couple of weeks to arrive from China though.

 

Of course I don't know how 'hacky' you like to get but if you're into coding then the great thing about these is that there's an alternative firmware you can apply that exposes their readings as BLE beacons that can be picked up by HA software or ESP32 Bluetooth etc. I use this to log values from 10 of these to a database via node-red.

 

May not be your thing but I know some people here might be interested.

[Adsibob]

The irony is that all my Tado thermostats (of which I have 10) have a hygrometer built into them. We're just not quite ready to install them, as was going to wait until after painting. I guess I could install a couple temporarily. The beauty of that is that once I have internet in (in about 3 weeks) I'll be able to monitor humidity and temperature remotely.

[Radian]

10 Tado's is going  to give you loads of info ? I  waste spend ages going over my daily logs from the little Chinese thermo/hygros. One of the more useful plots I have produced is the continuous display of dew-point which is a handy heads-up for potential condensation issues:

 

 

First sunny day in a while and it got quite toasty mid morning. No particular condensation risk throughout day or night. But I keep an eye on things in this room as it has three totally glass walls made from sliding patio doors in aluminium frames. They have thermal breaks but the very bottom edges have developed condensation when below zero outside, except for when we have the UFH on. With the dewpoint plot I know when to put it on - next step is to automate this with node-red so I don't have to do a thing.

[Ferdinand]

On 11/01/2022 at 18:42, Adsibob said:

I'm sure its quite damp as the cardboard on a a box of tiles that had been on the floor for a couple of weeks was almost soggy when I picked it up the other day to return it. Lucky Topps Tiles are so good about returns. But curiosity as to the level of humidity and whether it is improving during this humid period has got the better of me so I will buy one or two. Probably quite usseful for monitoring living conditions once we move in.

Any recommendations for a humidity sensor. Amazon seem to have too many to choose from: https://www.amazon.co.uk/s?k=humidity+meter&sprefix=humidity%2Caps%2C72&ref=nb_sb_ss_ts-doa-p_1_8

 

Go for one with a large number of very positive reviews, and as few -ve ones as possible.

 

I have had three or four of these - the only problem I have had is when they get knocked off somewhere and fail to bounce.

 

Alternatively a Black Friday household size dehumidifier may come with a built in humidity meter.

[Ferdinand]

On 11/01/2022 at 18:15, Adsibob said:

A more accurate title for this post would be:

 

Is there a place for a dehumidifier in every building project that involves large quantities of water, used on site in the construction process, whether it be in cement, plaster, screed, adhesive, grout or other substances?

 

In this post, @LA3222 made the point that on a relatively recently built passive house that given the amount of water used to build a house, a dehumidifier should be used as a matter of course.

What is standard practice with this? We have a combination of old walls and newly built extension (bricks and (wet) mortar) and a new loft conversion (which was all timber and tile, so not really any water). But we also had about 86m2 of concrete slab poured and about 86m2 of a 70mm to 80mm screed poured. We then re-plastered the whole five bedroom house and are now tiling three bathrooms. So there must be a lot of moisture in the fabric of the building, albeit the slab was laid some 6 months ago and the screed was laid exactly 3 months ago. 

There is still some tiling and some plastering to go, but otherwise we are pretty done with water (albeit we haven't painted yet and that must contain a fair bit of water).

 

I think there are two schools of thought on whether to speed up the natural drying/curing processes:

• On the one hand, dehumidifiers will speed the drying process up which is good.
• On the other hand, if a chemical process is rushed, it can lead to unforeseen consequences. 

 

Thoughts?

 

 

(Ooops old thread - never mind.)

 

I would say absolutely yes.

 

They can get expensive because you will need a low end commercial one. But like a digger I think that if you sell it on you should do OK after the project.

 

A few years ago I obtained a couple of commercial dehumidifiers from a commercial setup closing on retirement of the owner and saved myself about £1500 over new prices. One is a 40l/day, and one is 60l/day by rating, and in a house I had had skimmed the small one was pulling out a soft bucket of water every day for two or three days, with a fan heater running to raise it to 25C or so. No cracks. Saved my bacon when it was tight between the plasterer and the electrician.

 

(I have them also for rented properties as an insurance in case of disaster having once had to hire one, plus a 10l domestic one with a humidistat and internal tank).

 

As a place to start I would suggest the Broughton CR40, which is my smaller one above, and is compact. 

 

Around £550 new, or can be bought from Ebay most of the time. Size is knee high. 

 

 

The CR40 is comfortable to carry, but a small person might find it awkward - 23kg. Brochure attached for info.

 

Ebac are also a reliable supplier. Don't go mad with a really big one as they get very heavy very quickly, and you may need help getting it in your car if it is 40-60kg. Get one smaller one, then another one if it works.

 

Ferdinand

 

 

industrial_dehumidifier.pdf

[saveasteading]

Absolutely not. Air flow through the building shifts more moisture than a typical machine.

I have seen people getting them in when there is static water and what is needed is brooms and buckets.