Thursday 25 February 2016

Mould – The Black Scourge (And how to eradicate it)

As most of those that frequent this blog or my build website know, I am already 2 years into the process of building a house for myself and my wife, by myself, and still have a LONG way yet to go.
With the famous proverb "You can have it Fast, Cheap, and Good - Pick Any Two", I have elected to build cheap and good (actually very good), and therefore, I am far from fast.  Further delays with broken shoulders and bulged discs in lower back, and progress at times has literally been brought to a crawl!  This resulted in a partial structure being exposed to the winter elements because I was unable to proceed fast enough to allow framing and roof completion during summer of 2015.

Now, I have taken great pains to keep this partial structure dry during construction, first with a large overhead tarp (Big Ass Tarp - B.A.T.), and then with smaller tarps closer to the floor deck when the B.A.T. was shredded in a wind storm in Dec 2014.  And generally I have been successful in keeping bulk rain water off the structure.  So imagine my horror last December when I finally installed some construction lighting in the now very dark basement, only to turn the lights on and find I had mould and staining fungi all over my engineered beams.  Quite frankly, I was devastated.  It also did not help that I am allergic to the stuff and started getting chest issues from working in the basement.

Left - Big Ass Tarp (B.A.T.) measured 60' wide x 80' Long    Right - Current Configuration of Smaller Tarps have kept all bulk water off structure.

So what went wrong?  If it did not get wet from rain, why was there an issue?

Well, in all of my careful attention to what was falling from above, I did not focus ANY attention to what was rising from below.

You see, I basically have built my house above a temporary swimming pool. Granted a very shallow swimming pool, but a pool just the same.  The whole structure is built over a crushed gravel base.  Even the footings have a minimum of 6"-8" of consolidated 3/4" crushed rock beneath.  This will provide the drainage plane under the yet to be poured floor slab, and there lies the problem.  There is no concrete floor slab or sub slab poly keeping the moisture within the gravel drainage at bay.  There is a HUGE surface area (approx 1750 sq. ft.) of water that may only be 1/4" deep at times, but that is still a lot of moisture that can evaporate off and create a very high humidity environment in the basement.  Add to this all of the construction moisture present in the still curing foundation walls, the recently poured suspended garage slab, and from the storage of various salvaged wood I used for scaffolding (and therefore exposed to rain and saturated) that was stored in the basement (ironically to dry out).  When I started measuring the humidity after discovering the problem, I was in the very high 80's for RH% and clearly had been so for several months.

Now, realize at the time, that the basement was still very wide open from a ventilation stand point.  There was a 4'x8' door opening in the side of the foundation to service the basement exterior walk up stairs, and there is the stair opening in the floor assembly that will service the interior stairs to the basement.  So air movement was not an issue, but the humidity was still too high.  Add to this the crazy dew-points we have in North Vancouver, and the opportunity for condensation to form on the structure was high.
As an example, photo at right shows ice forming on UNDER side of tarp due to tarp surface cooling below dew-point of ambient exterior air due to night sky radiation.  This was a fully ventilated area.  As you can see in the background, there is no walls.

Do you still believe ventilation is the answer for attic mould???

The next factor is that any engineered wood (like my PSL beams) is more susceptible to wetting.  The glues in these beams readily absorb moisture, as does the heart wood often utilized in the manufacture of engineered wood.  The result was that my beams had reached a fibre saturation moisture content (roughly 32% WM), which is the point needed to inoculate wood for fungi growth. After inoculation, the moisture content only needs to be above 19% for the fungi to continue growing.

So, in the end, it was the humidity from below that bit me, not the moisture falling from the sky above.  So now what?  What are the possible steps to remediate?

Well, I can tell you that in a lot of construction, it would just be covered over with drywall and ignored.  And by rights the structure should be below 19% WM before covering up with drywall so technically the mould would be dormant by then.  But what happens if the humidity in the home is too high for extended periods of time (say there is a bathroom with a shower nearby, or the owner likes indoor plants).  A relative indoor humidity above 70%, for an extended period of time, could lead to the wood wetting up past 19% again.  With my allergies, leaving it was not a good idea, so I set out to remediate it.

I talked with some individuals in the building envelope industry including a group doing an attic mould remediation study.  I also had studied this subject intensively in the past, because as a previously practicing home inspector, I always struggled with the right information and advise to provide clients, when the inspected home had a mouldy attic.  I knew that you had two tasks: First remove the evidence of the fungi contamination, then kill or render dormant the actual fungi spore.  If you only killed off the spore, you would still be left with the staining which would present as a defect to the consumer, but more importantly would not allow you to identify if any new fungi growth occurred in the future, as it would be too hard to spot new staining overtop of the old staining.

The group doing the study recommended a cleaning protocol utilizing one of the following three options:

1) Scrub surface with soap and water
2) Scrub Surface with a mild bleach solution
3) Spray Surface with Concrobium Mold Control (Commercial product - not the stuff you buy in Big Box Stores)

This cleaning protocol was to 'reset' the appearance of the infected product before treating and preventing future fungi growth.

Well, I can report that all three strategies were woefully inadequate on the rough and porous surface of an engineered beam.  1 & 2 may work on a surface like painted drywall or even a real wood surface like a 2x4, but on the engineered wood they were generally ineffective. Photo at left shows a beam after being treated with both the soap & water solution and then a bleach solution.  While the cleaning removed some staining intensity, it is still clearly visible.

I then tried option 3 and sprayed the surface of all beams with the Concrobium Mold Control, which is supposed to have some stain removing capabilities.  In my tests, it was even less effective as the soap and water or bleach solutions at removing the staining.

Photo at right represents the results 48 hours after treatment.  Unfortunately, I did not have a clear 'before' photo but this beam started with substantially less staining than say the beam in the above photos. The staining present after treatment was very similar to the start point prior to treatment.

With all three cleaning protocols a bust, I regrouped and brought out the big gun.  Concrobium also make a product called Mold Stain Remover.  This is a mixture of Sodium carbonate peroxyhydrate (basically granular hydrogen peroxide - used for instance in non bleach cleaners like OxiClean) and Propylene Glycol Diacetate (a solvent, presumably to help allow the cleaner to penetrate past the surface of the material to be cleaned).  Together they pack a punch but generally break down into biodegradable by-products and personal protective gear required for application is minimal.  Rubber gloves are a good idea as it can irritate skin and some form of eye protection is recommended as it does burn if you get any in your eyes.  It also gives off a strong acid like odor when mixed, but this dissipates in less than 24 hours after spraying.

I have now sprayed the product twice in different areas of the basement.  The first time I mixed it with the hottest water out of the tap at our rental suite and all of the crystals generally dissolved.  The second time I specifically measured the temp and brought the starting point down to 100F (max recommended).  But by the time I sprayed, it had cooled to 70F and I found a lot of the crystals on the second application had not dissolved and were still in bottom of mix bucket. So I would be inclined to start with water slightly above 100F, so that after mixing and by the time you load the sprayer you are within the required 80-100F application range.  Also while writing this entry, I re-reviewed the application instructions and now realize you are supposed to add the crystals (part 1) to the warm water FIRST and stir to dissolve BEFORE adding part 2.  I added both together and then stirred on the second application (do not remember what I did on the first), this may have effected the ability for the crystals to fully dissolve in the mixture.  Regardless, the results were extremely impressive!

Photos on left are before treatment with the Mould Stain Remover but remember after treatment with the Mold Control product.  The right photos are after 1 treatment of the Mould Stain Remover. As you can see, the stains are gone on a majority of the surfaces, but there was still locations where the staining was present like the following images.

 What I suspect happened at these locations is that they did not get wet enough for long enough when sprayed.  The instructions state that the surface is to stay saturated for 60 mins.  SO I mixed up a second batch a few weeks later and have now all but eradicated the stains As is shown in the following photos.

Photos at left prior to treatment with the Mould Stain Remover but after previous treatment with Mold Control.  This elimination of the mould staining generally happened in the first 60 minutes after spraying.

But the best example is this spare beam I have sitting on my garage floor.  Photo on left was after using 3% H2O2 which although dimmed stains did not remove them.  Photo on right shows the complete removal of stains with the Concrobium Mould Stain Remover.

So there you have it.  A easy, fast, and relatively affordable method to remove mould stains from engineered wood.  I will now spray all the beams with the Mold Control product to kill or make inert any remaining mould spores and prevent future growth.  I will leave the test beam above untreated so that I can determine how quickly the mould would come back if left untreated.  I have to say, it was a HUGE physiological pick-me-up to walk into the basement after the second treatment and not be able to see any stains remaining.  Now I can count on a healthy basement with no future issues.


Unknown said...

Hi - I am just starting to read your blog, and it is exactly what I am looking for. We are currently building a home in Seattle, and are just about to begin on the foundation, with framing to follow in a month. I'm concerned about mold since we are unfortunately doing this during the rainy season. Do you have any suggestions on what you would do if you could do it over again? My biggest worry is that we will start closing up wet framing members and mold will slowly grow in our walls over time, creating an unhealthy living environment.

Thank you for your time!


SENWiEco Designs said...

Hi Mike,

Thanks so much for stopping by and leaving a comment.

You have asked a great question and the answer really depends on the time line. Are you building this by yourself or with a crew? The fact that you will be framing in a month tells me you probably have at least a small crew and will be able to proceed at a reasonable pace.

Based on time of year and your location I would do everything possible to keep any engineered wood dry. This would include engineered beams, lintels, floor trusses, plywood, roof trusses. If you cannot tarp the site, I would recommend draping all of the engineered components with poly as the framing progresses.

The tricky item will be the plywood floors. This really requires a large tarp with a 'structure' to drape it over and shed water. Yes this was a lot of work to upkeep, but worth it from my point of view to maintain quality of the plywood. If you plan to install a concrete slab above the plywood (say for a hydronic heating system), then you can relax this requirement a lot and just make sure you regularly sweep any accumulated water off the deck and get the roof on ASAP.

You do not have to worry about the 'real' wood. It can get wet and then will dry out. It just means that when building during the wet season you need to wait until the structure thoroughly dries before insulating and closing in. Make sure you use a moisture sensor and test a large number of studs, bottom, and top plates as well as all engineered beams and lintels. I would run fans and dehumidifiers (as well as heat if still in winter) for a week before trying to close in.

You do have an increased risk for fungi growth once wood reaches the fibre saturation stage (~ 32% WM), but in our climate, it is pretty close to impossible to prevent this even if the wood never receives bulk water, because of the humidity in our region. SO for a healthy home going forward, you just need to make sure you keep the humidity levels in the finished home at reasonable levels by ensuring a well sealed air barrier and continuous mechanical ventilation (HRV).

Concentrate on getting the roof on ASAP, by skipping any internal wall framing that is not bearing for above floor or roof. The next thing to concentrate on is getting your basement slab in as early as possible in the build to prevent evaporation from the water in teh granular layer below.

Aim to keep the framing duration down to 5-7 weeks including roof. Houses in my neighbourhood who have been able to do this have been ok and not shown any signs of fungi growth even when they have gotten saturated.

If like me, you are a solo builder or have a small crew and will take several months to frame, you really need to figure out a way to tarp the site or put off framing until it is drier. It is not just the risk of mould, a saturated engineered wood component looses a lot of strength if it becomes saturated. For instance an excessively wet floor truss will often fail once a load is applied.

Unknown said...

Thank you very much for your reply and recommendations.

We are working with a builder who has a subcontractor for framing. I will ask how long the duration of the framing will be, and also bring up some of these points with them. They plan to close up the house as quickly as possible, and then run fans and humidifiers to dry everything out. It will be a tight home and likely will have HRV.

We aren't doing concrete slabs above the plywood floors, so that particular area could be very important to keep dry. I believe my architect specified marine-grade plywood, and I will try to ensure the builder uses this. Do you think that marine-grade plywood will hold up better?

Thanks again!


Unknown said...

Actually, looking at the plans, it appears that the exterior sheathing is marine-grade, but the floors are more usual grade plywood..I'll have to try to keep these dry.

SENWiEco Designs said...

Hi Mike,

A few follow up comments.

Make sure the builder uses all plywood sheathing (walls and floors) and no OSB. Plywood is much better at dealing with moisture both short term and long term. It is also more permeable both when dry and more importantly when wet, which is needed for our walls in the Pacific North West.

I would just use standard exterior grade plywood for the walls not marine grade plywood. You will save a lot of money and the walls in general are less susceptible to getting soaked. Use some of the money saved and buy a couple of 10' tall rolls of Tyvek. Wrap the exterior walls with Tyvek as each floor is constructed to keep them dry. Do this even if you have plans for another sheathing membrane as your finished barrier. PS - if choosing between Tyvek and Typar, always choose Tyvek. It is a LOT more permeable compared to Typar.

For floors, you really need to come up with a method to keep them dry. This time of year in our region, they will get too saturated if not protected. This is not a problem for mould (as long as for only a few weeks), but is a problem for warping and delaminating, which can screw up your finished flooring if not putting down a hydronic thin slab on top. Yes marine ply wood possible help, but at a huge cost. So would just concentrate on developing a way of tarping the floors as you go.

If I did not have the opportunity for an overhead tarp and was doing this again, I would just drape tarps over the walls built at any given stage on the floor being framed. This would mean the tarp(s) settle/pool in the interior of the home. At these points install drains (like connected to temporary 'bag' downspouts and route to some form of drain including just holes in the floor that allow the water to drop down to a basement gravel layer below. This will allow fast installation and removal of the tarp(s) as construction progresses (just a staple gun to framed walls).