Stop The Mould Before It Starts

Everyone wants their bathroom to look like the bathrooms in these magazines.  They are fresh, sophisticated and NEW.  Do-It-Yourself renovations are becoming increasingly popular, especially for bathrooms.  People think it’s a relatively small space and can’t be too complicated and mostly cosmetic.  Nothing could be further from the truth. The smaller the space gets, the more important good design and proper planning and details become. It is very important to remember any job is only as good as its foundation.  Speaking from years of experience in remediating mouldy situations, proper building materials behind the cosmetic touches are key to beautiful, long lasting renovations.

Bathrooms by nature can be a mould spore heaven.  The tasks we do in there create moisture all the time.  The faster this moisture is removed the better.  Using materials that are waterproof or moisture resistant is key.   All the items below go hand in hand to create an environment that will not allow mould and mildew to flourish.

Drywall – regular vs. green board vs. cement board

Paper faced gypsum board and even treated ‘green’ board is known for regularly failing when exposed to water. Paint and caulking will not permanently keep out the water and when it does these materials fail. Manufacturers make several waterproof gypsum boards now. Use this everywhere except where you will have water splashing (i.e. tub surrounds and shower enclosures).  For this, cement board is best.

Regardless of what is covering the surface it is key to ensure the base materials are going to keep the water from reaching the framing and subfloor system.


When using paint in a moist space it is important to use a product that is made to handle it and always allow it to cure completely before steaming things up. There are specialty paints available to resist mildew and mould. A good primer/ sealer is the key to a good paint job.  Make sure to seal all cuts and all sides of trim used in a bathroom, especially if using MDF and not solid wood.


For tile applications , the first thing to understand is that water will eventually get behind it. The substrate MUST be waterproof BEFORE the tile is installed. Use only waterproof adhesives when installing the tile and then seal the grout.  Cement grout is not waterproof and water will seep under the tiles leading to all kinds of trouble.  Just like caulking, grout sealer is a maintenance issue and should be inspected occasionally and reapplied as necessary.


Caulking is a maintenance issue. The difference between brands can make the difference between failure in 6 months or 3 years. This is not the place to cheap out.  I always recommend a bead of silicone under the baseboard to prevent water from traveling under it. Do the same under the lip of your toilet. Water will get under and work itself under the vinyl or tile around the drain hole. Check all your edges in your bathroom again a few months after you start using it. Small cracks always appear in grout or counter edges etc. Clean, dry and seal those edges.

Handy Tip from a plumber friend, fill the tub or shower pan with water prior to caulking.  The principle is that the weight of the water will settle tub or pan downward or outward slightly.  Thus, the seal will last longer because it will never be stretched when you enter the tub.

Exhaust Fan

Condensation is your enemy. The faster you eliminate it, the better. So spend for the quieter, higher volume fan because cheap, noisy fans don’t get used. The key to the bathroom fans effectiveness is use.  It must be used whenever the tub/shower is used to draw the hot moist air from the room.  Another key is duration.  The fan needs to be on long enough to do its job.  This is definitely longer that the occupants stay in the room. Therefore it is not recommended to have a light/fan combo as it will be turned off on exit and not do a complete job.  Always wire it with a Dehumidistat. That way it will remain on until the humidity level drops below a set level.

Remember – The only reason mould grows is because water is where it should not be.  Remove the Water, Stop the Mould!

22 Sep | 2 replies

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