# Forum Home Renovation Sub Flooring  wall cracks from installing bigger subfloor vents?

## Farnsy

Hi guys,  I want to try DIY fix of damp problem in my subfloor. I've done research on this forum and I think I know how to proceed, but still a little concerned. If I knock out the terracotta vents and the adjacent bricks on both inner and outer leafs to install Aleta brass wire vents (2 bricks high by 2 wide), will I need to install a lintel or support of some kind on the inner leaf to stop the inner wall cracking above? Worst case I dread part of the wall could collapse before I can get a support in there.  I have 100year old federation double brick house with lime based render inside, sandstone foundations supporting all walls, terracotta vents in first two courses of bricks, just below damp course. No visible tidal marks, but one area has salt deposits in subfloor. Musty smells. Couple of hardwood beams holding up the floor joists (directly on top of sandstone foundation) have rotted away. Ground looks dry but when touching it it has a damp feel, more so near the permitter of the subfloor and particularly so down the side of house where I dont have path to run water away from the house. The worst bits of the ground have white caps (presumed mould).  Any advice will be greatly appreciated,
Farnsy. :Roll Eyes (Sarcastic):

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## Hoppy

Before you go to all that work check out the solar fans at www.environfan.net.au. I have had some experience with them and they work really well. The solar can work either to force air in or out, much better the trying to rely on cross flow ventilation which is sometime difficult in the underfloor environment

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## Bloss

Edited - duplicated post.

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## Bloss

You probably have no need to worry about a 'lintel' , but the process is easy anyway if you want to be certain. Measure the width of the hole you need and allow another 50-60mm extra and then buy enough gal steel bar cut to that length - for this purpose 45-50mm wide x 6mm will be plenty. Rather than simply knocking things out the method is to scrape out the mortar line above where you want to remove existing vent & bricks (so immediately above the vent). 
Scrape that out 60mm past where you need to create the opening width. You can use an old cold chisel, a big old screwdriver - anything that works really as the lime mortar will be soft anyway. You are among to clear sufficient space to insert that bar and have it overlap the opening by the 50mm or so. Once the mortar is clear simply tap the bar in place. 
Because the bar is able to support what is above it you then you can use a grinder and masonry blade to make the vertical cuts needed at the correct width for the new vent(s), and remove the mortar at the bottom of the opening and gently knock out the vent and brick to be removed. Then set the vents in place an fix with silicon or whatever you planned to use.

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## GeoffW1

Hi, 
Agree  :Arrow Up:  
and the opening in the inner skin does not have to exactly precisely line up with the new vent on the outside. Maximum efficiency is gained when it does of course, but if it is convenient to have it half a brick this way or that, it won't hurt much. 
My old Federation place was done like this on the inner brick skin (attach) 
Cheers

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## Farnsy

Thanks Hoppy. Do you happen to remember how much the enviro fan costs and how long have yours been running for?  
Before I came to this forum I had looked at some of the powered fans on the market. I didn't get a price on the envirofan, but the ultrafan I imagine is similar. Damp . My concern with the vent size fans is that a few people have said they tend to break down after running for a few years; and at $350 each per fan kit it could be expensive in long term. My current plan A is to install brass wire vents (~$25 each), see how that improves things over 12 months (hope musty smell at least gone by then). If that doesn't work then plan B, I put a cheap (~$30) but large household box fan (~35cm diameter) in at back of house subfloor to blast air out from the subfloor at a single point but drawing in fresh air from all the new bigger vents. If that don't work, then yes the ultra, eco, or envirofan's where my plan C.

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## Farnsy

Thanks both Bloss & GeoffW1, this is great advice & instruction you are giving.  :Wink 1:  
What composition of mortar do you think I should use for around the vents? say cement:lime:sand at 1:3:12 or 1:1:6?  
I was thinking I should try and match as close as possible the soft lime based mortar in the walls. Mosty for appearance sake, but also cause I read that modern cement mortar around old/soft bricks is likely to lead to brick cracking and/or interferare with moisture transfer (I assume spalling). I also read that the lime they used in the early 1900's is not the same as the lime (hydrated) available for purchase today. I hope thats not problem for me.  
I'm novice but keen to do whats best for the house. Thanks,
Farnsy.

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## GeoffW1

> What composition of mortar do you think I should use for around the vents? say cement:lime:sand at 1:3:12 or 1:1:6?  
> Farnsy.

  Hi, 
I'd use 1:2:9 or 1:3:12, and white cement if the existing mortar is a sandy white, as it was in my old place. I used 1:1:6 there and it was a mistake. It was too strong for the lime mortar surrounds. 
Mix up a few cowpats of different ratios first, and you can judge colour and crumbliness. 
Cheers

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## Compleat Amateu

Unless there is something really different about your brickwork, you will have no problem taking out 2 x 2 bricks to install Aleta vents; I've added about a dozen to my latest project with no problem.  This one is brick veneer (therefore single leaf only), but I have also previously done it through double solid walls with lime mortar as well.  No problems at all with cracking brickwork etc. 
If you are going ahead, a few points: Put the new vents where they will achieve the best result and/or be easiest to install.  Put another way, if the amount of work in installing a new vent in existing brickwork is the same as replacing a terracotta vent (and it pretty much is), then why just replace one with another?  Terracotta plus Aleta is better than Aleta alone.Be careful not to damage the dampcourse that will be the top of the holeBuy yourself: A set of kneepadsA bricksaw, great for easing out mortar once you have a hole big enough to get the blade intoa 3mm masons trowelA couple of scutching chisels with new teeth for cleaning mortar off the brickwork around the opening you have created, though with lime mortar a wire brush may do as well!Think about using smaller Aleta vents in areas of low ground clearance - if you have them.  This is where the ventilation will be most needed.  Aleta vents come in every combination from 1 brick size only up to 2 x 2 bricks.  Bunnings don't carry the full size and colour rangeThere is a whole separate conversation around the technique for getting the new vent into the hole and mortaring it in tightly, that's where the 3mm masons trowel comes into play.  I have seen a website somewhere that shows you how (look for "replacing bricks"), otherwise let me know and I'll go though that if needed.Good luck

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