Question: I have a 130-year-old home in St. Boniface that needs to have eavestroughs looked at, as they are dumping a lot of water beside the rubble foundation. I also need to look at grading, but my big question is about waterproofing and insulating my foundation. I want to work on one wall at a time this summer and insulate from the exterior at least two of the walls. Currently I am at the beginning of my research into the steps involved.
There is a rubble foundation, houses close by on either side of my house, a few cracks to fix, and water seeping in. A civil engineer friend recommended hydraulic cement for inside and outside fixing the cracks. I do not intend to ever finish the basement. My main goal in this undertaking is damp-proofing, insect control and heat loss. I do not want to dig all the way down and install drain tiles, etc. I will dig deep when it comes to cracks but that's it.
Manitoba Hydro has a pamphlet on insulating from the exterior, which seems pretty easy to follow. It involves digging only two feet down, which I think I read on a forum that recommendation has now changed to digging four feet down. It also calls for smoothing out the foundation wall and damp-proofing it before applying insulation.
So, all this background is to ask what are the basic steps you'd recommend. I can't imagine smoothing out the rubble foundation. Will the waterproofing compound do that? Does it have to be perfectly smooth before applying insulation? Because of the eavestrough and grading problems, some of the foundation is really wet. What happens when applying damp-proofing mixture over a wet foundation? Should I add that black dimpled stuff over the insulation?
Thanks.
Rachel Lovely
ANSWER: There is much debate about the proper way to insulate a stone or rubble foundation, or whether it should be insulated at all. Insulating older stone foundations, especially those with very unevenly sized components, can be a very tricky proposition. I admire your desire to attempt this repair, but it may best be left to professionals.
The first issue to deal with is the lack of smoothness you have alluded to. Because these foundations, often referred to as rubble, have many different-sized and shaped stones, providing a flat exterior surface for any kind of damp-proofing or insulation can seem insurmountable. The degree of difficulty often depends on the actual foundation and the amount of deterioration and movement of the stones. If the mortar in between the stones is not too deteriorated inside and out and there is little movement, smoothing the surface may be possible. If the foundation has significant deflection between the individual pieces, especially at the corners, it will likely be beyond your skill level to attempt. In that situation, some of the rubble will have to be removed, repositioned or replaced with concrete before proceeding. That may require temporarily supporting part of the floor structure while experienced masons or foundation contractors do the repairs.
If the foundation has not moved much and the stones are not appreciably larger in some areas than others, exterior damp-proofing may be practical. Unfortunately, partial excavation of the foundation will be nearly useless. Digging down to the bottom, regardless of whether there are footings or weeping tiles present, is essential. It does little good to insulate part of a foundation wall, and damp-proofing will only be effective if the entire wall is done.
After excavation, removing all loose mortar from between the stones is the first step. This can be done using a trowel or other tools, but may be extremely time consuming. Once complete, the next step requires a change in outlook. Instead of trying to just re-point the mortar joints, the entire foundation wall should be parged with a thin coat of mortar. This will require a large quantity of mortar to be mixed, but should give you a smooth enough surface for damp-proofing. Excavation of the soil away from the foundation should permit enough drying for damp-proofing application, as long as the weather co-operates.
The damp-proofing could be an applied liquid bitumen coating, rubberized membrane, or the dimple-board membrane you have suggested. While the bitumen may be the easiest to apply, the uneven surface of the foundation wall may make this more difficult. Also, any future movement between individual stones may still allow some water penetration. For that reason, a combination of applied damp-proofing and the dimple membrane may be your best choice. In that situation, gaps where the plastic membrane is not directly up against the foundation due to the uneven surface will still have reasonable moisture protection. Also, the rigid dimpled sheathing will give a smoother surface for application of rigid foam insulation on the exterior.
One other difficulty in this exterior insulation method is sealing the transition area at the top of the insulation, but that will have to be left for another discussion.
Extreme care must be taken when excavating around any foundation, but especially an older stone one. There is always the possibility of partial collapse when the exterior soil is disturbed, and proper support and bracing will be essential.
In a nutshell, this type of project is not normally within the skill set of most homeowners, so contacting a reputable foundation contractor should be the first step. You may be able to minimize your costs, and satisfy your desire for DIY, by helping with some of the old mortar removal or digging, but the bulk of the work should be left to professionals.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
