Base­ment floor a job best left for pro­fes­sion­als

Winnipeg Free Press - Section G - - HOMES - ARI MARANTZ

QMy Wolse­ley home was built in the 1920s, and my base­ment has gone through some heav­ing. Now I’m faced with re­mov­ing the cracked base­ment slab and re­plac­ing it. I have read sim­i­lar ar­ti­cles to yours, in re­gards to this type of project, and I think I can just iso­late one area and re­place the dam­aged con­crete. While I’m at it, I was think­ing of re­plac­ing the cast iron plumb­ing un­der­neath the slab as well. My goal is to fin­ish the base­ment with a half bath. I’ve never had an is­sue with mois­ture or sewer backup, but I will also be in­stalling a sump pump dur­ing the project. But, be­fore I em­bark on such a jour­ney, there are a cou­ple things that I am con­cerned about. When re­mov­ing the slab, and what­ever else that may lay un­der­neath, I’m wor­ried about struc­tural is­sues. I cer­tainly don’t want to tax the strength of my foun­da­tion by re­mov­ing any sup­port. My foun­da­tion walls have no vis­i­ble hor­i­zon­tal cracks, just some thin ver­ti­cal ones that run from my base­ment and I be­lieve the walls are around 16 inches thick. Also, af­ter I re­move the slab, how much crushed stone is re­quired be­fore I pour new con­crete and how thick must the con­crete slab be? I’ve heard of some base­ments be­ing fin­ished with only a vapour bar­rier and sub-floor over ei­ther dirt or crushed stone. Is this even an op­tion? Many, many thanks in ad­vance for your time and most ap­pre­ci­ated ex­per­tise. Re­gards, Wyeth Krauchi AN­SWER: Re­mov­ing and re­plac­ing a base­ment floor slab is a dif­fi­cult and very messy project, which may be be­yond your skill set as a home handy­man. A par­tial re­moval, as you sug­gest, will be much sim­pler but may not be suf­fi­cient for the plumb­ing up­grades you de­sire. I am a lit­tle con­fused by your re­quest as to the amount of your dam­aged base­ment floor slab you are plan­ning on re­mov­ing. In one sen­tence you state you will only re­move a por­tion of the floor, but you also de­sire to in­stall a bath­room, sump pit and pump, and re­place the older cast iron drains be­neath the slab. All of th­ese items are not nec­es­sar­ily pos­si­ble by only re­mov­ing a small sec­tion of the con­crete. You are fur­ther mud­dy­ing the wa­ters with your ques­tions about an air/vapour bar­rier be­low the new con­crete. That would be very de­sir­able, but only re­ally ef­fec­tive if most of the older floor is re­moved. De­spite th­ese dis­crep­an­cies, I will en­deav­our to pro­vide what­ever in­sight I can. Your first con­cern with pos­si­ble ef­fects on the foun­da­tion may only be valid if you are plan­ning on re­mov­ing most or all of the base­ment floor slab. The con­crete floor does pro­vide a struc­tural func­tion in pre­vent­ing in­ward move­ment of the bot­tom of the foun­da­tion walls, due to ex­cess soil pres­sure. Since your slab is al­ready dam­aged and heav­ing, some of this func­tion may be com­pro­mised, but it has to be se­verely buck­led to lose all of this func­tion. By re­mov­ing the en­tire slab, you will be sub­ject­ing the foun­da­tion to the pos­si­bil­ity of crack­ing or in­ward bow­ing, but that would de­pend largely on the amount of time the slab is miss­ing and the amount of rain­fall. Re­mov­ing and re­plac­ing a few small sec­tions of the floor may only serve to im­prove the strength and help pre­vent fur­ther prob­lems of this na­ture. The an­swer to your last ques­tion about the pos­si­bil­ity of re­mov­ing the en­tire floor and leav­ing only stone and a poly­eth­yl­ene air/vapour bar­rier should be com­mon sense. Firstly, my pre­vi­ous con­cern about in­ward foun­da­tion move­ment would be mul­ti­plied enor­mously. Se­condly, the thin plas­tic sheath­ing in­stalled over the soil or stone would eas­ily be­come dam­aged, over time, and ren­dered all but in­ef­fec­tive in pre­vent­ing mois­ture or soil gas in­tru­sion. It would also al­low mois­ture to be trapped be­neath, with po­ten­tial for mould growth. Fi­nally, how would you have a prac­ti­cal bath­room in a base­ment with­out a proper floor for the base? If you are talk­ing about only re­mov­ing small por­tions of the con­crete, patch­ing th­ese open­ings with con­crete af­ter your up­grades should not be that dif­fi­cult, even for a do-it-your­self-er. It is ad­mirable to en­deav­our to re­pair your dam­aged con­crete base­ment floor slab, es­pe­cially in an ef­fort to up­grade older plumb­ing drains and pro­tect your home from sewer backup with a back­wa­ter valve, sump pit and pump. Un­for­tu­nately, this type of work, es­pe­cially re­plac­ing the old drains and in­stal­la­tion of the rough-in for the new bath­room, is very spe­cial­ized work. I would not at­tempt this, un­less you have ex­ten­sive ex­per­tise in plumb­ing. The por­tion of the work that you may be able to tackle is break­ing up and haul­ing away the old con­crete and clay soil. Fill­ing in the voids around the new drains and sump with pea gravel or smooth stone, would also fall un­der this cat­e­gory. Fi­nally, mix­ing, pour­ing and fin­ish­ing four or five inches of new con­crete where the old dam­aged floor is re­moved may also be within your power, to keep costs down and sat­isfy your de­sire to be in­volved in the ren­o­va­tion. While it is al­ways a good idea to ask the types of ques­tions you have posed be­fore em­bark­ing on any ren­o­va­tion, the fact th­ese have to be asked should alert you to the like­li­hood you are in over your head. I would ini­tially con­sult a li­censed plumber to come to your home and en­sure your plans are prac­ti­cal or even pos­si­ble be­fore em­bark­ing on re­mov­ing sec­tions of your base­ment floor. Then you can de­cide how to pro­ceed and how much of the floor re­moval and re­pair you are will­ing and ca­pa­ble of tack­ling your­self. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the past pres­i­dent of the Canadian As­so­ci­a­tion of Home and Prop­erty In­spec­tors — Man­i­toba ( Ques­tions can be emailed to trained­eye@in­ Marantz can be reached at 204-2915358. Check out his web­site at



Re­pair­ing a dam­aged con­crete base­ment floor is spe­cial­ized work.

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