I have just recently found this website as my wife and I are in the process of buying a BISF House. We are first time buyers and this is an extremely exciting time in our lives after years of saving. I have researched the BISF House to death and every time I read something new I get more and more excited about getting stuck into renovating this type of property.
My question: Is it fairly simple and cost effective to redo/skim back the lower level external cement render on the lath and apply a new render with smooth finish? I’m not too interested in providing additional insulation(EWI) at this point but I would like to give the property a facelift. The front render is in good condition but we would like a smooth finish and the rear has had some poor patchwork done which will bug me if not repaired properly. The crack joints run vertically where the steel stanchions are (assumed) and I would like to redo the render to ensure the steelwork is better protected.
Just a side question: Should I be concerned that the render is cracking at the rear only and in line with the stanchions? Does this spell bigger issues? These seem like only very slight to slight cracks according to the IStructE guidlines.
Also, the render to the lean-to is terrible. This must be due to the timber or block moving more then the main structure and the lack of proper insulation internally. I’ll look to get this done as well.
Any comments would be much appreciated as I cannot seem to find anything about the cement render and metal lath refurbs.
Marc, thanks again. Much appreciated.
My wife and I are so excited now. Things are moving forward nicely with the sale so we can’t wait. Every new article or bit of info we read about BISF Houses just makes our choice to buy feel so right. So many plans, too many ideas:)
So happy to have a forum like this. Thank you.
Hi Ben, you’re very welcome.
Just for info, I was working on a patio door installation with a good friend a year or so ago and whilst cutting out the opening for the new doors we noticed that the render on either side of the existing window had separated and ballooned quite badly. We conducted the tap test and found large areas to be hollow as described above.
We continued to remove the existing dining room window and cut away the remaining render directly below using an angle grinder. Whilst doing this a very large area of the render wall actually fell away exposing the inner cavity and support stanchions, (which were in excellent condition btw).
Now on seeing this, it looked pretty horrific at the time, but as the house was due to be fitted with EWI the following week, we were instructed by the installers to simply remove any remaining render and screw a large sheet of OSB sterling board directly onto the vertical stanchions, in effect, simply boarding up the exposed area.
The installers then simply screwed the new insulation panels onto this board and after installing a scrim and mesh layer, the insulation was then simply applied on top of the EWI.
What I’m really getting at here is, even if you are unfortunate enough to have to remove large areas of render, the situation can be remedied quite cheaply. Even though you are not installing EWI in this instance, should you be required to board any large area, the board itself could be scrim coated and the render coating applied on top, omitting the EWI. You could always use cement board instead of timber OSB board too.
So all in all, there’s nothing really to fear even in the worst case scenario.
Good luck with your purchase
Warmest of welcomes Ben to the world of BISF House ownership.
I can fully appreciate your excitement at this stage of your purchase and your eagerness to get started.
One word of advice though before you start.
Modern renders, such as silicone render, should out perform the more traditional by far and it would be my first choice in this instance.
However, these renders cannot be applied during freezing conditions and I would suggest mid to late spring would be the best time to undertake this work.
Being steel framed, BISF properties do in fact expand and contract slightly, particularly during the extreme temperature variations which we do experience from time to time here in the UK. Standard cement render alone is not usually flexible enough to cope with this expansion and sometimes large cracks can appear when similar products are used.
Today however, you will also find flexible and fibre reinforced renders available on the market and it is these products that will perform best.
I am not an expert by any means in re-rendering on top of existing surfaces however I see no reason why this would not work providing that the subsurface is sound and depending on your current finish, primed according to the manufacturers instructions.
One tip to check for soundness is to tap the outer render at various points on the outside wall as voids can sometimes occur which will sound noticeable hollow when tapped by a screwdriver or wooden implement such as a wooden spoon.
The hollow sound indicates separation of the outer layer of render to the metal lathe bonded layer below.
If a large area is found to be hollow or badly cracked it may be worth removing the loose plaster before priming and adding a new layer of render.
If you area going to repair / replace the render at the rear of the house, always consider replacing the dining room window with patio doors at this stage. It’s a pretty simple process that a competitive DIYer should be be able to tackle, as the new render will finish off any rough edges rather nicely around the door frame.
The outhouse walls tend to be single brick skinned of either standard brick or block-work and it’s pretty common for the render here to crack where the wall joins the house or degrade due to a poor damp proof layer. Replacing this is generally straightforward as any loose matter can be chiselled off giving a sound surface for the new render.
All in all it should be pretty straightforward and you should find that the new silicone renders look very smart, crisp and clean when finished.
The render can be left with a smooth trowel finish or you can opt for a scratch coat with has a little more of an open grain appearance.
I hope this helps a little and what I’ve read makes sense as I’m writing this at 2am.
Any other queries please feel free to ask and I’m sure myself or one of our members will do our best to assist.