how to repair felting on a flat roof garage?

I bought my bungalow 4 yrs ago and put my foot through the roof of my detached, integral with next door, garage. Had to cut out the rotten board [chipboard]should have been marine ply, replace the cut out section and hot laid a patch over it don't know cost as the patch size was given to me.


Hot lay felt is available in some builders merchants like Travis Perkins, also a paper seam roller or a larger one if available.

To cut costs I am going to use only the hot laid underlay on my next patch, as far as I can see the top layer with mineral finish is just to make it look pretty.

Right as long as the board is sound cut/deep score around the bad patch plus 150 mm for overlap all around the patch area. Clear away all stones including those burried in the former hot layed pitch.
Hire a propane bottle and burner with lance [tell them what it's for ] and proceed with burning the base layer to clear away any dead pitch, once clean cut a section of underlay to fit. Lay the patch over the area and seal one edge using the roller gently to firm it down work away from this rolling as you go the roller is bound to get covered in pitch but a way to stop/reduce build up it is to have a can of water to dip it in keep warming to melt the pitch wet and roll, wet and roll until you reach other edge let set for about 2mins then run flame around edges rolling them down to blend in with old pitch allow to cool before replacing stones add more if needed use grano chips not pea shingle I think it's because granite chips absorb more heat so prevent heave of felt like you see on shed roof. of course this shouldn't occur on a hot laid roof.
My first is 1 1/2 yrs old and hasn't leaked and we've had some horrendous storms. If you are looking at cost you can use ordinary mineral felt but the thick one and cold laid pitch spread down after digging out the stone but don't bother burning base just lay patch over top but be prepared to have to do it again some time.

Rob
February 2008