New uPVC door installation - fastenings

2 May 2004
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United Kingdom

I have just installed a uPVC back door and although generally successful I wanted to run a couple of elementary questions regarding the use of frame fastenings to any experienced uPVC door installers ..

I've used Fischer 7.5x112 FFS screws which made the job quite easy, however I did find that after driving one screw in and out 2-3 times to get the frame packing spot on the screw slipped in the concrete wall blocks, i.e., the threaded portion of concrete presumably gave way (despite being tight the first couple times). The recommended drill hole size is 6mm (I used a new SDS bit to recommended depth) and the screw thread is 7.5mm OD which means the screw cuts into the block approx 0.75mm which doesn't seem a lot does it?

My question is basically to ask if it is simply not advised to remove the screws once tightened up? Or was I just unlucky with maybe a rogue part of the wall material? I kept clear of the mortar joints, about half way up the block in this case.

Also, how best to correct the matter? Neatest way to re-drill elsewhere and plug the old hole in the uPVC frame? I would prefer not to do if there is an alternative. What do the pros do if it doesn't work out first time?

And my other question was regarding the sinking of the countersunk head of the screws - how far into the uPVC frame should it be buried? I hardly have to drive it in before the frame starts 'sinking' on the inner face of the frame, not the whole frame. I doubt there is any internal reinforcement. To my mind it looks really naff to create substantial dips in the frame where the screw heads are located but is it the accepted norm that installers find they have to do this too?
This other screw manufacturer's video (2:58 in) seems to suggest so lol!

Thanks for any advice forthcoming...

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Firstly I countersink the PVC to sink the head into.
I fix the bottom hinge side first then the other bottom side. Fixings (for doors) should go at least 50mm into the block so I only run it in about 20mm the first time while getting everything set up. Then level up the frame and fix the hinge top side. Level and fix the other side.

Then double check all levels, Square and plumb. If good I then drive those 4 fixings in the rest of the way.
Then finally do another 2 intermediate fixings on either side while using a 6ft level to check for bows in both directions.

Dont do concrete fixings tight, Just nip them as they are self packing. Then foam around and make good.

For your loose fixing you could just redo it at an angle through your original hole.

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